Why is the precipitate collected by decantation and not by suction?

Question

the pracical about dertemining the sulphate as barium sulphate

Answer 1

The precipitate should never be collected by suction! Suction could break apart the supernatant and bring some (if not most) of it along with the precipitate, making the experiment meaningless. Needless to say, the experiment would need to be started over if this were the case. Otherwise the calculations would be off, but most likely no observations could be made if suction were involved instead of decantation.

Answer 2

Because BaSO4 is very insoluble and settles quickly, therefore repeated decants are easier, quicker, and don't effect the accuracy of the determination.