2. Chemists use the idea of the mole when comparing the number of particles of different substances.

3. How many atoms are there in 12 g of carbon (one mole)?

4. This is the number of atoms in 12 g of carbon or one mole of particles.

5. It is called the Avogadro constant.

6. If you started counting 220 million carbon atoms per second 85 million years ago, you might just have finished counting a mole of them about now.

7. 12 g of carbon contains 1 mole of carbon atoms, or 1 mol for short.

8. How many moles of sulphur atoms are there in 32 g of sulphur?

9. Notice that the mass of one mole is the equal to the relative atomic mass (or relative molecular mass) in grams.

10. So, how many moles of iron atoms are there in 56 g of iron?

11. If you know the A r or M r of a substance, you can easily work out the mass of one mole of that substance.

12. This is the relationship between moles, grams and A r or M r.

13. This 'magic triangle' might help you in calculations.

14. What is the amount in moles of carbon atoms in 6 g of carbon?

15. The mass in grams is 6.

16. The A r of carbon is 12.

17. There are 0.5 mol of carbon atoms in 6 g of carbon.

18. This is the relationship between moles, grams and A r or M r.

19. This 'magic triangle' might help you in calculations.

20. What is the mass of 2 moles of calcium carbonate, CaCO 3 ?

21. The M r of calcium carbonate is 100.

22. The amount in moles is 2.

23. 2 moles of calcium carbonate, CaCO 3, have a mass of 200 g.