# chem group 2 calculation question alevel aqa

to calculate the concentration, in mol dm−3, of a saturated solution of calcium hydroxide at 30 °C. Give your answer to 3 significant figures. Show your working.

answer is = 0.0209 mol/dm3 they did 0.155/ 74.1 (which i did) then they multiplied this by 10 which i don't get
(edited 1 month ago)
Original post by ricecakes1
to calculate the concentration, in mol dm−3, of a saturated solution of calcium hydroxide at 30 °C. Give your answer to 3 significant figures. Show your working.
answer is = 0.0209 mol/dm3 they did 0.155/ 74.1 (which i did) then they multiplied this by 10 which i don't get

Check the conversion of your units

100cm3 = 0.1dm3
Original post by Methene
Check the conversion of your units
100cm3 = 0.1dm3

yeah i realise it's my unit conversion that's incorrect but i don't understand how it's x10 cus i did (0.155/ 74.1) divided by 1000, how is it not that
Original post by ricecakes1
yeah i realise it's my unit conversion that's incorrect but i don't understand how it's x10 cus i did (0.155/ 74.1) divided by 1000, how is it not that

If you do 0.155/74.1 then you get 0.00209 mol per 100cm3. That's equivalent to 0.00209 mol per 0.1 dm3. The question asks for answer in mol dm-3, so you have to multiply by 10.

If the solubility units were g cm-3, then you would divide by 1000 to get to g dm-3
Original post by Methene
If you do 0.155/74.1 then you get 0.00209 mol per 100cm3. That's equivalent to 0.00209 mol per 0.1 dm3. The question asks for answer in mol dm-3, so you have to multiply by 10.
If the solubility units were g cm-3, then you would divide by 1000 to get to g dm-3

thanks got it