Question

Determine the Van't Hoff factor for$\mathrm{Ca}{\left({\mathrm{NO}}_3\right)}_2$ on complete (100%) dissociation.

Answer 1

Part 1: Van't Hoff Factor

The Van’t Hoff factor can be defined as the ratio of the concentration of particles formed when a substance is dissolved to the concentration of the substance by mass. It is denoted by the symbol ‘i’.

Part 2: Determining the Van't Hoff factor for$\mathrm{Ca}{\left({\mathrm{NO}}_3\right)}_2$ complete (100%) dissociation.

On complete dissociation, calcium nitrate will be :

$\underset{\mathrm{calcium}\mathrm{nitrate}}{\mathrm{Ca}{\left({\mathrm{NO}}_{\mathbf{3}}\right)}_{\mathbf{2}}\left(\mathrm{s}\right)}\to \underset{\mathrm{calcium}\mathrm{ion}}{{\mathrm{Ca}}^{2+}\left(\mathrm{aq}\right)}+\underset{\mathrm{nitrate}\mathrm{ions}}{2{\mathrm{NO}}_3^{-}\left(\mathrm{aq}\right)}$

Calcium nitrate on dissociation gives 2 moles of nitrate ions and one mole of calcium ions,

so the total number of moles of ions is $2+1=3$

It gives three ions, hence Van’t Hoff factor $=3$.