A chemist needs to neutralise aqueous hydrochloric acid solution (currently pH 1) to pH 7 or higher, so it can be safely disposed of. They have access to solid NaCl, NaBr and Na2CO3.

A) Which of the three solids should they add to the acid solution to achieve this?
ans: Na2CO3 [1 mark]
B) Hence give a balanced chemical equation showing the reaction of the hydrochloric acid with your chosen solid.
ans: 2HCl + Na₂CO₃ --> 2NaCl + H₂O + CO₂ [2 marks]
C) The hydrochloric acid solution contains 0.1 moles of HCl. If the chemist wants to react all of the HCl as per your equation above, what mass of the chosen solid should they add?
ans: need 0.05 mol Na₂CO₃, molar mass is 106 g mol^-1, so need 0.05 mol x 106 g mol^-1 = 53 g. [2 marks]