Pearson Edexcel International GCSE (9–1) · CHEMISTRY · Chapter
Elements, Compounds and Mixtures
69 practice questions
Topics covered
Practice questions
21–28 of 28 · Easy
Question 21
3 marks · Easy
Answer and see the solution →A student is testing three samples using paper chromatography. The chromatogram below shows the positions of the spots after the experiment was completed. The solvent front moved 9.0 cm from the pencil line.
Chromatogram with three samples and a solvent front (a) Which sample travelled furthest from the pencil line? [1]
(b) Calculate the R_f value for sample Y. [1]
(c) Explain what a high R_f value tells you about a dye's solubility in the solvent. [1]
(a)[1 mark]Which sample travelled furthest from the pencil line?
(b)[1 mark]Calculate the R_f value for sample Y.
(c)[1 mark]Explain what a high R_f value tells you about a dye's solubility in the solvent.
Question 22
1 mark · Easy
Answer and see the solution →How should you measure the distance a dye has travelled on a chromatogram to calculate its R_f value?
Question 23
3 marks · Easy
Answer and see the solution →Describe how you would carry out a paper chromatography experiment to determine if a black ink contains more than one dye. Include three steps in your description.
(a)[1 mark]Step 1:
(b)[1 mark]Step 2:
(c)[1 mark]Step 3:
Question 24
2 marks · Easy
Answer and see the solution →A scientist measures the distance from the pencil line to the centre of a dye spot as 2.5 cm and the distance from the pencil line to the solvent front as 7.8 cm. Calculate the R_f value for this dye. Give your answer to two decimal places.
Question 25
5 marks · Easy
Answer and see the solution →A student finds a mixture of iron filings and sulfur powder. She wants to investigate how to classify and separate these substances.
(a)[2 marks]State whether iron, sulfur, iron sulfide, and a mixture of iron and sulfur are elements, compounds or mixtures.
(b)[1 mark]Describe a physical method you could use to separate the iron filings from the sulfur powder in the mixture.
(c)[2 marks]Explain why you cannot separate iron sulfide into iron and sulfur by a physical method.
Question 26
5 marks · Easy
Answer and see the solution →A student is given a sample that may be pure aspirin, or may be aspirin mixed with impurities. The sample is white powder.
(a)[2 marks]Explain how you could use melting point to decide if the sample is pure or a mixture.
(b)[1 mark]The student finds the melting point is between 127°C to 134°C. What does this suggest about the sample? Give a reason.
(c)[2 marks]Suggest a separation technique the student could use to obtain pure aspirin from this sample, and briefly describe how it works.
Question 27
5 marks · Easy
Answer and see the solution →A chemist dissolves 10 g of sodium chloride in 1.0 litre of pure water.
(a)[2 marks]State whether the resulting solution is a pure substance, a compound, or a mixture. Give a reason.
(b)[1 mark]The boiling point of pure water is 100°C. Adding the salt changes the boiling point to 100.2°C. Calculate the increase in boiling point.
(c)[2 marks]Suggest a separation technique you could use to obtain pure water from this solution. State the process and what happens during it.
Question 28
5 marks · Easy
Answer and see the solution →Some students are studying how melting and boiling points differ between pure substances and mixtures, and how to separate mixtures.
(a)[1 mark]State what is meant by a pure substance in terms of melting and boiling points.
(b)[2 marks]Water is mixed with some sugar. Describe what happens to its melting point and boiling point, compared to pure water.
(c)[2 marks]Name one method that could be used to separate the sugar from the water and briefly describe how it works.