I Really need Chemistry help: Gas Laws?!

I have struggled with gas laws for some time, so if anyone could help me with these questions, I would be forever grateful. I've done 12 questions so far for practice, but need help with the last 6… So either breaking it down for me + answer, or just giving me the answer and allowing me to work backwards is acceptable!
Added (1). 1. A 34.0-L cylinder contains 369 g O2(g) at 23.3°C. What mass of O2(g) must be released to reduce the pressure in the cylinder to 5.21 atm, assuming the temperature remains constant?
Enter your answer with **3 significant figures.**
Added (2). 2. What is the density of CO2 gas (molar mass, 44.01 g mol-1) at 21.2oC and 131 kPa? Give your answer in grams per litre (g L-1), accurate to **three significant figures.**
Added (3). 3. Carbon monoxide, CO, and hydrogen, H2, react according to the reaction below.
2 CO(g) + 5 H2(g) --> C2H6(g) + 2 H2O(g)
What volume of the excess reactant remains if 18.6 L CO and 32.2 L H2 are allowed to react. Assume that the volumes of both gases are measured at 735oC and 1.19 atm.
Give your answer in litres, accurate to **two significant figures.**
Added (4). 4. Hydrogen peroxide, H2O2, is used to disinfect contact lenses. What volume of O2, in mL, of O2(g) at 36°C and 741 mmHg can be liberated from 50.0 mL of an aqueous solution containing 3.00% H2O2 by mass? The density of the aqueous solution of H2O2 is 1.01 g/mL.
2H2O2(aq)â†Â'2H2O(l)+O2(g)
Enter your answer with **3 significant digits.**
Added (5). 5. Calculate the volume of H2(g), measured at 21.9°C and 769 Torr required to react with 36.3 L CO(g), also measured at 21.9°C and 769 Torr. Assume the gases react as follows.
3CO(g)+7H2(g)â†Â'C3H8(g)+3H2O(l)
Enter your answer with 3 significant digits.
Added (6). 6. When solid NH4ClO4 decomposes, a mixture of gases is obtained:
2 NH4ClO4(s) ---> 4 H2O(g) + Cl2(g) + 2 O2(g) + N2(g)
In an experiment, 4.56 g NH4ClO4 decomposes completely in a rigid 5.00-L container. What is the total pressure in the container if the final temperature is 229oC?

Give your answer in atmospheres, accurate to three significant figures. Do not include the units as part of your answer.

Molar masses
(in g mol-1)
NH4ClO4, 117.492
H2O, 18.016
O2, 32.00
N2, 28.02
Cl2, 70.90
Added (7). MAJOR POINTS FOR THIS!

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