Pearson Edexcel International GCSE (9–1) · CHEMISTRY · Chapter
Elements, Compounds and Mixtures
69 practice questions
Topics covered
Practice questions
1–10 of 11 · Hard
Question 1
2 marks · Hard
Answer and see the solution →A student is given three samples: Sample A contains only carbon atoms, Sample B contains molecules of carbon dioxide, and Sample C contains both carbon dioxide and oxygen gas mixed together. Classify each sample as an element, a compound, or a mixture.
Question 2
5 marks · Hard
Answer and see the solution →A researcher is investigating two samples: Sample X is a pure substance, and Sample Y is a mixture. She records the melting and boiling behaviour of each sample while heating.
(a)[2 marks]Describe the expected melting behaviour of Sample X and Sample Y as they are heated.
(b)[2 marks]Explain how boiling point data can be used to decide whether Sample X or Sample Y is pure or a mixture.
(c)[1 mark]A sample melts sharply at 801°C and boils at exactly 1465°C with no temperature change during the phase transitions. State whether it is pure or a mixture, and justify your answer with evidence from the data.
Question 3
2 marks · Hard
Answer and see the solution →Give one way in which the proportions of substances in a mixture are different from those in a compound. Use an example to support your answer.
Question 4
2 marks · Hard
Answer and see the solution →A laboratory technician is given a mixture containing sand, sodium chloride, and water. State the steps required to separate and collect both the sand and pure sodium chloride crystals from this mixture.
Question 5
5 marks · Hard
Answer and see the solution →A chemist needs to separate and collect pure ethanol from a mixture of ethanol and water. Both substances are completely miscible. The boiling point of ethanol is 78°C and that of water is 100°C.
(a)[1 mark]Name the separation technique that should be used to obtain pure ethanol from the mixture.
(b)[2 marks]Describe how this technique separates ethanol from water. Include reference to their boiling points and any specific apparatus that must be used.
(c)[1 mark]State one reason why ethanol collected from this process is not completely pure.
(d)[1 mark]Draw a labelled diagram of the key apparatus used for this separation.
Question 6
2 marks · Hard
Answer and see the solution →A student is given a mixture containing sand, sodium chloride, and water. For each of the following, state the most suitable separation technique and explain your choice briefly.
(a)[1 mark]To obtain dry sand from the mixture.
(b)[1 mark]To obtain pure sodium chloride crystals from the mixture.
Question 7
2 marks · Hard
Answer and see the solution →A blue dye in a chromatography experiment travels 1.5 cm from the pencil line. The solvent front moves 5.0 cm from the pencil line. Calculate the R_f value for the blue dye. Show your working.
Question 8
5 marks · Hard
Answer and see the solution →A student wants to find out whether the green colour in a piece of candy is due to a single dye or a mixture of dyes. Describe how you would carry out a paper chromatography experiment to investigate this. Include details about:
(a)[1 mark]the preparation of the chromatography paper and application of the sample
(b)[1 mark]how to set up and run the chromatography
(c)[1 mark]how to mark the solvent front and why this is important
(d)[1 mark]what you would expect to observe if the green dye is a mixture of dyes
(e)[1 mark]one step you should take to make sure your results are reliable
Question 9
2 marks · Hard
Answer and see the solution →Explain why the R_f value must always be between 0 and 1 in a paper chromatography experiment.
Question 10
7 marks · Hard
Answer and see the solution →A chemist receives a coloured powder described as a mixture of food dyes and metal salts. She wants to find out if the powder is a mixture or a compound, and which dyes are present.
(a)[2 marks]State two differences between a mixture and a compound, using the chemist’s powder as an example.
(b)The chemist dissolves a small amount of the powder in water and runs a paper chromatography experiment alongside three known food dyes (dye A, dye B and dye C). The chromatogram below was produced:
Chromatogram from the experiment Spot distances from pencil line (cm) Sample Distance travelled by dye spot (cm) Powder 2.0 Dye A 2.0 Dye B 4.3 Dye C 6.0 (i)[2 marks]Calculate the R_f value for the dye in the powder. Show your working.
(ii)[1 mark]Suggest which dye(s) are present in the powder, using the chromatogram results.
(iii)[2 marks]Explain why it is important to measure from the pencil line to the centre of each spot when calculating the R_f value.