chemistry moles molecues?

Question

calculate the number of molecules in each of the following

71.0 g of Cl gas

40 g of water

4.0 of oxygen gas

132g of C2F2H4

can you show your work and teach me how to do it, write it so its easy to read and easy for a little kid to learn =)

thanks in advance

Answer 1

By deffinition, a mole is 6.02 x 10^23 atoms (or molecules). So all you need to do is determine the number of moles you have of the material.

For chlorine gas, which exists as Cl2, there are TWO MOLES of chlorine ATOMS in ONE MOLE of chlorine GAS! So be carefull you don't get mixed up with diatomic gases! They are asking for number of MOLECULES here.

So Cl2 is 2 x 35.45g/mole = 70.90g/mole

Now to get molecules:

(71.0g/70.90g/mol) x 6.02 x 10^23 =

6.03 x 10^23 molecules of Cl2

For water its:

40g/18g/mol =

You should be able to do the rest of them now.

Answer 2

Look at the atomic weights :
Cl => 35.453 g / mol
Cl gas is Cl2 => 35.453 x 2 = 70.906 g/mol
71.0 g / 70.906 = 1.00 mol

Molar mass H2O = 18.02 g/mol
40 g / 18.02 = 2.22 mol

Molar mass O2 = 31.9988 g/mol
4.0 g / 31.9988 = 0.125 mol

Molar mass C2F2H4 = 66.05 g/mol
132 g / 66.05 = 2.00 mol