Chemistry · Oct / Nov 2023 · Paper 62 · Question 1

Some seashells contain a mixture of the insoluble compounds calcium carbonate and silicon(IV) oxide only. Calcium carbonate reacts with dilute hydrochloric acid to form the soluble salt calcium chloride. Silicon(IV) oxide does not react with or dissolve in dilute hydrochloric acid. A student wants to find the percentage of silicon(IV) oxide in a seashell. The first four steps of the method the student uses are shown. step 1 The student grinds the seashell to form a powder. step 2 The student finds the mass of the powdered seashell. step 3 The student adds the powdered seashell to an excess of dilute hydrochloric acid and heats while stirring with a glass rod as shown in Fig. 1.1. step 4 The student filters the mixture as shown in Fig. 1.2. residue A B Fig. 1.1 Fig. 1.2

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