Help With Chem Please,,,,,?

Question

1) What is the mass of 1.33 x 10^4 moles of O2 at STP??

2) Write a balences equationfor the following;
hydrogen gas + oxygen gas -> water vapor
hydrogen gas + chlorine gas -> hydrogen chloride gas

3) A chemist determines the mass of a sample of gas to be 3.17g. It's volume is 942 ml at 14 C (degrees) and 1.09 atm. What is the moler mass of the gas?

If you can help me out..... How did you get your answers, I AM SO LOST right now.... and I knida need help with this stuff from where I can get it.

Please and Thank You!!!
~Baby-Blue~

Answer 1

1) The first one is wrong on the last person who answered, O2 weighs 32g/mol because there are 2 O's in it, 16 each. So in 1.33x10^4 (13,300mol) you have 4.256x10^5g of O2 (425.6kg).

2) Recognize that hydrogen, oxygen, and chlorine are diatomic gasses, so they always occur in pairs (H2, O2, Cl2). Others like this are nitrogen (N2), fluorine (F2), bromine (liquid @ room temp. Br2) and Iodine (solid at room temp, I2). So your equations would be:

2H2+O2-->2H2O
H2+Cl2-->2HCl

3) PV=nRT and solve for n, number of moles. Put everything in correct units, liters, atmospheres, moles, and kelvins, and R is a constant R=0.0821 L*atm/mol K. Kelvin temp=Celcius temp +273

Solving for n:
n=PV/RT=(1.09atm)(0.942L)/(0.0821L*atm/mol*K)(287K)
n=0.0436 mol

So, when we usually want to know a number of moles given a mass and having a molar mass we can look up, we say,
n=mass/molar mass

in this case, we need to find molar mass, so:
mass/n=molar mass
3.17g/0.0436mol=72.71g/mol

Answer 2

1. 239.4 kgs. (if 1 mol weights 18grs, then...)

2. Just write the molecules and balance the equation in order to have the same quantities of each atom in each side.
a. 2H2 + O2 = 2H2O
b. H2 + Cl2 = 2HCl

3. Use the gases equation.
pV = nRT
1.09*0.942/0.082*287 = 0.0436 mols

and n = m/MM then MM = 3.17/0.0436 = 72.7 grs/mol