Homework: Compounds and Mixtures – Levels 6–8
Table Salt from Rock Salt
Rock salt forms when sea water evaporates. It contains a mixture of sand and salt.
Pure salt for using on food can be made by separating pure salt from the mixture.
The flow chart shows how this can be done.
Task

Complete the diagrams by filling in the missing labels.
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Water acts as a solvent in this experiment. Explain what ‘solvent’ means.
Draw labelled diagrams to show how the particles of salt and water are
arranged in step 5.
Explain how salty water is separated from sand in step 4. Draw a diagram to
show how the particles of sand and salt are arranged before and after step 4 to
help your explanation.
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
At the end of the experiment the sand still contains some salt. Suggest some
changes to the experiment to make sure as much salt as possible is separated.
Mark scheme
Level
You should:
6

explain the meaning of the word ‘solvent’


draw a diagram to show the particles in dissolved salt
explain how filtering works in terms of salty water passing
through the filter but not sand.

make one suggestion for increasing the amount of salt, e.g.
grinding up the rock salt, using hot water, more stirring or
washing water through the filter paper

use high level scientific vocabulary to explain filtration, e.g.
solid, solution, dissolved, filter paper

draw diagrams to show the arrangement of particles after
filtering.

discuss more detailed improvements to the separation by
making at least two suggestions for improvements
explain filtration using clear particle diagrams of the
particles before and after filtration
discuss filtration by talking about the relative size of the
holes in the filter paper and the particles involved.
7
8
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