C4: Quiz 4 – Answers
1)
a)
i) copper oxide + hydrochloric acid –> copper chloride + water
ii) CuO + 2 HCl –> CuCl2 + H2O
b) Gently warm the acid with a Bunsen burner to give the particles of acid more energy to react with the copper oxide.
We then add copper oxide a little bit at a time to the acid and stir the mixture. We keep adding copper oxide until the copper oxide is in excess, which is when all of the acid has reacted – we will know when the copper oxide is in excess because the solid copper oxide that we add will remain unreacted and be clearly visible in the beaker.
We then filter the mixture to remove any excess solid copper oxide. We filter the mixture by pouring the mixture through a funnel that is lined with filter paper. The solid copper oxide will be unable to pass through the filter paper and will therefore sit on the filter paper. The filtrate (the liquid that passes through the filter paper) will contain water and dissolved copper chloride.
We obtain the copper chloride crystals from the filtrate by undertaking crystallisation. We undertake crystallisation by pouring our mixture into an evaporating dish and gently heating the solution using a Bunsen burner. When we see crystals starting to form, we remove the evaporating dish from the heat and leave the solution somewhere to cool so that the salt crystals become larger. We then filter the crystals out of the solution and leave the crystals in a warm place to dry. We can speed up the drying process by placing the crystals in a drying oven or a desiccator.
1) A student undertakes an experiment to obtain pure dry crystals of copper chloride. She obtains the copper chloride by reacting copper oxide with hydrochloric acid.
a)
i) Write the word equation for this reaction.
ii) Write the balanced chemical equation for this reaction.
b) Explain how the student can obtain a pure sample of copper chloride crystals. Write quite a lot and explain each of the steps in detail.