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.
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