Presentation based on moles and masses

1. Moles and masses

2. The Mole
• It is an amount of atoms/molecules.
• Exactly it is 6.0221 x 10
23
atoms or molecules, if we were able
to count them all.
• We don’t need to count them, we can weigh them instead.
• This is because it is the atomic/molecular mass, in grams.
• Atomic mass is abbreviated to RAM or Ar. Molecular mass can be
abbreviated to RFM (relative formula mass) or Mr.
• So 1 mole is 12g of carbon atoms, or 24g of magnesium atoms.

3. Formula mass
• If we had up the RAMs of all the atoms in a molecule, we have the
formula mass number or the relative formula mass, RFM
• E.g. H2O
• 1+1+16 = 18
• So 1 mole of water molecules, has a mass of …

4. Formula mass
• If we had up the RAMs of all the atoms in a molecule, we have the
formula mass number or the relative formula mass, RFM
• E.g. H2O
• 1+1+16 = 18
• So 1 mole of water molecules, has a mass of 18g

5. What is the mass of 1 mole
of …
CaCO3
NaCl
H2SO4
CuCl2
Na
• Number of moles = mass
relative mass
• Rearrange so,
• Mass =
• What is the mass of 3 moles of
CaCO3 ?
• What is the mass of 0.5 moles of
H2SO4?

6. • Balance the below equations:
1. Mg + O2  MgO
2. AgNO3 + MgCl2  AgCl + Mg(NO3)2

7. • Balance the below equations:
1. Mg + O2  MgO
2. AgNO3 + MgCl2  AgCl + Mg(NO3)2
ANSWERS
1. 2Mg + O2  2MgO
2. 2AgNO3 + MgCl2  2AgCl + Mg(NO3)2

8. 2Mg + O2  2MgO
This means that 2 moles of magnesium are reacting with 1 mole of
oxygen, to produce 2 moles of magnesium oxide.
Find the masses in g

9. 2Mg + O2  2MgO
This means that 2 moles of magnesium are reacting with 1 mole of
oxygen, to produce 2 moles of magnesium oxide.
Find the masses in g
2x24 + 16x2  2x(24+16)
48g + 32g  80g
80  80

10. 2Mg + O2  2MgO
48g + 32g  80g
48g of magnesium reacts with 32g of oxygen to produce 80g of
magnesium oxide.
What if we only had 1g of magnesium, how much magnesium oxide
would be produced?

11. 2Mg + O2  2MgO
48g + 32g  80g
48 48 48
1g 0.67 1.67g
So 1g of magnesium makes 1.67g of magnesium oxide
What if we had 2g of magnesium?

12. 2Mg + O2  2MgO
48g + 32g  80g
48 48 48
1g 0.67 1.67g
1x2 0.67x2 1.67x2
2 1.33g 3.33g
So 2g of magnesium makes 3.33g of magnesium oxide

13. How much magnesium chloride is produced
from 5g of magnesium?
• Mg + HCl  MgCl2 + H2
• Start by balancing the equation

14. How much magnesium chloride is produced
from 5g of magnesium?
• Mg + 2HCl  MgCl2 + H2
• 1 mole of magnesium reacts with 2 moles of hydrochloric acid to
produce 1 mole of magnesium chloride and 1 mole of hydrogen.
• Now we need to write the RFM under each formula and express it
in g

15. How much magnesium chloride is produced
from 5g of magnesium?
• Mg + 2HCl  MgCl2 + H2
• 24 + 2x36.5  (24 + 35.5 + 35.5) + (2x1)
• 24g + 73g  95g + 2g
• Now to get the masses involved where we have only 1g of Mg,
divide everything by 24

16. How much magnesium chloride is produced
from 5g of magnesium?
• Mg + 2HCl  MgCl2 + H2
• 24 + 2x36.5  (24 + 35.5 + 35.5) + (2x1)
• 24g + 73g  95g + 2g
• 24 24 24 24
• 1g + 3.04g  3.96g + 0.08g
• So 1g of magnesium produces 3.96g of magnesium oxide.
• What about 5g of magnesium? Multiply all by 5

17. How much magnesium chloride is produced
from 5g of magnesium?
• Mg + 2HCl  MgCl2 + H2
• 24 + 2x36.5  (24 + 35.5 + 35.5) + (2x1)
• 24g + 73g  95g + 2g
• 24 24 24 24
• 1g + 3.04g  3.96g + 0.08g
• 1x5 +3.04x5  3.96x5 + 0.08x5
• 5g + 15.2g  19.8g + 0.42g
• So 5g of magnesium produces 19.8g of magnesium chloride.

19. • RFM
• 24g magnesium makes 40g (24+16) of magnesium oxide
• For 1 g divide all by 24
• 1g of magnesium makes 40/24 = 1.67g of magnesium oxide

21. • RFM
• Iro(III)oxide  iron
• 112+48  112
• 160g  112g
• 160 tonnes  112 tonnes
• 160  112
• 160 160
• 1  0.7
• 1x300  0.7x300
• 300tonnes  210tonnes
• Answer = 210 tonnes of iron

23. • 138g of salicylic acid makes 180g of aspirin
• Divide all by 138 to get 1g
• 1g makes 180/138 = 1.30g
• Times all by 2
• 2g of salicylic acid makes 2.61g of aspirin

24. • RFM
• 2x (23+1+12 + 3x16)  12 + 2x16
• 168g  44g
• Divide by 168
• 1g  44/168 = 0.26
• Multiply by 11
• 11g  0.26x11 = 2.88g
• 11g of sodium hydrogencarbonate makes 2.88 g of carbon dioxide

25. • RFM
• 63.5 + 12 + 3x16  63.5 + 2x35.5
• 123.5  134.5
• Divide all by 134.5 to get 1g of copper chloride
• 123.5/134.5 = 0.92  1
• Multiply by 11
• 0.92x11 = 10.1 g  11g
• 10.1g of copper carbonates makes 11g of copper chloride.