Question

The vapour pressure of water at 20°C is 17.5 mm Hg. If 18 g of glucose (C₆H₁₂O₆) is added to 178.2 g of water at 20°C, the vapour pressure of the resulting solution will be ______.

Options

• 17.675 mm Hg

• 15.750 mm Hg

• 16.500 mm Hg

• 17.325 mm Hg

Answer 1

The vapour pressure of water at 20°C is 17.5 mm Hg. If 18 g of glucose (C₆H₁₂O₆) is added to 178.2 g of water at 20°C, the vapour pressure of the resulting solution will be 17.325 mm Hg.

Explanation:

Given: Vapour pressure of pure water P° = 17.5 mm Hg

Mass of glucose = 18 g

Molar mass of glucose = 180 g/mol

Mass of water = 178.2 g

Molar mass of water = 18 g/mol

Moles of glucose = `18/180` = 0.1 mol

Moles of water = `178.2/18` = 9.9 mol

Mole fraction of water `x_"water" = 9.9/(9.9 + 0.1)`

= `9.9/10`

= 0.99

Vapour pressure of solution 

`P_"solution" = x_"water" * P^circ`

= 0.99 × 17.5

= 17.325 mm Hg