what is the ratio of weight of helium and oxygen taken together in a vessel with total pressure of 10 atm? given that partial pressure of helium is 2 atm.
Answers
we have to find the ratio of weight of helium and oxygen taken together in a vessel with total pressure of 10 atm and also partial pressure of helium is 2 atm.
solution : according to Dalton's law of partial pressure,
partial pressure of oxygen + partial pressure of helium = total pressure
⇒partial pressure of oxygen = 10 atm - 2 atm = 8 atm
⇒partial pressure of oxygen = 8 atm
we also know, partial pressure of a gas = total pressure × mole fraction of the gas
if we find partial pressure of oxygen,
8 atm = 10 × mole fraction of oxygen
⇒mole fraction of oxygen = 0.8
now, mole fraction of oxygen = no of moles of oxygen/(moles of oxygen + moles of helium) = 0.8
⇒(w₁/32)/(w₁/32 + w₂/4) = 0.8
⇒w₁/32 = 0.8w₁/32 + 0.8w₂/4
⇒0.2w₁/32 = 0.8w₂/4
⇒w₁/8 = 4w₂
⇒w₁/w₂ = 8 × 4 = 32/1
Therefore the ratio of their weight is 32 : 1