Question

Calculate the mass of substance 'A' which in gaseous form occupies 10 litres at 27C and 700 mm pressure. The molecular mass of 'A' is 60.

Answer 1

The formula used to calculate this is PV = nRT , n=PV/RT

given values P = 700mm = 700/760 = 0.92atm (1atm = 760mmHg) , V = 10L , R= 0.0821Latm/mol K , T = 27°C = 27+273= 300K.

putting all the values we get no. of moles of A = 0.92atm × 10L/0.0821Latm/mol K×300K = 0.374moles

mass of unknown substance = no. of moles of A × molecular mass of A = 0.374 × 60g (given) = 22.43grams

Answer 2

Simply:-

T=27+273=>300 K

P=700/760=>0.92atm

then,

By expression :PV= nRT(n stands for mole)

Putting all the required values

n=0.374

Mole =mass/molecular mass

So,

Mass=22.464g