Separation, chromatography and purity

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?

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

16.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?

17.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?

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

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

20.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?

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

22.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?

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

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

25.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?

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

27.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?

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

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

30.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?

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

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

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

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

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

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

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

38.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?

39.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?

40.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?

41.Compare paper chromatograms of safe food dyes using a teacher-selected solvent. What is the independent variable?

42.Compare paper chromatograms of safe food dyes using a teacher-selected solvent. Which observation or quantity is the dependent variable?

43.Compare paper chromatograms of safe food dyes using a teacher-selected solvent. Which decision best controls another factor in this comparison?

44.Compare paper chromatograms of safe food dyes using a teacher-selected solvent. Why should the class repeat measurements or check multiple comparable observations?

45.A class is evaluating an application of separation, chromatography and purity. Which statement identifies a relevant limitation?

46.Compare paper chromatograms of safe food dyes using a teacher-selected solvent. Which conclusion is most justified by a controlled comparison?

47.Compare paper chromatograms of safe food dyes using a teacher-selected solvent. Select the two practices that strengthen the validity of this comparison.

48.When evaluating evidence about separation, chromatography and purity, select the two scientifically defensible statements.

49.Design a fair investigation for this question: Compare paper chromatograms of safe food dyes using a teacher-selected solvent. Identify what to compare, what to record and one control.

50.Explain one use of the science in separation, chromatography and purity and evaluate one limitation of the evidence or application.

51.On a chromatogram, a dye spot travels 3.6 cm and the solvent front travels 6.0 cm from the same baseline. What is Rf?

52.An unknown gives one visible spot with the same Rf as a reference in one solvent. Which conclusion is justified?