chemistry question

Question

<sup>A flask contains a mixture of nitrous oxide (N2O) and oxygen (O2) with partial pressures of 425 torr and 786 torr respectively.

What is the ratio of the number of moles of N2O to the number of moles of O2 in this flask? In other words, what is the value of the quotient n(N2O) ÷ n(O2)?

Express your answer to 2 significant figures.</sup>

Answer 1

This is an example of Dalton's Law of Partial Pressure. The total pressure exerted by a mixture of gases is equal to the sum of the partial pressures of the gases in the mixture. 

PP N₂O = 425 torr

PP O₂ = 786 torr

_Ptotal = 425 torr + 786 torr = 1211 torr

mole fraction N₂O = 425/1211 = 0.35

mole fraction O₂ = 786/1211 = 0.65

Ratio of N₂O to O₂ = 0.35/0.65 = 0.54

 

If you wanted to do this more simply, you could just take the ratio of 425/786 = 0.54 since the partial pressure is proportional to the moles.