Molality and mole fraction

Exercise 6

    

What is the molality of a $10\%$ aqueous solution of $NaCl$?

$100\;g$ solution contain $10\;g\;NaCl$. $90\;g$ water contain $10\;g\;NaCl$ $n_{NaCl}$ $=$ $\frac{10}{M_{NaCl}}$ $\mu_{NaCl}$ $=$ $\frac{n_{NaCl}\cdot 1000}{m_{H_2O}}$ $=$ $\frac{10\cdot 1000}{90\cdot M_{NaCl}}$ $=$ $1.91$