Edexcel IGCSEChemistryGeneral Applications11 Marks

This question is about acids, bases and salts. (a) A student adds dilute hydrochloric acid to copper(II) oxide. (i) State the colour change observed during the reaction.

(a)(i)State the colour change observed during the reaction.[1]
(a)(ii)Write the ionic equation for the reaction.[2]
(a)(iii)Identify the type of reaction that occurs.[1]
(b)Ammonium chloride is a salt. (i) Describe a chemical test to show that a solution contains ammonium ions.[2]
(b)(ii)A student measures the pH of a solution of ammonium chloride and finds it to be 5. Explain why ammonium chloride solution is acidic.[2]
(c)Sulfuric acid is a strong acid. (i) Explain what is meant by a strong acid.[1]
(c)(ii)Dilute sulfuric acid reacts with sodium hydroxide to form sodium sulfate and water. 2NaOH(aq) + H₂SO₄(aq) → Na₂SO₄(aq) + 2H₂O(l) A student titrates 25.0 cm³ of 0.100 mol/dm³ sodium hydroxide solution with dilute sulfuric acid. She finds that 12.5 cm³ of sulfuric acid is required for neutralisation. Calculate the concentration of the sulfuric acid in mol/dm³.[2]

Mark scheme

Marking points from the official mark scheme. The mark or mark type is shown in brackets.

B1 for (a)(i) black solid disappears / blue solution forms
M1 for (a)(ii) CuO + 2H⁺ → Cu²⁺ + H₂O
A1 for (a)(ii) correct spectator ions omitted
B1 for (a)(iii) neutralisation / acid-base reaction
M1 for (b)(i) add sodium hydroxide / warm
A1 for (b)(i) produces ammonia gas, turns damp red litmus blue
M1 for (b)(ii) ammonium ions react with water / partially dissociate / hydrolyse
A1 for (b)(ii) producing H⁺ ions / removing OH⁻ ions
B1 for (c)(i) fully dissociates / ionises in water
M1 for (c)(ii) moles NaOH = 0.100 x 25.0/1000 = 0.0025 mol
A1 for (c)(ii) moles H₂SO₄ = 0.0025 / 2 = 0.00125 mol AND concentration = 0.00125 / (12.5/1000) = 0.100 mol/dm³

On Oracle Prep you can write or photograph your own answer and have it marked by AI against this mark scheme, with feedback on what you missed.