A mixture of dihydrogen and dioxygen at one bar pressure contains 20% by weight of dihydrogen. Calculate the partial pressure of dihydrogen.

Solution

Since the mixture H₂ and O₂ contains 20% by weight of hydrogen, therefore if H₂ = 20g, then O₂ = 100 - 20 = 80 g
$therefore$ No. of moles of dihydrogen (H₂)
$space equals space 20 over 2 space equals space 10 space moles$
No. of moles of dioxygen (O₂) = $equals space 80 over 32 space equals space 2.5 space moles$
Partial pressure of a gas = mole fraction of the gas X total pressure,
$therefore space space space Partial space pressure space of space dihydrogen space left parenthesis straight p subscript straight H subscript 2 right parenthesis space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space equals fraction numerator straight n subscript straight H subscript 2 end subscript over denominator straight n subscript straight H subscript 2 end subscript plus space straight n subscript straight O subscript 2 end subscript end fraction space cross times space straight P subscript total space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space equals space fraction numerator 10 over denominator 10 plus 2.5 end fraction cross times 1 space bar space equals space 0.8 space bar$