Question

Sodium hydroxide is a common ingredient in drain cleaners such as drano. The mole fraction of sodium hydroxide in a saturated aqueous solution is 0.310. What is the molality of the solution?

Answer 1

Answer: The molality of NaOH solution is 24.69 m

Explanation:

We are given:

Mole fraction of sodium hydroxide = 0.310

This means that 0.310 moles of sodium hydroxide is present in 1.00 moles of solution

Moles of water (solvent) = [1.00 - 0.310] = 0.690 moles

To calculate the number of moles, we use the equation:

$\text{Number of moles}=\frac{\text{Given mass}}{\text{Molar mass}}$

Moles of water = 0.690 moles

Molar mass of water = 18 g/mol

Putting values in above equation, we get:

$0.690mol=\frac{\text{Moles of water}}{18g/mol}\\\\\text{Mass of water}=(0.690mol\times 18g/mol)=12.42g$

To calculate the molality of solution, we use the equation:

$Molality=\frac{n_{solute}\times 1000}{W_{solvent}\text{ (in grams)}}$

Where,

$n_{solute}$ = Moles of solute = 0.310 moles

$W_{solvent}$ = Mass of solvent = 12.42 g

Putting values in above equation, we get:

$\text{Molality of }NaOH=\frac{0.310\times 1000}{12.42}\\\\\text{Molality of }NaOH=24.96m$

Hence, the molality of NaOH solution is 24.69 m