Question

An aqueous solution of NaOH was made and its molar mass from the measurement of osmotic pressure at 27°C was found to be 25 g mol$^{-1$.}
Calculate the percentage dissociation of NaOH in this solution.

Hint:

In osmotic pressure calculations, remember that dissociation increases the effective number of particles. The van't Hoff factor \(i\) plays a key role in determining the extent of dissociation.

Answer 1

The osmotic pressure (\(\Pi\)) is determined by the equation: \[ \Pi = i \cdot M \cdot R \cdot T \] The terms are defined as: - \( i \): van't Hoff factor - \( M \): solution molarity - \( R \): gas constant - \( T \): temperature in Kelvin. Given that the molar mass of NaOH is 25 g/mol, its molarity is contingent on the dissolved mass. Osmotic pressure measurements allow for the determination of \( i \), the degree of dissociation, which can then be used to calculate the percentage dissociation using: \[ \text{Percentage dissociation} = \frac{(i - 1)}{i} \times 100 \]