Acids, Bases and Salt Preparations
6 marks · NormalWrite a balanced chemical equation for the reaction between sodium carbonate and dilute nitric acid.
Describe how you would prepare a pure sample of sodium nitrate using the reaction in part a. Include the main steps and explain how you would separate and obtain the pure salt.
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{Na2CO3(aq) + 2HNO3(aq) -> 2NaNO3(aq) + CO2(g) + H2O(l)}
(b) Add sodium carbonate to excess dilute nitric acid until no more effervescence occurs. Filter to remove any excess solid. Heat the solution to evaporate water until crystals start to form, then leave to cool so sodium nitrate crystals form. Filter, then dry the crystals between filter papers.
Common mistakes: forgetting to balance the equation; not including all main steps in salt preparation
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Marking points
M1 (a) · 1 mark · Correctly writes correct reactants and products for sodium carbonate and nitric acid.
A1 (a) · 1 mark · Balances the chemical equation.
M1 (b) · 1 mark · Describes adding sodium carbonate to dilute nitric acid until reaction stops / no more effervescence.
M1 (b) · 1 mark · Describes filtering to remove excess solid carbonate.
M1 (b) · 1 mark · Describes heating to concentrate the solution (evaporate water).
A1 (b) · 1 mark · Mentions cooling to crystallise salt and drying crystals with filter paper.
Worked solution
(a) The balanced chemical equation is:
(b) To prepare a pure sample of sodium nitrate:
1. Add sodium carbonate to dilute nitric acid until there is no more fizzing (to ensure all acid is used).
2. Filter the mixture to remove any unreacted solid carbonate.
3. Heat the filtrate to evaporate most of the water until crystals begin to form.
4. Leave the solution to cool so sodium nitrate crystals form.
5. Filter and dry the crystals between filter papers to obtain a pure sample.