Edexcel GCSE Chemistry

Topic Questions

GCSEChemistryEdexcelTopic Questions9. Separate Chemistry 29.1 Qualitative Analysis: Tests for Ions

9.1 Qualitative Analysis: Tests for Ions

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1a2 marks

Sodium hydroxide can be used to test for cations. 

Upon the addition of sodium hydroxide, some cations form coloured precipitates. 

Sodium hydroxide is added to a solution containing iron(II) ions, Fe2+, and iron(III) ions, Fe3+

Draw one line from the iron ion to the colour of the precipitate formed.

screenshot-2024-01-24-103352

How did you do?

1b1 mark

Sodium hydroxide solution was added to a different solution. 

A white precipitate was formed.

What could the identify of the metal ions be?

  ☐ A Copper and aluminium
  ☐ B Aluminium and calcium
  ☐ C Calcium and copper
  ☐ D Aluminium and ammonium

How did you do?

1c1 mark

What could be done to distinguish between the two ions identified in part b)?

How did you do?

1d2 marks

To test for ammonium ions, sodium hydroxide is added and the solution gently heated. 

Place ticks in boxes by the two statements that are correct about this reaction.

 ammonia gas is formed   
 the gas formed turns limewater cloudy   
 chlorine gas is formed  
 the gas formed turns damp red litmus paper blue  
 the gas formed gives a squeaky pop sound with a lit splint  

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2a1 mark

A student had the three potassium halide solutions shown below:

  • potassium chloride
  • potassium bromide
  • potassium iodide

What should they add to the solutions to identify each of these solutions?

  ☐ A Dilute hydrochloric acid followed by barium chloride
  ☐ B Dilute nitric acid followed by barium nitrate
  ☐ C Dilute hydrochloric acid followed by silver nitrate
  ☐ D Dilute nitric acid followed by silver nitrate

How did you do?

2b3 marks

When tested with the correct reagent, halides produce distinctive coloured precipitates which can be used to distinguish them from each other.

Draw one line from each of the potassium halide solutions to the colour of the precipitate it forms.

screenshot-2024-01-24-093332

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2c2 marks

The student also had a solution of potassium carbonate.

What could they add to this solution to identify the carbonate ion?

What would they observe? 

They should add _______________________________________________. 

They would observe ____________________________________________.

How did you do?

2d1 mark

The student could perform a flame test to confirm the presence of potassium ions in the solution in part c).

What colour flame would be seen?

 

  ☐ A Green
  ☐ B Orange-red
  ☐ C Lilac
  ☐ D Yellow

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3a2 marks

Instrumental analysis can be used to analyse elements and compounds.

Give two advantages of using instrumental analysis over chemical tests.

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3b1 mark

Flame photometry is one instrumental method that can be used to identify metal ions.

In addition to being able to identify the metal ions in solution, what other piece of information can flame photometry tell us about the sample?

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3c1 mark

The resulting output from a flame photometer can be compared against those of known metals.

Figure 1 shows the output for manganese, strontium, titanium and an unidentified solution.

XJfKyTIO_flame-emission-spectrum

Figure 1

 Which metal ion is present in the unidentified solution?

  ☐ A Manganese
  ☐ B Strontium
  ☐ C Titanium
  ☐ D Manganese and strontium

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4a1 mark

A student carried out a flame test on a salt containing potassium chloride.

The steps they carried out are written below. 

The steps shown are not in the correct order. 

 step J  Hold the platinum wire it in a blue bunsen burner flame until there is no colour change
 step K  Dip a platinum wire into dilute hydrochloric acid
 step L  Hold the wire in a blue bunsen burner flame until a colour is observed
 step M  Dip the loop of the wire into the salt 

Write the steps in the correct order. 

 first step           last step   
               

How did you do?

4b1 mark

Give the colour of the flame produced by the potassium ions in the salt. 

How did you do?

4c1 mark

Why would it not be possible to tell from the flame test if the sample contained both potassium and sodium ions?

How did you do?

4d1 mark

Which other method can be used to identify the presence of potassium ions in potassium chloride?

  ☐ A Chromatography
  ☐ B Using litmus paper 
  ☐ C Measuring the boiling point of the solution
  ☐ D Flame photometry

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5a2 marks

Chemical tests can be done to identify the cations found within a solution. 

Two of these cations include sulfate ions and carbonate ions. 

Place ticks in boxes by the two statements which are are true about testing for sulfate ions.

 A cream precipitate of barium sulfate is formed   
 Dilute acid followed by barium chloride is used to test for sulfate ions  
 The substance produced turns limewater cloudy  
 A white precipitate of barium sulfate is formed  
 Nitric acid followed by silver nitrate solution is used to test for sulfate ions  

How did you do?

5b1 mark

The ionic equation for the reaction that occurs when testing for sulfate ions is shown below:

Ba2+ (...)  +   SO42- (...)    →     BaSO4 (...)

What is the correct state symbol for each species?

  ☐ A l, l, s
  ☐ B aq, l, s
  ☐ C aq, aq, s
  ☐ D l, aq, l

How did you do?

5c1 mark

A student carried out a test to confirm the presence of carbonate ions in magnesium carbonate. 

They added dilute hydrochloric acid and bubbled the gas produced through limewater. 

Name the salt produced in this reaction. 

How did you do?

5d1 mark

What will you observe happen to the limewater in the presence of carbon dioxide?

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1a2 marks

A sample of potassium carbonate is contaminated with a small amount of sodium carbonate.
When a flame test is carried out on the sample, a bright yellow flame is seen.

Describe how you could show that potassium and sodium ions are present in this sample.

How did you do?

1b3 marks

Higher Only

Hydrochloric acid reacts with a solution of sodium carbonate. 

2HCl (aq) + Na2CO3 (aq) → 2NaCl (aq) + CO2 (g) + H2O (l)

Write the ionic equation for this reaction.

How did you do?

1c6 marks

A student tests solutions of three ionic substances, K, L and M.
The student carries out the same two tests on each of the three solutions.

Test 1 add dilute nitric acid and then silver nitrate solution.
Test 2 add a few drops of sodium hydroxide solution and warm the mixture.

Figure 7 shows the results of the tests and the student’s conclusions about the identity of each substance.

ionic substance test 1  test 2   student’s conclusion
K   white precipitate   colourless solution    ammonium chloride
L   white precipitate   white precipitate    aluminium chloride
M   no precipitate   green precipitate    iron(II) sulfate

Figure 7

None of the student’s conclusions are fully justified.

Explain which part of each conclusion is justified and what further work can be carried out to fully justify each conclusion.

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2a4 marks

A technician was asked to find the concentration of potassium ions in a dilute solution using a flame photometer.

i)
The technician first produced a calibration curve using solutions with known concentrations of potassium ions.
Figure 9 contains the data for the calibration curve.

concentration of potassium ions in mol dm-3

 display reading
0.025 180
0.050 280
0.100 440
0.200 580
0.500 900

Figure 9

Use the information in Figure 9 to plot the calibration curve on the grid below.

(3)

fig-q7ai-1cho-2h-paper-1-nov-2021

ii)
The technician then obtained a reading of 360 for a dilute solution containing potassium ions.

Use the calibration curve to find the concentration of the potassium ions in this solution.
(1)

concentration = ...................................... mol dm-3

How did you do?

2b2 marks

Higher Only

In the test for chloride ions, silver nitrate solution is added to a solution containing chloride ions.
A white precipitate forms.

Write the ionic equation for this reaction.

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2c6 marks

Higher Only

A student was given a container of ammonium iron(II) sulfate, (NH4)2Fe(SO4)2 .
The student was also given a dilute solution of sodium hydroxide and access to other laboratory reagents.

Describe the tests the student should carry out to identify the ions in the ammonium iron(II) sulfate, including appropriate equations for the reactions involved.

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3a3 marks

A student was asked to identify the ions present in three different solutions of compounds, A, B and C.

The student's results from a series of tests on each solution are shown in Figure 1.

Test
Compound Flame Test Add dilute hydrochloric acid Add sodium hydroxide solution Add dilute hydrochloric acid and barium chloride Add dilute nitric acid and silver nitrate
A blue-green flame fizzing blue precipitate fizzing, no precipitate no reaction
B red flame no reaction white precipitate no reaction cream precipitate
C yellow flame no reaction no reaction white precipitate no reaction

Figure 1.

Identify the two ions present in each of the compounds A, B, and C.

A: ____________________ and ____________________ 

B: ____________________ and ____________________ 

C: ____________________ and ____________________ 

How did you do?

3b1 mark

What is the purpose of adding dilute acid in the tests with barium chloride and silver nitrate?

How did you do?

3c1 mark

Suggest what could be seen if the acid was not added?

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3d3 marks

Explain why nitric acid is used before using silver nitrate instead of hydrochloric acid or sulfuric acid.

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4a3 marks

Minerals from a quarry were taken to a laboratory for analysis.

Four samples of minerals, A, B, C and D were submitted for identification of their ions. 

In the laboratory, water is added to each mineral to form solutions and further tests are carried out.

The results of these tests are shown in Table 1.

Table 1

Test A B C D
Add sodium hydroxide solution blue precipitate  no change white precipitate green precipitate
Add dilute hydrochloric acid fizzed fizzed no change no change
Add dilute hydrochloric acid and barium chloride no change no change white precipitate no change
Add dilute nitric acid and silver nitrate no change yellow precipitate no change cream precipitate

It was concluded that mineral B contained two negative ions and the positive ion was unidentified.

How do the results show this?

 

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4b2 marks

It was believed that the positive ion present in mineral B was lithium.

Describe a further test, including the expected result, that could be used to confirm the presence of lithium ions.

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4c3 marks

Mineral C formed a white precipitate with sodium hydroxide solution.

i)
Identify which two metal ions this could be.
(1)
ii)
Describe a further test that would confirm the identify of the ion and give the result.
(2)

How did you do?

4d1 mark

State an instrumental method that could be used to distinguish between the three metal ions from part (c).

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4e2 marks

Identify the ions in minerals A and D.

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5a5 marks

An unknown salt sample, X, has been sent off for analysis for identification.

A small sample of the unknown salt, X, is put into a flame photometer and its line spectrum is generated.

The line spectrum is compared to the line spectrum of Group 1 elements to see if the metal ion present in X can be identified.

The line spectra are shown in Figure 1.

line-spectrum

Figure 1

State which elements are or are not present in the unknown salt sample, X.

Give reasons for your answers.

How did you do?

5b2 marks

Describe other chemical tests that could be carried out to identify any unidentified elements.

You should not include any references to flame photometry.

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5c2 marks

Give two advantages of using a flame emission spectroscopy machine, rather than chemical tests, to identify samples.

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1a2 marks

Qualitative tests can be used to identify ions in substances.

Sodium hydroxide solution is warmed with a solution of ammonium ions.
Ammonia gas is given off.

Describe the test to show the gas is ammonia.

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1b3 marks

Two tests were carried out on copper sulfate solution.

i)
Sodium hydroxide solution was added to a small amount of copper sulfate solution.
A blue precipitate of copper hydroxide formed.

Complete the word equation for the reaction.
Include state symbols.

(2)

copper sulfate (aq) + sodium hydroxide (aq) → .......... (..........) + ............ (..........)

ii)
Dilute hydrochloric acid was added to a different sample of copper sulfate solution. Barium chloride solution was then added.

State what would be seen.

(1)

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1c6 marks

A technician found some colourless crystals in an unlabelled beaker in a laboratory.

The technician knew that the substance was potassium chloride, potassium carbonate, sodium chloride or sodium iodide.

Plan a series of tests the technician could carry out to identify the colourless crystals.

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21 mark

Scientists test a solution from a bottle that is known to contain a copper (II) compound.

Table 1 shows their results.

Table 1

Test Result
Flame test Yellow flame
Add sodium hydroxide solution Blue precipitate formed
Add dilute nitric acid followed by silver nitrate solution Yellow precipitate formed

Which statement below is true?

  ☐ A The flame test was performed incorrectly
  ☐ B Bromide ions are present, so the compound is CuBr2
  ☐ C The test tube was contaminated for the sodium hydroxide test
  ☐ D The copper compound in the bottle was contaminated with another metal compound

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3a2 marks

Qualitative tests are used to identify ions.

A student carries out a flame test on an unknown solid.
A red flame is seen.
The student concludes that the solid is lithium carbonate.

Explain why this conclusion is not justified.

How did you do?

3b2 marks

The following tests were carried out on a substance containing two ions.

1)
A flame test on the solid substance produced a yellow colour.
2)
Dilute hydrochloric acid was added to a solution of the substance followed by a few drops of barium chloride solution.
A white precipitate formed.

Give the name and formula of the substance.
 
Name of substance ...........................................................................................
 
Formula of substance........................................................................................

How did you do?

3c1 mark

The test for chloride ions was carried out on a solution.
Dilute nitric acid was added to the solution, followed by a few drops of silver
nitrate solution.
A white precipitate formed.

Why is it necessary to add dilute nitric acid in this test?

  ☐ A To neutralise the solution
  ☐ B Nitrate ions are needed for the test to work
  ☐ C To make sure that no carbonate ions are present
  ☐ D The test only works in alkaline conditions

How did you do?

3d5 marks

Higher Only

Sodium hydroxide solution is used to identify some cations present in compounds.

i)
Sodium hydroxide solution is warmed with a solution of ammonium ions.
Ammonia gas is given off.

Describe the test to show the gas is ammonia.

(2)

ii)

Sodium hydroxide solution is also used to distinguish between iron(II) ions, Fe2+ and iron(III) ions, Fe3+, in solution.

You are given a solution containing iron(II) ions and another solution containing iron(III) ions.

Describe what is seen when sodium hydroxide solution is added to each of these solutions.

(2)

iii)
Iron(III) ions, Fe3+, react with hydroxide ions in solution to form iron(III) hydroxide.

Complete the ionic equation for this reaction.

(1)

   Fe3+ + 3OH– → .............................................................................................

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41 mark

A compound is suspected of containing calcium ions, Ca2+.

Which test would not help to positively identify calcium?

      Test Result
  ☐ A Flame test Orange-red flame
  ☐ B Add sodium hydroxide solution White precipitate forms
  ☐ C Add nitric acid and silver nitrate White precipitate forms
  ☐ D Flame photometry Characteristic lines match the reference spectrum

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5a1 mark

Figure 3 shows two tests carried out on a white solid and the results of the tests.

  test results
test 1 flame test carried out a yellow flame
test 2 dilute hydrochloric acid added
gas given off passed into limewater		 effervescence occurs
the limewater goes milky

Figure 3

Which ion is shown to be present by the result of test 1?
  ☐ A lithium
  ☐ B sodium
  ☐ C potassium
  ☐ D calcium

How did you do?

5b2 marks
i)
State the name of the gas given off in test 2.

(1)

ii)
State the name of the ion shown to be present in the white solid by the result of test 2.

(1)

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5c3 marks

A flame photometer can be used to measure the concentration of potassium ions in a solution.

Figure 4 shows the photometer readings for three different concentrations of potassium ions in solutions.

fig-4-q2c-1cho-2f-paper-1-june-2018

Figure 4

i)
A solution containing a concentration of potassium ions of 35 mg dm-3 is placed in the photometer.
The photometer reading is 7.0.

Plot this point on the graph and then draw the straight line of best fit.

(2)

ii)
Another solution of potassium ions gives a photometer reading of 9.0.

Use the graph to find the concentration of potassium ions in this solution.

(1)

concentration =....................................... mg dm-3

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61 mark

Which is not an advantage of using instrumental methods rather than small-scale lab methods for identifying ions?

  ☐ A Instrumental methods are more accurate
  ☐ B Instrumental methods are faster
  ☐ C Instrumental methods are cheaper
  ☐ D Instrumental methods are more sensitive

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7a2 marks

Qualitative tests are used to identify ions in compounds.

Solid X contains two ions.

The tests for these ions and their results are shown in Figure 10.

test result
flame test on solid X red-orange flame
dilute nitric acid is added to an
aqueous solution of X, followed by silver nitrate solution		 white precipitate forms

Figure 10

Use the information in Figure 10 to name the cation and the anion in solid X.

name of cation ..................................

name of anion ...................................

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7b2 marks

Another solid, Y, also contains two ions.
A test was carried out on solid Y.
A few drops of sodium hydroxide solution were added to a solution of solid Y.
A white precipitate formed.

i)
Give the reason why this test does not identify the cation in solid Y.
(1)
ii)
Give the reason why this test does not identify the anion in solid Y.
(1)

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7c1 mark

Instrumental methods are often used for analysis.

Give a reason why instrumental analysis may be better than other methods of analysis.

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7d5 marks

Higher Only

Iron(II) sulfate solution reacts with sodium hydroxide solution to form a pale green precipitate of iron(II) hydroxide, Fe(OH)2.

i)
Write the ionic equation for this reaction.
(3)
ii)
The green iron(II) hydroxide precipitate gradually turns brown when exposed to air.
Explain this observation.
(2)

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8a6 marks

Qualitative tests are carried out on ionic substances to identify the ions present in the substances.

 

The test for a given ion must be unique to that ion.

 
i)
Explain why the test for a given ion must be unique to that ion.
 
(2)
 
ii)
In the test for the carbonate ion, CO32–, dilute hydrochloric acid is added to the solid being tested.
 
State the name of the gas produced in the test if carbonate ions are present.
 
(1)

iii)
Tests for three ions are described.
 
Draw one straight line from the test for each ion to the observation that shows that ion to be present.
Each observation may be correct for one test, more than one test, or for none of the tests.
 
(3)

fig-q7aiii-1cho-2f-paper-1-june-2019

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8b6 marks

A white solid is known to be a chloride in which the metal ion is sodium, potassium, calcium or aluminium.

 

A chemist was told to carry out a test for each metal ion that could be present in this white solid.

 

Describe tests to show the presence of each of these metal ions.

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91 mark

Which element is present in this flame emission spectrum?

q5-9-1-flame-emission-spectrum---example

q5-9-1-reference-line-emission-spectra-chart

  ☐ A Helium
  ☐ B Mercury
  ☐ C Hydrogen
  ☐ D Neon

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10a4 marks

Tests are carried out to identify the ions in two solids, P and Q.

A flame test is used to identify the metal ions in each of these solids.

i)
Describe how to do a flame test.

(2)

ii)
Different metal ions produce different coloured flames.

Draw one straight line from each metal ion to its flame colour.

(2)

fig-q4aii-1cho-2f-paper-1-nov-2020

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10b3 marks

P and Q dissolve in water to form colourless solutions.

Figure 7 shows the results of tests on these solutions.

test results
solution of P solution of Q
dilute hydrochloric acid added, then barium chloride solution a white precipitate remains colourless
dilute nitric acid added, then silver nitrate solution remains colourless a yellow precipitate

Figure 7

i)
The anions in solutions of P and Q can be identified from the results of the tests shown in Figure 7.

Draw one straight line from each solution to the anion present.
(2)

fig-q4bi-1cho-2f-paper-1-nov-2020

ii)
The formula of barium chloride is BaCl2.
Give the total number of ions in the formula BaCl2.
(1)

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10c3 marks

A few drops of sodium hydroxide solution are added to a solution of iron(II) sulfate.
Iron(II) hydroxide is formed.

i)
State what would be seen.
(2)
ii)
One other product is formed in this reaction.

What is the name of this other product?
(1)
  ☐ A iron(II) chloride
  ☐ B sodium chloride 
  ☐ C sodium sulfate 
  ☐ D water

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111 mark

A student adds a few drops of dilute nitric acid followed by a few drops of silver nitrate solution to a test tube containing an unknown colourless solution. A white precipitate is seen.

What ions could be present in the solution?

  ☐ A Ammonium ions
  ☐ B Chloride ions
  ☐ C Sulfate ions
  ☐ D Magnesium ions

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12a1 mark

A chloride ion, a fluorine atom and a nanoparticle are all types of particle.

Which of the following shows the particles in order of size, starting from the smallest?

  ☐ A nanoparticle, fluorine atom, chloride ion
  ☐ B nanoparticle, chloride ion, fluorine atom 
  ☐ C fluorine atom, nanoparticle, chloride ion 
  ☐ D fluorine atom, chloride ion, nanoparticle

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12b5 marks

A solution, X, is thought to contain chloride, bromide or iodide ions.

i)
The solution is tested to see whether it contains one of these ions.
In the test, a few drops of two different solutions are added to X.

Name the two solutions that are added in the test.
(2)

solution 1  ...........................................................
solution 2 ............................................................

ii)
The student carrying out the test records the following result.

A precipitate forms in the test tube. The precipitate is a cream/yellow colour.

Explain why the anion in X cannot be known for certain.

(2)

iii)
The metal ions in X could be identified using a flame test.
There is a more sensitive and accurate instrumental method that can be used.

Give the name of an instrument that can be used to identify the metal ions in X.
(1)

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131 mark

Scientists test a solution of compound X. The table shows their results.

Test Result
Acidified silver nitrate solution White precipitate
Add sodium hydroxide solution Green precipitate

Which two ions are present in compound X?

  ☐ A Fe3+ and Cl-
  ☐ B Fe3+ and SO42-
  ☐ C Fe2+ and Cl-
  ☐ D Fe2+ and SO42-

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14a
Sme Calculator3 marks

A student carried out some tests on copper sulfate.

A flame test was carried out on some copper sulfate crystals.

The student used the following method.

step 1

dip a wire in hydrochloric acid, then hold the wire in a roaring Bunsen burner flame
step 2

dip the wire in hydrochloric acid again, then dip the wire in the copper sulfate crystals
step 3

hold the wire with the copper sulfate in the roaring Bunsen burner flame.
i)
State why in step 1 the wire is dipped in hydrochloric acid and held in a roaring Bunsen burner flame.

(1)

ii)
State why in step 2 the wire is dipped in hydrochloric acid again before dipping it in the copper sulfate crystals.

(1)

iii)
What colour should be seen when the flame test is carried out on copper sulfate?

(1)

  ☐ A blue-green
  ☐ B lilac
  ☐ C orange-red
  ☐ D yellow

How did you do?

14b3 marks

A solution of the copper sulfate was tested in a flame photometer.

i)
Give an advantage of using a flame photometer, rather than a flame test, to test for copper ions.

(1)

ii)
Figure 7 shows some values obtained when producing a calibration graph for copper ions in a flame photometer.

Draw a line of best fit through the points.

fig-q4bii-1cho-2f-paper-1-nov-2021

(1)

iii)
A solution containing copper ions gave a display reading of 0.030.

Use the calibration graph in Figure 7 to find the concentration of copper ions in this solution.

(1)

concentration of copper ions = ................................. ppm

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14c2 marks

The student tested an unknown solution for sulfate ions by

    1. adding a few drops of dilute sulfuric acid to the unknown solution
    2. then adding a few drops of barium chloride solution.

A white precipitate was formed.

The student cannot conclude from this result that the unknown solution contains sulfate ions.

Explain what the student should change to obtain a valid result.

How did you do?

14d
Sme Calculator3 marks

Calculate the percentage by mass of copper in copper sulfate, CuSO4

(relative atomic masses: Cu = 63.5
relative formula mass of CuSO4 = 159.5)


Give your answer to the nearest whole number.

percentage by mass of copper = ..........................

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