Question

Prepare a pure crystal of potush alum

Answer 1

Explanation:

Potash alum is prepared by dissolving an equimolar mixture of hydrated aluminium sulphate and potassium sulphate in minimum amount of water containing a little of sulphuric acid and then subjecting the resulting solution to crystallisation, when octahedral crystals of potash alum separate out

Answer 2

Answer:

Preparation

This compound usually available in chemical shops, but can be prepared too. Since it has relatively low solubility, it will readily crystallize from any solution, containing enough of K+, Al3+, SO42- ions.

Some possible ways are:

Dissolve Al in sulfuric acid, producing Al2(SO4)3. Reaction is very slow due to protective film on aluminum. Then add K2SO4 and crystallize.

Dissolve Al in KOH (warning: reaction very intensive, can start boiling), getting potassium aluminate:

Al + KOH + 3H2O → K[Al(OH)4] + 3H2(g).

Then add sulfuric acid:

K[Al(OH)4] + 2H2SO4 → KAl(SO4)2 + 2H2O

Explanation:

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