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Which one of the statements given below-concerning properties of solutions, describes a colligative effect? |
Boiling point of pure water decreases by the addition of ethanol Vapour pressure of pure water decreases by the addition of nitric acid Vapour pressure of pure benzene decreases by the addition of naphthalene Boiling point of pure benzene increases by the addition of toluene |
Vapour pressure of pure benzene decreases by the addition of naphthalene |
In a solution, the vapor pressure of a volatile solvent decreases when a non-volatile solute is added. This is known as vapor pressure lowering or Raoult's law. According to Raoult's law, the vapor pressure of a component in a solution is proportional to its mole fraction. When naphthalene is added to benzene, naphthalene acts as a non-volatile solute. It reduces the vapor pressure of the benzene solvent compared to its pure form. This decrease in vapor pressure is a colligative effect and is a consequence of the presence of a non-volatile solute. Therefore, the statement (3) Vapour pressure of pure benzene decreases by the addition of naphthalene describes a colligative effect. |
