Question

Why is the vapor pressure of an aqueous solution of glucose lower than that of water?

Answer 1

Pure water has high vapor pressure as the water molecules can easily escape from the surface. When the glucose was added to the water, then that liquid can be known as a solution which consists of solute and solvent. The relative lowering of vapour pressure is the property that can be exhibited by the solutions containing a solute like glucose.

Complete answer:
The solution is a homogeneous mixture of solute and solvent. The solute will be present in a small quantity whereas the solvent will be present in a higher quantity.
Relative lowering of vapor pressure is the phenomenon in which the addition of any solute like glucose makes the vapor pressure of the solution can be lowered as glucose is a nonionic solute that decreases the vapor pressure of the glucose solution.
Whereas the water is a solvent and does not have any non-ionic solutes which makes the compound with high vapour pressure.
Thus, the vapour pressure of an aqueous solution of glucose is lower than that of water due to the presence of non-ionic solute-like glucose.

Note:
Colligative properties are the properties in which the properties of the solution will not depend on the nature of the solution but depends upon the ratio of the solute to the solvent. Relative lowering of vapor pressure, the elevation of boiling point, depression in freezing point, and osmotic pressure are the four colligative properties.