Pearson Edexcel International GCSE (9–1) · CHEMISTRY · Section
Paper chromatography
21 practice questions
Practice questions
1–10 of 10 · Normal
Question 1
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 2
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 3
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 4
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.
Question 5
1 mark · Normal
Answer and check →Which of these would not be a correct safety precaution for a paper chromatography experiment using organic solvents?
- A.Wear gloves when handling solvents.
- B.Use a well-ventilated area.
- C.Taste the dyes after the experiment.
- D.Avoid contact of solvent with skin.
Question 6
2 marks · Normal
Answer and see the solution →Give two reasons why different dyes in a mixture travel different distances up the paper in chromatography.
Question 7
4 marks · Normal
Answer and see the solution →You want to check whether a green dye in a drink is a single substance or a mixture of dyes. You will use paper chromatography to investigate.
(a)[2 marks]Describe how you would set up and carry out this experiment, naming all key steps.
(b)[2 marks]Explain how you would use the chromatogram to decide if the green dye is pure or a mixture.
Question 8
2 marks · Normal
Answer and see the solution →State two reasons why the line for the origin is drawn with pencil, not pen, in a paper chromatography experiment.
Question 9
4 marks · Normal
Answer and see the solution →A student uses paper chromatography to separate a mixture of coloured dyes. The chromatogram below shows the results. The student also spotted two known dyes, X and Y, on the same piece of chromatography paper.
Chromatogram from a mixture and two known dyes Spots shown on chromatogram Sample Distance moved from origin (cm) Mixture (green) 4.8 Dye X (blue) 1.7 Dye Y (orange) 4.8 Solvent front 6.0 (a)[2 marks]State which dye(s), X or Y, is present in the mixture. Give a reason for your answer.
(b)[2 marks]Explain why the blue spot (Dye X) did not reach as far up the paper as the orange spot (Dye Y).
Question 10
3 marks · Normal
Answer and see the solution →In a chromatography experiment a spot of red dye moves 3.2 cm from the pencil line. The solvent front moves 6.4 cm from the pencil line.
Calculate the R_f value for the red dye. Show your working.