[vdesign]

Hello everyone, I am having some trouble with these chemestry problems. If you have any suggestions on resolving these problems, your help shall be very appreciated. Thank you very much.

1.
A concentrated hydrogen peroxide solutions are explosively decomposed by traces of transition metal ions:    2H2O2 (aq) → 2H2O (l) + O2 (g)
What volume of pure O2 (g), collected at 27.0°C and 746 torr would be generated by the decomposition of 125g of a 50.0% by mass of hydrogen peroxide solution?

2.
Metallic molybdenum can be produced from the mineral molybdenite, MoS2. The mineral is first oxidized in air to molybdenum trioxide and sulfur dioxide. Molybdenum trioxide is then reduced to metallic molybdenum using hydrogen gas. The balanced equations are:
   MoS2 (s) + 7/2 O2 (g) → MoO3 (s) + 2SO2 (g)
   MoO3 (s) + 3 H2 (g) → Mo (s) + 3H2O (l)
Calculate the volume of air and hydrogen gas at 17.0 C and 1.00 atm that are necessary to produce 1000 g of pure molybdenum from MoS2.Assume that air contains 21.0% of oxygen by volume and assume 100% yield for each reaction.

3.
Sodium azide (NaN3), the explosive compound in automobile air bags, decomposes according to the equation:   2NaN3(s) → 2Na(s) + 3N2(g)
What mass of sodium azide is required
to provide the nitrogen needed to inflate a 75.0L bag to a pressure of 1.3 atm at 25°C.?

4.
You have two gas filled balloons, one containing He and the other H2. The H2 balloon is twice the size of the He balloon, with a pressure of 1 atm and it is outside in the snow at - 5°C. The He balloon has a pressure of 2 atm and is in a warm building at 23°C. a) What balloon contains the greater number of molecules?  b) Which balloon contains a greater mass?


Thanks everyone...

[AWK]

Show your attempts
Start from a look at Borek textbook:
http://www.chembuddy.com/?left=balancing-stoichiometry&right=toc

[vdesign]

OK, well for number 3, i got m=518.52g and for number 4 i have that the He balloon has a bigger number of molecules and eventually has a greater mass.
Once again I have no idea if my results are correct...

[Borek]

For 3 you are exactly three times off.