Question

A certain quantity of a gas occupies 100ml when collected over water at 15${}^{\circ }$C and 750mm pressure. If it occupies 91.9ml in dry state at STP. Find the vapour pressure of water at 15${}^{\circ }$C.

• A. 12.8mm
• B. 14.8mm
• C. 13.58mm
• D. 15.7mm

Answer 1

The correct option is C

13.58mm

Let the aqueous tension at 288K be 'P' mm . The presence of dry gas at 288 K =(750-P)

Now $P_1$ = (750-P) mm

$P_2$ = 760 mm

$V_1=100ml,V_2=91.9ml$

$T_1=288K,T_2=273.15K$

$\therefore \frac{P_1{V}_1}{T_1}=\frac{P_2{V}_2}{T_2}$

$P_1=\frac{P_1{V}_2\times T_1}{V_1\times T_2}$

$750-P=\frac{760\times 91.9\times 288}{100\times 273.15}$

750 - P = 736.4112

P = 13.588 mm.