Sec 3 Combined Science (Chemistry) Experimental Chemistry & Purification topical questions

Match each measurement to the most suitable piece of apparatus.

A suspension of chalk in water is filtered. State which material is the residue and which is the filtrate, and name the property of chalk that makes filtration work.

Sample S melts sharply at 156 °C; the data book gives element X as melting at 156 °C. Sample T, said to be X with impurity, melts over 151–155 °C. What can be concluded about S and T?

On a chromatogram, a sweetener sample shows two spots. One spot is at the same height as a known permitted colour; the other matches no known sample run. State what can be concluded.

Describe how pure, large crystals of copper(II) sulfate are obtained from its solution, naming the key stage at which heating stops.

A simple distillation is set up to obtain pure water from salt solution. Explain three set-up details that make the distillation work well.

A mixture contains sand, salt and water. Plan how to recover the dry sand and the dry salt, naming the property used at each step.

Copy and complete the table by naming a collection method for each gas, using the properties given.

A fermented mixture contains ethanol (boiling point 78 °C), water (100 °C) and dissolved sugar. Explain why fractional distillation, and not simple distillation, is needed to collect the ethanol, and state what the thermometer reads while ethanol distils.

Chromatography is run on ink P and known dyes X, Y and Z on the same paper. The finished chromatogram shows: P has three spots, at heights matching X, matching Y, and one matching nothing on the paper. A second ink, Q, shows a single spot at height matching Z. Compare what can be concluded about P and Q.

Use the data to answer the questions. Naphthalene melts at 80.2 °C; camphor melts at 179 °C; ethanol boils at 78 °C; water boils at 100 °C. (a) Sample P melts sharply at 80.2 °C. Sample Q melts over 74–80 °C. Identify P and describe Q. (b) A liquid boils steadily at 78 °C. Another boils over 85–100 °C. What does each behaviour suggest?

A student investigates how much gas is made when marble chips react with dilute acid. Suggest an apparatus plan for measuring the total gas volume every 20 seconds, and name one other measurement the student should record at the start for a fair comparison with a second trial.