Vapor Pressure: Solution containing dissolved KI
Boiling point: Solution containing dissolved MgI₂
Freezing point: Solution containing dissolved KI
Explanation:
Water is a volatile solvent while KI and MgI₂ are non-volatile solute. Addition of non-volatile solute decreases vapor pressure of the pure solvent. This phenomenon is called lowering in vapor pressure.
Lowering in vapor pressure is a colligative property that means lowering in vapor pressure only depends upon the number of solute particles dissolved.
More the number of solute particles, more will be the lowering in the vapor pressure.
Equal number of moles of KI and MgI₂ are added in water. KI dissociates into two ions and MgI₂ dissociates into three ions as follows:
KI ⇒ K⁺ + I⁻
MgI₂ ⇒ Mg²⁺ + 2I⁻
Therefore, more lowering will occur in case of solution of MgI₂.
Hence, KI will have more vapour pressure.
Lowering in vapor pressure causes elevation in boiling point and depression in freezing point and both these are colligative properties.
So, more the number of solute particles, more will be elevation in boiling point and depression in freezing point.
Therefore, solution containing MgI₂ will have more boiling point.
Since, depression in freezing point will occur more in case of solution containing MgI₂, therefore freezing point of solution containing KI will be more.
