Vapour pressure of a pure liquid A is 10.0torr at 27^(@)C. The vapour pressure is lowered to 9.0 torr on dissolving one gram of B in 20g of A. If the molar mass of A is 200 g mol^(-1) then calculate the molar mass of B.

Vapour pressure of a pure liquid A is 10.0torr at 27^(@)C. The vapour

1.	Vapour pressure of a pure liquid A is 10.0torr at 27^(@)C. The vapour pressure is lowered to 9.0 torr on dissolving one gram of B in 20g of A. If the molar mass of A is 200 g mol^(-1) then calculate the molar mass of B.
Answer» Solution :`P _(A)^(@) = 10` torr,` P_("solution") = 9` torr, `W_(A) = 20g, W_(B) =1G, M _(A) =200 g mol ^(-1), M _(B) =` ? `(Delta P )/(P _(A) ^(@))= (W_(B) xx M _(A))/(M _(B) xx W _(A))` ` (10 -9)/(10) = (1XX 20 0)/( M _(B) xx 20)` `M _(B) = (200)/(20) xx 10 =100 g mol ^(-1)`