Acids, Bases and Salt Preparations

5 marks · Easy

This question is about preparing soluble salts and writing chemical equations for their formation.

(a)

Write the balanced chemical equation for the reaction used to prepare hydrated magnesium sulfate crystals using magnesium carbonate and dilute sulfuric acid.

[2 marks]

(b)

A student wants to prepare pure sodium chloride crystals from sodium hydroxide and hydrochloric acid. Write the balanced chemical equation for this reaction.

[1 mark]

(c)

State one key difference between the methods used for preparing magnesium sulfate crystals and sodium chloride crystals in the laboratory.

[1 mark]

(d)

Calculate the mass of sodium chloride produced when 0.100 mol of hydrochloric acid reacts completely with sodium hydroxide. (Relative formula mass, NaCl = 58.5)

[1 mark]

Work this out on paper, then compare with the answer and worked solution below. With a free account you can submit written answers for marking.

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(a) \ce{MgCO3(s) + H2SO4(aq) -> MgSO4(aq) + CO2(g) + H2O(l)} · must show Correct reactants, correct products, correct balancing, State symbols

(b) \ce{NaOH(aq) + HCl(aq) -> NaCl(aq) + H2O(l)} · must show Correct reactants, correct products, correct balancing, State symbols

(c) Magnesium sulfate is made by adding excess solid to acid and filtering, sodium chloride is made using titration of acid and alkali. · must show Mention of titration for NaCl, Mention of excess solid/filtering for MgSO4

(d) 5.85 g

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Marking points

A1 (a) · 1 mark · Correct reactants and products, including state symbols

A2 (a) · 1 mark · Balanced equation with correct stoichiometry

B1 (b) · 1 mark · Correct balanced equation with state symbols for sodium chloride preparation

B2 (c) · 1 mark · Correctly identifies a key difference: excess solid/filtering vs. titration

M1 (d) · 1 mark · Calculation of mass of NaCl (working must be shown for full credit): m = n × Mr = 0.100 × 58.5 = 5.85 g

Worked solution

a) The balanced equation for preparing hydrated magnesium sulfate from magnesium carbonate and dilute sulfuric acid is:

b) The balanced chemical equation for preparing sodium chloride from sodium hydroxide and hydrochloric acid is:

c) Key difference: Magnesium sulfate is prepared by reacting excess magnesium carbonate with acid and then filtering off unreacted solid. For sodium chloride, titration is used as you cannot filter off an excess, and an indicator is used to determine when neutralisation is complete.

d) Moles of HCl = 0.100 mol. According to the equation, 1 mol HCl produces 1 mol NaCl.

Mass = moles × relative formula mass = 0.100 × 58.5 = 5.85 g.