1. Avogadro and the Mole

2. HIGHER GRADE CHEMISTRY CALCULATIONS
Avogadro and the Mole..
Avogadro’s constant is the number of ‘elementary particles’ in one mole of a substance. It has the value of 6.02 x 1023 mol-1.
Worked example 1.
Calculate the number of atoms in 4 g of bromine.
Step 1:- Identify the elementary particles present  Br2 molecules
1 mole  x 1023 Br2 molecules
Step 2:- Change from moles to a mass in grams
160g  x 1023 Br2 molecules
Step 3:- Use proportion.
4 g  /160 x 6.02 x 1023 Br2 molecules
 x 1023 Br2 molecules
Step 4:- Change from number of molecules to number of atoms.
1.505 x 1023 Br2 molecules  2 x x 1023 Br atoms
 x 1023 Br atoms

3. Calculations for you to try.
How many atoms are there in 0.01 g of carbon?
The elementary particles  C atoms.
1 mole  x C atoms.
12 g  x C atoms.
So g  0.01/12 x 6.02 x C atoms.
 x 1020 C atoms
How many oxygen atoms are there in 2.2 g of carbon dioxide?
The elementary particles  CO2 molecules.
1 mole  x CO2 molecules
44 g  x CO2 molecules
So g  2.2/44 x 6.02 x C atoms.
 x CO2 molecules
The number of oxygen atoms  2 x 3.01 x 1022
 x O atoms
Higher Grade Chemistry

4. Calculations for you to try.
Calculate the number of sodium ions in 1.00g of sodium carbonate.
The elementary particles  (Na+)2CO32- formula units
1 mole  x 1023 (Na+)2CO32- formula units
106g  x 1023 (Na+)2CO32- formula units
So g  1.00/106 x 6.02 x (Na+)2CO32- formula units
 x (Na+)2CO32- formula units
The number of Na+ ions  2 x 5.68 x 1021
 x 1022 Na+ ions
4. Calculate the number of protons in 0.1g of nitrogen gas?
The elementary particles  N2 molecules.
1 mole  x N2 molecules
28 g  x N2 molecules
So g  0.1/28 x 6.02 x C atoms.
 x N2 molecules
The number of N atoms  2 x 2.15 x 1022
The number of protons  7 x 2 x 2.15 x 1022
 x 1023.
Higher Grade Chemistry

5. Calculations for you to try.
5. A sample of the gas dinitrogen tetroxide, N2O4, contained x 1022oxygen atoms. What mass of dinitrogen tetroxide was present?
The elementary particles  N2O4 molecules
1 mole  x N2O4 molecules
1 mole  x x O atoms
 x O atoms
So x O atoms  mol of N2O4
2.408 x 1022
2.408 x 1024
 mol
1 mole of N2O4  g
So mole  g
Higher Grade Chemistry