Topic 1b: Experimental techniques
Answers End of Topic Questions mark scheme Question Correct answer
Marks
1
Draw a pencil line about 1 cm from the bottom of a strip of filter paper. Spot the four samples of ink onto the line leaving space between each.
1 mark 1 mark
Put the filter paper into a beaker containing a small amount of water (making sure the level of the water is below the line).
1 mark
Identify the 2 inks that produce the same pattern and positions of dyes on the chromatogram. 2 a)
The ink may not dissolve in the water.
2 b)
Use another solvent, e.g. alcohol.
1 mark 1 mark o
o
3
The boiling point will be higher than 78 C, e.g. 80 C.
1 mark
4
Impurities will lower the melting point of ice.
1 mark
5
The condenser is kept cool (by the constant flow of water).
1 mark
6
Heat the sodium chloride solution in an evaporating basin.
1 mark
Evaporate all the water/leave to crystallise (once saturated).
1 mark
7 a)
Filtration/filtering.
1 mark
7 b)
Fractional distillation.
1 mark
7 c)
Distillation.
1 mark
8 a)
Compound A.
1 mark
8 b)
Compound D.
1 mark
8 c)
Rf = approx. 0.50
1 mark
The solvent has travelled twice as far as the compound (allow measurements).
1 mark
The substance cannot travel further than the solvent (or travel exactly the same distance).
1 mark
Total:
18 marks
8 d)
Cambridge IGCSE Chemistry Teacher Pack
40
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