Pearson Edexcel International GCSE (9–1) · CHEMISTRY · Chapter
Elements, Compounds and Mixtures
69 practice questions
Topics covered
Practice questions
31–40 of 69
Question 31
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 32
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 33
2 marks · Normal
Answer and see the solution →Give two reasons why chromatography is useful for separating the components of ink.
Question 34
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 35
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 36
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 37
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 38
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 39
1 mark · Easy
Answer and see the solution →State which part of the chromatography paper you should draw the starting line on before adding the sample in a paper chromatography experiment.
Question 40
3 marks · Easy
Answer and see the solution →The chromatogram below was obtained by separating a mixture of food dyes A and B. The solvent front travelled 6.0 cm from the pencil line. The diagram shows the position of the spots:
Chromatogram of food dyes A and B (a) State how the R_f value for dye B can be calculated. [1]
(b) Calculate the R_f value for dye B. Give your answer to two decimal places. [2]
(a)[1 mark]State how the R_f value for dye B can be calculated.
(b)[2 marks]Calculate the R_f value for dye B. Give your answer to two decimal places.