Pearson Edexcel International GCSE (9–1) · CHEMISTRY · Chapter
Elements, Compounds and Mixtures
69 practice questions
Topics covered
Practice questions
11–20 of 30 · Normal
Question 11
3 marks · Normal
Answer and see the solution →Explain why fractional distillation is able to separate ethanol from water, but simple distillation cannot produce pure ethanol from the mixture.
Question 12
4 marks · Normal
Answer and see the solution →The table shows the boiling points of four different substances found in a mixture. Substance Boiling point (°C) Propane -42 Methanol 65 Ethanol 78 Water 100 (a)[1 mark]State which substance would be collected first if the mixture is separated by fractional distillation.
(b)[1 mark]Explain why.
(c)[1 mark]Two of the substances have boiling points within 13°C of each other. Identify them.
(d)[1 mark]Suggest which technique should be used to separate the solid impurities from this mixture before distillation.
Question 13
1 mark · Normal
Answer and check →Which of the following is the correct definition of the residue in filtration?
- A.The liquid that passes through the filter paper
- B.The solid left behind on the filter paper
- C.The mixture before filtration begins
- D.The solution obtained after crystallisation
Question 14
2 marks · Normal
Answer and see the solution →Give two reasons why chromatography is useful for separating the components of ink.
Question 15
4 marks · Normal
Answer and see the solution →(a)[3 marks]A student wants to separate a mixture of ethanol, water, and some insoluble sand. Describe the sequence of separation techniques they should use to obtain pure ethanol.
(b)[1 mark]Explain why each technique is used at each stage.
Question 16
3 marks · Normal
Answer and see the solution →A student has a mixture containing 20.0 g of potassium nitrate (which is soluble in water) and 8.0 g of sand (which is insoluble in water).
She adds 100 cm³ of water and stirs the mixture, dissolving all of the potassium nitrate but none of the sand.
She filters the mixture to separate the sand from the solution and then uses crystallisation to obtain solid potassium nitrate from the filtrate.
Calculate the mass of residue and filtrate obtained after filtration. State which substances are present in each.
Question 17
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 18
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 19
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 20
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.