Unit 22 : Chemical Laboratory Techniques
Unit 22: Chemical Laboratory Techniques
Pupils’ Booklet
Name: _________________________________________________
Page
Completed
Pupil Assessed
Teacher
Assessed
Section 1: Preparing Substances
Copper Sulphate
2,3
Measuring the purity of a
4,5
substance by Titration
Precipitation Reaction
6
Metal Salt by titration
7-8
Organic compound antifebrin 9
Extracting organic
10-13
compounds
Extracting paracetamol
14
Section 2: Calculations
Green Chemistry
15
Section 3: Qualitative Analysis
Identifying organic
17
compounds
Solubility in water and pH
18
Testing with carbonates
19
Brady’s reagent
20
Benedict’s Test
21
Acidified potassium
22
dichromate (vI) soluition
Testing with Bromine water
23
Infrared Spectroscopy
24-26
Section 4 Identifying Inorganic Compounds
Flame Test
27
Testing for Negative ions
28-31
Section 5 Quantitative Analysis of compounds
Acid-base Titrations
32-33
Calculating iron content of
34-35
tablets
1
Unit 22 : Chemical Laboratory Techniques
Section 1: Preparing Substances
Preparing Copper Sulphate
Copper (II) Sulphate can be made by reacting copper carbonate with an acid.
This will neutralise the acid to form a salt.
Write a word equation for this reaction
Write a balanced symbol equation for this reaction
Risk Assessment
Chemical or procedure
Equipment
Risk and Hazard
How to control and
reduce risk
Method
Results
Mass of evaporating dish
/g
Mass of evaporating dish
+ crystals / g
Mass of crystals / g
2
Unit 22 : Chemical Laboratory Techniques
Calculating Percentage Yield
The formula for calculating the percentage yield is
Actual number of moles = mass of product (g) ÷ mass of one mole (in g)
What is the Mass of one mole of CuSO4.5H2O
Cu = 63.546 S = 32.06 O = 15.999 H =1.008
Therefore Actual number of moles =
Expected number of moles = concentration (in moldm-3) x volume (in dm3)
Concentration = 1 moldm-3
Volume used = 20 cm3 ÷ 1000 = 0.02 dm3
Therefore expected number of moles =
Percentage yield =
3
Unit 22 : Chemical Laboratory Techniques
Preparing Substances: Measuring the Purity of a Substance by Titration
Carrying out a titration is one of the way to show exactly how pure a substance
is. Copper (II) sulphate crystals can be tested for purity by titrating with
EDTA.
Risk Assessment
Chemical or procedure
Equipment
Risk and Hazard
How to control and
reduce risk
Mass of emptied
bottle/g
Mass of copper sulphate
added to flask /g
Method
Results
Mass of bottle plus
copper sulphate /g
Results from titrations
Initial volume (cm3)
Final Volume (cm3)
Titre (cm3)
4
Unit 22 : Chemical Laboratory Techniques
Average Titre = ____________________
Calculations
Number
of moles of EDTA = concentration of EDTA (mol dm-3) x volume of average titre (in dm3)
Concentration of EDTA = 0.01 mol dm-3
Volume of average titre ÷ 1000 = _____________
Copper ions and EDTA react in the ratio 1:1
Number of moles of copper sulphate
in 250 cm3
= 10 x number of moles of EDTA
How many grams is this equivalent to?
Mass = number of moles of copper sulphate x Mass of one mole of copper sulphate
Mass of one mole of copper sulphate =____________
So, the percentage purity is given by
% purity = (mass worked out from titration ÷ mass weighed out) x 100
5
Unit 22 : Chemical Laboratory Techniques
Preparing Substances: Precipitation Reactions
Describe what a precipitate is
Write a symbol equation for when a solution of silver nitrate is reacted with a
solution of sodium chloride then silver chloride and sodium nitrate is formed.
Describe how silver chloride can be obtained from the solution
Research Task
Write the word and symbol equation for two other precipitation reaction
6
Unit 22 : Chemical Laboratory Techniques
Preparing Substances : Metal Salt by titration
Sodium chloride can be made by reacting sodium hydroxide solution with
hydrochloric acid solution.
Once you have found the correct amounts you need, prepare the correct
mixture in an evaporating basin without the indicator
Chemical or procedure
Equipment
Risk and Hazard
How to control and
reduce risk
Method
7
Unit 22 : Chemical Laboratory Techniques
Results
Initial burette
reading (cm3)
Final burette
reading (cm3)
Titre (cm3)
Average Titre(cm3) = ____________________
Volume required to neutralise sodium hydroxide solution _________________
8
Unit 22 : Chemical Laboratory Techniques
Preparing Substances: Organic Compound Antifebrin
Aniline and ethanonic anhydride react according to the equation:
Risk assessment
Chemical or procedure
Risk and Hazard
How to control and
reduce risk
Melting point of antifebrin =
9
Unit 22 : Chemical Laboratory Techniques
Preparing Substances: Extracting Organic Compounds
You are going to investigate which solvent is optimum for extracting pigments
from herbs and leaves.
Solvent
Type of Bonding
Water
Ethanol
Ethyl ethanoate
Propanone
Petroleum ether (mixture of
hydrocarbons similar to hexane)
Risk assessment
Chemical or procedure
Equipment
Risk and Hazard
How to control and
reduce risk
Method
10
Unit 22 : Chemical Laboratory Techniques
Results
Solvent
Mass of
Mass of
dried herbs evaporating
/g
dish /g
Mass of
evaporating
dish +
pigment /g
Mass of
Pigment /g
Which solvent is best at extracting pigment from dried herbs?
What type of bonding does the best solvent have?
What type of bonding do you think the dried herbs have? How do you know?
11
Unit 22 : Chemical Laboratory Techniques
Research Task
1. Soxhlet apparatus provides a way to remove solvent from extracted
chemicals
a. Draw and label a diagram of this equipment
b. Describe the advantages of this method
12
Unit 22 : Chemical Laboratory Techniques
Using thin-layer chromatography (TLC)
Use the pigment extracted from the dried herbs
Explain with the help of a diagram how Rf values are calculated
Results
13
Unit 22 : Chemical Laboratory Techniques
Preparing Substances : Extracting Paracetamol
Risk assessment
Chemical or procedure
Risk and Hazard
How to control and
reduce risk
Results
Mass of 2
paracetamol
tablets /g
Mass of
evaporating dish/g
Mass of evaporating
dish + paracetamol /g
Mass of crystals
/g
Melting Point of Paracetamol before recrystallization =
Melting Point of Paracetamol after recrystallization =
14
Unit 22 : Chemical Laboratory Techniques
Section 2: Calculations
Green Chemistry
The atom economy of a chemical reaction is a measure of how much of the
starting materials becomes useful product. Inefficient, wasteful processes have
low atom economies.
The atom economy of a reaction is calculated using the following formula
Calculate the atom economy of the following reactions:
Zinc oxide + Hydrochloric acid  zinc chloride + water
ZnO +
2HCl

ZnCl2
+ H 2O
Calculate the Mass of each compound
Calculate % atom economy
In the second reaction:
Zinc carbonate + hydrochloric acid  Zinc chloride + water + carbon dioxide
ZnCO3 + 2HCl  ZnCl2 + H2O + CO2
Calculate the mass of each compound
Calculate % atom economy
15
Unit 22 : Chemical Laboratory Techniques
Which method has the lowest atom economy? What else needs to be considered
when choosing a method?
Explain the difference between yield and atom economy
16
Unit 22 : Chemical Laboratory Techniques
Section 3 Qualitative Analysis of Compounds
Identifying Organic Compounds
What is a functional group?
What is the functional group of the following
Series
Functional Group
Alkene
Haloalkane
Alcohol
Aldehyde
Ketone
Carboxylic acid
Ester
17
Unit 22 : Chemical Laboratory Techniques
Qualitative Analysis of Compounds : Solubility in Water and pH
Risk assessment
Chemical or procedure
Equipment
Compound name
Risk and Hazard
How to control and
reduce risk
Method
Type of Compound
Soluble in water?
pH if soluble
18
Unit 22 : Chemical Laboratory Techniques
Qualitative Analysis of Compounds: Testing with Carbonates
Explain what carbonates or hydrogen carbonates identify
Risk assessment
Chemical or procedure
Risk and Hazard
Equipment
Method
Compound name
Type of Compound
How to control and
reduce risk
Did it effervescence?
19
Unit 22 : Chemical Laboratory Techniques
Qualitative Analysis of Compounds : Brady’s reagent
Explain what Brady’s reagent identifies
Risk assessment
Chemical or procedure
Equipment
Compound name
Risk and Hazard
How to control and
reduce risk
Method
Type of Compound
Did crystals form? Colour?
20
Unit 22 : Chemical Laboratory Techniques
Qualitative Analysis of Compounds : Benedict’s test
What is Benedict’s used to test for?
Risk assessment
Chemical or procedure
Equipment
Compound name
Risk and Hazard
How to control and
reduce risk
Method
Type of Compound
Colour of precipitate
21
Unit 22 : Chemical Laboratory Techniques
Qualitative Analysis of Compounds : Acidified potassium dichromate (VI)
solution
What does acidified potassium dichromate (VI) solution test for?
Risk assessment
Chemical or procedure
Equipment
Compound name
Risk and Hazard
How to control and
reduce risk
Method
Type of Compound
Observations
22
Unit 22 : Chemical Laboratory Techniques
Qualitative Analysis of Compounds :Testing with Bromine Water
What is bromine water used to test for?
Risk assessment
Chemical or procedure
Equipment
Compound name
Risk and Hazard
How to control and
reduce risk
Method
Type of Compound
Colour of bromine
water
Colour litmus
turns
23
Unit 22 : Chemical Laboratory Techniques
Describe how amines that are insoluble in water can be identified
Infrared Spectroscopy
Infrared Spectroscopy can be used to identify functional groups. Infrared
radiation makes the bonds in molecules bend and stretch
Example
C-H Stretch
C=O stretch
;
24
Unit 22 : Chemical Laboratory Techniques
Identify the peaks on the following Infrared Spectrums
1. Ethanonic acid (carboxylic acid)
O-H 3400-2400 cm-1, C=O 1725-1700 cm-1, C-O 1300-1000 cm-1
2. Propanal (aldehyde)
C=O (aldehyde)1740-1720 cm-1, C-H(stretch) 3000-2850 cm-1
25
Unit 22 : Chemical Laboratory Techniques
3. 1-aminobutane (amine)
C-N (amines) 1350-1000 cm-1, N-H (stretch) 3500-3100 cm-1,
N-H (bend) 1640-1550cm-1
4. 2-methyl-1-Butanol (Primary alcohol)
O-H (alcohols) 3600-3200 cm-1
26
Unit 22 : Chemical Laboratory Techniques
Section 4 Identifying Inorganic Compounds
Flame Test for positive ions (cations)
Explain what happens to metal ions when they are placed in a flame
Draw a diagram to explain how emission spectra are formed
Explain how a spectroscope can be used to separate the colours of an emission
spectrum.
Risk Assessment
Chemical or
procedure
Risk and Hazard
How to control and reduce
risk
27
Unit 22 : Chemical Laboratory Techniques
Results
Substance
Flame colour
Metals ion (cation)
Testing for Negative Ions (anions): Chloride, Bromide, iodide
Negative ion
Precipitate Colour
Bromide
Iodide
Chloride
Pale yellow
Yellow
white
Equipment
Effect of adding concentrated
ammonia
Soluble
Partially soluble
Soluble (in dilute)
Method
1. Dissolve a spatula of each substance in a 2cm depth of
water in a test tube
2. Add a few drops of silver nitrate solution
3. Record the colour of the precipitate
Risk Assessment
Chemical or procedure
Hazard and Risk
How to control or reduce
risk
Results
Substance
A
B
C
D
E
F
G
Colour of precipitate
Type of negative ion
28
Unit 22 : Chemical Laboratory Techniques
Testing for Negative Ions (anions):Sulphate
Equipment
Method
1. Dissolve a spatula of each substance in a 2cm depth of
water in a test tube
2. Add a few drops of barium chloride solution
3. Record the colour of the precipitate
Risk Assessment
Chemical or procedure
Hazard and Risk
How to control or reduce
risk
Results
Substance
Colour of precipitate
Type of Negative ion
Testing for Negative Ions (anions): Carbonates
Equipment
Method
1. Put a couple of spatulas of the solid substance into a test
tube, add hydrochloric acid, collect any gas produced with a
delivery tube into a test tube of limewater.
2. If the limewater goes cloudy it’s a carbonate
Risk Assessment
Chemical or procedure
Hazard and Risk
How to control or reduce
risk
29
Unit 22 : Chemical Laboratory Techniques
Substance
Did it fizz with acid?
Effect on limewater
Testing for Negative Ions (anions):nitrate
Equipment
Method
1. Put ½ a spatulas of the solid substance into a test tube,
add a few drops of sodium hydroxide, then a small piece of
aluminium foil and warm carefully.
2. Test any gas with damp red litmus paper. If nitrate is
present the litmus paper will turn blue
Risk Assessment
Chemical or procedure
Substance
Hazard and Risk
Observations
How to control or reduce
risk
Effect on litmus paper
30
Unit 22 : Chemical Laboratory Techniques
Testing for Negative Ions (anions): sulphite
Equipment
Method
1. Put ½ a spatulas of the solid substance into a test tube,
add a few drops of hydrochloric acid.
2. Test any gas with damp blue litmus paper. If the gas is
colourless and turns the litmus paper red a sulphite is
present
Risk Assessment
Chemical or procedure
Substance
Hazard and Risk
Observations
How to control or reduce
risk
Effect on litmus paper
31
Unit 22 : Chemical Laboratory Techniques
Section 5 Quantitative Analysis of Compounds
Acid-base Titrations
Vinegar can be analysed by using an acid-base titration. This may be done to
test the quality of the vinegar being produced.
Sodium hydroxide is used to neutralise the acetic acid in the vinegar.
Bromothymol blue is used as an indicator. It will change from blue to a plae
yellow at the end point of the reaction.
Word equation for this reaction
Ethanoic acid + sodium hydroxide  sodium ethanoate + water
Symbol equation
CH3COOH + NaOH  CH3COONa + H2O
A 10 cm3 sample of vinegar is titrated with 0.1 M NaOH.
Risk Assessment
Chemical or Procedure
Hazard and Risk
How to control or reduce
risk
Results
1
2
3
4
Initial Volume
Final Volume
Titre
32
Unit 22 : Chemical Laboratory Techniques
Average Titre: ___________________________
Average Titre in dm3 (÷1000) = ______________
Number of moles of NaOH = Volume (dm3) x Concentration (M)
From equation, 1 mole of sodium hydroxide reacts with 1 mole of ethanoic acid
So, number of moles of ethanoic acid =
Concentration of
ethanoic acid
= number of moles of ethanoic acid ÷
volume (dm3) of ethanoic acid
Volume of ethanoic acid used = 10 ÷1000 = _________
33
Unit 22 : Chemical Laboratory Techniques
Quantitative Analysis of Compounds : Calculating Iron content of Tablets
Iron tablets are an important supplement for many people, especially growing
children and pregnant or menstruating women. It is important that the tablets
can be analysed to ensure the correct composition. A redox titration is carried
out on the iron tablet using acidified potassium manganite (VII)
Experiment
Part 1
a) Using a weighing bottle, weigh accurately five iron tablets.
b) Place the iron tablets into a 100 cm3 conical flask and add approximately
50 cm3 of 1 mol dm-3 sulfuric acid.
c) Stopper the conical flask, shake its contents well and then leave the tablets
to dissolve. This is a slow process and should be carried out at least one day
before the titration is to be attempted. The outer coating of each tablet is
insoluble in water, but slowly breaks down in the acidic solution. The solution will
need filtering before carrying out the titration.
Part 2
a) Without disturbing the residue, which will have settled to the bottom of the
flask, carefully filter the solution directly into a 100 cm3 graduated
(volumetric) flask.
b) Rinse the residue in the filter paper into the graduated flask using a small
volume of de-ionised water.
c) Add dilute sulfuric acid to make the solution in the graduated flask up to the
mark.
d) Ensure that the contents of the graduated flask are fully mixed. You now
have an acidified solution of iron(II) sulfate.
e) Fill a burette with the 0.0200 mol dm-3 potassium manganate(VII) solution
provided.
f) Pour some of the contents of the graduated flask into a clean 250 cm3
beaker and, using a 25 cm3 pipette and a pipette filler, measure out a 25.0 cm3
sample of the iron(II) sulfate solution into a clean 250 cm3 conical flask.
g) Using a 25 cm3 measuring cylinder, measure out 25 cm3 of the 1 mol dm3sulfuric acid provided and add this to the contents of the conical flask.
h) Titrate this acidified sample of iron(II) sulfate solution by adding potassium
manganate(VII) from the burette until the first permanent pink colour is seen.
i) You will only be able to carry out three titrations and if you are careful, you
should be able to obtain at least two results that are concordant. Record
the three results that you obtain.
j) Calculate and record the mean volume of potassium manganate(VII) solution
used in the titration (the average titre).
34
Unit 22 : Chemical Laboratory Techniques
Results
Mass of iron Tablets used: _____________
1
2
3
Initial Volume
(cm3)
Final Volume
(cm3)
Titre (cm3)
Average Titre (cm3) _____________________
Average Titre (dm3) ÷ 1000 _____________________
Number of moles of MnO4- = Volume (dm3) x Concentration (M)
Symbol Equation
MnO4- + 5Fe2+ + 8H+  Mn2+ + 5Fe3+ + 4H2O
From equation, 5 moles of Fe2+ reacts with 1 mole of MnO4So, number of moles Fe2+ = Number of moles of MnO4- x 5
Mass of Fe2+ in the tablets is = number of moles Fe2+ x Mass of one mole of Fe
Mass of one mole of Fe2+ = 56g
As there are 5 tablets divide by 5 to find out the mass of Fe2+ in each tablet
35