Chem Class- October 21, 2009

We've now moved on to calculations of molar mass and moles. First though, Mr. D checked our homework that was assigned last class and then we went over number 5. The question for that asked what the purpose of using a satndard term to describe a certain number was. It's basically created to abbreviate something, making it more convenient, faster and easier.
Also: " Mr. D stole my noodles :(.... but I got dem back :)"

Ok, back to Chemistry. First of all, we started with the Atomic Mass.

The atomic mass is the mass of one mole of atoms in an element. It is also the mass of 1.0 mole of 'C' atoms in 12.0 g  (Eg: The mass of 1.0 mol of 'Ca' atoms is 40.1 g).

Molecular Mass is the mass of 1.0 mole of molecules of an element or a compound.
It's good to remember those that are diatomic: N2, O2, F2, CL2, Br2, I2, Hr (the special seven)
It's also good to remember those that are polyatomic: P4 and S8
You can assume, now, that all the rest are monoatomic

Finding the Molar Mass of Compounds
Eg: Find the molar mass of Ammonium Phosphate

NH4(+) and PO43(-) is (NH4)3PO4
3 N = 3(14.0)
12 H = 12(1.0)
1 P = 1 (31.0)
4 O = 4 (16.0)
          _______
          149.0 g/mol

Converting Mass<----->Moles
Conversion Factor g/mol or mol/g

Eg: Find the mass of 2.5 mol of water
1mol/18.0g x 1/2.5 mol = 1/45 g =45 g

Eg: Find the number of moles in a 391 g sample of Nitrogen dioxide
NO2
1 N = 1(14.0)
2 O = 2 (16.0)
         _______
          46.0 g

391 g x 1 mol/46 g = 8.5 mol