What is meant by sparingly soluble?

Dissolving only to a very small extent in water; Mg(OH)₂ is an example.

What is Mg(OH)₂ used for, and how does it work?

An antacid; it neutralises excess stomach acid: Mg(OH)₂ + 2HCl → MgCl₂ + 2H₂O.

How are CaO and CaCO₃ used to treat flue gases?

They react with SO₂ to remove it: CaO + SO₂ → CaSO₃ and CaCO₃ + SO₂ → CaSO₃ + CO₂.

Why must SO₂ be removed from flue gases?

It is an acidic gas that causes acid rain.

How do you test for sulfate ions?

Add dilute HCl, then BaCl₂ solution; a white precipitate of BaSO₄ shows sulfate ions.

Write the ionic equation for the sulfate test.

Ba²⁺(aq) + SO₄²⁻(aq) → BaSO₄(s)

Why is BaCl₂ used in the test for sulfate?

BaSO₄ is insoluble, so a white precipitate forms only with sulfate ions.

Why is the solution acidified in the sulfate test?

To remove carbonate ions, which would also give a white precipitate with Ba²⁺.

Why not use sulfuric acid to acidify?

It would add sulfate ions and give a false positive.

Why is BaSO₄ safe to use in a barium meal?

It is insoluble, so it is not absorbed and toxic Ba²⁺ ions are not released.

Why can't BaCO₃ be used for a barium meal?

It reacts with stomach acid to release toxic Ba²⁺ ions.

Group 2 compounds and their usesAQA A-Level Chemistry: Flashcards

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Question

How does the solubility of the Group 2 hydroxides change down the group?

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How does the solubility of the Group 2 hydroxides change down the group?: It increases.
How does the solubility of the Group 2 sulfates change down the group?: It decreases.
What is meant by sparingly soluble?: Dissolving only to a very small extent in water; Mg(OH)₂ is an example.
What is Mg(OH)₂ used for, and how does it work?: An antacid; it neutralises excess stomach acid: Mg(OH)₂ + 2HCl → MgCl₂ + 2H₂O.
What is Ca(OH)₂ used for in agriculture?: To neutralise acidic soil.
How are CaO and CaCO₃ used to treat flue gases?: They react with SO₂ to remove it: CaO + SO₂ → CaSO₃ and CaCO₃ + SO₂ → CaSO₃ + CO₂.
Why must SO₂ be removed from flue gases?: It is an acidic gas that causes acid rain.
How do you test for sulfate ions?: Add dilute HCl, then BaCl₂ solution; a white precipitate of BaSO₄ shows sulfate ions.
Write the ionic equation for the sulfate test.: Ba²⁺(aq) + SO₄²⁻(aq) → BaSO₄(s)
Why is BaCl₂ used in the test for sulfate?: BaSO₄ is insoluble, so a white precipitate forms only with sulfate ions.
Why is the solution acidified in the sulfate test?: To remove carbonate ions, which would also give a white precipitate with Ba²⁺.
Why not use sulfuric acid to acidify?: It would add sulfate ions and give a false positive.
Why is BaSO₄ safe to use in a barium meal?: It is insoluble, so it is not absorbed and toxic Ba²⁺ ions are not released.
Why can't BaCO₃ be used for a barium meal?: It reacts with stomach acid to release toxic Ba²⁺ ions.

Exam questions on Group 2 compounds and their uses

Magnesium hydroxide is sparingly soluble in water. Group 2 hydroxides are used in medicine and in agriculture.
Write an equation for the reaction of magnesium hydroxide with hydrochloric acid in the stomach, and explain how this relieves indigestion.2 marks
A student tests three colourless solutions, sodium sulfate, sodium carbonate and sodium chloride, by adding acidified barium chloride solution to a sample of each.
Explain why the barium chloride solution is acidified when testing for sulfate ions.2 marks
A coal-fired power station removes sulfur dioxide from its flue gases using calcium compounds. Relative atomic masses: Ca 40.1, C 12.0, S 32.1, O 16.0.
Calcium oxide reacts with sulfur dioxide in the flue gases. Write an equation for this reaction and explain why the reaction takes place and why the sulfur dioxide must be removed.3 marks

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Written by the Exaim team, led by Shaun Daswani (Head of Upper Secondary, Improve ME Institute; MSc Financial Mathematics, Imperial College London; BSc, UCL) and Jason Daswani (operational lead, Improve ME Institute; LSE).