GCSE chemistry help - concentration calculation

This may be a an easy question but I’m not sure I’ve done it correct so any examples or methods to the answer would be very helpful :smile:

A student had 0.625 dm3 of a 18g/dm3 solution. She evaporated off some of the water
so the new volume was 0.500 dm3 what is the new concentration of this solution?

for my answer I got 22.5 g/ dm3 because it did 0.625 divided by 0.5 = 1.25 which gives u how the volume has changed then multiplied the concentration by it so 18 x 1.25 = 22.5
but I wasn’t sure if I was meant to be using concentration equations to figure it out
ty for any replies !

Reply 1

Chi42

That is the correct answer. Perhaps the intended way is working out the mass of solute with concentration x volume:
18 * 0.625 = 11.25 g.
Then recalculate a concentration with this mass divided by the new volume:
11.25 / 0.500 = 22.5 g/dm3