Help please. Mass of solution? Chemistry.?

Question

Hello,

I need to find out the mass of the solution in g. Any help would be appreciate.

I have 250 cm3 of a solution of NaOH of concentration 0.400 moldm -3 and 250 cm3 of a solution of HCL of concentration 0.400 moldm-3 that I mix.

Thanks in advance

I think its 36.5g for HCL and 40g for NaOH so 76.5g combined but not sure.

Answer 1

This question is either impossibly difficult or impossibly easy.

If you assume that the densities of the initial solutions are near enough 1 g/mL, you have a total mass of 500g.

If you're not allowed to assume that, then unless you have access to tables of densities of solutions, the only way you can find out is by actual weighing.  Since you don't know how much volume the dissolved Na+, OH-, H+(aq), and Cl- ions occupy, you can't even work it out from the molar masses, because you don't know the mass of the water that isn't there to make room for them.

Or do you mean the masses IN solution? in that case, you just multiply volume by concentration to get moles, and multiply moles by molar mass to get grams.

Notice that after mixing you don't have any NaOH or HCl; what you do have (because you had just enough of each to neutralise the other) is NaCl.

Answer 2

RMM of NaOH = 23 + 1 + 16 = 40 so in 250ml of 0.4 moldm-3 there is

40 x 0.4 x 0.25 = 4 g NaOH dissolved

RMM of HCl = 35.5 +1 = 36.5 so in 250 ml of 0/4 moldm-3 there is

36.5 x 0.4 x 0.25 = 3.65 g