AS Level Chemistry B (Salters) CHEMISTRY IN DEPTH
APPROVED 2025 EXAM WITH MARKING SCHEME.
1 This question is about Group 2 compounds.
Group 2 hydroxides can be used to neutralise acidity in a variety of contexts. Magnesium
hydroxide may be used to neutralise excess stomach acidity and calcium hydroxide may be used
to neutralise acidity in soils.
The hydroxides are formed when the oxides react with water.
(a) Write an equation to show the ions formed when calcium oxide reacts with water.
[1]
(b) A student shakes a small amount of magnesium oxide in a test tube with water. A white
suspension is formed.
The student then adds dilute hydrochloric acid, drop by drop with shaking, until no further
changes are seen.
Describe how the appearance of the contents of the test tube changes during the addition of
the acid.
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(c) Barium chloride solution is used to test for the presence of sulfate ions in solution.
Write an ionic equation for this test.
Include state symbols.
[2]
,(d) A student is provided with a solid sample of an unknown Group 2 hydroxide, X(OH)2.
The student describes how 250 cm3 of a solution of this solid is made up in a volumetric
flask.
Step 1 The mass of a weighing boat is measured and recorded.
Step 2 Solid is added to the boat and the new mass measured and recorded.
Step 3 The contents of the boat are tipped into a beaker.
Step 4 Deionised water is added.
Step 5 The mixture is stirred using a glass rod until all of the solid is dissolved.
Step 6 The glass rod is removed.
Step 7 The solution is poured through a funnel into the volumetric flask.
Step 8 The solution is made up to the mark with deionised water.
Step 9 The flask is stoppered and inverted several times.
Step 10 The concentration of the solution is calculated.
Describe two errors in this practical procedure made by the student and state the effect of
each error on the concentration of the solution.
Error ..........................................................................................................................................
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Effect on concentration .............................................................................................................
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Error ..........................................................................................................................................
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Effect on concentration .............................................................................................................
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[4]
, (e) * A student uses a titration to identify the unknown Group 2 metal X in a sample of X(OH)2.
The student records the following data.
Mass of weighing boat + X(OH)2 = 4.64 ± 0.005 g
Mass of weighing boat = 4.44 ± 0.005 g
The sample of X(OH)2 is dissolved and made up to 250 cm3 of solution in a volumetric flask.
The student titrates this solution with 0.0250 mol dm–3 HCl.
The student calculates correctly that the concentration of X(OH)2 is 0.0106 mol dm–3.
Use this data to calculate the Mr for X(OH)2 and use this to identify the metal X.
Given that the percentage uncertainty is greatest for the mass, apply this percentage to the
value of Mr when quoting your result. [6]
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APPROVED 2025 EXAM WITH MARKING SCHEME.
1 This question is about Group 2 compounds.
Group 2 hydroxides can be used to neutralise acidity in a variety of contexts. Magnesium
hydroxide may be used to neutralise excess stomach acidity and calcium hydroxide may be used
to neutralise acidity in soils.
The hydroxides are formed when the oxides react with water.
(a) Write an equation to show the ions formed when calcium oxide reacts with water.
[1]
(b) A student shakes a small amount of magnesium oxide in a test tube with water. A white
suspension is formed.
The student then adds dilute hydrochloric acid, drop by drop with shaking, until no further
changes are seen.
Describe how the appearance of the contents of the test tube changes during the addition of
the acid.
...................................................................................................................................................
...................................................................................................................................................
...................................................................................................................................................
. .......................................................................................................................................... [2]
(c) Barium chloride solution is used to test for the presence of sulfate ions in solution.
Write an ionic equation for this test.
Include state symbols.
[2]
,(d) A student is provided with a solid sample of an unknown Group 2 hydroxide, X(OH)2.
The student describes how 250 cm3 of a solution of this solid is made up in a volumetric
flask.
Step 1 The mass of a weighing boat is measured and recorded.
Step 2 Solid is added to the boat and the new mass measured and recorded.
Step 3 The contents of the boat are tipped into a beaker.
Step 4 Deionised water is added.
Step 5 The mixture is stirred using a glass rod until all of the solid is dissolved.
Step 6 The glass rod is removed.
Step 7 The solution is poured through a funnel into the volumetric flask.
Step 8 The solution is made up to the mark with deionised water.
Step 9 The flask is stoppered and inverted several times.
Step 10 The concentration of the solution is calculated.
Describe two errors in this practical procedure made by the student and state the effect of
each error on the concentration of the solution.
Error ..........................................................................................................................................
...................................................................................................................................................
Effect on concentration .............................................................................................................
...................................................................................................................................................
Error ..........................................................................................................................................
...................................................................................................................................................
Effect on concentration .............................................................................................................
...................................................................................................................................................
[4]
, (e) * A student uses a titration to identify the unknown Group 2 metal X in a sample of X(OH)2.
The student records the following data.
Mass of weighing boat + X(OH)2 = 4.64 ± 0.005 g
Mass of weighing boat = 4.44 ± 0.005 g
The sample of X(OH)2 is dissolved and made up to 250 cm3 of solution in a volumetric flask.
The student titrates this solution with 0.0250 mol dm–3 HCl.
The student calculates correctly that the concentration of X(OH)2 is 0.0106 mol dm–3.
Use this data to calculate the Mr for X(OH)2 and use this to identify the metal X.
Given that the percentage uncertainty is greatest for the mass, apply this percentage to the
value of Mr when quoting your result. [6]
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