if 250cm3 of limewater had aprox 1g dm-3 of Ca(OH)2... what is the molarity of the Ca(OH)2?

Question

i assume you do the whole "formula mass" thing, i am just confused by the "1g dm-3".
many many thanks

Answer 1

You are right to be confused. Personally, I think that the person who originally wrote the question got it wrong. If it is 1g per dm3, the molarity is 1/74 M, irrespective of the volume of the solution. If the question should have read that the 250cm3 contained 1g of calcium hydroxide, then the answer would be 4/74 M.

Answer 2

1 g in 250 cm3 is 4 g in 1 litre.
Mol mass of the calcium compound is 74.

Moles per litre is 4/74 = .054 (molarity)