Remark
The question with these kind of problems is "Which R do you use?" That's where dimensional analysis is so handy. You must look at the units of the givens and choose your R accordingly. You'll see how that works in a moment.
You need to list the givens along with their units and in this case the property you want to solve for. You need all that to determine the R value
Givens
n = 0.25 moles
T = 35°C = 35 + 273.15 = 308.15°K
V = 6.23 L
Pressure = P in kPa
Which R
The units of the R you want has to have units of moles, kPa, °K and liters
The R that you want is 8.314
Formula
PV = nRT
P 6.23 = 0.25 * 8.314 * 308.15 Combine the left
P*6.23 = 640.5
P = 640.5/6.23 = 102.81 The answer should be 100 kpA of 1.0 * 10^2 kPa
because the number of moles has only 2 sig digs.
But if sig digs are not a problem 102.8 is likely close enough.
Second Question
You are going to have to clean up the numbers. I think I've got only 1 chance at this. The partial pressures of the 2 gases will add up to the total pressure. So the total pressure was 100 approx and the water vapor was 3.36 kPa. The difference is
Total = air + water vapor
100.18 = air + 3.36 about Subtract 3.36 from both sides.
100.18 - 3.36 = 96.82 about. Pick the answer that is closest to that. I'll clean up the numbers if I can.
Answer C
