Question

A 2 M solution of NaCl in water is at 20.0 oC. The density of the solution was measured to be 1.0768 g/mL at this temperature. Calculate the molality of the salt solution. Express your answer numerically to three significant figures.

Answer 1

Molality of the NaCl solution is 2.084 mol/kg.

Step-by-step explanation:

Molarity of the solution is the moles of compound in 1 Liter solutions.

`Molarity=\frac{\text{Mass of compound}}{\text{Molar mas of compound}* Volume (L)}`

Molarity of the NaCl solution = 2 M

This means that in 1 liter solution there are 2 moles of NaCl.

Volume of the NaCl solution, V = 1 L = 1000 mL

Density of the solution = d = 1.0768 g/mL

Mass of solution= m

`Mass=Density* volume`

`m=d* V=1.0768 g/mL* 1000 mL=1076.8 g`

Mass of 2 moles of NaCl =58.5 g/mol × 2 mol = 117 g

Mass of solution = Mass of solvent + mass of solute

Mass of solvent = Mass of solution - mass of solute

= 1076.8 g - 117 g = 959.8 g

Mass of solvent = 959.8 g = 0.9598 kg

`Molality=\frac{\text{Mass of compound}}{\text{molar mass of compound}* mass of solvent(kg)}`

Molality of the NaCl solution:

`=(117 g)/(58.5 g/mol* 0.9598 kg)=2.084 mol/kg`