Question

1.4dm cube of a gas STP weight 1.26×10 raise to -3 kg Calculate Molecular mass
Mass of 1 mole Number of gas molecules

Answer 1

1.4dm cube of a gas STP weight 1.26 × 10^ -3 kg. Calculate Molecular mass.

solution : volume of gas , V = 1.4dm³ = 1.4L

mass of gas , m = 1.26 × 10^-3 Kg = 1

26g

at STP(standard temperature and pressure)

temperature , T = 273K

and pressure , P = 1atm

applying equation, PV = nRT

or, 1atm × 1.4L = n × 0.082 × 273

or, n = 1.4/(0.082 × 273) = 0.06178560 ≈ 0.06

hence, no of mole of gas = 0.06

so, given weight/molecular weight = 0.06

or, molecular weight = given weight/0.06

= 1.26/0.06 = 21

hence, molecular mass of gas = 21g/mol.