TEST FOR GASES

Gas Test Result

Hydrogen Ignite the gas Burns with a squeaky pop

Oxygen Place a glowing splint in the gas Splint catches fire

Carbon Dioxide Pass into limewater Limewater turns milky

Nitrogen Dioxide Observe colour from heating G2 or LI Nitrate Gas is brown

Ammonia NH3 Place damp red litmus paper in gas Litmus paper turns blue

Chlorine Place damp litmus paper in gas Litmus rapidly bleaches

Hydrogen ChloridePlace damp blue litmus paper in gas Steamy fumes turn it red

Place cotton wool of ammonia White smoke of NH4Cl

Sulfur Dioxide Place paper w/ potassium dichromate(VI) in gas Turns from orange to green

TEST FOR CATIONS

GROUP 1 & 2 CATIONS: FLAME TEST

A clean nichrome test wire is dipped into concentrated hydrochloric acid. Dipped into the solid and placed in the hottest part of the Bunsen flame.

Li+ Lithium Ca2+ Calcium

Na+ Sodium Sr2+ Stronium

K+ Potassium Ba2+ Barium

Magnesium + Sodium Hydroxide = Magnesium Oxide Mg(OH)2 insoluble white precipitate

NH4+ AMMONIUM: MIX WITH AQUEOUS NaOH

Test: Warm unknown solid or solution with aqueous NaOH

Result: Ammonium salt gives off ammonia gas - Turns damp red litmus paper blue

TEST FOR ANIONS

Halogen Ion Test Results

Chlorine ChlorideDilute nitric acid + silver nitrate sol

White precipitate – Ag+Cl-Soluble in dilute ammonia

Damp litmus paper Rapidly bleaches litmusAdd dilute sulfuric acid Steamy fumes of HCl

Bromine Bromide

Dilute nitric acid + silver nitrate solCreamy precipitate – Ag+Br-Soluble in concentrated ammonia

Add Cl water. Bromide oxidized to Bromine

Solution turns colourless to brown

Add dilute sulfuric acid Steamy fumes (HBr), Brown Gas (Br2)

Iodine Iodide

Dilute nitric acid + silver nitrate solYellow precipitate – Ag+I-Insoluble in dilute & conc. ammonia

Add Cl or Br water + hexane. Iodide ions oxidized to iodine

Colour of solution turns red-brown when iodine present

Add starch Turns blue-black

Add dilute sulfuric acidClouds of violet gas (I2), egg smell (H2S), yellow solid (S)

TEST FOR ANIONS

AnionFormula

Test Result

Sulfate SO42- Add dilute hydrochloric acid to suspected sulfate &

aqueous barium chlorideWhite precipitate

Sulfite SO32- Add dilute sulfuric acid & warm. Sulfite gives off SO2,

test with paper soaked in potassium dichromate (VI)SO2 turns it from orange to green

Carbonate CO32-

Add dilute sulfuric acid to solid. Carbonate gives off CO2, test with lime water

CO2 turns limewater milky

If Li or G2 Carbonate, heat solid to decompose Gives of CO2

Hydrogen-carbonate HCO3

-

To distinguish between CO32-and HCO3

-

1. Add unknown to boiling water, fizzing of CO2 occurs, test CO2 by passing in limewater

2. Add solution of unknown to solution of CaCl3. pH paper, CO3

2- has high pH

1.Limewater turns milky2. No precipitate CaHCO3

-is soluble.3. HCO3

- is neutral

Nitrate NO3-

Add Al powder & NaOH solution & warm.Nitrate is reduced to ammonia, detect with damp red litmus paper

Litmus paper turns blue

TEST ALCOHOLS

Type Test Result Formula

Primary

Distillation. Heat with potassium dichromate [IV] & dilute sulfuric acid

Aldehyde. Butanol -> ButanalTest for aldehyde. Add benedicts solution and boil. Red precipitate means –CHO group present.

- H2O, + O

Reflux. Heat with potassium dichromate [IV] & concentrated sulfuric acid. Then distilled

Carboxylic AcidButanol -> Butanoic acid

- H2O, + 2 O

SecondaryReflux. Heat with potassium dichromate [IV] & sulfuric acid

KetoneButanol -> Butanone

- H2O, + O

Adding Sodium

Add sodium to the alcoholSodium dissolves, bubbles of gas, white precipitate of Sodium Propoxide

DECOMPOSITION OF CARBONATES AND NITRATES OF G1 and G2

Nitrates Formula Products

G1 KNO3 -> KNO2 + ½O2 Metal nitrate, Oxygen

G1 LithiumG2

4LiNO3 -> 2Li2O + 4NO2 + O2

2Ca(NO3)2 -> 2CaO + 4NO2 + O2Metal oxide, Nitrogen dioxide, Oxygen

Carbonates Formula Products

G1 Do not decompose Do not decompose

LithiumG2

Li2CO3 -> Li2O + CO2

CaCO3 -> Li2O + CO2Metal oxide, Carbon dioxide

TEST FOR ORGANIC FUNCTIONAL GROUPS

Group Series Test Result

C=C AlkenesAdd bromine waterAdd potassium manganite(VII)

Brown -> ColourlessPurple -> Colourless

C-OHAlcohol and Carboxylic acids

Add PCl5. Steamy fumes of HCl

Define between Alcohol and Carboxylic: add sodium carbonate

HCl turns damp blue litmus paper red.

Carboxylic acid fizzes CO2

Alcohol does not react

C-Halo HalogenoalkanesWarm in NaOH.Add nitric acid & silver nitrate

Same results as halogen tests

ORGANIC TECHNIQUES

Heating under reflux

Used to speed up slow reactions with heat and prevent organic reactant/product from boiling off with a reflux condenser. The cold water cools down any vapour so it returns back into the flask.

Used for Primary alcohol to carboxylic acid (2nd) Secondary alcohol to ketone Convert halogenoalkane to alcohol Convert alcohol to bromoalkane

Distillation

Used to separate volatile organic substances from non-volatile inorganic species (acids and alkalis). There must be a large enough difference in boiling temperatures of organic substances present to separate them.

Calculate boiling temperature: Vapour comes over + 2 °C of the boiling temperature of the particular substance that is being condensed and collected.

Safety

Both must be carried out in a fume cupboard if vapour is harmful There must be some outlet to the air, otherwise pressure will build up Gloves must be warn with corrosive substances i.e. concentrated acids and

alkalis Never heat with a Bunsen flame because organic substances are flammable

UNITS OF MEASURE

Units Units Convert

Molar Mass g mol-1

Concentration mol dm-3 OR g dm-3 mol dm-3 x MM = g dm-3

Volume cm3 OR dm3 cm3 / 1000 = dm3

Enthalpy kJ mol-1

Heat produced energy J OR kJ J / 1000 = kJ

Energy Density gm cm-3

ENTHALPY CALCULATIONSTemperature rises -> exothermic reaction -> negative enthalpy changeTemperature lowers -> endothermic reaction -> positive enthalpy change

ENTHALPY OF COMBUSTION – copper calorimeter

Experiment

1. Weigh spirit burner containing ethanol2. Known volume of water added to copper calorimeter3. Measure temperature of water in calorimeter ever minute for four minutes4. Light the burner after 4.5 minutes5. Measure temp of water every minutes till it has reached 20°C over room temp.6. Extinguish burner and reweigh7. Stop reading temperature 5 minutes after reaching maximum temperature

Calculation(kJ) Heat produced: Mass of water x s.h.c x change in temp(mol) Moles of Ethanol burned: Mass of ethanol / molar mass(jK mol-1) Enthalpy of combustion of ethanol: Heat produced / Number of moles

Errors- Some heat released when burning heats air and not water- Incomplete combustion of ethanol

Improve- A screen placed around calorimeter to maximize transfer of heat- Stir water continuously for even temperature- Burner and contents of burner should be weighed immediately after

ENTHALPY OF REACTION – solid and cup

Experiment

1. Measure volume of solution of known concentration and pipette into a polystyrene cup in a glass beaker

2. Weigh solid in powder so it is in excess3. Measure temperature of solution every 30 seconds for 2 minutes.4. Pour in solid at 2.5 minutes and stir solution5. Measure temperature every 30 seconds until maximum temperature is reached

Calculation(kJ) Heat produced: Mass of solution x s.h.c x change in temp(mol) Moles of Solution: Concentration x volume(jK mol-1) Enthalpy of reaction: Heat produced / Number of moles

Errors - Reaction is slow and loses heat to surroundings

Improve- Use powder instead of lumps to speed up reactions so less time for cooling- Stir continuously- Place lid on cup to prevent heat loss trough evaporation

ENTHALPY OF NEUTRALISATION – acid and cup

Experiment

1. Measure known volume and concentrate of acid solution into polystyrene cup2. Measure temperature of acid3. Measure temperature of alkali (slight excess)4. Calculate mean of both temperatures5. Measure out alkali and add to acid in cup6. Stir mixture and measure maximum temperature reached

Calculation(kJ) Heat produced: Mass of both solution x s.h.c x change in temp(mol) Moles of Solute (limiting reagent): Concentration x volume(jK mol-1) Enthalpy of neutralisation: Heat produced / Number of moles

Errors - Heat absorbed by polystyrene cup or thermometer (all three exp.)

Improve- Stir immediately upon mixing the two solutions- Weigh polystyrene cup before and after adding acid (all three exp.)- Make sure one of reactants is in excess

CALCULATIONS

Moles Solutions Gases

Mass = moles x molar massMoles = mass / molar massMolar mass = mass / moles

Moles = concentration x volumeConcentration = moles / volumeVolume = moles / concentration

Volume = moles x molar volumeMoles = volume / molar volumeMolar volume = volume / moles

PERCENTAGE YIELD% Yield = (actual yield / theoretical yield) x 100(actual = amount in question, theoretical = what you calculate)

1. Calculate moles of known reactant (mass / molar mass)2. Stoichiometry of reactant to product3. Calculate mass of product (moles x molar mass)4. Amount in question / amount in step 3 x 100 = percentage yield

Reasons for yield less than 100%: Competing reactions, handling losses during purification, side reactions

CALCULATING ERROR(Error value x number of times error occurs / change in reaction) x 100 = Error %

E.g. What’s the percentage error in the temperature change is there is uncertainty of 0.1°C each reading.[ (0.1 x 2 times used) / 5.5 temperature change x 100] = 3.36%

INITIAL RATE OF REACTIONVolume / Time = Initial rate of reaction

DRYING AGENTSDrying agents remove water from organic compoundsE.g. Calcium chloride, potassium chloride, or magnesium sulfate.  These are all types of salts (ionic compounds where metals are bonded to non-metals.)

HESS LAW

ΔHr = ΔH(products) – ΔH(reactants)TITRATIONS

Preparation of Standard Solution1. Calculate mass of solid needed to make solution and weigh in a weighing beaker2. Pour solid into a beaker and fill with 50cm3

distilled water. Stir until dissolved3. Pour the solution into a standard 250cm3 volumetric flask. Make sure all of it has gone in.4. Fill the flask until the bottom of the meniscus is level with the mark on the flask5. Put a stopped in the flask and shake to mix thoroughly

Preform a TitrationSol A – unknown concentrationSol B – known concentration/standard solution

1. Draw some of solution A into pipette with pipette filler to rinse. Discard the rinsings2. Fill pipette with solution A to the bottom of the meniscus and discharge into conical flask3. Rinse burette with solution B. Discard the rinsings.4. Close tap of burette and fill with solution B up to the meniscus. Open tap to remove air5. Record the initial volume in the burette6. Run the liquid from the burette into the conical flask, continually swirling the solutions7. Add the last bits of solution B drop by drop, stop when the indicator is at end point colour8. Read the burette to 0.05cm3 9. Repeat until 3 concordant titres have been obtained – within 0.2cm3

of one another.

Indicator Use for Acid Alkali End point

Methyl Orange Most titrations Red Yellow Orange

Phenolphthalein Weak acids e.g. ethanoic acid Colourless Purple Pale Pink

Titration Calculations1. Calculate number of moles in standard solution (volume x concentration)2. Stoichiometry to calculate moles of second selection3. Calculate concentration of second solution (moles / volume)

Minimizing errors

Due to apparatus Due to poor technique

Pipettes and burettes measure to a certain degree of accuracy

Not rinsing out the burette or pipette with correct solutions

Titrations are planned to give titres between 20 – 30cm3 to minimize apparatus error

Not removing air bubbles in the burette

Smaller titre have a higher percentage of possible error.

Running solution from burette too quickly and overshooting the end point

Not shaking thoroughly

SYMBOLS

Sulfuric Acid H2SO4

Nitric Acid HNO3

Hydrochloric Acid HClPotassium Dichromate (VI) K2Cr2O7

G2 Sulfate G2SO4 G1 Sulfate G12SO4

G2 Nitrate G2(NO3)2 G1 Nitrate G1NO3

G2 Hydroxide G2(OH)2 G1 Hydroxide G1OHAPPARATUS

ENTHALPY EXPERIMENTS

Why solid is not included in the calculation for heat for reaction: It’s heat capacity is negligible

Why record temperature after adding solid in reaction: to allow coolingWhy record temperature before adding solid in reaction: to ensure constant temperature

How to know there is no more acid in separating tunnel: No more CO2 or bubbles

Calcium hydroxide and water forms limewater

Ammonia – Red paper to BlueHydrogen Chloride – Blue paper to Red or Ammonia on cotton -> white smoke

SulFATE SO42- HCl acid and aqeous BaCl -> white precipitate of barium sulfate

SulFITE SO32- H2SO4 gives of SO2 -> turns C2K2O7 orange to green

Carbonate CO32-

H2SO4 -> Gives of CO2 -> CO2 turns limewater milky

Hydrogencarbonate – Fizzes CO2 in boiling water. OR Add to CaCl, forms soluble CaHCO3

Nitrate -> Add Al powder and NaOH -> reduced to ammonia

Ammonium + Sodium Hydroxide -> Ammonia gas -> ammonia gas turns red paper blue

Halogenoalkanes are more soluble in ethanol

Carboxylic acid and sodium carbonate fizzes CO2

Sodium carbonate is used to neutralize acid

Add solution mass together when working heat energy from neutralisation

G2 Sulfate G2SO4 G1 Sulfate G12SO4

G2 Nitrate G2(NO3)2 G1 Nitrate G1NO3

G2 Hydroxide G2(OH)2 G1 Hydroxide G1OH