Chemistry · Oct / Nov 2025 · Paper 62 · Question 1
0620
As printed in the paper
The question as text
Eggshells are made from a mixture of calcium carbonate and other insoluble substances. Calcium carbonate reacts with dilute hydrochloric acid. The equation for the reaction is shown. CaCO3(s) + 2HC! (aq) CaC! 2(aq) + H2O(l) + CO2(g) The other substances in eggshells do not react with dilute hydrochloric acid. A student finds the percentage by mass of calcium carbonate in an eggshell. Fig. 1.1 shows the first three steps of the method the student uses. step 1 Grind the eggshell into small pieces. step 2 Find the mass of the small pieces of eggshell. step 3 Add the small pieces of eggshell to excess dilute hydrochloric acid and warm the mixture while stirring it small pieces of eggshell small pieces of eggshell balance pestle mortar eggshell dilute hydrochloric acid conical glass rod Fig. 1.1
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Show the answer and mark scheme
1(a)(i)[1]
effervescence/fizzing/bubbles
1(a)(ii)[2]
M1 test with universal indicator
M2 turns red/orange
OR
M1 add (more) acid
M2 no fizzing/bubbles/effervescence
1(b)(i)[2]
M1 diagram showing filter paper in a funnel (both funnel and paper must be visible)
M2 labels
1(b)(ii)[2]
M1 (dilute) hydrochloric acid
M2 calcium chloride
1(b)(iii)[2]
M1 2.00 – 0.11 = 1.89
M2 (1.89 ‣ 2.00) × 100 = 94.5
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