Pearson Edexcel International GCSE (9–1) · CHEMISTRY · Chapter
Elements, Compounds and Mixtures
69 practice questions
Topics covered
Practice questions
41–50 of 69
Question 41
2 marks · Easy
Answer and see the solution →In a paper chromatography experiment, the pencil line was drawn 1.0 cm from the bottom of the paper. The solvent front travelled 7.2 cm from the pencil line, and a blue dye moved 5.0 cm from the pencil line. Calculate the R_f value for the blue dye.
Question 42
2 marks · Easy
Answer and see the solution →Explain why two different dyes can have the same colour but different R_f values in paper chromatography.
Question 43
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 44
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 45
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 46
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 47
2 marks · Normal
Answer and see the solution →State what is meant by the term "Rf value" in paper chromatography, and explain why the Rf value is always less than 1.
Question 48
4 marks · Normal
Answer and see the solution →The following steps outline a method to separate a mixture of food colourings using paper chromatography.
(a)[1 mark]Name the purpose of drawing the line in pencil at the bottom of the chromatography paper.
(b)[1 mark]Explain why it is important that the solvent level in the beaker is below the pencil line.
(c)[1 mark]Describe what you would observe on the paper after the experiment if the mixture contained three different dyes.
(d)[1 mark]State one safety precaution you should take when carrying out this experiment.
Question 49
3 marks · Normal
Answer and see the solution →In a paper chromatography experiment, the solvent front moved 8.2 cm from the pencil line. One of the dyes in a mixture moved 5.3 cm from the pencil line.
Calculate the Rf value for this dye. Show your working.
Question 50
4 marks · Normal
Answer and see the solution →The chromatogram below shows the results of a chromatography experiment. The solvent front travelled 7.5 cm from the pencil line. There are three spots on the same chromatogram, labelled X, Y, and Z. The distances from the pencil line to the centres of the spots are:
Chromatogram data Spot Distance from pencil line (cm) X 1.9 Y 4.2 Z 6.0 (a)[2 marks]Calculate the Rf value for spot Y. Show your working.
(b)[1 mark]Which spot is most soluble in the solvent? Give a reason.
(c)[1 mark]Explain how you could use Rf values to identify a dye in the mixture.