Question

Calculate the molality of a saline solution in which 50.0 g of NaCl is dissolved in 0.750 kg of water.

Answer 1

Answer: Molality of a saline solution = 1.14 moles per kg

Explanation:

Given mass of NaCl (m)= 50.0 g

Mass of solvent = 0.750 kg

Molar mass of NaCl (M)= 23 g + 35.5 g = 58.5g  [Atomic mass of Na = 23 u , atomic mass of Cl = 35.5 u]

Number of moles (n) =$\dfrac{m}{M}$

$\dfrac{50}{58.5}=.8547$

Molality = $\dfrac{\text{Number of moles }}{\text{Mass of solvent in kg}}$

$=\dfrac{0.8547}{0.750}=1.1396\approx1.14\text{ moles per kg]$

Hence, molality of a saline solution = 1.14 moles per kg