Question

The vapour pressure of solution obtained by mixing 0.2 mol of NaCl in 72g of water at 25°C will be ______ torr.

[Given: vapour pressure of water at 25°C is 24.2 torr]

Options

• 1

• 2

• 3

• 4

Answer 1

The vapour pressure of solution obtained by mixing 0.2 mol of NaCl in 72g of water at 25°C will be 2 torr.

Explanation:

`("P"^0 - "P"_"s")/"P"_"s" = "i"."n"/"N" ⇒ "P"^0/"P"_"s" - 1 = (2 xx 0.2)/4`

⇒ `"P"^0/"P"_"s" = 1 + 1/10`

⇒ `"P"^0/"P"_"s" = 11/10`

∴ P_s = `(10  "P"^0)/11`

= `(10 xx 24.2)/11` torr

i.e. P_s = 22 torr

= `22/11`

= 2 torr