Edexcel IGCSE Chemistry Chapter 22, pages 185 - 186 ANSWERS
Remaining questions will be addressed at a later stage.
1. 69 x 0.602 = 41.5
71 x 0.398 = 28.3
69.8
2. Total abundance = 100 + 5.10 + 3.36 = 108.46
28 x (100/108.46) = 25.8
29 x (5.10/108.46) = 1.4
30 x (3.36/108.46) = 0.9
28.1
3. a) Relative atomic mass is the weighted average mass of the isotopes of an element.
b) RAM Cu: 63 x 0.691 = 43.5
65 x 0.309 = 20.1
63.6
RAM S: 32 x 0.950 = 30.4
33 x 0.0076 = 0.3
34 x 0.0422 = 1.4
35 x 0.0002 = 0.0
32.1
Relative formula mass of CuS = 63.6 + 32.1 = 95.7
4. a) CO2 = 12 + (2 x 16) = 44
b) (NH4)2SO4 = 2(14 + 4 x 1) + 32 + 4 x 16 = 132
c) Na2CO3.10H2O = (2 x 23 + 12 + 3 x 16) + 10(2 x 1 + 16)
= 106 + 180 = 286
d) Cr2(SO4)3 = 2 x 52 + 3(32 + 4 x 16) = 104 + 96 = 200
e) (NH4)2SO4.FeSO4.6H2O
= 2(14 + 4 x 1) + 32 + 4 x 16 + 56 + 32 + 4 x 16 + 6(2 x 1 + 16)
= 284 + 108 = 392
Edexcel IGCSE Chemistry Chapter 22, pages 185 - 186 ANSWERS
Remaining questions will be addressed at a later stage.
5. a) RAM carbon = 12 x 3 = 36
RFM propane = 3 x 12 + 8 x 1 = 44, so % by mass of carbon = 36/44 x 100 = 82%
b) RFM hydrated magnesium sulfate crystals = (24 + 32 + 4 x 16) + 7(2 x 1 + 16)
= 120 + 126 = 246
So % by mass of water = 126/246 x 100 = 51%
6. a) RFM urea = 12 + 16 + 2(14 + 2 x 1) = 60, of which 28 is N, so 28/60 x 100 = 47%
b) RFM potassium nitrate = 39 + 14 + 3 x 16 = 101, of which 14 is N, so 14/101 x 100 = 14%
c) RFM ammonium nitrate = (14 + 4 x 1) + (14 + 3 x 16) = 80,
of which 28 is N, so 28/80 x 100 = 35%
d) RFM ammonium sulfate = 2(14 + 4 x 1) + 32 + 4 x 16 = 132,
of which 28 is N, so 28/132 x 100 = 21%
7. a) 207 + 2(14 + 3 x 16) = 331g
b) 1 mole methane = 16g, so 4.30 x 16g = 68.8g
c) 1 mole sodium carbonate = 286g, so 0.24 x 286g = 68.64g
8. a) 1 mole of copper sulfate crystals = 250g, so 50g/250g = 0.2 moles
b) 1 mole of iron = 56g, so 1,000,000g/56g = 17857 moles
c) 1 mole sulfur dioxide = 64g, so 0.032g/64g = 0.0005 moles
9. a) 1 mole sodium chloride = 58.5g, so 4 x 58.5g = 234g
b) 1 mole calcium hydroxide = 76g, so 37g/76g = 0.48 moles
c) 1 mole calcium = 40g, so 1000g/40g = 25 moles
d) 1 mole copper oxide = 80g, so 80g x 0.125 moles = 10g
e) 4g/0.1 mol = 40g/mol
f) RFM is its molar mass (M), so 1g/0.004 mol = 250g/mol
m
n M