99

Laboratory Equipment

A p p e n d i x A

Beaker

©H

ayde

n-M

cNei

l, L

LC

Florence Flask

Watch Glass

Litmus PaperStirring Rod

Filter Flask

Clamp Holder

Clamp

Ring Stand

Hot Plate

Weighing Dish

Spotting Plate

Spatulas and Scoops

Evaporating Dish

Mortar and Pestle

RingForceps

Safety Goggles

Tongs

Test Tube Brush

17 mL Crucible

44 mm Crucible LidErlenmeyerFlask

Evaporating Dish

44 mm Crucible Lid

Test Tube Holder

100

A p p e n d i x A • Laboratory Equipment

Appendix

A

PlasticWash Bottle

©H

ayde

n-M

cNei

l, L

LC

Funnel

Test Tubes

Ruler

Thermometer, –20°C – 100 °C

Buret Clamp

Buret

Pasteur Pipet

Petri Dish

Graduated Cylinders

Centrifuge

Dropper/BeralPipets

Test Tube Rack

BüchnerFunnel

VolumetricFlask

PlasticWash Bottle

101

Units and Constants

A p p e n d i x BTable B.1. International System of Units (SI Units).

Quantity Unit Abbreviation

mass kilogram kg

length meter m

time second s

temperature Kelvin K

amount of substance mole mol

electric current Ampere A

Table B.2. SI Derived Units.

Quantity SI Unit Alternate Name Alternate Units

volumem3

dm3 liter L

velocity sm

acceleration sm2

force skgm

2 Newton N

energys

kgm2

2

Joule J

densitymkg

3

cmg

3

frequency s1

Hertz Hz

pressuremskg

2 Pascal Pa

powers

kgm3

2

watt W

electric potentials Akgm

3

2

volt V

102

A p p e n d i x B • Units and Constants

Appendix

B

Table B.3. SI prefixes.

Prefix Symbol Meaning

tera T 1012

giga G 109

mega M 106

kilo k 103

hecto h 102

deca da 101

deci d 10–1

centi c 10–2

milli m 10–3

micro µ 10–6

nano n 10–9

pico p 10–12

When using the prefixes for conversions, there are two ways to set up the conversion factor, as shown below.

Example: How many nm in 1 m?

11

10 1 10mmnm nm

99# #=c m

or

110

1 1 10mnmm nm9

9# #=-c m

Either calculation is correct and both give the same answer. It just depends on whether you want to think of 1 m 1 109 nm or 1 nm 1 10–9 m.

103

A p p e n d i x B • Units and Constants

Appendix

B

Table B.4. Conversion factors.

Length1 inch 2.54 cm (exactly)

1 mile 5280 ft1 m 39.37 in

1 km 0.6215 mi1 light-year 9.46 1015 km

1 A 1 10–10 m

Volume1 cm3 1 mL

1 quart 0.9463 L1 fluid ounce 29.57 mL

1 gallon 3.785 L1 gallon 4 quarts1 quart 2 pints

Mass1 pound 16 oz

1 pound 453.6 g1 kg 2.205 pounds

TemperatureT(K) T(°C ) 273.15

T(°C) 95 [ T(°F) 32 ]

Pressure1 atm 1.013 105 Pa

1 atm 760 mm Hg1 atm 14.70 lb/in2

1 mm Hg 1 torr

Energy1 J 0.2390 calories

1 Calorie 1 kcal 1000 calories1 BTU 1055 J

1 kWh 3.6 106 J1 eV 1.60 10–19 J

Table B.5. Constants.

Constant Abbreviation Value

Planck’s constant h 6.6256 10–34 J∙s

Avogadro’s number 6.0221367 1023

Charge on an electron e 1.6022 10–19 C

Electron radius re 2.81792 10–15 m

Mass of an electron 9.109387 10–28 g

Mass of a proton 1.672623 10–24 g

Mass of a neutron 1.674928 10–24 g

Atomic mass unit amu 1.66057 10–27 kg

Molar volume 22.41383 L/mol

Gas constant R.

K molJ

8 314:

. gK molL atm0 0820::

Speed of light c 2.99792458 108 m/s

Acceleration due to gravity g .sm9 81 2

Rydberg constant for hydrogen RH 1.0967758 107 m–1

104

A p p e n d i x B • Units and Constants

Appendix

B

105

A p p e n d i x CIons

Common Monatomic IonsMonatomic ions not following general rules for charge. There are other possible ions for many of these metals but these are the most common and are the ones you are responsible for knowing.

Name Formula

Chromium Cr2+, Cr3+

Manganese Mn2+

Iron Fe2+ or Fe3+

Cobalt Co2+ or Co3+

Nickel Ni2+ or Ni3+

Copper Cu+ or Cu2+

Zinc Zn2+

Silver Ag+

Cadmium Cd2+

Tin Sn2+, Sn4+

Mercury Hg22+ or Hg2+

Lead Pb2+, Pb4+

106

A p p e n d i x C • Ions

Appendix

C

Polyatomic Ions

Name Formula

Ammonium NH4+

Carbonate Co32–

Hydrogen carbonate or bicarbonate HCO3–

Hypochlorite ClO–

Chlorite ClO2–

Chlorate Clo3–

Perchlorate ClO4–

Chromate Cro42–

Dichromate Cr2O72–

Cyanide CN–

Thiocyanate SCN–

Hydroxide OH–

Nitrate No3–

Nitrite NO2–

Phosphate Po43–

Hydrogen phosphate HPO42–

Dihydrogen phosphate H2PO4–

Permanganate MnO4–

Peroxide O22–

Sulfite SO32–

Sulfate So42–

Hydrogen sulfate or bisulfate HSO4–

oxyanions and oxyacids

Description Anion Acid

2 less oxygens than “ate” compound Hypo ite Hypo ous acid

1 less oxygen than “ate” compound ite ous acid

MEMORIZE ate ic acid

1 more oxygen than “ate” compound Per ate Per ic acid

Example: Sulfate is SO42–, remove two of the oxygens to get hyposulfite (SO2

2–) which becomes hyposulfurous acid (H2SO2) with the addition of two hydrogens.

107

A p p e n d i x DSolubility

Solubility Rules1. Compounds containing alkali metal ions (Li+, Na+, K+, Rb+, Cs+) and the ammonium

ion NH4+ are soluble.

2. Nitrates (NO3–), bicarbonates (HCO3

–), acetates (C2H302–), and chlorates (ClO3

–) are soluble.

3. Halides except Ag+, Hg22+, and Pb2+ are soluble.

4. Sulfates (SO42–) are soluble, except Ag+, Hg2

2+, Pb2+, Ca2+, Sr2+, and Ba2+.

Insolubility Rules1. Carbonates (CO3

2–), phosphates (PO43–), and chromates (CrO4

2–) are insoluble except for those containing alkali metal or ammonium ions.

2. Hydroxides (OH–) are insoluble except for those containing alkali metals. Hydroxides of Ca2+, Sr2+, and Ba2+ are slightly soluble.

3. Sulfi des are insoluble except when paired with alkali metal ions, ammonium, Ca2+, Sr2+, or Ba2+.

108

A p p e n d i x D • Solubility

Appendix

D

ksp Values for Some Common Salts

Compound Formula ksp

aluminum hydroxide Al(OH)3 4.6 10–33

barium carbonate BaCO3 5.1 10–9

barium chromate BaCrO4 2.2 10–10

barium hydroxide Ba(OH)2 5 10–3

barium sulfate BaSO4 1.1 10–10

calcium carbonate CaCO3 3.8 10–9

calcium fluoride CaF2 5.3 10–9

calcium hydroxide Ca(OH)2 5.5 10–6

calcium phosphate Ca3(PO4)2 1 10–26

copper(I) chloride CuCl 1.2 10–6

copper(I) sulfide Cu2S 2.5 10–48

copper(II) chromate CuCrO4 3.6 10–6

copper(II) hydroxide Cu(OH)2 2.2 10–20

iron(II) carbonate FeCO3 3.2 10–11

iron(II) hydroxide Fe(OH)2 8.0 10–16

iron(II) sulfide FeS 6 10–19

iron(III) hydroxide Fe(OH)3 4 10–38

lead(II) chloride PbCl2 1.6 10–5

lead(II) chromate PbCrO4 2.8 10–13

lead(II) hydroxide Pb(OH)2 1.2 10–5

lead(II) sulfate PbSO4 1.6 10–8

lead(II) sulfide PbS 3 10–29

lithium carbonate Li2CO3 2.5 10–2

lithium fluoride LiF 3.8 10–3

magnesium carbonate MgCO3 3.5 10–8

magnesium fluoride MgF2 3.7 10–8

magnesium hydroxide Mg(OH)2 1.8 10–11

magnesium phosphate Mg3(PO4)2 1 10–25

nickel(II) carbonate NiCO3 6.6 10–9

silver bromide AgBr 5.3 10–13

silver carbonate Ag2CO3 8.1 10–12

silver chloride AgCl 1.8 10–10

silver chromate Ag2CrO4 1.1 10–12

silver iodide AgI 8.3 10–17

silver nitrite AgNO2 6.0 10–4

silver sulfide Ag2S 6 10–51

silver sulfite AgSO3 1.5 10–14

zinc carbonate ZnCO3 1.4 10–11

zinc hydroxide Zn(OH)2 1.2 10–17

zinc sulfide ZnS 2 10–25

109

A p p e n d i x EStandard Deviation

In most real experiments, the “true” value of a quantity is not known. Therefore, we must fi nd a way to use our data to get the best possible estimate of the true value for the quantity being determined. One common estimate of the true value is the mean (X–

). The mean is simply the arithmetic average of all the data points:

...XnX

nx x x xni 1 2 3= =+ + + +/

where X–

= the mean value (or average), = “the sum of,”Xi = the individual data points (i = 1, 2, 3, …, n), andn = the total number of data points.

One way to express precision is by means of the standard deviation. To discuss this, we must fi rst discuss the normal distribution.

If a very large number of determinations of a quantity are done, all of the values will not be exactly the same, due to random errors.

On these graphs, X–

represents the mean, which is the best estimate of the true value. The width of the curve indicates the precision of the measurements. A tall, thin curve would indicate good precision, while a broad, fl at curve would show poor precision.

The standard deviation can be used to measure the width of a normal distribution. The standard deviation is defi ned as:

1s

nX Xi

2

=-

-

^^

hh/

where s = the standard deviation, n = the number of observations.

110

A p p e n d i x E • Standard Deviation

Appendix

E

The usefulness of the standard deviation is that it is expressed in units of the original measurement, and can be used to describe the position of any observation rela-tive to the mean. It can be shown mathematically that, for a distribution with an infi nite number of replicate measurements, 68.3% of the observed values will fall within ± 1s of the mean; 95.5% will fall within ± 2s of the mean; and 99.7% within ± 3s of the mean.

Measured characteristic

Freq

uenc

y

68%

95%

99%

-3s -2s -1s +1s +2s +3s

68%68%

95%95%

99%99%

Figure E.1.

ExampleSuppose that a density determination of a liquid is done in the laboratory, and the following data are obtained:

Experiment Number Density (g/mL)

1 2.60

2 2.90

3 2.70

4 2.90

5 2.50

From this data, calculate the average and standard de-viation for the results.

Step 1: Calculate the sum of the data: Xi = 13.60

Step 2: Calculate the average of the values:

13.60 2.720XnX

di== =

/

Step 3: Calculate the deviation of each result (d = | Xi – X

–| ), the sum of the deviations ( | d | ), the square of d

values ( | d |2 ), and the sum of the square of the d values ( | d |2 ). Tabulate these values in a new table:

Experiment

NumberXi | Xi – X

–| | Xi – X

–|2

1 2.60 | 2.60 – 2.720 | = 0.12 0.014

2 2.90 | 2.90 – 2.720 | = 0.18 0.032

3 2.70 | 2.70 – 2.720 | = 0.020 0.00040

4 2.90 | 2.90 – 2.720 | = 0.18 0.032

5 2.50 | 2.50 – 2.720 | = 0.22 0.048

n = 5 Xi = 13.60 (Xi – X–

)2 = 0.13

Step 4: The standard deviation can then be calculated from the formula:

. .s5 10 13 0 177=-

=^ h

Thus, we could state that the result of the density de-termination together with its standard deviation is 2.72 ± 0.18 g/mL. (Note that the average cannot have more signifi cant fi gures than the measurements that make up the average and that the standard deviation has the same number of decimal places as the average.)

The value of the standard deviation gives us some idea of the spread of our data points, or the precision of our determinations. A student with a standard deviation in this case of 0.100 will have a higher degree of precision in his or her experiment, but it does not necessarily mean that the experiment has a high degree of accuracy.

It is very important to realize at this stage that you can

have a very small deviation in your data (indicating high

precision) but your result may be signifi cantly off (if the

accuracy is low).