Separation & Purification

9.In a chromatography experiment, the solvent front moves 8 cm and a substance moves 5 cm. What is the Rf value?

10.A pure substance melts at a sharp temperature, while an impure substance melts over a range. Which statement is correct?

11.A student wants to separate a mixture of two miscible liquids with boiling points of 80 °C and 82 °C. Which technique is most appropriate?

12.A chromatogram shows two spots from an unknown sample. The Rf values are 0.45 and 0.70. A known substance has Rf 0.70 under the same conditions. What can be concluded?

13.A student is given a mixture of calcium sulfate, magnesium chloride and water. The table shows some information about these substances. | Substance | Solubility in water | State at room temperature | |-----------|---------------------|---------------------------| | calcium sulfate | insoluble | solid | | magnesium chloride | soluble | solid | Which sequence of steps should the student use to obtain magnesium chloride crystals?

14.A student performs paper chromatography on a mixture of colourless amino acids. After the solvent front has moved 10 cm, the chromatogram is dried and sprayed with a locating agent. Two spots appear at distances 4.0 cm and 7.5 cm from the baseline. What is the Rf value of the slower-moving amino acid?

15.The diagram shows the apparatus for fractional distillation of a mixture of ethanol and water. Which labelled part allows the rising vapour to evaporate and condense repeatedly, so that only the vapour of the lower-boiling liquid reaches the condenser?

16.A pure sample of a solid melts at 150 °C. An impure sample of the same solid would be expected to melt:

17.A student carries out paper chromatography on a sample of leaf extract. The chromatogram shows three spots. The Rf values of known pigments are: chlorophyll a = 0.60, chlorophyll b = 0.45, carotene = 0.95, xanthophyll = 0.70. The spots have Rf values 0.45, 0.60 and 0.95. Which pigments are present in the leaf extract?

18.A student wants to separate a mixture of two miscible liquids with boiling points of 80 °C and 130 °C. Which method is most suitable?

19.In paper chromatography, why must the baseline be drawn in pencil?

20.A mixture of sand and salt is separated by adding water, stirring, and filtering. What is the residue?

21.A student measures the boiling point of a liquid sample and finds it boils at 101 °C at standard pressure. Pure water boils at 100 °C. What does this suggest?

22.Which separation technique relies on differences in boiling points?

23.A student performs paper chromatography on a dye and obtains a single spot with Rf = 0.8. The solvent front moved 10 cm. How far did the dye travel?

24.Which apparatus is used to condense vapour during distillation?

25.In paper chromatography, what is the purpose of using a pencil to draw the baseline?

26.A student places a spot of black ink on a pencil line on chromatography paper and places the paper in a solvent. The solvent level is above the pencil line. What is the likely result?

27.A chromatogram shows a solvent front at 8 cm and a spot at 4.8 cm. What is the Rf value?

28.A student obtains a chromatogram of a colourless amino acid mixture. After drying, the student sprays the paper with a locating agent and heats it. Which row describes the correct procedure?

29.Which separation technique would be used to obtain pure water from a mixture of water and ethanol?

30.A mixture of sand and salt is separated by adding water, stirring, and filtering. What is the filtrate?

31.A student wants to obtain crystals of copper(II) sulfate from a solution. After heating to evaporate some water, what should the student do next?

32.A mixture contains two miscible liquids with boiling points of 78°C and 82°C. Which method is most suitable to separate them?

33.A solid is heated and melts over a range of temperatures from 120°C to 125°C. What does this indicate?

34.In the distillation apparatus, what is the purpose of the condenser?

35.A student is given a mixture of calcium sulfate (insoluble), magnesium chloride (soluble), and water. Which order of techniques will produce dry magnesium chloride crystals?

36.A mixture of two liquids is separated by fractional distillation. The liquid with the lower boiling point distils first. Which statement about the process is correct?

37.A student carries out paper chromatography on a mixture of colourless amino acids. After the solvent front has moved 10 cm, the chromatogram is dried and sprayed with a locating agent. Two spots appear at distances 4.0 cm and 7.0 cm from the baseline. What are the Rf values of the two amino acids?

38.A student is given a mixture of three solids: A (soluble in water, melting point 80 °C), B (insoluble in water, melting point 150 °C), and C (soluble in water, melting point 200 °C). The student adds water, stirs, and filters. The residue is then dried and weighed. Which solid(s) are in the residue?

39.The table shows the Rf values of three pigments under the same solvent conditions. | Pigment | Rf value | |---------|----------| | P | 0.43 | | Q | 0.57 | | R | 0.75 | A student runs a chromatography experiment on an unknown sample. The solvent front moves 12 cm. A spot from the unknown appears at 6.84 cm from the baseline. Which pigment is present in the unknown?

40.A student measures the boiling point of a liquid sample and finds it boils at 97 °C at standard pressure. Pure water boils at 100 °C. What does this suggest about the sample?

41.Which of the following is the correct reason for using a pencil to draw the baseline in paper chromatography?

42.In paper chromatography, the solvent level should be above the pencil line to allow the solvent to travel up the paper.

43.Match each separation technique to its correct description.

44.Arrange the following steps in the correct order to obtain crystals of copper(II) sulfate from a solution.

45.Which of the following are true about Rf values? (Select all that apply)

46.Which apparatus is used to cool and condense vapour during distillation?

47.Fractional distillation is used to separate two or more miscible liquids with different boiling points.

48.Arrange the following steps in the correct order to obtain pure dry crystals of copper(II) sulfate from a solution of copper(II) sulfate.

49.Which of the following statements about Rf values are correct? (Select all that apply)

50.A pure substance melts over a range of temperatures.

51.Complete the sentence: In paper chromatography, substances with higher solubility travel ___ up the paper.

52.In a chromatography experiment, the solvent front moved 12 cm and a substance moved 7.2 cm. Calculate the Rf value of the substance.

53.State what a pure substance would look like on a paper chromatogram.

54.Complete the sentence: If a sample contains impurities, its melting point will appear ___ than the pure substance.

55.In a paper chromatography experiment, the solvent front moved 8.0 cm and a substance moved 5.2 cm. Calculate the Rf value of the substance. Give your answer to two decimal places.

56.Complete the sentence about simple distillation.

57.Explain why a student should remove the delivery tube from the water when heating is stopped in a distillation setup.

58.In a chromatography experiment, the solvent front moved 12 cm and a substance moved 7.2 cm. Calculate the Rf value of the substance.

59.In a paper chromatography experiment, the solvent front moved 8.0 cm and a substance moved 5.2 cm. Calculate the Rf value of the substance. Give your answer to two decimal places.