NaCl solution

[john doe]

i was wondering if any of you could help me figure out how much distilled water should be added to 5g of NaCl so that it completely dissolves. Thanks

[arit]

I'm pretty confident I got it right, but no guarantees.
I had some problems finding out the solubility product for NaCl, one site told me that it is ~36 (mol/l)² (at 25 C), so that's what I'm using. It might be completely wrong though.

Because we want the solution to be saturated: Q = Ksp.
Q = c(Na+)c(Cl-) ; Ksp = 36

(n(Na+) / V(H2O)) * (n(Cl-) / V(H2O)) = 36 (mol/l)²
<=> (n(Na+)n(Cl-)) / (V(H2O)²) = 36 (mol/l)²
(NaCl -> Na+ + Cl-, so n(NaCl) = n(Na+) = n(Cl-))
<=> n(NaCl)² / (V(H2O)²) = 36 (mol/l)²
<=> n(NaCl) / V(H2O) = 6 mol/l
<=> V(H2O) = n(NaCl) / 6 mol/l

So we get V(H2O) = (5g/(22.99g/mol+35.45g/mol))/6 (mol/l) = 0.0855578371 l ~ 0.09 l

Hope this helps.

[john doe]

Thanks that helps me out a lot. And 25(c) is about the temp which im going to be working in, so im pretty sure u got it right, ill just check it over to make sure it makes sense before i use it. Thanks