We have 500g of a substance and want to know how many of a particular atom we have.
First we need to find how many Moles are in 500g of that substance
We do that by
1 mol substance
500g substance ___________________
= How many moles of substance
Molar Mass g substance
Now that we have the number of moles we need to find the number of molecules
6.02*1023 molecules
Number of moles ___________________
1 mole
= Number of molecules
now we have found the number of molecules (or atoms in an element) we have to find the
number of atoms of the element we are seeking.
Number of atoms
Number of each Molecule __________________________= number of atoms
Each molecule
Lets find the number of each type of atom in H2O in 500g H2O
First we find how many mols we have:
1 mol = 18 g
1 mol H2O
500 g H2O ___________________= 27.78 mol H2O
18 g H2O
then how many molecules we have;
1 Mol = 6.02*1023 Molecules
6.02*1023 Molecules
27.87 Mol H2O ______________________
1 Mol H2O
= 1.68*1025
Now how many Hydrogen atoms and oxygen atoms
Molecules
1 Molecule H2O = 2 Hydrogen Atoms
1 Molecule H2O = 1 Oxygen Atoms
1.68*1025
1.68*10
2 H Atoms
Molecules H2O _______________= 3.36*1025
1 Molecule H2O
25
1 O Atoms
Molecules H2O ________________= 1.68*1025
1 Molecule H2O
H Atoms
O Atoms