1. The Mole Concept and Avogadro's constant Topic 4.4

2. The Mole-demystified Another definition-”Amount of substance…”- more like chemistry ! Ream of paper (500) Dozen of eggs (12) Pair of socks (2)

3. The mole & coins! Suppose you had to count a vast number of coins What is the quickest method? If the mass of a certain number of coins is known, the total number can be weighed and then the amount can be calculated.

4. The Mole-demystified 2 Quantity of 6.02x10 23 Why this magic number? It is the number of particles present in exactly 12 grams of the isotope carbon-12 Called the Avogadro Constant

5. The mole If you weigh out 12g of carbon-12, you will get 6.02x10 23 of carbon atoms

6. The mole All elements measured relative to carbon-12 Amount of substance (mol)= number of particles/6.02 x 10 23 mol -1 Number of particles= amount of substance (mol) x 6.02 x 10 23 mol -1 Mole is the same number regardless of the representative particle: atom, molecule, ion, electron

7. The mole

8. Example 1 Calculate the number of molecules of water in 0.01mol of water Number of water molecules=0.01mol x 6 x 10 23 mol -1 = 6 x 10 21 How many carbon atoms are there in 0.02 mol of carbon dioxide? How many oxygen atoms are there in 0.02 mol of carbon dioxide?

9. Molar Mass Molar mass is the mass of 1 mole of the substance Number of moles=mass in g/mass of 1 mole in g A mole of carbon atoms, C, has a mass of 12g A mole of hydrogen atoms, H, has a mass of 1g BUT a mole of hydrogen molecules has a mass of 2g

10. Molar mass- example Calculate the molar mass of aluminium sulfate, Al 2 (SO 4 ) 3 2 x Al= 2 x 26.98g/mol= 53.96g/mol +3 x S= 3 x 32.06g/mol= 96.18g/mol +12 x O= 12 x 16.00g/mol=192.00g/mol Molar mass= 342.14g/mol

11. Relative atomic mass, Relative atomic mass- the weighted average mass (according to relative abundances) of all the naturally occurring isotopes of an element compare with an atom of the carbon-12 isotope, which has a mass of exactly 12

12. Amount of substance vs mass