Question

HCL acid is available as a stock solution with a concentration of 10 mol/L. If you need (2.100*10^0) L of (2.3*10^0) mol/L hydrochloric acid, approximately how much distilled water will you need to make the dilution?

Answer 1

mL x M = mL x M
2100 x 2.3 = ?mL x 10

Answer 2

but doesn't the litres in the mol/L have to be converted to mL?

Answer 3

No. I converted the 2.100E0 L to mL so the answer on the other side will come out with mL. But the 10 mol/L stock solution has the same units as the 2.3 mol/L which makes things ok. You could change them, of course, but if you change one you must change the other. But it won't change anything with the answer.
Note that the problem didn't specify volume in L or mL. I just like to work in mL so I converted that but you could leave everything in L and the answer would be in L.

Answer 4

When I did the equation you gave me I got 483mL but that wasn't the answer.

Answer 5

Right. You must use 483 mL of the 10M HCl stock solution. So how much water must be added? That's 2100-483 = 1617 mL. I suspect that since the problem uses exponent notation as well as L, that the answer must be expressed the same way. I'm assuming you are allowed 2 significant figures (from 2.3M and that 10. is to two placers) so I would express 1617 mL as 1.6E3 L.

Answer 6

Thank you for all your help it was much appreciated :D