Page 17 - Chemistry - XI

6. Pour off the solution by decantation and separate the crystals.
7. Wash the crystals with a small quantity of cold water and alcohol to remove the adhering mother liquor,

and then wash with alcohol to remove water.
8. Dry the crystals in the folds of the fi lter paper gently and store in airtight bag.

Observations
Colour of the crystals : White

Shape of the crystals : Octahedral
Yield (amount of crystals formed) : _____________ g

Result
White octahedral crystals of pure potash alum are obtained.

EXPERIMENT - 6

Objective
To obtain pure crystals of copper sulphate from given impure sample.

Materials Required
Beaker, glass funnel, tripod stand, china dish, glass rod, burner, wire gauze, and fi lter paper

Procedure

1. Take about 25–30 mL of water and add small quantities of impure sample of copper sulphate at a time.
2. Stir the solution till it dissolves completely. Add a few drops of dilute H SO to make the solution clear.
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3. Filter the solution with the help of a fi lter paper and collect fi ltrate in a china dish. Insoluble impurities
will be left at the fi lter paper as residue.
4. Heat the china dish on a wire gauze till the crust of tiny crystals is formed on a side. This indicates the
crystallisation point.

5. Cool the hot saturated solution by keeping it undisturbed.
6. Decant off the mother liquor carefully and wash the crystals with a small quantity of water and alcohol.
7. Dry the crystals in the folds of the fi lter paper gently and store them in airtight plastic bag.

Observations
Colour of the crystals : Blue
Shape of the crystals : Triclinic
Yield (amount of crystals formed) : _____________ g

Precautions

1. Add a few drops of dil. H SO to copper sulphate solution.
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2. The fi ltrate is to be evaporated up to crystallisation point.
3. The solution should be cooled very slowly without disturbing it.

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