HELP! Ideal Gas Law Question for Practice TEST!

HELP! Ideal Gas Law Question for Practice TEST!?
Problem #1
SO3 is produce in enormous quantities each year for use in the synthesis of sulfuric acid.

S(s) + O2(g) = SO2(g)
2SO2(g) + O2(g) = 2SO3

What volume of O2(g) at 350 deg C and pressure of 5.25 atm is needed to completely convert 5.00 g sulfur to sulfur trioxide?

Please show work. I already did the problem but didn't get the correct answer I am unsure of where my mistake was.

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Problem #2. Conc Hydrogen peroxide solutions are explosively decomposed by traces of transition metal ions ex Mn or Fe:

2H2O2(aq) = 2H2O(l) + O2(g)

What volume of pure O2(g) collected at 27 deg C and 746 torr would be generated by decomposition of 125 g of a 50.0% by mass hydrogen peroxide solution? Ignore any water vapor that may be present.

So I solved this one and divided the Molar mass by 1/2 to account for the 50.0%. Is that right? The answer to this question isn't given.

Question 1:
Equation:
2S + 3O2 → 2SO3
2mol S reacts with 3mol O2 to produce 2mol SO3
molar mass S = 32g/mol
5g S = 5/32 = 0.15625 mol S
This will react with 0.15625*3/2 = 0.234375 mol O2

Calculate volume using gas law equation:
PV = nRT
5.25*V = 0.234375 * 0.082057*623
V = 12.000/5.25
V = 2.28 litres. O2 required

Question 2:
Equation:
2H2O2 → 2H2O + O2
2mol H2O2 decomposes to produce 1 mol O2

H2O2 solution = 50% H2O2: 125g = 62.5g H2O2
Molar mass H2O2 = 34g/mol
62.5 g H2O2 = 62.5/34 = 1.838 mol H2O2

This will produce 1.838/2 = 0.919 mol O2

PV = nRT
0.982 * V = 0.919 * 0.082057*300
V = 24.16/0.982
V = 24.6 L O2 produced