Question

Determine the concentration of a solution (in% by mass, % by volume, % by mass volume, molarity and ppm) containing 5 grams of NaCl and 50 ml of water. What is the mole fraction of NaCl in the solution?

Answer 1

$\rho$ (H₂O)$=$ 1 g/ml

m (H₂O) $= \rho*V= 1 g/ml * 50ml = 50g$

1) % by mass = $\omega$ (NaCl) $= m(NaCl)/(m(H2O)+m(NaCl))*100$ % = $5g/(5+50)g*100$ % = 9.1%

2) % by mass volume = $m(NaCl)/V$$(H2O)$ $*100$ % = 5g/50ml * 100% = 10 g/ml

3) n(NaCl) = m(NaCl)/M(NaCl) = 5g / 58.5g/mol = 0.0855 mol

molarity = M = n(NaCl)/V(H₂O)= 0.0855 mol/ 0.05 L = 1.71 mol/L = 1.71 M

4) ppm = m(NaCl)/(m(NaCl)+m(H₂O)) *10⁶ = 5g/(50+5)g *10⁶= 90909 ppm

5) n (H₂O) = m(H₂O) /M(H₂O) = 50g / 18g/mol = 2.78 mol

mole fraction of NaCl =$\eta$ (NaCl) = n(NaCl)/(n(H₂O)+n(NaCl)) = 0.0855 mol / 2.78 mol = 0.03