cleapps recipe book

The CLEAPSS

Recipe Book

Introduction to this Edition Recipe Cards were first produced in 1991 but very quickly demand led to an increase in the scope and range of the information included. Over the ensuing 20 years we have added more and more information whilst retaining the card format which users found useful. This 2011 edition sees a change from cards to A4 sheets. The A5 card has become too small to contain all the information required for some topics, and we believe that there is no further scope for reducing the size of the print. We have extended the number of separate entries from 74 to 106 to allow for more information on some topics and to make other information easier to locate. We have added colour and some photographs, where these are useful. The loose leaf A4 format also allows plenty of room for you to insert recipes and instructions of your own.

Risk Assessment Where a risk assessment includes control measures these have been incorporated into the instructions, as describe in our Guidance Leaflet G90, Making and Recording Risk Assessments in School Science. Each recipe therefore includes model risk assessments but does not include factors that you have to thinks about, such as technician and teacher experience, and prep room conditions. As in the previous edition, there is no mention of general bench solutions. In the past such solutions were often much more concentrated than required and posed unnecessary hazards and risks. The principle we follow (as in COSHH) is that the concentration of any reagent should be the lowest at which the procedure works satisfactorily to give the intended result. Sometimes, therefore, we suggest solutions which may appear to be an odd concentration but this nevertheless is the most suitable. For example, 0.4 M sodium hydroxide solution is IRRITANT, whereas 0.5 M is CORROSIVE.

Making solutions The recipes also make use of the laboratory jug as a measuring tool. Although apparently not particularly accurate, we routinely achieve concentrations of between 1.95 and 2.05 M when using a jug to prepare 2M sulfuric(VI) acid from concentrated sulfuric(VI) acid during the Practical Techniques in Chemistry course. Clearly, using a jug can produce solutions with concentrations that are sufficiently accurate for many laboratory purposes. You will find more detail about making solutions in section 7.6 of the Handbook. If you run into difficulties not covered in either the Recipe Book or the Handbook, phone CLEAPSS on 01895 251496 but do try the index first.

Contents Recipe sheet NumberAgar 1

Alcohol/water and propanone/water solutions

2

Alginate beads 3

Aluminium solutions 4

Ammonia gas 5

Ammonia solution (ammonium hydroxide)

6

Ammonium chloride 7

Ammonium vanadate(V) solution 8

Azo dyes 9

Barium solutions 10

Benedicts qualitative reagent 11

Benedicts quantitative reagent 12

Biochemical indicators and tests 13

Bismuth nitrate(V) solution 14

Biuret reagent 15

Brodies fluid 16

Bromine water 17

Buffer solutions 18

Calcium chloride and nitrate(V) solutions

19

Calcium hydroxide solution 20

Carbon dioxide 21

Cerium(IV) solutions 22

Chemiluminesence reactions 23

Chlorine gas 24

Chlorine water 25

Chromatography solvents and locating agents

26

Chromium(III) chloride and chrome alum solutions

27

Citric acid 28

Clock reactions

29

Recipe sheet NumberCobalt(II) chloride solution and thermochromic liquid

30

Copper(II) solutions 31

Crude oil alternative 32

2,4-Dinitrophenylhydrazine solution

33

3,5-Dinitrosalicylic acid 34

Drosophila food base 35

Electroplating solutions 36

Enzymes 37

Etching solutions 38

Ethanoic acid 39

Fehlings solutions 40

Fixatives used before preserving biological specimens

41

Gases less commonly used in schools

42

Hydrochloric acid 43

Hydrogen gas 44

Hydrogen peroxide 45

Indicators (acid-base) 46

Indicator (universal) 47

Indicators (carbon dioxide) 48

Indicators for redox, precipitation and complexometric titrations

49

Iodine solution 50

Iron(II) solutions 51

Iron(III) solutions 52

Lead(II) nitrate(V) 53

Lithium chloride 54

Magnesium sulfate(VI) 55

Manganese(II) sulfate(VI) 56

Mercury solutions 57

Methanal solution 58

Methanoic acid 59

Recipe sheet NumberNickel sulfate(VI) 60

Nitric(V) acid 61

Nylon rope experiment 62

Oscillating reactions 63

Oxygen gas 64

Phosphoric(V) acid 65

Plant mineral requirement solutions

66

Potassium and sodium phosphates

67

Potassium chloride 68

Potassium chromate(VI) 69

Potassium dichromate(VI) 70

Potassium hydroxide 71

Potassium iodide 72

Potassium manganate(VII) 73

Preservatives used after fixing biological specimens

74

Ringers and other saline solutions for physiological use

75

Sandells solution 76

Silver nitrate(V) 77

Slime 78

Soap and bubble solutions 79

Sodium carbonate 80

Sodium chlorate(I) solution 81

Sodium chloride 82

Sodium ethanoate 83

Recipe sheet NumberSodium hydrogencarbonate 84

Sodium hydroxide 85

Sodium silicate, the crystal (chemical) garden and silicate gels

86

Sodium thiosulfate 87

Stains for bacterial activity 88

Stains for cell contents 89

Stains for electrophoresis 90

Stains for fungal material 91

Stains for metabolic activity 92

Stains for plant material 93

Standard solutions for titration 94

Strontium chloride 95

Sulfur dioxide 96

Sulfur dioxide solution 97

Sulfuric(VI) acid 98

Testing for gases 99

Testing for negative ions 100

Testing for positive ions 101

Testing for organic functional groups

102

Tin(II) chloride 103

Water (sea and hard) 104

Winklers method for dissolved oxygen

105

Zinc sulfate(VI) 106

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1 Agar For microbiological activities using purchased media, follow the instructions on the bottle. The recipes are grouped into agars for microbiology and agars for other activities. All agars for microbiological work need to be sterilised before and after use. General Hazards Agar inhaled as a fine powder may cause an allergic reaction or other respiratory

problems. The use of agar that could isolate human pathogens (eg, blood agar) should be avoided.

Control measures

Use a balance in a non-working fume cupboard, ie, not switched on, with the sash down, to weigh out agar. Use heatproof gloves to protect from scalding when handling freshly-sterilised molten agar.

Procedure for preparing technical agar (also called agar-agar)

Mix 1.5 g of agar with 10 ml of water into a paste. Slowly add more water with stirring until the volume is 100 ml. Heat the mixture with stirring on a boiling water bath to 95 C in the required container. This preliminary heating can be omitted if the agar is going to be sterilised immediately, unless it is necessary to decant the agar into smaller containers. In acid media, the amount of agar should be increased from 1.5 to 2 g. If the solidified agar in any recipe is too sloppy or too firm, repeat the procedure using slightly more or less agar. The agar gel is not stable in strongly alkaline solutions.

Usual sterilising conditions

(If required) Autoclave the container(s) with the made-up suspension(s) for 15 minutes at 15 psi (121 C).

Agars for microbiology China blue lactose agar

Use 3.6 g of China blue lactose agar powder in 100 ml of distilled water. If this mix proves too thin for rough handling by students, then thicken by adding 0.5 g of agar-agar (just thickener, no nutrients).

Crystal violet agar. A selective (against Gram positive) medium for soil bacteria

In a fume cupboard which is not switched on, add 0.005 g of crystal violet (HARMFUL, DANGEROUS FOR THE ENVIRONMENT) to 1 litre of liquid nutrient agar solution. The resultant solution is low hazard.

Glucose nutrient agar

Add 0.5% w/v of glucose to molten nutrient agar.

Malt agar for fungi Mix 2 g of malt extract with 2 g of agar with 10 ml of water into a paste. Slowly add more water with stirring until the volume is 100 ml. Autoclave the suspension at 10 psi (115 C) for 10 minutes.

Mannitol yeast extract agar for growing root nodule bacteria

Mix 10 g agar in 1 litre of water, and dissolve in a boiling water bath. Add 0.5 g K2HPO4, 0.2 g MgSO4.7H2O, 0.2 g NaCl, 0.2 g CaCl2.6H2O,10 g mannitol, and 0.4 g yeast extract. Dispense as required and sterilise by autoclaving before use.

Nitrogen-free mineral salts agar for growing nitrogen-fixing bacteria

Dissolve 0.05 g FeCl3.6H2O in 500 ml distilled water. Add 2 g K2HPO4, 0.25 g MgSO4.7H2O and 10 g glucose. Check the pH and adjust, if necessary, to 8.3 using 0.1 M NaOH. Pour into a bottle containing 1 g CaCO3 and 7.5 g agar powder. Mix and autoclave at 121 C for 20 minutes. Before pouring plates, swirl to thoroughly mix the CaCO3 and agar.

Nutrient agar for bacteria

Mix 2 g of Bovril, 0.5 g of sodium chloride and 1.5 g of agar with 10 ml of water into a paste. Slowly add more water with stirring until the volume is 100 ml. Heat/sterilise the suspension as in Usual sterilising conditions above.

Starch malt agar for growth of fungi and digestion of starch

Mix 3 g of light malt powder (from home-brewing shops), 0.5 g of peptone (to promote growth) in 20 ml of water. Also make a paste containing 1 g of soluble starch in 10 ml of hot water. Add these two solutions to 1.5 g of agar with stirring and slowly add more water with stirring until the volume is 100 ml. Stir before decanting into smaller containers (if required) and sterilising. Autoclave the suspension at 10 psi (115 C) for 10 minutes.

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Agars for other activities These should be made up as required, and not stored for long periods to avoid any unwanted microbial activity. Dispose of as soon as possible after the activity. Sterilise in an autoclave any which are suspected of microbial contamination. Agar for starch synthesis

Mix 0.5 g of glucose-1-phosphate and 1.5 g of agar with 10 ml of water. Slowly add more water with stirring until the volume is 100 ml. Boiling, not sterilising, should be sufficient.

Electrolytic agar Add one gram of sodium sulfate(VI) or other electrolyte to the hot agar solution before pouring.

Ferroxyl agar gel for rusting experiments

Add 1.4 g of agar, 2 g of sodium chloride, 0.1 g of potassium hexacyanoferrate(III) and 1 ml of phenolphthalein solution to the 100 ml of water and warm, with stirring, to 95 C. Pour the solution into Petri dishes.

Indicator agar Add 1 ml of the chosen indicator solution to the agar solution before pouring.

Mayonnaise agar for lipase activity (1)

Dilute 4 g salad cream or mayonnaise with 5 ml water and add 1 ml 0.1 M sodium hydroxide solution (IRRITANT). Add about 1 ml of this alkaline mixture to a solution of bromocresol green dye (about 0.003 g in 100 ml water) until the mixture just turns blue-green and stir to ensure even distribution. Boil the resultant mixture with 2 g agar, cool to 50-60 C then pour thin layers in Petri dishes. The plates will need to be incubated at 30 C for 24 hours before being examined for orange-yellow areas produced by lipases.

Mayonnaise agar for lipase activity (2)

Alternatively, mayonnaise agar can be made up without the dye and, after incubation, the plates can be flooded with 0.4 M copper(II) sulfate solution and left for 30 minutes before being examined. Clear areas in the blue-green matrix indicate where lipases have broken down the fatty acids in the mayonnaise.

Milk agar for protease activity

Stir together 2 g low-fat milk powder (Marvel is recommended as it contains very little fat), 1 g agar and 100 ml water. Heat as for technical agar and pour into Petri dishes in very thin layers. Proteases should produce clear patches by breaking down proteins in the milk within 30 minutes or so.

Phenolphthalein indicator agar

Use 2 g agar in 100 ml boiling distilled (or deionised) water in a beaker. Add 10 ml of 0.2 M sodium carbonate solution and 5 ml of phenolphthalein into the beaker and stir well. Carbon dioxide in the atmosphere causes the colour to fade on storage, so the agar is better prepared shortly before it is required.

Starch agar for amylase activity

Mix a paste containing 1 g of soluble starch in 10 ml of cold water. Add 1.5 g of agar, stir well and slowly add more water with stirring until the volume is 100 ml. Heat as for technical agar above.

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2 Alcohol/water and propanone/water solutions Quoted flash points appear to vary slightly between sources. To prepare molar solutions, liquids can be weighed in tared containers. 2 M propanone solution is used in a rate of reaction experiment called the iodination of propanone. To prepare 100 ml of an x% (v/v) solution of ethanol in water

Add x ml of ethanol to a 100 ml measuring cylinder. Add water up to the 100 ml mark. Label the solution. If it is highly flammable, then it needs the hazard warning label but, if flammable, a

label is not needed. However, the hazard classification needs to be written on any risk assessment.

% ethanol 0 10 20 30 40 50 60 70 80 90 100 Flash point (C) - 49 36 29 26 24 22 21 20 17 13 Density (g cm-3) at 20 C 1.00 0.98 0.97 0.96 0.95 0.93 0.91 0.89 0.86 0.83 0.78 Hazard - FLAMMABLE HIGHLY FLAMMABLE

To prepare 1 litre of 1 M methanol solution

Weigh out 32 g of methanol in a tared container or measure out 41 ml of methanol in a measuring cylinder.

Add this to a 1000 ml measuring cylinder or 1 litre measuring jug. Add water up to the 1 litre mark. Label the solution harmful.

To prepare 1 litre of 1 M ethanol solution

Weigh out 46 g of ethanol in a tared container or measure out 58 ml of ethanol in a measuring cylinder.

Add this to a 1000 ml measuring cylinder or 1 litre measuring jug. Add water up to the 1 litre mark. The solution is low hazard.

To prepare 1 litre of 2 M propanone solution

Weigh out 116 g of propanone in a tared container or measure out 147 ml of propanone in a measuring cylinder.

Add this to a 1000 ml measuring cylinder or 1 litre measuring jug. Add water up to the 1 litre mark. The solution is low hazard.

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3 Alginate beads In studies of enzymes or the physiology of yeast cells, a valuable technique is to immobilise the enzyme or cells inside beads of sodium alginate. The beads containing the enzyme/cells can then be used as usual or packed into a column (eg, a syringe barrel) and a suitable substrate passed over them. The products are collected at the bottom of the column and the immobilised enzymes or cells can be used again. When making up the alginate and enzyme solutions it is essential to use purified water; otherwise calcium ions in the water will cause the alginate to set prematurely. Alginate beads can usually be stored overnight, covered and refrigerated but are unlikely to keep longer than their non-immobilised components. Always trial practicals to confirm activity of organisms or enzymes. Preparing immobilised enzymes/cells in alginate beads

Make up a solution of the enzyme to be studied (see Recipe sheet 37 for enzymes), or a suspension of yeast cells using purified water.

Sprinkle 2 g of sodium alginate in 100 ml of warm, purified water and mix using a mechanical stirrer. Allow the solution to cool. Initially the mixture will form glutinous lumps, but it becomes smooth over time.

Dissolve 3 g of calcium chloride-6-water in 200 ml of purified water in a 250 ml beaker. Mix 2 ml of the enzyme/suspension with 8 ml of the 2% sodium alginate solution. Variations on these

proportions may be used. Draw this up into a 10 ml syringe. Add the sodium alginate/enzyme (or cell) mixture one drop at a time to the calcium chloride solution

making sure the tip of the syringe is held above the solution in the beaker. Allow the beads to harden for a few minutes before straining them out of the beaker.

Hardened alginate beads in calcium chloride solution

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4 Aluminium solutions Hydrated aluminium salts such as the chloride (AlCl6.6H2O, M = 241.5 g mol-1), sulfate(VI) (Al2(SO4)3.16H2O, M = 630 g mol-1) and nitrate(V) (Al(NO3)3.9H2O, M = 375 g mol-1) absorb water (ie, they are hygroscopic) and become damp on storage. Do check these chemicals before use. Aluminium potassium sulfate(VI), also known as potassium aluminium sulfate, alum and potash alum is easily stored and suitable for all activities where aluminium ions are required for testing. However, it is not all that soluble in water, although it does make large octagonal crystals. Aluminium solutions are acidic. Aluminium potassium sulfate(VI)

Formula: AlK(SO4)2.12H2O Molar mass: 474.39 g mol-1 Solubility: 11 g per 100 ml General Hazards See Hazcard 2B. Aluminium salts in water are acidic.

Never use anhydrous aluminium chloride to make solutions. It reacts violently with water producing toxic fumes of hydrogen chloride.

Mass (g) of solid to be used

Concentration required

Volume (ml) of solution required Hazard warning label 100 250 1000

0.01 M Ten-fold dilution of the 0.1 M solution - 0.1 M 4.74 11.86 47.44 - 0.2 M 9.49 23.72 94.88 -

Saturated (20 C) 12 29 114 - Aluminium chloride (hydrated)

Formula: AlCl3.6H2O Molar mass: 241.43 g mol-1 Solubility: 83 g per 100 ml General Hazards See Hazcard 2A. Aluminium salts in water are acidic.




0.01 M Ten-fold dilution of the 0.1 M solution - 0.1 M 2.41 6.03 24.14 - 0.5 M 12.07 30.18 120.72 -

Saturated (20 C) 90 225 900 IRRITANT Preparing solutions of aluminium salts

Wear eye protection. Measure out the indicated quantity of the aluminium salt. Add the solid to about two thirds of the final volume of water in a beaker or laboratory jug. Stir to dissolve, warming if necessary. Pour the solution from the beaker into an appropriate measuring cylinder or laboratory jug and add

water to the required level. Pour into a labelled bottle.

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5 Ammonia gas Ammonia is less dense than air and very soluble in water so it has to be collected by the downward displacement of air (upward delivery). Theoretically, 2.1 ml of fresh concentrated (880) ammonia solution produces 1 litre of gas, although this is never achieved in practice, so always use an excess. Older stocks of concentrated ammonia will be less concentrated. If the fountain experiment is to be carried out, a round bottom flask is substituted for the gas jar in the diagram below. Many standard text books use a calcium oxide drying tube. There is no real need for this. General Hazards See Hazcards 5 & 6. Ammonia begins to bubble off from 880 ammonia at about

55 C so heat gently and use anti-bumping granules to allow the ammonia to boil off gradually.

Preparing ammonia gas

Use a fume cupboard. Wear goggles. Add 10 ml of concentrated ammonia to the boiling tube

(CORROSIVE). Set up the equipment as shown on the right. Warm the boiling tube gently for about 5 minutes. Knowing when the gas jar is full is not easy. Placing

moist red litmus at the neck of the inverted flask is not a good indicator that the flask is full of gas. It is a matter of judgement and experience. It might be better to use a fresh boiling tube of concentrated ammonia for each gas jar or flask required.

When the collection is finished, place a cover slip or, better still, a large bung into the opening of the gas jar. Store the gas jar upside down because ammonia is lighter than air.

The residual ammonia solution can be poured down the sink in a fume cupboard with plenty of water.

Heatgently

10 ml of concentratedammonia solution

Inverted gas jarheld by a clamp

Anti-bumping granules

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6 Ammonia solution (ammonium hydroxide) The concentration of 35% (w/v) ammonia solution, (also known as 880 ammonia), is 18.1 mol dm-3. Educational suppliers commonly supply this concentration although other concentrated solutions, eg, 25% (w/v) are available. If kept for long periods, the concentration of ammonia solutions decreases because of leakage of gas from the container. If the concentrated ammonia is several years old it would be wise to test the concentration of the solution before diluting further. It is sensible not to store diluted ammonia solutions for long periods. It is better to prepare diluted solutions only when required. Solutions less than 1 M should be made by further dilution of 1 M ammonia solution and are best made fresh before use. If you have other concentrations of concentrated ammonia, then contact CLEAPSS for more advice. Some of the values below are different from previous Recipe Cards as more precise information is now available. Formula: NH3 Molar mass: 17.03 g mol-1 Solubility: infinite General Hazards Concentrated ammonia; see Hazcards 5 & 6.

Take great care when opening bottles of concentrated ammonia on hot days. Volume of 880 ammonia to be used



0.1 M Ten-fold dilution of the 1 M solution - 0.5 M Two-fold dilution of 1 M solution - 1 M 28 55 138 - 2 M 55 111 276 - 5 M 138 276 691 IRRITANT

Preparing ammonia solutions

Use a fume cupboard if concentrated ammonia or solutions more concentrated than 5 M ammonia are used. Wear goggles (a face shield is preferable when handling large volumes) and chemical resistant gloves.

Measure the indicated quantity of ammonia solution in an appropriate measuring cylinder. Add the liquid to about two thirds of the final volume of water in an appropriate beaker or laboratory

jug. Pour the solution from the beaker into an appropriate measuring cylinder or laboratory jug and add

water to the required level. Pour into a labelled bottle and mix well. Add a hazard warning if appropriate.

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7 Ammonium chloride Formula: NH4Cl Molar mass: 53.5 g mol-1 Solubility: 36 g per 100 ml General Hazards See Hazcard 9A.




0.1 M Ten-fold dilution of the 1 M solution - 0.5 M 2.68 6.69 26.75 - 1.0 M 5.34 13.38 53.50 -

Saturated (20 C) 40 100 400 - Preparing ammonium chloride solution

Measure out the indicated quantity of ammonium chloride. Add the solid to about two thirds of the final volume of water in a beaker or laboratory jug. Stir to dissolve, warming if necessary. Pour the solution from the beaker into an appropriate measuring cylinder or laboratory jug and add

water to the required level. Pour into a labelled bottle.

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8 Ammonium vanadate(V) solution Also known as ammonium polytrioxovanadate(V) and ammonium metavanadate. Ammonium vanadate solution is used to illustrate the various oxidising states exhibited by vanadium. Ammonium vanadate is not very soluble in pure water and has to be dissolved in alkali first, before making acidic for use. Formula: NH4VO3 Molar mass: 117 g mol-1 Solubility: 0.52 g per 100 ml General Hazards Ammonium vanadate(V) is TOXIC. See Hazcards 9B, 91 and 98A.

Preparing 100 ml of 0.1 M ammonium vanadate solution

Wear goggles. Dissolve 1.17 g of ammonium vanadate(V) in 20 ml of 2 M sodium hydroxide in a beaker. (The odour

of ammonia may be detected but it will cause no harm.) Transfer the solution to a 100 ml measuring cylinder. Add 1 M sulfuric(VI) acid to bring the total volume to 100 ml. The yellow solution is irritant because of the presence of sulfuric(VI) acid.

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9 Azo dyes It is a myth that all azo dyes are carcinogens. The dyes can be prepared in schools as long as sensible laboratory procedures are observed. On the whole, the more soluble a dye and the presence of sulfonic acid groups on the benzene ring, then the safer the dye (eg, Orange II and methyl orange). See Guide G195 for preparation of azo dyes from ethyl 4-aminobenzoate. The recipes below can be used safely in schools. General Hazards Sulfanilic acid (4-aminobenzenesulfonic acid), see Hazcard 4B. Sodium nitrate(III)

(sodium nitrite); see Hazcard 93. Naphthalen-2-ol; see Hazcard 70. N,N-dimethylphenylamine; see Hazcard 4B. Sodium hydroxide; see Hazcard 91. Ethanoic acid; see Hazcard 38A. Sodium carbonate; see Hazcard 95A. Methyl orange; see Hazcard 32.

Preparing azo dyes as described is a two-stage process.

Stage 1: Preparing the diazonium salt of sulfanilic acid

Solution A: Add to a boiling tube, 0.6 g of sulfanilic acid,

0.2 g of anhydrous sodium carbonate and 10 ml of purified water.

Warm the mixture to boiling and then cool under the tap. Add 0.3 g of sodium nitrate(III) and agitate the test tube until the salt dissolves.

Solution B: In another boiling tube, cool down 8 ml of

1 M hydrochloric acid using an ice-water bath.

Add solution A to solution B. The diazonium salt settles out. It is more stable then many others and will keep for some hours.

Test for the presence of free nitrous acid with starch-iodide paper. If the paper does not turn blue, add a little more sodium nitrate(III). Swirl the contents of the boiling tube and divide the contents into two test tubes.

Stage 2 (a): Preparing Orange II (IRRITANT) and dying cotton with it

Wear goggles. Wear disposable nitrile gloves. In a test tube, dissolve 0.25 g of naphthalen-2-ol* in 4 ml of 1 M sodium hydroxide solution by

warming. Cool the solution in an ice-water bath and pour it into a Petri dish. Using forceps, add white cotton wool or cotton cloth (eg, bandage material) to the Petri dish to soak up

the solution. Add the contents of the test tube containing the diazonium salt onto the cotton. The dye will appear. Remove the cotton with forceps from the Petri dish and rinse it under cold water to remove any solid

dye. This is a soluble dye so do not do this for too long. Allow the cotton to dry. * Other phenols, benzene diols, cresols and naphthols can be used with the diazonium salt of sulfanilic acid to produce other dyes.

Stage 2 (b): Preparing methyl orange (TOXIC)

Wear goggles. Wear disposable nitrile gloves. In a test tube, add 0.2 ml of N,N-dimethylphenylamine to 0.2 ml of glacial ethanoic acid and agitate the

mixture well. Add the contents of the test tube containing the diazonium salt to the test tube containing

N,N-dimethylphenylamine. Leave for 5 minutes for the red dye to form. Add 2 ml of 2 M sodium hydroxide solution, heat to boiling and allow the solution to cool. The solid orange sodium salt of methyl orange should form.

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10 Barium solutions Purified water should be used to avoid cloudiness caused by the precipitation of barium sulfate(VI). Barium chloride is classified as TOXIC if swallowed and barium nitrate(V) as HARMFUL if swallowed. All solutions of barium nitrate(V) are LOW HAZARD. Barium chloride is more soluble in water than barium nitrate(V). General Hazards Barium chloride; see Hazcard 10A. Barium nitrate(V); see Hazcard 11.

Barium chloride

Formula: BaCl2.2H2O Molar mass: 244.26 g mol-1 Solubility: 26 g per 100 ml Mass (g) of solid to be used



0.01 M Ten-fold dilution of 0.1 M solution - 0.1 M 2.44 6.11 24.43 HARMFUL 0.5 M 12.21 30.53 122.13 HARMFUL

Saturated (20 C) 36 90 260 TOXIC Barium nitrate

Formula: Ba(NO3)2 Molar mass: 261.37 g mol-1 Solubility: 9 g per 100 ml Mass (g) of solid to be used



0.01 M Ten-fold dilution of 0.1 M solution - 0.1 M 2.61 6.53 26.14 -

Saturated (20 C) 9 45 90 - Preparing barium salts solutions

Wear eye protection. Wear disposable nitrile gloves when weighing and preparing the solution. Measure out the indicated quantity of the solid barium salt. Add the solid to about two thirds of the final volume of water in a beaker or laboratory jug. Stir to dissolve, warming if necessary. Pour the solution from the beaker into an appropriate measuring cylinder or laboratory jug and add


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12 CLEAPSS 2011

11 Benedicts qualitative reagent Benedicts solution or DNSA (see Recipe sheet 34) should be used in place of Fehlings solution to test for reducing sugars because it is less hazardous. Glucose, lactose and maltose are reducing sugars and give a positive test. Sucrose is a non-reducing sugar and does not give a positive result. Benedicts solution is less satisfactory in testing for non-reducing sugars and aldehydes in organic chemistry in which case Fehlings or Sandells solutions will be needed. No hazard warning symbol is required on the bottle as the concentrations of each of the constituents are low. This solution is not suitable for colorimetric work. See Recipe sheet 12 for Benedicts quantitative reagent or Recipe sheet 34 for DNSA. To differentiate between reducing sugars, enzyme tests are required. General Hazards Sodium carbonate; see Hazcard 95A. Copper sulfate(VI); see Hazcard 27C.

Procedure to produce 1 litre of solution

Wear eye protection. Measure out 170 g of trisodium citrate-2-water and 100 g of anhydrous sodium carbonate (or 256 g of

hydrated sodium carbonate). Add the solids to about 850 ml of purified water in a 1 litre beaker. Stir to dissolve, warming if necessary. Add 17.4 g of copper(II) sulfate(VI)-5-water and stir to dissolve. Pour the solution into an appropriate measuring cylinder and dilute to the final volume. Filter if necessary. Pour into a labelled bottle and mix well.

Procedure for carrying out the test

The material under test is mixed with about 1 ml of water in a test tube or vial, and about 3 ml of Benedict's reagent is added.

Place the test tube in a boiling water bath for about 5 minutes. The colour should progress from blue (with no glucose present) to green, yellow, orange, red, and

then brick red or brown as glucose concentration increases.

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12 Benedicts quantitative reagent The procedure detects the loss of blue colour as the sugar reduces the copper(II) ions to copper(I). It can be used either in volumetric or colorimetric methods. The addition of thiocyanate forms a complex and prevents the precipitation of copper(I) oxide. See also Recipe sheet 34 for DNSA which is an alternative test for reducing sugars. General Hazards Sodium carbonate; see Hazcard 95A. Copper sulfate(VI); see Hazcard 27C.

Potassium thiocyanate; Hazcard 95C. Potassium hexacyanoferrate(II) see Hazcard 79. The volumetric method uses hot liquids.

Preparing 1 litre of Benedicts quantitative solution (BQS)

Wear eye protection. Measure out 75 g of anhydrous (or 160 g of hydrated) sodium carbonate, 200 g of trisodium citrate-2-

water and 125 g of potassium thiocyanate. Add these solids to 700 ml of boiled distilled water in a 1 litre beaker. Stir to dissolve, reheating if necessary.

Measure out 18 g of copper(II) sulfate(VI), dissolve in 100 ml of purified water and add this, with constant stirring, to the solution made in step 1.

Add 0.25 g of potassium hexacyanoferrate(II) and pour the solution into a suitable volumetric flask. Dilute to the final volume with purified water and mix well. For the colorimetric procedure below, dilute

35 ml of this solution to 100 ml with water. (No hazard warning label is required at these concentrations.)

Using the solution: volumetric procedure

Place a 0.3% solution of glucose in a burette. Place 10 ml of BQS into a 100 ml conical flask, heat to boiling and add about 2 g of anhydrous sodium

carbonate. Add the glucose solution in 0.5 ml amounts, boiling each time until the blue or green colour just

disappears. Record the total volume of glucose added. When nearing the endpoint it is advisable to boil for 30 seconds to avoid overshooting.

Repeat the procedure to confirm your result. To measure the concentration of glucose in an unknown solution, repeat the procedure with glucose

solutions of unknown concentration. By comparing the volume obtained on titration of the known and unknown samples, the %

concentration of the unknown can be calculated.

% 0.3 x A = titration volume for known glucose solution B = titration volume for unknown glucose solution (Some methods suggest adding a few drops of 1% aqueous methylene blue solution to act as an indicator. It should be added when enough glucose solution has been added to turn the original solution a very pale blue colour.)

Using the solution: colorimetric procedure

Place a 1% solution of glucose in a burette. Place water in another burette and prepare a series of glucose solutions of varying concentration from

0 to 1%. In a series of labelled fresh test tubes, add 1 ml of each solution prepared in step 2, to 10 ml of BQS.

Place these in a boiling water bath for a few minutes. Allow the solutions to cool and any precipitates to settle. Use a red or yellow filter in the colorimeter. Obtain the absorbance of light through each solution. Use these readings to construct a glucose concentration calibration curve. Use the calibration curve to identify unknown concentrations of glucose solution.

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13 Biochemical indicators and tests Amino acid, polypeptide and protein tests See also Recipe Sheet 15 for the Biuret test. Coles modification of Millons reagent

Test for soluble proteins

Wear goggles and gloves. Dissolve 10 g of mercury(II) sulfate(VI) in 100 ml of 2 M sulfuric(VI) acid (solution A). Separately, dissolve 1 g of sodium nitrate(III) (nitrite) in 100 ml of water (solution B). Before use, mix two volumes of solution A with one of solution B. A reddish-brown colouration or precipitate indicates the presence of soluble proteins.

See Hazcards 62, 93, 98A. Solution A and the combined solution are TOXIC.

Marquiss reagent

Test for alkaloids

Wear goggles and gloves. Use a fume cupboard. Add 2 drops of 40% methanal solution to 3 ml of concentrated sulfuric(VI) acid just before use. This is a spot test and various colours appear. See http://en.wikipedia.org/wiki/Marquis_reagent.

See Hazcards 63 and 98. Label the solution CORROSIVE and TOXIC.

Ninhydrin For amine groups

Wear eye protection. Dissolve 0.1 g of ninhydrin in 100 ml of water. A purple colour, known as Ruhemann's purple, is produced when ninhydrin reacts with primary and secondary amines, indicating the presence of amino acids. Can be used as a spray or a dip, but needs to be heated, in an oven at 110 C or with a hairdryer, for the colours to appear.

See Hazcard 66. No hazard warning is required on the solution.

Sakaguchi test

Test for proteins containing arginine

Wear goggles. Dissolve 5 g of sodium hydroxide in 100 ml of water (solution A). Dissolve 1 g of napthalen-1-ol in 100 ml of water (solution B). For the test, one drop of sodium chlorate(I) solution (10-14% available chlorine, see Recipe sheet 81) is required as well. Proteins containing arginine appear an intense red colour.

See Hazcards 70, 89 & 91.

Carbohydrate tests See also 3,5-dinitrosalacylic acid (DNSA), Benedicts solution, Sandells solution and Fehlings solution. Molischs solution

For all carbo-hydrates

Wear goggles. Dissolve 5 g of napthalen-1-ol in 100 ml of ethanol. The solution containing a possible carbohydrate is combined with a small amount of Molisch's reagent in a test tube. After mixing, a small amount of concentrated sulfuric(VI) acid is slowly added down the sides of the sloping test tube, without mixing, to form a lower layer. Look for a purple ring at the interface of the two layers.

See Hazcards 40A, 70 & 98. Label the solution HIGHLY FLAMMABLE & HARMFUL.

Periodic acid Schiff (PAS) reaction

For poly-saccharides

Wear goggles and chemical-resistant gloves. Dissolve 1 g of iodic(VII) acid (periodic acid) in 100 ml of water. Used in conjunction with Schiffs reagent. Changes from colourless to purple.

Iodic(VII) acid is CORROSIVE & OXIDISING. No hazard warning is required on the solution.

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Cellular respiration Janus green B

Wear eye protection and disposable nitrile gloves when making up the solution. Dissolve 0.3 g of the dye in 100 ml of purified water. Dilute this solution ten times with water before use. Colour changes are from blue to salmon pink. See Guidance leaflet PS88 for more details including a practical activity.

No hazard label is required on the solution.

Methylene blue

Wear eye protection, and gloves to avoid staining the skin. Dissolve 1 g solid in 100 ml water and add 0.6 g sodium chloride. The blue indicator turns colourless as the dye is reduced.

See Hazcards 32 and 40. No hazard label is required on the solution.

TTC Dissolve 1 g of 2,3,5-triphenyl tetrazolium chloride (TTC) in 100 ml of water. (A 0.5% solution is less expensive and gives just as good results but takes longer. It works well with maize seedlings.) Turns red as the dye is reduced.

Low hazard.

Tasting and genetics studies Phenylthio-carbamide

This is also called PTC, phenylthiourea or PTU. Dissolve 0.05 g in 100 ml of water. Filter paper is soaked in the solution and then hung up to dry before cutting into strips. See Handbook 15.13 for details on tasting investigations.

The solid is VERY TOXIC; see Hazcard 35. The solution is low hazard.

Vitamin C DCPIP solution

Also called 2,6-dichlorophenol indophenol, and phenol-indodichlorophenol. Dissolve 0.1 g of dye in 100 ml of water. The standard vitamin C solution should also be 0.1% (w/v). Add the blue dye until the colour does not disappear.

Both are low hazard chemicals.

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14 Bismuth nitrate(V) solution The solutions need to be kept acidic to avoid the formation of insoluble basic salts. Formula: Bi(NO3)3.5H2O Molar mass: 395 g mol-1 General Hazards See Hazcards 67 & 73B. Preparing 100 ml of 0.1 M of bismuth nitrate(V) solution

Wear goggles. Dissolve 5.34 g of bismuth(III) nitrate(V)5-water in 70 ml of 1 M nitric(V) acid. Transfer the solution to a 100 ml measuring cylinder. Make up to 100 ml with 1 M nitric(V) acid. Label the solution CORROSIVE.

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15 Biuret reagent Biuret reagent tests for proteins. Previous methods and recipes for this solution have used more concentrated solutions than that described below. This meant that Y7 and 8 pupils were precluded from doing this experiment according to the advice on Hazcard 91 (sodium hydroxide). However, the procedure below uses 0.1 M sodium hydroxide and 0.01 M copper(II) sulfate(VI) solutions and teachers might find that further dilution is possible. It may be necessary to make acidic samples alkaline before the test for proteins is carried out. Coomassie blue can also be used to test for proteins. It is available in a test kit with instructions for use. Its advantages are that it does not require heating and is very sensitive.

Qualitative Biuret Reagent This does not keep so only prepare what is required. General Hazards Sodium hydroxide (solid) and 2 M solution. See Hazcards 91. Copper sulphate, see

Hazcard 27C. Preparing 1 litre of Qualitative Biuret reagent

Wear goggles. Weigh out 0.75 g of copper(II) sulfate(VI)-5 -water. Prepare 1 litre of 2 M potassium or sodium hydroxide solution. Dissolve the copper(II) sulfate(VI) in the alkali and label the solution CORROSIVE.

Procedure and use of Biuret solution suitable for Y7 and 8

Wear suitable eye protection. Prepare 0.01 M copper(II) sulfate(VI) solution (Recipe Sheet 31). Prepare 0.1 M sodium hydroxide solution (Recipe Sheet 85). Place the sample of a liquid to be tested in a test tube to a depth of 10 mm. Add the same volume of 0.1 M sodium hydroxide solution and agitate the test tube. Add a few drops of the 0.01 M copper(II) sulfate(VI) solution and agitate the test tube. A purple or pink colouration indicates the presence of protein.

Quantitative Biuret Reagent This does keep. General Hazards Sodium hydroxide (solid) and a 2 M solution see Hazcard 91. Copper(II) sulfate(VI)

see Hazcard 27C.

Wear goggles. Dissolve 1.5 g of copper(II) sulfate(VI)-5-water crystals and 6 g of potassium sodium tartrate-4-water in

500 g of purified water. Add 375 ml of 2 M sodium hydroxide with stirring. If a precipitate occurs, add 1 g of potassium iodide. Pour this mixture into a 1000 ml volumetric flask and dilute to 1 litre. Mix well. Label this solution

CORROSIVE as it is a 0.75 M sodium hydroxide solution. For quantitative analysis, a series of standards can be produced with solutions of varying % dilutions of a protein such as albumen, using a colorimeter with a 540 nm (green) filter. Unknown proteins solutions can then be compared against these standards.

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16 Brodies fluid Also known as manometer or manometric fluid. Water strongly adheres to glass so requires an emulsifier to avoid water droplets sticking to the walls of the manometer and affecting the readings, and to reduce capillary action in small bore manometers. General Hazards Sodium azide is VERY TOXIC and contact with acids liberates a very toxic gas. (See

Hazcard 95B). For eosin, see Hazcard 32. Once in solution, the solution is LOW HAZARD. Sodium azide may be omitted but the fluid will not keep as well and there will be mould growth.

A. Preparing 1 litre of Brodies fluid

Wear eye protection. Weigh out 46 g of sodium chloride, 10 g of sodium tauroglycocholate (bile salts), 0.2 g sodium azide

(optional) and 0.5 g of eosin. Make up to 1 litre with distilled or deionised water.

B. Brodies fluid substitute for short term use

44 g of sodium bromide. 1 g of liquid detergent (eg washing-up liquid). 0.3 g of Evans blue.

C. Simple version for short-term use

Use water with a food dye such as cochineal and a few drops of detergent.

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17 Bromine water The solubility of bromine in water is 4 g, (ie, 1.25 cm3 ) in 100 g of water at room temperature. This would be a 4% (w/v) solution. And its concentration would be 0.25 M. Solutions equal to or greater than 0.06 mol dm-3 (ie, a 0.3% v/v solution) are TOXIC. Solutions equal to or more concentrated than 0.006 mol dm-3 (0.1% w/v or 0.03% v/v) but more dilute than 0.06 mol dm-3 should be labelled HARMFUL. Aqueous solutions of bromine should be prepared just before use. If stored for long periods, especially though the summer, the solution becomes paler as bromine vapour is lost. Do not make this solution for the first time without seeking practical advice from a more-experienced colleague. General Hazards Bromine is VERY TOXIC and CORROSIVE (see Hazcard 15A). Hazcard 15B deals with

bromine water. 0.025 M bromine water has a considerable vapour of bromine gas above it. It should be dispensed from a fume cupboard. More-dilute solutions can be used in a well-ventilated room but staff should discourage any direct inhalation of the vapour. Sodium chlorate(I) is CORROSIVE (see Hazcard 89), 2 M hydrochloric acid; see Hazcard 47A, Potassium bromate(V) is TOXIC, (see Hazcard 80).

Preparing 1 litre of 0.02 M solution (HARMFUL) of bromine water

Method 1 Use a fume cupboard. Wear goggles or a face shield and chemical-resistant gloves. Using a disposable plastic pipette, add 1 ml of bromine to 500 ml of water in a 1 litre beaker. Add a stirrer bar and place on a magnetic stirrer to dissolve the bromine. This can take over

20 minutes. Dilute to 1 litre with water. Alternatively, an ampoule containing 1 ml of bromine can be crushed under 500 ml of water, stirred

using a magnetic stirrer until it dissolves and made up to 1 litre with water. The solution must be decanted so that no broken glass is present.

Method 2

Use a fume cupboard. Wear goggles or a face shield. Consider wearing gloves. Dissolve 4.76 g of potassium bromide in 76 ml of water, add 14 ml of 10% (available chlorine) sodium

chlorate(I) solution (CORROSIVE) and 10 ml of 2 M hydrochloric acid (IRRITANT). Dilute to 1 litre with water.

Method 3 This reaction is slow and it is better to leave the solution 24 hours before it is used.

Use a fume cupboard. Wear eye protection. Add 1.12 g of potassium bromate(V) (TOXIC), 12 g of potassium bromide and 14 ml of 2 mol dm-3

hydrochloric acid (IRRITANT) into a 1 litre jug or measuring cylinder. Add water to 1 litre.

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18 Buffer solutions Buffer solutions retain their pH on addition of small amounts of acid, alkali or on dilution. Unless stated otherwise, buffers are low hazard but eye protection should be worn during preparation. The pH value of a buffer is slightly altered by temperature but this is not usually significant. The values used in the Recipe Sheet are for 20 C. A definition for pH suitable for schools is minus the logarithm (to the base 10, ie log10) of the hydrogen ion concentration in an aqueous solution. For a more advanced explanation, consult http://en.wikipedia.org/wiki/PH. There is also a pOH scale and pH + pOH =14. A pH meter should be calibrated with standard buffers before it is used. These may be prepared from tablets or commercial solutions. Use distilled or deionised water to make up buffers. Single-component buffers are very quick to make up but the values may not always be convenient. The majority of buffers involve two components mixed in certain proportions. For accurate work, it is wise to check their pH with a calibrated pH meter. A universal buffer mixture can be used to obtain an array of buffer solutions from pH 2 to 11. The stock solution can, usefully, be stored for several months. Buffers (especially those between pH 4 and pH 7) do not keep well. Moulds develop which affect pH readings and block the junctions on pH probes. Commercial buffer solutions contain a mould inhibitor which allows longer storage. To save time buffers can be stored as pre-weighed dry components or as frozen solutions. Before use, make sure frozen solutions are returned to room temperature, that all components are fully dissolved, and check the pH. Special biological buffers (eg, TRIS) are available that do not use phosphate(V) or ethanoate ions which might interfere with some biochemical processes. They are named Good buffers after their developer, Norman Good. Different enzymes are inhibited by different reagents, so check the protocol and choose the correct buffer system.

Single component buffers

pH 1.7 buffer

Dissolve 1.27 g of potassium hydrogen-ethanoate-1-ethanedioic acid-2-water (potassium tetroxalate) in 10 ml of hot water and make up to 100 ml with cold water.

Low hazard See Hazcard 36A.

pH 4 buffer Dissolve 1.01 g of potassium hydrogenphthalate in 10 ml of hot water and make up to 100 ml with cold water. The solution does not keep well because of mould growth.

Low hazard See Hazcard 13B.

pH 7 buffer Dissolve 0.77 g of ammonium ethanoate in 100 ml of cold water. The solution does not keep well because of mould growth.

Low hazard See Hazcard 9B.

pH 9.2 buffer

Dissolve 0.38 g of sodium tetraborate-10-water in 100 ml of water. Low hazard See Hazcard 14.

pH 12.6 buffer

Use saturated limewater solution. Low hazard but wear eye protection. See Hazcard 18.

Temperature effects on single component buffers

Temperature / C 5 10 15 20 25 30 40 50 60 70 80 90 pH 4 buffer 4.01 4 4 4 4.01 4.01 4.03 4.06 4.09 4.12 4.16 4.2 pH 9.2 buffer 9.39 9.33 9.27 9.23 9.18 9.14 9.07 9.02 8.97 8.93 8.89 8.85

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Buffers for pH probe calibration

pH 4 buffer Dissolve 1.012 g of potassium hydrogenphthalate in 10 ml of hot water and make up to 100 ml with cold water. The solution does not keep well because of mould growth.

See Hazcard 13B

pH7 buffer 0.339 g of citric acid and 4.306 disodium hydrogenphosphate(V)-12-water (or 1.707 g of anhydrous salt) dissolved in water and made up to 100 ml with water.

See Hazcard 9B.

pH10 buffer 0.477 g sodium tetraborate-10-water and 18.3 ml of 0.1 M sodium hydroxide (from a burette) is made up to 100 ml with water.

See Hazcards 14 and 91.

NB Although masses are given to 3 decimal places, it would be acceptable to work to 2 decimal places.

Double component buffers

To prepare these buffers, make up the individual components, then mix the quantities given for the required pH. For accurate work, confirm the values with a calibrated pH meter and probe. Using a solid and a solution.

General Hazards As 0.1 M sodium hydroxide solution is IRRITANT, wear eye protection when preparing the buffers. All the resulting buffers are low hazard. See Hazcards 13B, 36C and 91.

3 10.21 g potassium hydrogen phthalate and 223 ml of 0.1 M hydrochloric acid

Dilute each mixture to 1 litre solution with distilled or deionised water.

4 10.21 g potassium hydrogen phthalate

5 10.21 g potassium hydrogen phthalate and 226 ml of freshly-made 0.1 M sodium hydroxide solution

6 6.81 g potassium dihydrogen phosphate and 56 ml of freshly-made 0.1 M sodium hydroxide solution

7 6.81 g potassium dihydrogen phosphate and 291 ml of 0.1 M sodium hydroxide solution

8 6.81 g potassium dihydrogen phosphate and 467 ml of freshly-made 0.1 M sodium hydroxide solution

9 4.77 g sodium tetraborate-10-water and 46 ml of 0.1 M hydrochloric acid

10 4.77 g sodium tetraborate-10-water and 183 ml of freshly-made 0.1 M sodium hydroxide solution

11 2.1 g sodium bicarbonate and 227 ml of freshly-made 0.1 M sodium hydroxide solution

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Mixing two prepared solutions Consult the relevant Recipe Sheets for the preparation of the solutions. General Hazards

All these buffers are low hazard. See relevant Hazcards for more information.

The citric acid/disodium hydrogenphosphate(V) buffer system

A is 0.2 M disodium hydrogenphosphate(V) and B is 0.1 M citric acid.

pH A (ml) B (ml) pH A (ml) B (ml) pH A (ml) B (ml) 2.2 2.00 98.00 4.2 41.40 58.60 6.2 66.10 33.90 2.4 6.20 93.80 4.4 44.10 55.90 6.4 69.25 30.75 2.6 10.90 89.10 4.6 46.75 53.25 6.6 72.75 27.25 2.8 15.85 84.15 4.8 49.30 50.70 6.8 77.25 22.75 3.0 20.55 79.45 5.0 51.50 48.50 7.0 82.35 17.65 3.2 24.70 75.30 5.2 53.60 46.40 7.2 86.95 13.05 3.4 28.50 71.50 5.4 55.75 44.25 7.4 90.85 9.15 3.6 32.20 67.80 5.6 58.00 42.00 7.6 93.65 6.35 3.8 35.50 64.50 5.8 60.45 39.55 7.8 95.75 4.25 4.0 38.55 61.45 6.0 63.15 36.85 8.0 97.25 2.75

The ethanoic acid/sodium ethanoate buffer

system The ammonia/ammonium chloride buffer

system Add the stated volume of A (0.2 M sodium ethanoate solution) to the stated volume B

(0.2 M ethanoic acid)

Add the stated volume of A (0.2 M ammonia) to the stated volume of B (0.2 M ammonium

chloride solution) pH A (ml) B (ml) pH A (ml) B (ml) 3.8 12.0 88.0 8.4 12.5 87.5 4.0 18.0 82.0 8.6 18.5 81.5 4.2 26.5 73.5 8.8 26.0 74.0 4.4 37.0 63.0 9.0 36.0 64.0 4.6 49.0 51.0 9.25 50.0 50.0 4.8 60.0 40.0 9.4 58.5 41.5 5.0 70.5 29.5 9.6 69.0 31.0 5.2 79.0 21.0 9.8 78.0 22.0 5.4 85.5 14.05 10.0 85.0 15.0

The sodium hydrogencarbonate/sodium

hydroxide) system buffer system The phosphate(V) buffer system. (potassium

salts may also be used) Add the stated volume of A (0.1 M sodium

hydroxide) to 50 ml of 0.05 M sodium hydrogencarbonate and dilute to 100 ml

(Wear eye protection.)

Add the stated volume of A [0.2 M sodium dihydrogenphosphate(V)] to the stated

volume of B [0.2 M disodium hydrogenphosphate(V)]

pH A (ml) pH A (ml) B (ml) 9.6 5.00 6.0 87.7 12.3 9.8 6.20 6.5 68.5 31.5 10.0 10.70 7.0 39.0 61.0 10.2 13.80 7.5 16.0 84.0 10.4 16.50 8.0 5.3 94.7 10.6 19.10 10.8 21.20 11.0 22.70

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Universal Buffer solutions

The Universal Buffer: Recipe 1

Wear eye protection. To prepare the stock solution, add 9.9 g of disodium hydrogenphosphate-12-water, (or 4.6 g disodium

hydrogenphosphate-2-water) (see Hazcard 72), 7.0 g of citric acid (see Hazcard 9) and 3.5 g of boric acid (see Hazcard 14) to 250 ml of 1 M sodium hydroxide solution (see Hazcard 91) and dilute to 1000 ml with distilled/deionised water. This solution keeps well. Label the solution IRRITANT.

To make any buffer between 3.5 and 10

Wear eye protection. Place 0.1 M hydrochloric acid in a burette. Place 20 ml of the stock solution in a 250 ml beaker on a magnetic stirrer. Clamp a pH probe into the

solution. Add the acid to the solution in the beaker with constant stirring until the required pH is obtained. If too

much acid is added, use a little more stock solution to increase the pH value. Add distilled/deionised water to make the final solution 100 ml.

The Universal Buffer: Recipe 2

Wear eye protection. To 500 ml of water, add 2 ml of concentrated ethanoic acid (see Hazcard 38A), 3 ml of 85%

phosphoric(V) acid (see Hazcard 72), and 2.4 g of boric acid (see Hazcard 14), and make the solution up to one litre with distilled/deionised water.

Prepare 0.2 M sodium hydroxide solution (see Hazcard 91), and label the solution IRRITANT. To make any buffer between 2 and 11

Wear eye protection. Put 0.2 M sodium hydroxide solution in a burette. Place 100 ml of the acid solution in a 400 ml beaker on a magnetic stirrer. Clamp a calibrated pH

probe into the solution. Add 0.2 M sodium hydroxide to the acid solution until the required pH is obtained.

Buffer solutions: Biological Two component buffers are often used for biological systems. However, if an enzyme is affected by one, or more, of the component ions, eg, phosphate(V), ethanoate or ammonium ions, specialist buffers are required. The cheapest specialist biological buffer is tris(hydroxymethylamino)methane (IRRITANT) known as TRIS. The solutions made up from the data below are low hazard.

TRIS buffers

pH Volume of 0.1 M TRIS solution

Volume of 0.1 M hydrochloric acid

7.0 100 93.2 7.5 100 80.6 8.0 100 58.4 8.5 100 29.4 9.0 100 11.4

A full range of biological buffers can be found at www.sigmaaldrich.com/life-science/core-bioreagebnts/bioogical-buffers.html. For products and applications such as extraction of materials or electrophoresis, see protocols at www.ncbe.reading.ac.uk.

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19 Calcium chloride and nitrate(V) solutions Hydrated calcium chloride and nitrate(V) absorb water from the atmosphere. On occasions, the solid completely dissolves to leave a clear solution. Distilled or deionised water should be used to make solutions. In hard water areas, solutions may be cloudy if tap water is used. Do not use anhydrous calcium chloride to make solutions. General Hazards See Hazcard 19A

Formula: CaCl2.6H2O Molar mass: 219.08 g mol-1 Solubility: 74 g per 100 ml Preparing 100 ml of 0.1 M of calcium chloride solution

Wear eye protection. Dissolve 2.19 g of calcium chloride-6-water in 70 ml of water. Transfer the solution to a 100 ml measuring cylinder. Make up to 100 ml with water. The solution is low hazard.

Formula: Ca(NO3)2.4H2O Molar mass: 236.15 g mol-1 Solubility: 121 g per 100 ml Preparing 100 ml of 0.1 M of calcium nitrate(V) solution

Wear eye protection. Dissolve 2.36 g of calcium nitrate-4-water in 70 ml of water. Transfer the solution to a 100 ml measuring cylinder. Make up to 100 ml with water. The solution is low hazard.

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20 Calcium hydroxide solution (Limewater) Saturated calcium hydroxide solution, commonly called lime water, is a 0.02 M aqueous solution of calcium hydroxide with a pH of 12.4. It does not keep for long periods in large bottles because it reacts with carbon dioxide from the atmosphere. It would be wise to start afresh each year. Lime water, in small bottles designed for class use, will quickly cease to work. Class sets need to be tested before handing out to the class. 1 M hydrochloric acid can be used to clean bottles that previously contained limewater. Formula: Ca(OH)2 Molar mass: 74.09 g mol-1 Solubility: 0.15 g per 100 ml General Hazards Calcium hydroxide solid; see Hazcard 18. Splashed droplets of limewater in the eye

have caused quite severe irritation, so the solution should also be labelled and treated as an IRRITANT even though strictly its dilution is such that it is not formally classed as hazardous.

Preparing make 2.5 L of lime water in a bottle

Wear eye protection. Place 5 g of calcium hydroxide in a 600 ml beaker and half-fill it with water. Stir the suspension and pour it via a funnel into a 2.5 litre bottle. Fill the bottle with water, stopper and shake it. Leave the bottle overnight for the suspension to settle. When required, decant the limewater solution, slowly without agitating the sediment, into smaller

bottles for use in lessons. Add more water and/or calcium hydroxide suspension when the level becomes low.

Preparing a large continual supply

If a large stock is required, keep an excess of calcium hydroxide in an aspirator protected by a soda-lime tube, as shown below, and top up with distilled water as necessary.

Use about 100 g calcium hydroxide for a 10 litre aspirator. It might take a week to fully settle.

Absorption tubefilled with soda lime

Calcium hydroxide

Limewater

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21 Carbon dioxide Carbon dioxide is prepared by the action of dilute hydrochloric or nitric acid on calcium carbonate, usually as marble chips. If powdered calcium carbonate is used, the rate of gas production may be too rapid to be easily controlled. The gas is collected over water or by downward delivery. (Downward delivery uses a tube into the bottom of an upright gas jar. It is also known as upward displacement of air and relies on the fact that carbon dioxide is more dense than air.) Although carbon dioxide is slightly soluble in water (at room temperature, the solubility of carbon dioxide is about 6.4 cm3 of carbon dioxide per 100 ml of water), the rate at which it dissolves is slow. However, if necessary, the gas can be collected over warm water in which it is less soluble. Collection by downward delivery is quicker but it is difficult to ascertain exactly when the gas jar is full. However, downward delivery is necessary for burning magnesium in carbon dioxide, in order to avoid water interfering with the reaction. Soda water is a saturated solution of carbon dioxide in water (carbonic acid). General Hazards See Hazcards 20 & 47A.

Wear eye protection. In the 250 ml Bchner flask, add several lumps of marble chips. Add enough water to immerse the base of the thistle funnel tube. Set up the apparatus as shown in the diagram. The inverted measuring cylinder should be full with water. Now add 5 ml of 5 M hydrochloric acid (IRRITANT) down the thistle funnel. Once the measuring cylinder is full of gas, it indicates the apparatus has been completely purged.

Remove it and replace with an inverted gas jar full of warm water. Keep collecting gas jars of gas. When full of gas, either slide a gas jar cover in place or put a large

bung into the gas jar. If the rate of gas production slows down but more gas is needed, add further 5 ml portions of 5 M

hydrochloric acid.

Add 5 mol dm hydrochloric acid-3

250 ml measuring cylinder

Warm water

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22 Cerium(IV) solutions Cerium(IV) compounds have a variable water content, which makes preparing accurate concentration solutions very difficult. This is why the mass given in the recipe is approximate.

Cerium(IV) solutions, which have an intense yellow colour, are used in redox titrations.

Cerium(IV) solutions are more stable in solution than potassium manganate(VII) solutions.

Cerium(IV) solutions need to be prepared in dilute sulfuric(VI) acid. [Hydrochloric acid must be avoided as cerium(IV) ions oxidise the chloride ions slowly to chlorine.]

Cerium(IV) solutions should be standardised against sodium ethanedioate solution before use.

General Hazards The solids are irritating to the eyes, respiratory system and skin.

Preparing 1 litre of 0.1 M cerium(IV) ions

Wear eye protection. Measure out about 64 g of ammonium cerium(IV) sulfate(VI)-2-water or 40 g of cerium(IV) sulfate(VI)-

4-water. Add the solid to about 500 ml of 1 M sulfuric(VI) acid in a beaker. Stir to dissolve, warming if necessary. Pour the solution into a 1-litre volumetric flask and make it up to the mark with water. Pour into a labelled bottle. The solution is low hazard.

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23 Chemiluminesence reactions Luminol (3-aminobenzene-1,2-dicarboxylic hydrazide or 3-aminophthalhydrazide) in alkaline solution is oxidised to the 4-aminobenzene-1,2-dicarboxylate ion with the evolution of oxygen. Goggles should be worn when preparing the solutions if using solid sodium hydroxide but spectacles are suitable for the demonstrations using the solutions. Recipe D is ideal for a chemiluminescent fountain demonstration using ammonia (see picture below).

Four recipes illustrating chemiluminesence reactions A Solution A: Dissolve 0.4 g of luminol and 4 g of potassium hydroxide or sodium

hydroxide in 1000 ml of water. Label the container IRRITANT. Solution B: Dilute 50 ml of fresh (10-14% available chlorine) sodium chlorate(I)

solution to 1000 ml. Label the container IRRITANT. In a darkened room, mix equal volumes of solutions A & B together. The addition

of a pellet of potassium hydroxide or sodium hydroxide may produce more light.

See Hazcards 4B, 89, 91. Wear goggles to prepare the solution.

B Dissolve 0.2 g of luminol and 1 g of potassium hydroxide or sodium hydroxide in 1000 ml of water. To a known volume of this solution add an equal volume of 20 vol hydrogen peroxide solution.

In a darkened room, sprinkle a few crystals of potassium hexacyanoferrate(III) onto the surface of the solution and observe the trails of light.

The addition of a pellet of potassium hydroxide or sodium hydroxide may produce more light.

See Hazcards 4B, 50, 79, 91. Wear goggles to prepare the solution.

C Solution A: Dissolve 0.2 g luminol, 4 g of anhydrous sodium carbonate, 24 g of sodium hydrogencarbonate, 0.5 g of ammonium carbonate and 0.4 g of hydrated copper(II) sulfate(VI) in 1000 ml water.

Solution B: Prepare 1000 ml of 5 vol hydrogen peroxide solution. Mix equal volumes of A and B in a dark room or in a box with spy holes.

See Hazcards 4B, 27C, 50, 95A.

D Solution A: Mix together 0.2 g luminol, 11 g of anhydrous sodium carbonate, 8 g of sodium hydrogencarbonate, 0.5 g of ammonium carbonate and 0.4 g of copper(II) sulfate(VI) in 1000 ml water. Add 25 ml of 10 vol hydrogen peroxide.

Solution B: Dissolve 0.1 g of cobalt(II) chloride and 0.1 g of sodium nitrate(III) (ie, sodium nitrite) in 1000 ml of water.

Mix equal volumes of A and B in a dark room or in a box with spy holes.

See Hazcards 4B, 9A, 25, 27C, 50, 89, 93, 95A.

The chemiluminescent fountain demonstration

The flask is originally filled with ammonia. Two containers labelled A and B which contain 1 litre each of solution A & B in Recipe D are used to supply the solution in the fountain. The solutions are connected via a T-piece into a single tube which is inserted into the flask.

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24 Chlorine gas Version 1: Concentrated hydrochloric acid on potassium manganate(VII) The reaction of concentrated hydrochloric acid on potassium manganate(VII) is the more common and reliable of the two methods. However it uses more-hazardous starting chemicals. It produces chlorine quickly. The glassware is difficult to clean at the end and more-concentrated hydrochloric acid is required to remove manganese(IV) oxide stains. Do not make this solution for the first time without seeking practical advice from a more-experienced colleague. General Hazards See Hazcards 22A, 20 & 81. Double check that you are using concentrated

hydrochloric acid and not concentrated sulfuric(VI) acid. Explosions have resulted from using the wrong acid.

Use a fume cupboard. Make sure it is working. Wear goggles. Set up the equipment as in the illustration below. Make sure that the thistle funnel tube nearly reaches

the base of the flask. Place at least 5 g of potassium manganate(VII) (OXIDISING & HARMFUL) in the Bchner flask. Pour the concentrated hydrochloric acid (CORROSIVE) down the thistle funnel. Collect the gas in a gas jar. When the contents of the gas jar are clearly green, assume the gas jar is

full. Or (optional), plug the gas jar with a large wad of mineral wool, or cotton wool, and put some damp blue litmus paper on top. It takes time for the chlorine to diffuse through the wool and bleach the litmus. When the bleaching is complete the jar will be full. Remove it and replace the mineral wool with a gas jar cover or a large bung.

More gas jars of gas can be collected. To dispose of the reaction mixture, pour it down the fume cupboard sink with lots of water. The stained

glass may need treating with a little concentrated hydrochloric acid before washing further.

Mineral wool

Moist blue litmus

At least 5 g of Potassium Manganate(VII)

Wooden block

Gas jar

Delivery tube as fardown as possible

In a fume cupboard, pour concentrated hydrochloric acid down the thistle funnel

Bchner flask

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30 CLEAPSS 2011

Version 2: 5 M hydrochloric acid added to sodium chlorate(I) solution This reaction is slower than first version and is easier to control. The glassware is easy to clean at the end of the procedure. Sodium chlorate(I) solution is difficult to store and must be less than 1 year old to obtain a good supply of chlorine. Domestic bleach is not suitable. As the reaction subsides, either the acid or the sodium chlorate(I) solution can be alternatively added to the reaction vessel to supply more gas. The gas preparation arrangement (shown below) is known as the Andrews method. It is an alternative arrangement to using a thistle funnel. The arrangement in version 1 can also be used. Do not make this solution for the first time without seeking practical advice from a more-experienced colleague. General Hazards See Hazcards 22A, 20 & 89. Sodium chlorate(I) is a solution provided by the

supplier often as sodium hypochlorite. Sodium chlorate(V) is a solid. Do not get them mixed up.

Use a fume cupboard. Make sure it is working. Wear goggles. Place at least 50 ml sodium chlorate(I) solution (CORROSIVE) in the Bchner flask. Set up the equipment as in the illustration below. The magnetic stirrer is optional but it does appear to

make the procedure more efficient. Pour the 5 M hydrochloric acid (IRRITANT) into the separating funnel. Turn the stirrer on and drip the acid into the flask. The solution will now bubble as the chlorine is

produced. Collect the gas in a gas jar. When the contents of the gas jar are clearly green, assume the gas jar is

full. Or (optional), plug the gas jar with a large wad of cotton or mineral wool and put some damp blue litmus paper on top. It takes time for the chlorine to diffuse through the cotton wool and bleach the litmus. When the bleaching is complete the jar will be full. Remove it and replace the mineral wool with a gas jar cover or a large bung.

To dispose of the reaction mixture, pour it down the fume cupboard sink with lots of water.

Separating funnel

5 M hydrochloric acid

Magnetic stirrer

Sodium chlorate(i)solution

Mineral wool

Moist blue litmus

Gas jarDelivery tube as fardown as possible

Rubber tubing

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25 Chlorine water The solubility of chlorine in water is about 0.6 g in 100 ml of water at room temperature. This would be a 0.6% (w/v) solution. Its concentration would be 0.085 M. An aqueous solution of chlorine should be prepared just before use. It does not keep for more than just a few days and should not be stored. It is very difficult to make up solutions of known concentration. All that is required for displacement reactions is that the solution works. It should, therefore, be trialled before use. Do not make this solution for the first time without seeking practical advice from a more experienced colleague. Three methods are described below. General Hazards Chlorine gas is TOXIC and CORROSIVE (see Hazcard 22A). Hazcard 22B deals with

chlorine water. Freshly-made chlorine water is formally LOW HAZARD but it has a considerable vapour of chlorine gas above it. It is better dispensed from a fume cupboard. More dilute solutions can be used in a well-ventilated room but staff should discourage direct inhalation of the vapour.

Method 1 Use a fume cupboard. Wear goggles or a face shield and chemical-resistant gloves. Bubble chlorine gas into 250 ml water in a gas jar until the solution goes light green. Use the

equipment for preparing chlorine gas but fill the gas jar half-full with water.

Method 2 Sodium chlorate(I) solution is an aqueous solution. Do not become confused with sodium chlorate(V), which is a solid.

10% w/v available chlorine sodium chlorate(I) solution does not store well. Over two years it may become completely useless.

Use a fume cupboard. Wear goggles or a face shield and chemical-resistant gloves. Place 10 ml of 10% w/v available chlorine sodium chlorate(I) solution (CORROSIVE) in 1 litre beaker. Add about 80 ml of water and 10 ml of 2 M hydrochloric acid. Stir well. Dilute to a suitable volume with more water.

Method 3 Sodium dichloroisocyanurate is used for purifying water.

Use a fume cupboard. Wear eye protection. Add 3 g of sodium dichloroisocyanurate (OXIDISING; HARMFUL), to 100 cm3 of water. When the solution

is clear, add 100 cm3 of 1 mol dm-3 hydrochloric acid.

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26 Chromatography solvents and locating agents A mixture of compounds is placed on a stationary phase such as paper, or silica on thin layer plates. Chromatography involves passing a solvent through the stationary phase which separates the components of the mixture due to subtle differences in a compound's partition coefficient between the mobile solvent and the stationary phase. A locating agent is used to emphasise where the components of the mixture end up after the chromatography has finished. This is particularly important for colourless components of mixtures. Control measures for all of the following solutions

Solutions are better made up in a fume cupboard. Wear eye protection. There must be no sources of ignition in the vicinity.

Substances separated

Amino acids Solvent: Butan-1-ol, glacial ethanoic acid, water; 6:1:2 by volume.

Locator: Apply ninhydrin and heat in an oven at 110 C or with a hairdryer.

See Hazcards 38A, 66, 84B. Label solvent HARMFUL and CORROSIVE.

Analgesics, eg, aspirin, paracetamol

Solvent: Ethyl ethanoate, hexane, ethanoic acid; 10:9:1 by volume.

Locator: UV light or iodine vapour. Do not look directly at UV radiation sources.

Label the solvent HIGHLY FLAMMABLE and CORROSIVE. See Hazcards 43A, 54A.

Anthocyanins (plant pigments)

Solvent: 100 ml 50% aqueous methanol solution with 1 ml of ethanoic acid or 1 ml concentrated hydrochloric acid in 100 ml ethanol.

Locator: Natural colour. (The components are light sensitive so run the chromatograms in the dark if possible and quickly note or photograph the results.)

Label the solvent HIGHLY FLAMMABLE and TOXIC. See Hazcards 38A, 40B.

Inks from Biro pens

Solvent: Butan-1-ol, ethanol, water; 3:1:1 by volume. The addition of a few drops of 880 ammonia is said to produce a better chromatogram.

Locator: Natural colour.

Label the solvent HIGHLY FLAMMABLE and HARMFUL. See Hazcards 6, 40A, 84B.

Chlorophyll Solvent: Propanone, petroleum spirit (100-120 C); 1 :9 by volume or cyclohexane, propanone, ethoxyethane; 2:1:1 by volume.

Locator: Natural colour of dyes and UV light. Do not look directly at UV light. (The components are light sensitive so the results should be noted or photographed quickly.)

Label the solvents HIGHLY FLAMMABLE. See Hazcards 45A, 85 or 42, 45B, 85.

Lipstick Solvent: 3-Methylbutan-1-ol,propanone and water; 2:1:9 by volume.

Locator: Natural colour.

The solvent is LOW HAZARD See Hazcards 84C, 85.

Metal ions Solvent: Propanone, hydrochloric acid (conc), Distilled water; 17:2:1 by volume.

Locator: Use conc ammonia solution followed by 0.1% dithio-oxamide (rubeanic acid).

Label solvent HIGHLY FLAMMABLE and IRRITANT Label the locator CORROSIVE. See Hazcards 35, 47A, 85.

Nitration of methyl benzoate

For separating the crude products obtained from the nitration of methyl benzoate. Solvent: Ethoxyethane, pet ether (80/100 C); 1:9 by volume. Locator: UV light. Do not look directly at UV radiation sources.

Label the solvent HIGHLY FLAMMABLE and HARMFUL. See Hazcards 42, 45A.

Sugars Solvent: Ethyl ethanoate, pyridine, water, 8:2:1 by volume. Locator: Dab Benedicts solution on the chromatogram and dry in

an oven at 110 C.

Label the solvent HIGHLY FLAMMABLE. See Hazcards 4C, 8, 43A.

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27 Chromium(III) chloride and chrome alum solutions The colour of chromium(III) solutions varies with temperature and storage. Use cold water to dissolve the salt and do not heat the solutions. Prepare just before use. General Hazards Chromium (III) salts are IRRITANT. See Hazcard 24.

Formula: CrCl3.6H2O Molar mass: 266.5 g mol-1 Solubility: 58 g per 100 ml Preparing 100 ml of 0.1 M chromium(III) chloride solution

Wear eye protection. Dissolve 2.67 g of chromium(III) chloride-6-water in 70 ml of cold pure water. Make up to 100 ml with pure water. The solution is low hazard.

Formula: CrK(SO4)2.12H2O Molar mass: 499.4 g mol-1 Solubility: 22 g per 100 ml Preparing 100 ml of 0.1 M chromium(III) potassium sulfate(VI) solution

Wear eye protection. Dissolve 5.0 g of chromium(III) potassium sulfate(VI)-12-water in 70 ml of cold pure water. Make up to 100 ml with pure water. The solution is low hazard.

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28 Citric acid Also known as 2-hydroxypropane-1,2,3-tricarboxylic acid. It can purchased in either an anhydrous or monohydrate form. Values in italics below are for the monohydrate form. General Hazards See Hazcard 36C.

Formula: C6H8O7 Molar mass: 192.12 g mol-1 Solubility: 133 g per 100 ml Formula: C6H8O7.H2O Molar mass: 210.14 g mol-1 Solubility: 133 g per 100 ml Mass (g) of solid to be used



0.01 M Ten-fold dilution of 0.1 M solution - 0.1 M 1.92 (2.10) 4.80 (5.35) 19.21 (21.01) - 0.5 M 9.60 (10.51) 24.02 (26.27) 96.06 (105.07) - 1.0 M 19.21 (21.01) 48.03 (53.54) 192.12 (210.14) -

Saturated (20 C) 150 450 1500 IRRITANT Procedure

Wear eye protection. Measure out the indicated quantity of the solid citric acid. Add the solid to about two thirds of the final volume of water in a beaker or laboratory jug. Stir to dissolve, warming if necessary. Pour the solution from the beaker into an appropriate measuring cylinder or laboratory jug and add


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29 Clock reactions These are used for rate of reaction investigations. Solutions should be made a day before use and stored in the place where they will be used to attain room temperature. Clock reactions need to be tried out beforehand so that concentrations can be tweaked to give reasonable times. Summer and winter temperature variations can also alter reaction times. The suggested amounts are for student activities. These reactions, however, make excellent demonstrations and the volumes can be significantly increased. The asterisk by the name of a solution indicates that this reagent is involved in the main reaction and its concentration can be varied. However, the amount of each solution must remain as specified. Varying reaction temperature will alter the time lapse for the clock. The addition of transition metal ions, eg, copper(II) ions, as a catalyst can also be investigated. However, you need to trial the experiment as the sequence that components are added is very important. The hydrogen peroxide/potassium iodide reaction (The Harcourt-Essen reaction)

Solution A 1% starch solution (indicator) Solution B* 4 vol hydrogen peroxide Solution C* 0.1 M hydrochloric acid Solution D 0.01 M sodium thiosulfate Solution E* 0.05 M potassium iodide Add 5 drops of solution A to a suitable beaker plus 10 ml each of solutions B to E in that order.

See Hazcards 47A & B, 67, 95C. Wear eye protection.

The thiosulfate/acid reaction (disappearing cross)

Solution A 0.1 M sodium thiosulfate Solution B 1 M hydrochloric or 0.05 M sulfuric(VI) acid Add 1 ml of the acid for every 10 ml of sodium thiosulfate. Once the run is complete, dispose of the contents in 0.5 M sodium carbonate solution to stop the reaction and neutralise sulfur dioxide.

See Hazcards 47A, 95C & 98. Wear eye protection. Do not use temperatures above 50 C.

The potassium iodate/sodium metabisulfite reaction (The Landolt iodine clock)

Solution A 1% starch solution (indicator) Solution B* 0.025 M potassium iodate(V) solution (5.35 g per 1000 ml of solution) Solution C* 0.025 M sodium metabisulfite solution (4.75 g per 1000 ml of solution. Prepare in a fume cupboard.) Add 5 drops of solution A to a suitable beaker plus 10 ml each of solutions B and C.

See Hazcards 80, 92. Wear eye protection.

The reaction between iron(III) ions and iodide ions

Solution A 1% starch solution (indicator) Solution B 0.01 M sodium thiosulfate Solution C* 0.025 M iron(III) chloride using 0.1 M hydrochloric acid to dilute a more concentrated iron(III) solution Solution D* 0.025 M potassium iodide Mix 5 drops of solution A followed by 10 ml each of solutions B, C and D in that order.

See Hazcards 41, 47B, 55, 67, 95C. Wear eye protection.

The potassium iodide/potassium persulfate reaction

Solution A Dissolve 0.25 g of sodium thiosulfate in 100 ml of 1% starch solution Solution B* Dissolve 13.50 g of potassium persulfate in 1000 ml of solution Solution C* 0.1 M potassium iodide Mix 5 ml of solution A with 50 ml each of solutions B and C in that order.

See Hazcards 47B, 95B, 95C. Wear eye protection.

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36 CLEAPSS 2011

30 Cobalt(II) chloride solution and thermochromic liquid General Hazards Cobalt salts are TOXIC (See Hazcard 25). Reported carcinogenic and sensitisation

warnings about cobalt compounds have become more severe in recent years. CLEAPSS has not received any reports from educational establishments of cobalt salts causing harm. The concerns for health are in mining and metallurgical applications used on a daily basis and in large doses.

Formula: CoCl2.6H2O Molar mass: 237.9 g mol-1 Solubility: 97 g per 100 ml Preparing 100 ml of 0.1 M cobalt(II) chloride solution

Wear eye protection. Wear disposable gloves and consider weighing the solid in non-working fume cupboard with the sash window low enough to stop any particles being inhaled.

Dissolve 2.38 g of cobalt(II) chloride-6-water in 70 ml of water. Make up to 100 ml with pure water. The solution should be labelled TOXIC.

Formula: Co(NO3)2.6H2O Molar mass: 291 g mol-1 Solubility: 155 g per 100 ml Preparing 100 ml of 0.1 M cobalt(II) nitrate solution

Use the method above but dissolve 2.91 g of cobalt(II) nitrate-6-water in 70 ml of water. Formula: CoSO4.7H2O Molar mass: 281.1 g mol-1 Solubility: 97 g per 100 ml Preparing 100 ml of 0.1 M cobalt(II) sulfate solution

Use the method above but dissolve 2.81 g of cobalt(II) sulfate(VI)-7-water in 70 ml of water.

Thermochromic liquid Used in models of hot-water systems.

Dissolve 40 g of hydrated cobalt(II) chloride in 1 litre of ethanol without heating. Add drops of water and stir until pink. A drop or two of ammonia solution will precipitate the hydroxide

which shows the flow in the model. Label the solution TOXIC & HIGHLY FLAMMABLE.

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31 Copper(II) solutions It is advisable to use distilled or deionised water to make these solutions. Solutions of copper(II) salts are sometimes cloudy. If this is the case, add 1 ml of 1 M sulfuric acid and stir. Continue this procedure until the solution is clear. The Health & Safety Executive provide hazard classifications for solutions by % (w/v). We generally measure concentration in mols per dm-3 rather than % (w/v), which leads to inconsistencies in hazard classification between different copper salts with the same concentration. In the tables below the hazard classifications in brackets are consistent with that for copper sulfate(VI), the most commonly used copper(II) salt, but are not strictly correct. General Hazards Copper(II) salts are HARMFUL if swallowed. See Hazcard 27A, B & C.

Formula: CuSO4.5H2O Molar mass: 249.68 g mol-1 Solubility: 32 g per 100 ml Mass (g) of solid to be used



0.01 M Ten-fold dilution of 0.1 M solution - 0.1 M 2.50 6.24 24.97 - 0.5 M 12.49 31.21 124.84 - 1.0 M 24.97 62.42 249.68 HARMFUL

Saturated (20 C) 40 100 400 HARMFUL Formula: CuCl2.2H2O Molar mass: 170.48 g mol-1 Solubility: 76 g per 100 ml Mass (g) of solid to be used



0.01 M Ten-fold dilution of 0.1 M solution - 0.1 M 1.71 4.26 17.05 - 0.5 M 8.52 21.31 85.24 - 1.0 M 17.05 42.62 170.48 (HARMFUL)

Saturated (20 C) 80 200 800 HARMFUL Formula: Cu(NO3)2.3H2O Molar mass: 241.6 g mol-1 Solubility: 138 g per 100 ml Mass (g) of solid to be used



0.01 M Ten-fold dilution of 0.1 M solution - 0.1 M 2.42 6.03 24.15 - 0.5 M 12.08 30.19 120.75 - 1.0 M 24.15 60.34 241.50 (HARMFUL)

Saturated (20 C) 140 350 1400 HARMFUL Procedure

Wear eye protection. Measure out the indicated quantity of copper(II) salt. Add the solid to about two thirds of the final volume of water in a beaker or jug. Stir to dissolve, warming if necessary. Pour the solution from the beaker into an appropriate measuring cylinder or laboratory jug and add


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32 Crude oil alternative Real crude oil (and petrol) contain benzene in concentrations greater than 0.1% and must not be used in school science (COSHH Regulations). A synthetic mixture can be prepared using mainly aliphatic hydrocarbons to illustrate the principle of fractional distillation of crude oil in industry. An alternative name for petroleum spirit is petroleum ether. On storing for several months, the lighter fractions evaporate away so the procedure should be tested to see that enough low boiling point fractions can be distilled off. Further details on the procedure can be found in L195, Safer Chemicals, Safer Reactions and section 13 of the Handbook. Standard fractional distillation equipment using a fractionating column is unsuitable as very high temperatures are required. Use apparatus similar to the diagram below. General Hazards Petroleum spirit is HIGHLY FLAMMABLE and HARMFUL (see Hazcard 45A).

Preparing 100 ml of synthetic crude oil

Wear eye protection. Do not prepare the mixture near sources of ignition. Mix together 55 ml of liquid paraffin (medicinal), 20 ml of paraffin oil (kerosene), 11 ml of white spirit,

4 ml of petroleum ether (100-120 C), 4 ml of petroleum ether (80-100 C) and 6 ml of petroleum ether (60-80 C).

Add a squeeze of black oil paint (eg, Winsor and Newtons Ivory Black) from a tube and stir well. After adding to a labelled bottle, shake the mixture well. Label the container HIGHLY FLAMMABLE &

HARMFUL. Always shake the mixture well before use. The paint will separate out if the bottle is left still for some

time. Note The recipe is not written in stone. Another possibility, if you have an even lower fraction of petroleum spirit, is:

Mix together 50 ml of liquid paraffin (medicinal), 20 ml of paraffin oil (kerosene), 10 ml of white spirit, 5 ml of petroleum ether (100-120 C), 5 ml of petroleum ether (80-100 C), 5 ml of petroleum spirit (60-80 C) and 5 ml of petroleum spirit (40-60 C).

75 x 10 mm test tubesto collect the fractions

1 ml of water in a test tube to compare volumes(optional)

Side-arm boiling tube

Mineral fibre with 6 ml of crude oil

Heat Block of wood to hold the test tubes

0 360 C thermometer

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33 2,4-Dinitrophenylhydrazine solution The solid is also known as 2,4-DNP and the solution is called Bradys reagent. It is used to identify organic compounds with carbonyl groups by producing orange or yellow insoluble derivatives which, if purified by recrystallisation, give sharp melting points. Solid 2,4-DNP is supplied moist as there may be an explosion risk if very dry solid is handled. Unopened bottles of 2,4-DNP already contain 20% to 33% water. Two r

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