25.3 g of sodium carbonate,Na₂CO₃ is dissolved in enough water to make 250 mL of solution. If sodium carbonate dissociates completely, molar concentration of sodium ion,
Na⁺and carbonate ions, ${\mathrm{CO}}_3^{2-}$respectively are (Molar mass of Na₂ CO₃ = 106 mol^-1)

Molarity of ${\mathrm{Na}}_2{\mathrm{CO}}_3$ solution $=\frac{25.3\times 1000}{106\times 250}=0.955\mathrm{M}$
                     ${\mathrm{Na}}_2{\mathrm{CO}}_3⟶2{\mathrm{Na}}^{+}+{\mathrm{CO}}_3^{2-}$
Initial conc.         0.955       0             0
After dissociation                 2 x 0.955      0.955
$\begin{array}{l}\therefore \left[{\mathrm{Na}}^{+}\right]=2\times 0.955\mathrm{M}=1.910\mathrm{M}\\ \left[{\mathrm{CO}}_3^{2-}\right]=0.955\mathrm{M}\end{array}$