1. The Mole

2. What is a mole? 1 mole is the amount of substance that
contains as many particles (atoms,
molecules) as there are in 12.0 g of C-12.

3. The Mole 1 dozen = 12 1 gross = 144 1 ream = 500 1 mole = 6.02 x 1023
There are exactly 12 grams of carbon-12 in one mole of carbon-12.

4. Avogadro’s number and the mole – periodic table
All the elements described on the periodic table has the mass number equivalent to the quantity of 1 mol
Carbon-12 is quite significant – all other elements are standardised against carbon-12.

5. Molar mass
The mass of one mole of any substance is known as its molar mass (symbol M), where the molar mass is equal to the relative atomic (or molecular or formula) mass measured in units of grams per mole (g mol–1).

6. Calculating RMM
The relative molecular mass of a molecule is therefore the sum of the relative atomic masses of the constituent elements, as given in the molecular formula. The symbol for RMM is Mr.
Worked example 1
Determine the relative molecular mass of the following molecules.
a Water (H2O)
b Methane (CH4)
c Sulfuric acid (H2SO4)

7. Calculating RMM Worked example 1
Determine the relative molecular mass of the following molecules.
a Water (H2O)
b Methane (CH4)
c Sulfuric acid (H2SO4)
Solution
a Mr(H2O) = = 18.0
b Mr(CH4) = = 16.0
c Mr(H2SO4) = 2 X X 16.0 = 98.1
Solution
a Mr(H2O) = = 18.0
b Mr(CH4) = = 16.0
c Mr(H2SO4) = = 98.1

8. Calculating RFM Worked example 2
Determine the relative formula mass of the following ionic compounds.
a Sodium chloride (NaCl)
b Magnesium hydroxide (Mg(OH)2)
c Aluminium carbonate (Al2(CO3)3)
Solution
a RFM(NaCl) = = 58.5
b RFM(Mg(OH)2) = ( ) 2 = 58.3
c RFM(Al2(CO3)3) = ( ) 3 = 234
The technique employed to calculate relative formula mass (RFM) is
identical to that used for relative molecular mass. The only difference is that
RFM is used for ionic compounds, which cannot be described as molecules.

9. Avogadro’s number is called “Avogadro’s Number”
Avogadro’s number describes how many atoms are there within a mole.
There is Avogadro’s number of particles in a mole of any substance.

10. Mass and mole
Because of the relationship of the mole, we can write that
n = number of moles
m = mass (g)
M = molar mass ( g )

11. Sample Question
How many atoms are there within 1.5 mol of carbon?

12. Calculating number of particles
How many atoms are there within 1.5 mol of carbon?

13. Sample Question
How many moles is atoms worth?

14. Changing mass to mol
In a 6 g solution of pure carbon, how many carbon atoms does it contain?

15. Molar mass
The molecular mass (m) of a substance is the mass of one molecule of that substance.

16. Changing mol to mass
With a solution that has 2 mol of lithium, where the molecular mass of lithium is 7, find the actual mass of the solution

17. Practise Give the molar masses of the following compounds:
1. sodium fluoride -NaCl
2. potassium hydroxide -KOH

18. Answer (1 x 23 ) + (1 x 19 ) = 42 grams/mole of sodium fluoride
2. (1 x 39) + (1 x 1) + (1 x 16) = 56 grams/mole of potassium hydroxide