Alum makes the specks clump

The idea

In coagulation, a coagulant such as alum makes fine suspended particles clump together; the larger clumps settle by gravity (sedimentation) and are separated by decantation or filtration.

Cleaning muddy water

Muddy water stays cloudy even after standing. A little white powder, alum (fitkari), is stirred in.

What do you think alum does to the tiny particles?

• It makes them clump together so they settle
• It dissolves them
• It makes them lighter and float

Add the alum

Add alum to the water and let the minutes pass. Then pour off the clear water.

Coagulation

In coagulation, a coagulant such as alum (fitkari) makes the fine suspended particles clump together. The larger clumps settle by gravity (sedimentation) and can be separated from the water by decantation or filtration.

Everyday coagulation. Making cheese (paneer) from milk: an acid such as lemon juice or vinegar is the coagulant and makes the milk proteins coagulate.

Notes

Coagulation: a coagulant (alum) makes fine particles clump; the clumps settle and are separated by decantation or filtration.

Check yourself

Alum acts as a coagulant. What does it do?

After the particles clump, what makes the clumps sink?

Which steps separate the settled clumps from the water?

In making paneer, the lemon juice or vinegar is the…

• Makes the water boil. It has nothing to do with boiling.
• Makes fine suspended particles clump together — correct. Yes.
• Makes the particles dissolve. It clumps them.
• Gravity (sedimentation) — correct. Yes.
• A magnet. The clumps are not magnetic.
• Sunlight. Sunlight does not make them sink.
• Sublimation or deposition. Those are for solids and vapours.
• Decantation or filtration — correct. Yes.
• Distillation only. The clumps are solid; they can simply be removed.
• coagulant, which coagulates the milk proteins — correct. Yes.
• solvent that dissolves the milk. It makes the proteins clump.
• condenser. A condenser cools vapour.