What problems might arise if a hot solution is filtered by vacuum filtration?

If a hot solution is filtered by vacuum filtration, this filtration will not be efficient.

This is because, the hot solution will not be containing any crystals, therefore, filtration will be somehow useless at this point.

You need to allow crystals to be formed in the solution either be letting the solution cool by itself or by applying an ice bath.

30litre of li2o is 1.0002mole approximately 1 mole

The answer is accuracy