A gas filled in a bulb of capacity 25.1 mL at 27°C and 750 mm pressure weighs 0.072 g. If 1 litre of hydrogen at S.T.R weighs 0.09 g, calculate the molecular mass of the gas.

A gas filled in a bulb of capacity 25.1 mL at 27°C and 750 mm pressur

1.	A gas filled in a bulb of capacity 25.1 mL at 27°C and 750 mm pressure weighs 0.072 g. If 1 litre of hydrogen at S.T.R weighs 0.09 g, calculate the molecular mass of the gas.
Answer» Solution :Let the volume of the gas at STP be `V_(2)` mL `P_(1) = 750 MM, V_(1) = 25.1 mL, T_(1) = 27^(@) C = 300 K` `P_(2) = 760 mm, V_(2) = ?, T_(2) = 273 K` According to the gas equation: `(P_(1)V_(1))/T_(1) = (P_(2)V_(2))/T_(2)` or `V_(2) = (P_(1)V_(1)T_(2))/(T_(1)P_(2))` Substituting the values, we get `V_(2) = (750 xx 25.1 xx 273)/(300 xx 760)` = 22.5 mL Mass of 22.5 mL of `H_(2)` at S.T.P. `=0.09/1000 xx 22.5 = 2.025 xx 10^(-3) G` V.D. = `("Mass of 22.5 mL of gas at S.T.P")/("Mass of 22.5 mL of H_(2) at S.T.P")` `=0.072/(2.025 xx 10^(-3))` = 35.55 Hence, MOLECULAR mass `=2 xx V.D. = 2 xx 35.55 = 71.1`