Question

A certain mass of hydrogen gas collected over water at 6degrees Celsius and 765mmHg pressure has a volume of 35cm3. Calculate the volume when it is dry at STP
[SVP of water at 6degrees Celsius = 7mmHg]

Answer 1

$P_{total} = P_{H_2}+P_{H_2O}$

$765=P_{H_2}+ 7$

$P_{H_2} = 758 mmHg$

Use Combined Gas Law

$\frac{P_1V_1}{T_1}=\frac{P_2V_2}{T_2}$

$P_1 = 758 mmHg$

$V_1= 0.035 L$

$T_1 (K) = 273+6 = 279 K$

$P_2 = 760 mmHg$ (pressure at STP)

$V_2=?$

$T_2=273 K$ (temperature at STP)

$\frac{758\times0.035}{279}=\frac{760\times V_2}{273}$

$V_2 = 0.034 L$