Question

A solid mixture contains four constituents P, Q, R and S. P consists of tiny grains and it is mixed with cement for plastering the walls. Q is a white solid which is recovered on a large scale from sea water by the process of evaporation. R is in the form of tiny particles of a material whose corrosion is called rusting. And S is a white solid which is used in making ordinary dry cells.
(i) What could P, Q, R and S be?
(ii) How would you separate a mixture containing P, Q, R and S?
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Answer 1

(i) P is mixed with cement for plastering the wall, so P must be sand.
Q is a white solid recovered from seawater by the process of evaporation, so Q must be sodium chloride.
R is a material whose corrosion is called rusting, so R must be iron fillings.
S is a white solid used for making ordinary dry cells, so S must be ammonium chloride.

(ii) Iron filings can be separated by a magnet. The remaining mixture can be heated and ammonium chloride will sublime that can be collected by an inverted funnel. The other two can be mixed in water and then filtered. Salt being soluble in water will dissolve in it that can be obtained by evaporation of water. Sand can be collected as a residue of the filtration process.