Thanks Mark. About metaborate:
Originally Posted by albada
The octohydrate has twice the molecular weight of the tetrahydrate. So 2.2g of it would have half the number of moles. But each mole of it is equivalent to two moles of the tetrahydrate. When dissolved, wouldn't it be the same?
(The situation seems quite different to something like, say, sodium carbonate, where the one mole of Na2CO3 can have zero, one, seven or ten molecules of water. Obviously then the water of crystallization has to be taken into account when weighing out.)