Practical Endorsement GCE Chemistry
PAG4 Qualitative analysis of ions
4.2 Identifying unknowns 2
LEARNER
4.2 Identifying unknowns 2
LEARNER
Introduction
In this practical activity, you are given four unknown solutions. Using the chemicals provided you should carry out
a series of tests to allow you to identify each solution A–D.
Aims and Skills
 to identify the positive and negative inorganic ions in a mixture of salts, using appropriate apparatus and
procedures.
 to make accurate observations and record in an appropriate format
 to safely and carefully handle liquids and solids, including irritant and toxic substances
 to apply investigative approaches by deciding the tests to carry out
Intended class time
 1 hour
Chemicals
Label
A (for PAG 4.2)
B (for PAG 4.2)
C (for PAG 4.2)
D (for PAG 4.2)
-3
1.0 mol dm
HNO3(aq)
Identity
Unknown solution
3
1.0 mol dm aqueous nitric
acid, HNO3(aq)
0.05 mol dm-3
AgNO3(aq)
0.05 mol dm–3 aqueous silver
nitrate(V), AgNO3(aq)
0.2 mol dm-3
BaCl2(aq)
0.2 mol dm3 aqueous
barium chloride, BaCl2(aq)
0.4 mol dm-3
NaOH(aq)
0.4 mol dm3 aqueous
sodium hydroxide, NaOH(aq)
Hazard information
Assume all solutions are:
WARNING
Causes serious eye irritation
DANGER
Causes severe skin burns and eye
damage
Wear splash-proof goggles/face shield
Currently not classified as hazardous at this
concentration
Solutions cause skin to blacken and will stain
clothing and some bench surfaces.
Currently not classified as hazardous at this
concentration
WARNING
Causes skin irritation and serious eye
irritation
Health and Safety
 Wear eye protection at all times.
This document may have modified from the original – check the master version on OCR Interchange if in doubt.
© OCR 2016
Page 1
v3.0 – Feb 2020
Practical Endorsement GCE Chemistry
PAG4 Qualitative analysis of ions
4.2 Identifying unknowns 2
LEARNER
Equipment
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splash-proof goggles
pH indicator paper
wash bottle containing distilled (or de-ionised) water
measuring cylinder (25 cm3)
beaker (100 cm3)
glass rod
conical flask (100 cm3)
test-tube rack
four test tubes
dropping pipettes
spatula
Bunsen burner
test-tube holder
Procedure
Before starting your practical work, read the information below.
Decide how you will organise your practical work and make a note of this.
Decide which observations you need to make and/or which measurements you need to take.
Ensure that you record all of your results in a suitable format.
The identities of the solutions A–D are listed below in no particular order:
 aqueous ammonium chloride, NH4Cl(aq)
 aqueous sodium chloride, NaCl(aq)
 aqueous sodium carbonate , Na2CO3(aq)
 aqueous sodium sulfate, Na2SO4(aq)
1. Plan and carry out a series of tests that would allow you to identify each solution A–D.
2. You should carry out the minimum number of tests required. Each test should produce a positive result
for at least one of the solutions A–D. You can use any of the chemicals supplied.
3. Record the tests you carried out.
4. Record all the observations for your tests on solutions A–D.
Analysis of results
1. Record your conclusions for each test.
2. Record the identity of each solution.
Extension opportunities
1. Write the equations for the reactions that you have observed.
2. Write the methods for the experiments that you have carried out.
Records
As evidence for the Practical Endorsement, you should have recorded evidence of your methods, and all of your
observations and measurements in a suitable format. All work should be clearly dated.
In addition, in preparation for the assessment of practical work in the written examinations and to help you
develop your understanding of the underlying chemical theory, you should complete the questions in the Analysis
and Extension Opportunities sections. For calculations, you should show full workings and give final answers to
the appropriate number of significant figures.
This document may have modified from the original – check the master version on OCR Interchange if in doubt.
© OCR 2016
Page 2
v3.0 – Feb 2020