Pearson Edexcel International GCSE (9–1) · CHEMISTRY · Chapter
Acids, Alkalis and Titrations
83 practice questions
Topics covered
Practice questions
81–83 of 83
Question 81
6 marks · Normal
Answer and see the solution →Potassium carbonate is a weak alkali. A student decides to find out how much sulfuric acid is needed to neutralise a sample of potassium carbonate solution.
(a)[1 mark]State one observation that shows potassium carbonate solution is alkaline when tested with a suitable indicator.
(b)[1 mark]Write the name or formula of the ion responsible for the alkaline nature of potassium carbonate solution.
(c)[2 marks]The student prepares for titration by placing 25.0 cm³ of potassium carbonate solution into a conical flask. Describe how to add the acid during the titration and how to recognise when to stop.
(d)[2 marks]Suggest a suitable indicator for this titration and explain why universal indicator is not used.
Question 82
6 marks · Normal
Answer and see the solution →A student titrates 25.0 cm³ of sodium carbonate solution with hydrochloric acid. The burette readings below are recorded.
Burette readings Reading Volume (cm³) Initial 3.10 Final 25.60 (a)[1 mark]Calculate the volume of hydrochloric acid added. Give your answer to two decimal places.
(b)[2 marks]Write a balanced equation for the reaction between sodium carbonate solution and hydrochloric acid.
(c)[3 marks]State the ion produced in sodium carbonate solution that is responsible for its alkaline pH, and explain its formation using an ionic equation.
Question 83
6 marks · Normal
Answer and see the solution →A teacher claims that both sodium hydroxide and sodium carbonate solutions can be used in titrations with hydrochloric acid, but there are important reasons to choose one over the other.
(a)[2 marks]Explain why sodium carbonate solution is considered an alkali, stating the ion responsible for its alkaline nature.
(b)[2 marks]Describe two reasons why, in a titration of hydrochloric acid, sodium hydroxide might be preferred over sodium carbonate.
(c)[2 marks]A student uses phenolphthalein as an indicator for a titration of sodium carbonate with hydrochloric acid. Predict the colour change at the endpoint and what this shows about the pH change.