12.3 Identification of Ions & Gases

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1a2 marks

Two substances, C and D, were analysed. Solid C was a salt and solution D was an aqueous solution of chromium(III) chloride.
The tests on solid C, and some of the observations, are in the following table.

diagram-ions-q1

Identify solid C.

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1b1 mark

Describe the appearance of solution D.

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1c6 marks

Tests were carried out on solution D.
Complete the observations for tests 1, 2 and 3.

Test 1
Drops of aqueous sodium hydroxide were added to solution D.
Excess aqueous sodium hydroxide was then added to the mixture.
Observations:

[3]

ii)

Test 2
Excess aqueous ammonia was added to solution D.
Observations:

[2]

iii)

Test 3
Dilute nitric acid was added to solution D followed by aqueous silver nitrate.
Observations:

[1]

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1d1 mark

Chromium(III) can be converted to chromium(VI). Chromium(VI) is hazardous.
Suggest one safety precaution when using chromium(VI).

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8a1 mark

Two metal salt solutions, X and Y, were analysed. Solution X was iron(II) chloride.
The tests on X and Y, and some of the observations, are given in the following tables.
Complete the observations in the tables.

test

observations

tests on solution X

Appearance of solution X

............................................................................

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8b1 mark

The solution was divided into four equal portions.

tests	observations
Dilute nitric acid and aqueous silver nitrate were added to the first portion of solution	............................................................................

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8c2 marks

tests	observations
Aqueous sodium hydroxide was added to the second portion of solution and the mixture shaken	............................................................................

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8d1 mark

tests	observations
Excess aqueous ammonia was added to the third portion of solution.	............................................................................

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8e2 marks

tests	observations
An oxidising agent was added to the fourth portion of the solution. Aqueous sodium hydroxide was then added to the mixture.	............................................................................

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8f1 mark

tests	observations
tests on solution Y The solution was divided into three equal portions. Dilute hydrochloric acid was added to the first portion of the solution.	white precipitate formed
Aqueous sodium hydroxide was added to the second portion of the solution and the mixture shaken. Aluminium powder was added to the mixture and it was warmed gently. The gas given off was tested with damp red litmus paper.	effervescence pungent gas evolved, litmus paper turned blue
Aqueous potassium iodide was added to the third portion of the solution.	pale yellow precipitate

What conclusions can you draw about solution Y?

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9a8 marks

A mixture of two solids, M and N, was analysed.
Solid M was zinc sulfate which is water-soluble and solid N was insoluble.
The tests on the mixture, and some of the observations, are in the table.

Complete the observations in the table.

Tests	Observations
Distilled water was added to the mixture in a boiling tube and shaken. The contents of the tube were filtered and the filtrate and residue kept for the following tests.
The filtrate was divided into four portions.
Test 1 (i) Drops of aqueous sodium hydroxide were added to the first portion of the filtrate. Excess aqueous sodium hydroxide was then added. (ii) Drops of aqueous ammonia were added to the second portion of the filtrate. Excess aqueous ammonia was then added.
Test 2 About 1 cm³ of dilute nitric acid followed by silver nitrate solution was added to the third portion of the filtrate.
Test 3 About 1 cm³of dilute nitric acid followed by barium nitrate solution was added to the fourth portion of the filtrate.
Test 4 Tests on the residue Appearance of the residue.	black solid
Test 5 Dilute hydrochloric acid was added to a little of the residue. The mixture was heated and the gas given off was tested with damp blue litmus paper.	effervescence pungent gas, bleached litmus paper
Test 6 Aqueous hydrogen peroxide was added to a little of the residue. The gas given off was tested.	effervescence glowing splint re-lit

State the expected observation in Test 1 part (i).

[3]

ii)

State the expected observation in Test 1 part (ii).

[2]

iii)

State the expected observation in Test 2.

[1]

iv)

State the expected observation in Test 3.

[2]

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9b1 mark

Identify the gas given off in Test 5.

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9c1 mark

Identify the gas given off in Test 6.

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9d2 marks

What conclusions can you draw about solid N?

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21a5 marks

An aqueous solution of substance X was analysed. Substance X was an iron(III) salt containing one other cation. The tests on X and some of the observations are in the following table. Complete the observations in the table

tests	observations
Colour of solution X	dark yellow
i) Drops of aqueous sodium hydroxide were added to about 2 cm³ of the solution. Excess aqueous sodium hydroxide was added to the test-tube. The mixture was heated. The gas given off was tested with damp indicator paper.	.......................................................................................... .......................................................................................... [3] pungent smell, indicator turned blue,pH 10
ii) Experiment (i) was repeated using aqueous ammonia instead of aqueous sodium hydroxide	.......................................................................................... .......................................................................................... [2]
To about 2 cm³ of solution X was added dilute sulphuric acid. Two pieces of zinc were added. The mixture was heated and the gas given off tested. After 10 minutes the mixture was filtered and test (a)(i) was repeated	lighted splint popped green precipitate insoluble in excess
A few drops of hydrochloric acid were added to about 2 cm³ of solution X. About 1 cm³ of barium chloride solution was added to the mixture.	white precipitate

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21b3 marks

Name the gas given off when sulfuric acid was added to the solution.

[1]

ii)

What type of chemical reaction occurs in (d). Explain your answer.

[2]

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21c2 marks

What conclusions can you draw about the anion and the other cation in substance X?

anion ................................................................................................................................
cation ................................................................................................................................

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24a6 marks

A mixture of two solid compounds D and E was analysed. Solid D was a zinc salt which is soluble in water. Solid E was an insoluble metal carbonate. The tests on the mixture and some of the observations are in the following table.

Test 1: About half of the mixture of D and E was placed in a test-tube. The mixture was heated.

Observations: Green to black, condensation formed

The rest of the mixture of D and E was added to distilled water in a boiling tube. The contents of the tube were filtered. The filtrate and the residue were kept for the following tests.

Complete observations for the following tests that were carried out on the residue

Test 1:
The residue was transferred from the filter paper in to a test-tube. About 3 cm³ of dilute sulphuric acid was
added. The gas was tested with limewater.

Observations: ....................................................................................................................

[2]

ii)

Test 2:
The solution obtained in (c) was divided into two equal portions.

The first portion was added excess aqueous sodium hydroxide, a little at a time.

Observations: pale blue precipitate

To the second portion was added excess aqueous ammonia, a little at a time.

Observations: ....................................................................................................................

[4]

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24b6 marks

Three tests were carried out on the filtrate.

Complete the observations for each test.

The filtrate from (a) was divided into three approximately equal portions.

Test 1: To the first portion were added drops of aqueous sodium hydroxide, a little at a time with shaking.

Observations: ...........................................................................................................................

[2]

Excess aqueous sodium hydroxide was added.

Observations:...........................................................................................................................

[1]

ii)

Test 2: To the second portion was added excess aqueous ammonia a little at a time.

Observations: ...........................................................................................................................

[3]

Test 3 : To the third portion were added drops of dilute hydrochloric acid and aqueous barium chloride.

Observations: white precipitate

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24c2 marks

What conclusions can you draw about the identity of solid D?

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24d1 mark

What conclusion can you draw about the identity of the cation in solid E?

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29a6 marks

A solid compound X was analysed. Solid X was an aluminium salt. The tests on X and some of the observations are written below.

Test 1

One spatula measure of X was placed into a hard-glass test tube. The solid was heated gently then heated strongly. The gas was tested with pH indicator paper.

Observations:

Condensation at top of tube, paper went red

Complete the other observations.

Test 2

Distilled water was added to X and shaken to dissolve. The solution was divided into five portions in test-tubes.

To the first portion, drops of aqueous sodium hydroxide were added.
Excess aqueous sodium hydroxide was then added.

Observations: ......................................................................................................................................

[3]

ii)

To the second portion, drops of aqueous ammonia were added.
Excess ammonia was then added.
Observations ......................................................................................................................................

[3]

To the third portion of solution, hydrochloric acid and barium chloride solution were added.

Observations: No visible change

To the fourth portion of solution, nitric acid and lead nitrate solution were added.

Observations: No visible change

To the fifth portion, aqueous sodium hydroxide and a spatula measure of aluminium granules were added. The mixture was warmed and the gas tested with indicator paper.

Observations: Pungent gas, paper went blue, pH 10

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29b1 mark

What does Test 1 tell you about the gas given off?

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29c2 marks

What conclusions can you draw about X from the tests done to the third and fourth portion of solution in part a).

Third portion: .......................................................................

Fourth portion: ....................................................................

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29d1 mark

Identify the gas given off in the fifth portion in part a)

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29e2 marks

What conclusions can you draw about substance X?

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31a3 marks

A sample of solid C was analysed. C is a mixture of two salts, D and E. Solid D is insoluble lead carbonate and solid E is water-soluble.

The tests on C, and some of the observations are in the following table.

Complete the observations in the table.

tests	observations
1. Describe the appearance of C.	pale green solid
2. Using a spatula, place a little of C in a hard glass test-tube. Inside the top of the tube suspend a piece of damp indicator paper. Heat C gently until gas comes out of the tube.	paper turns blue pH 8 to 11
3. Using a spatula, place a little of C in a test-tube. Add about 2cm³ of dilute nitric acid and test the gas.	.................................................. ..................................................

Solid C was added to a boiling tube containing distilled water. The tube was shaken to mix the contents. The contents of the boiling tube were filtered.

tests on the residue in the filter paper

observations

4. Place the funnel in a test-tube.
Pour dilute nitric acid onto the residue contained in the funnel.
Add 2cm³ of potassium iodide to the solution collected in the tube.

yellow precipitate

tests on the filtrate	observations
Divide the filtrate into three test-tubes
5. To the first portion add dilute hydrochloric acid and about 1cm³of aqueous barium nitrate.	white precipitate
6. To the second portion of solution, add excess aqueous ammonia.	green precipitate
7. To the third portion of solution, add an equal volume of aqueous sodium hydroxide. Warm the mixture gently. Test the gas with indicator paper.	green precipitate paper turned blue pH 8 - 11

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31b1 mark

Name the gas given off in test 3.

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31c1 mark

Name the gas given off in test 7.

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31d4 marks

What conclusions can you draw about salt E?

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33a6 marks

A mixture of two compounds, B and C, was tested.

Compound B was a water-soluble zinc salt and compound C was insoluble.

The tests and some of the observations are in the following table.

Complete the observations in the table.

tests	observations
1. One measure of the mixture was heated gently then heated strongly. The gas released was tested with cobalt chloride paper.	condensation at the top of the tube paper turned pink

The rest of the mixture was added to about 25 cm³ of distilled water in a boiling tube. The contents of the tube were shaken and filtered. The following tests were carried out.

tests	observations
Tests on the filtrate The solution was divided into 2 cm³ portions in four test-tubes.
2. Drops of aqueous sodium hydroxide were added to the first portion of the solution. Excess aqueous sodium hydroxide was added.	i) .............................................. .................................................. .................................................. [3]
3. Using the second portion test 2 was repeated using aqueous ammonia instead of aqueous sodium hydroxide.	ii)............................................... .................................................. .................................................. [3]
4. To the third portion of sothe lution was added hydrochloric acid and barium nitrate solution.	white precipitate
5. To the fourth portion of sothe lution was added nitric acid and silver nitrate solution.	no visible reaction
Tests on the residue
6. Some of the residue was placed into a test-tube. Dilute hydrochloric acid was added and the gas given off was tested with limewater.	rapid effervescence limewater turned milky

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33b1 mark

What does test 1 indicate?

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33c2 marks

What conclusions can you draw about compound B?

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33d2 marks

What does test 6 indicate?

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34a1 mark

Two salt solutions K and L were analysed. Each contained the same chloride anion but different metal cations. K was a copper(II) salt.

The tests on the solutions and some of the observations are in the following table.

Complete the observations in the table.

tests

observations

1. Appearance of the solutions

K = ..................................................

L = yellow

2. The pH of each solution was tested

K = pH 3

L = pH 2

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34b7 marks

The tests on solution K and some of the observations are in the following table.

Complete the observations in the table.

tests	observations
3. Drops of aqueous sodium hydroxide were added to solution K. Excess aqueous sodium hydroxide was then added to the test-tube.	i) ............................................. ................................................. [2]
4. Experiment 3 was repeated using aqueous ammonia instead of aqueous sodium hydroxide.	ii) drops ........................................ [1] iii) excess ........................................ [2]
5. A few drops of hydrochloric acid and about 1cm³ of barium chloride solution were added to a little of solution K.	iv) .................................................. [1]
6. A few drops of nitric acid and about 1cm³ of silver nitrate solution were added to a little of solution K.	v) .................................................. [1]

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34c2 marks

The tests on solution L, and some of the observations, are in the following table.

Complete the observations in the table.

tests	observations
7. Drops of aqueous sodium hydroxide were added to solution L. Excess aqueous sodium hydroxide was then added to the test-tube.	red-brown precipitate
8. Experiment 7 was repeated using aqueous ammonia instead of aqueous sodium hydroxide.	red-brown precipitate
9. A few drops of hydrochloric acid and about 1cm³ of barium chloride solution were added to a little of solution L.	i) .................................................. [1]
10. A few drops of nitric acid and about 1cm³ of silver nitrate solution were added to a little of solution L.	ii) .................................................. [1]

How did you do?

34d1 mark

What does test 2 indicate?

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34e2 marks

Identify the metal cation present in solution L.

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Tests	Observations
Test 1: Appearance of solid U.	Pink crystals
Test 2: Solid U was heated gently and then strongly in a test-tube.	condensation droplets formed on the sides of the test-tube
Solid U was added to distilled water in a test-tube and shaken until dissolved.
Test 3 part (i): The solution was divided into three equal portions in separate test-tubes and the following tests carried out. Several drops of aqueous sodium hydroxide were added to the first portion of the solution and the test-tube shaken.	pale brown precipitate
Test 3 part(ii): Then hydrogen peroxide solution was added to the mixture and the gas given off was tested.	effervescence glowing splint re-lit
Test 4: Dilute nitric acid was added to the second portion of the solution followed by barium nitrate solution.
Test 5: Dilute nitric acid was added to the third portion of the solution followed by silver nitrate solution.

Tests	Observations
Test 1 on liquid L Appearance of liquid L
Test 2 Liquid L was divided into three equal portions in separate test-tubes. (i) An iodine crystal was added to the first portion of liquid L. The test-tube was stoppered and the contents shaken. (ii) An equal volume of liquid M was added to the test-tube, the contents shaken and left to stand for five minutes.	(i) liquid turned orange (ii) two layers were formed, pink top layer and orange lower layer
Test 3 To the second portion of liquid L, dilute nitric acid and barium nitrate solution were added.
Test 4 To the third portion of liquid L, dilute nitric acid and silver nitrate solution were added.

Tests	Observations
Test 1 Appearance of liquid M.	Colourless liquid with an antiseptic smell
Test 2 Appearance of liquid N.
Test 3 A few drops of M were transferred to a dry watch glass. The liquid was touched with a lighted splint.	Burns with a yellow flame
Test 4 Test 3 was repeated using liquid N.
Test 5 A little of liquid M was added to a crystal of iodine in a test-tube. The test-tube was shaken.	Orange-brown solution
Test 6 To a little of liquid N, a few drops of dilute nitric acid was added, followed by silver nitrate solution.

Tests	Observations
i) The appearance of the liquids.	P ............................................................... [1] Q colourless, smell of vinegar R colourless, no smell
ii) The pH of the liquids was tested using Universal Indicator paper.	P ............................................................... [1] Q pH 5 R pH 7
iii) A piece of magnesium ribbon was added to a little of each liquid. The gas given off by liquid P was tested.	P ..................................................................... ................................................................. [2] Q slow effervescence R no reaction
iv) To a little of liquid P, hydrochloric acid and aqueous barium chloride was added.	............................................................... [2]
Liquid R was heated to boiling in a test-tube. A thermometer was used to record the constant temperature of the vapour produced.	Temperature = 100 °C

liquid	test	result
aqueous sodium iodide
hexene
dilute nitric acid

CIE IGCSE Chemistry

Topic Questions

12.3 Identification of Ions & Gases

Tests	Observations
Test 1 Appearance of solid E.	White crystalline solid
Test 2 A little of solid E was heated in a test-tube.	Colourless drops of liquid formed at the top of the tube
Test 3 A little of solid E was dissolved in distilled water. The solution was divided into four test-tubes and the following tests were carried out. To the first test-tube of solution, drops of aqueous sodium hydroxide were added. Excess sodium hydroxide was then added to the test-tube.
Test 4 Test 3 was repeated using aqueous ammonia solution instead of aqueous sodium hydroxide.
Test 5 To the third test-tube of solution, dilute hydrochloric acid was added, followed by barium chloride solution.	No reaction
Test 6 To the fourth test-tube of solution, aqueous sodium hydroxide and aluminium powder were added. The mixture was heated.	Effervescence Pungent gas given off Turned damp litmus paper blue

tests	observations
Several drops of aqueous sodium hydroxide were added to the second portion of the solution. Excess aqueous sodium hydroxide was then added to the test-tube.

tests	observations
Aqueous ammonia was added to the third portion, dropwise and then in excess.

tests	observations
To the fourth portion of the solution, dilute nitric acid and aqueous silver nitrate were added.

tests	observations
To the fifth portion of the solution, about 1 cm³ of dilute nitric acid and barium nitrate solution were added.

Tests	Observations
Appearance of solid S	Black solid
Hydrogen peroxide was added to solid S in a test tube, and a glowing splint then inserted into the tube.	Slow effervescence, splint relit
Dilute sulfuric acid was added to solid S in a test-tube. The mixture was heated to boiling point.	Blue solution formed
The solution was divided into three equal portions into test-tubes. To the first portion of the solution, excess sodium hydroxide was added.	i) ..................................................... [1]
To the second portion of the solution, about 1 cm³ of aqueous ammonia solution was added.	ii) ..................................................... [2]
Excess ammonia solution was then added to the second portion.	iii) ..................................................... [2]
To the third portion of the solution, dilute hydrochloric acid was added followed by barium chloride solution.	iv) ..................................................... [2]

tests	observations
i) Describe the appearance of E	................................................................................ [2]
Using a spatula salt E was placed in a hard glass test-tube. Inside the top of the tube was suspended a piece of damp blue litmus paper next to a piece of damp red litmus paper. E was heated gently until gas came out of the tube.	Red litmus went blue then blue litmus went red
E was dissolved in water to make an aqueous solution. The solution was divided into three test-tubes: ii) To the first portion, was added a few drops of dilute nitric acid and about 1 cm³of aqueous silver nitrate. iii) To the second portion of solution E, was added about 1 cm³ of lead nitrate solution. iv) To the third portion of solution E, was added about 1 cm³of aqueous sodium hydroxide. The mixture was boiled gently and the gas given off was tested with indicator paper	................................................................................ [2] ................................................................................ [2] ................................................................................ [2]

tests	observations
1) The pH of the solution was tested using indicator paper	orange, pH 4
The solution was divided into three test-tubes
2) To the first portion was added a piece of magnesium ribbon. The gas was tested with a lighted splint.	i) .................................................. [2]
3) To the second portion of A was added sodium carbonate. The gas was tested with limewater.	ii) .................................................. [2]
4) To the third portion of liquid A was added a spatula measure of solid B. The mixture was boiled gently. By using a teat pipette the solution was transferred to another test tube. Excess aqueous ammonia was added.	green solution formed dark blue solution formed

tests	observations
1. Test the pH of the liquids using indicator paper. Note the colour of the paper.	P = red pH 1 i) Q = .......... pH .......... [2] R = orange pH 5
2. Add a 5 cm piece of magnesium to about 3cm³ of liquid P in a test–tube. Test the gas given off.	bubbles of gas given off lighted splint pops
3. Repeat test 2 using liquids Q and R. Do not test for any gases.	ii) Q ................................................. R .................................................. [2]
4. To about 2cm³ of liquid, P add 1 spatula measure of sodium carbonate. Test the gas given off.	iii) ............................................ .................................................. .................................................. [3]
5. By using a teat pipette add aqueous silver nitrate to about 1 cm³ of liquid P.	white precipitate
6. By using a teat pipette add liquid Q to about 1 cm³ of aqueous iron(II) sulfate.	green precipitate