What is the partial pressure of oxygen at s.t.p. in a gaseous mixture containing 100 cm3 of oxygen and 900 cm3 of nitrogen gas?

A. 1.0 atm
B. 0.1 atm
C. 9.0 atm
D. 0.9 atm

Correct Answer:

Option B – 0.1 atm

Explanation

Partial pressure is found by Dalton’s Law:
Px = PTotal ( nx / nTotal )
where
Px = partial pressure of gas x
PTotal = total pressure of all gases
nx = number of moles of gas x
nTotal = number of moles of all gases

Step 1
Find PTotal
Standard pressure is 1 atm.

Step 2
Add up the number of moles of the component gases to find nTotal
nTotal = noxygen + nnitrogen
nTotal = 100 + 900
nTotal =1000cm3

Step 3
Now you have all the information needed to plug the values into the equation and solve for Poxygen
P-oxygen = PTotal ( n-oxygen / nTotal )
oxygen = 1 atm ( 100 / 1000 )
oxygen= 0.1atm