An experiment was done to determine the percentage of calcium carbonate, CaCO₃, in a sample of limestone rock. 4.0 g of the crushed rock was added to 50 cm³ of 2.0 mol/dm³ hydrochloric acid, which was in excess: CaCO₃ + 2HCl → CaCl₂ + H₂O + CO₂. The excess hydrochloric acid required 28.0 cm³ of 2.0 mol/dm³ sodium hydroxide for complete neutralisation: NaOH + HCl → NaCl + H₂O.

1. aCalculate the number of moles of hydrochloric acid added to the rock. [2]
2. bCalculate the number of moles of sodium hydroxide that reacted with the excess hydrochloric acid. [1]
3. cHow many moles of hydrochloric acid were in excess? [1]
4. dHow many moles of hydrochloric acid reacted with the calcium carbonate in the rock? [1]
5. eCalculate the number of moles of calcium carbonate in the 4.0 g sample of rock. [2]
6. fCalculate the mass of calcium carbonate in the 4.0 g sample of rock. [2]
7. gCalculate the percentage composition by mass of calcium carbonate in the rock. [2]

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