Question

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

Answer 1

Given: V₁ = 10 litres                        

T₁ = 27+ 273 = 300K              

P₁ = 700 mm

S.T.P conditions: V₂ = ?

T₂ = 273K

P₂ = 760 mm

Using the gas equation,

`("P"_1"V"_1)/"T"_1 = ("P"_2"V"_2)/"T"_2`

V₂ = `("P"_1"V"_1"T"_2)/("T"_1"P"_2)`

= `(700 xx 10 xx 273)/(300 xx 760)` litres

Molecular weight A = 60

∴ Weight of 22.4 litres of A at STP = 60 g

weight of substance A= `(700 xx 10 xx 273)/(300 xx 760)` litres of A at S.T.P = `60/22.4 xx (700 xx 10 xx 273)/(300 xx 760)` g

or 22.45 g