Mole fraction?

a ridgid 8.2L flask contains a mixture of 2.5 moles of h2 , .5 mol of O2 and sufficent Ar so that the partial pressure of Ar in the flask is 2.00 atm. the temp is 127 C.

a. calculate the total pressure in the flask

b. calculate mole fraction of H2 in the flask

c. calculate density ( in g L-1) of the mixture in the flask

the mixture in the gas is ignited by a spark, and the reaction represented below occurs untill ne of the reactants is completly comsumed.

2H2 (g) +O2 (g) ----> 2H2O(g)

d. give the mole fraction of all species present in the flask at the end of the reaction.

i get the total pressure i just dont know how to do mole fraction.

I think your problem may just be the definition.

Mole fraction of X = (moles X)/(total moles).

In your case,

Mole fraction H2 = (Moles H2)/(Moles H2 + moles O2 + moles Ar)

To find moles Ar, use PV = nRT, where P is the partial pressure of Ar.

Or (a bit easier), use the same equation with P equal to total pressure to get total moles, and use that as your denominator in the mole fraction question.