Calculate the number of moles of hydrogen contained in 18 litres of the gas at `27^(@)C` and 70 cm pressure. Given that R=0.0821 litre atm `K^(-1)`. Further, if the mass of hydrogen taken as above is found to be 1.350 g, calculate the molecular mass of hydrogen.

Answer

`2.015 g mol^(-1)`

Explanation

According to ideal gas equation ,
`PV = nRT ` or `n = (PV)/(RT)`
`V = 18 L , P = 0.92 "bar" , T = 27 + 273 = 300 K , R = 0.083 L "bar" K^(-1) mol^(-1)`
`:. N = ((0.92 "bar") xx (18 L))/((0.083 L "bar" K^(-1) mol^(-1)) xx (300 K)) = 0.67 mol`
Molecular mass of `H_(2)(M) = ("Mass of" H_(2))/("No. of moles of"H_(2)) = ((1.350 g))/((0.67 mol)) = 2.01 5 g mol^(-1)`