Chemistry - Liquid Solution Question with Solution | TestHub

Isotonic solutions are those which have the same osmotic pressure at a given temperature.

Osmotic pressure is given by $\pi =iCRT$, where $i$ is the van't Hoff factor, $C$ is the molar concentration, $R$ is the gas constant, and $T$ is the temperature.

For two solutions to be isotonic, their effective concentrations must be equal: $i_1{C}_1=i_2{C}_2$.

For $0.1$ M urea and $0.1$ M sucrose:
Urea is a non-electrolyte, so $i=1$. Effective concentration $=1\times 0.1=0.1$ M.
Sucrose is a non-electrolyte, so $i=1$. Effective concentration $=1\times 0.1=0.1$ M.
Since $i_1{C}_1=i_2{C}_2$, these two solutions are isotonic.

For $0.1$ M urea and $0.1$ M KCl:
KCl dissociates into $K^{+}$ and $C{l}^{-}$, so $i=2$. Effective concentration $=2\times 0.1=0.2$ M.
They are not isotonic.

For $0.1$ M KCl and $0.1$ M ${\text{CaCl}}_2$:
${\text{CaCl}}_2$ dissociates into $C{a}^{2+}$ and $2C{l}^{-}$, so $i=3$. Effective concentration $=3\times 0.1=0.3$ M.
They are not isotonic.

Answer: $0.1$ M urea and $0.1$ M sucrose