chemistry
posted by Anonymous .
A chemist weighed out 5.31 g of a mixture containing unknown amounts of BaO(s) and CaO(s) and placed the sample in a 1.50 L flask containing CO2(g) at 30.0°C and 750. torr. After the reaction to form BaCO3(s) and CaCO3(s) was completed, the pressure of CO2(g) remaining was 230. torr. Calculate the mass percents of CaO(s) and BaO(s) in the mixture.

Use PV = nRT, substitute the numbers, and calculate mols CO2 initially, redo the formula and recalculate with new numbers to determine the moles CO2 remaining. The difference equals moles CO2 reacted.
Then let X = mass BaO
Let Y = mass CaO.
========================
X + Y = 5.31
(X/molar mass BaO) + (Y/molar mass CaO) = moles CO2 consumed (from above.)
Solve the two simultaneous equations for X and Y,
Then %BaO = (mass BaO/5.31)*100 = ??
%CaO = (mass CaO/5.31)*100 = ??
Post your work if you get stuck. 
i have a hard time understanding how to calculate the moles of CO2 remaining?
how do you use the PV=nRT for the remaining CO2? 
The problem states that after the CO2 has reacted with BaO and CaO, the remaining pressure is 230 torr. So plug that back into PV = nRT for P, along with the other numbers, and calculate a new n. Subtracting the two will give you the amount that reacted.

for T, do I have to convert C to Kelvin? would they yield the same answers?

X + Y = 5.31
(X/molar mass BaO) + (Y/molar mass CaO) = moles CO2 consumed (from above.)
Solve the two simultaneous equations for X and Y,
^I don't really understand this part either. 
why is moles of CO2 consumed equal to the combined moles of BaO and CaO?