Question 1
FA student uses paper chromatography to find out which colourings are in a green sweet coating.
The student puts a spot of the green colouring and spots of three known colourings, J, K and L, on a start line. The student puts the paper in a beaker of water.
The diagram shows the chromatogram. The solvent moved 8.0 cm from the start line.
a.[1]
The student draws the start line in pencil, not in ink.
Explain why.
b.[1]
The start line must be above the level of the water in the beaker.
Explain why.
c.[2]
Which two known colourings are in the green colouring?
Explain how you know.
d.[2]
Calculate the Rf value of colouring K. Use the scale on the diagram.
Use the equation: Rf = distance moved by the substance ÷ distance moved by the solvent
e.[2]
Name the mobile phase and the stationary phase in this experiment.
2.1 Purity and separating mixtures Questions
51 exam-style questions on OCR GCSE Chemistry 2.1 Purity and separating mixtures, covering 2.1.1 Pure substances and melting point data, 2.1.2 Relative formula mass and empirical formula, 2.1.3 Formulations as useful mixtures, 2.1.4 Techniques for separating mixtures, and 2.1.5 Chromatography and Rf values. Each one has a worked solution and a mark scheme showing where the marks go.