CHAPTER 6 PAGE 73

COMPLETE CHEMISTRY FOR CAMBRIDGE IGCSE: ANSWERS

EDUCATALYST 1

CHAPTER 6 USING MOLES

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1 6.02 × 1023 atoms 2 6.02 × 1023 molecules 3 Avogadro constant 4 a. 1 g b. 127 g c. 35.5 g d. 71 g 5 a. 32 g b. 64 g 6 138 g 7 a. 9 moles


EDUCATALYST 2

b. 3 moles 8 a. 6.02 × 1023sodium ions b. 35.5 g

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1 a. magnesium + oxygen → magnesium oxide b. 2 moles c i. 32 g ii. 8 g 2 a. copper(II) carbonate → copper(II) oxide + carbon dioxide

b. CuCO3 124 g, CuO 80 g, CO2 44 g

C i. 11 g

ii. 20 g


EDUCATALYST 3

PAGE 77 1 room temperature and pressure (20°C and 1 atmosphere) 2 the volume occupied by 1 mole of the gas molecules: 24 dm3 3 24 dm3 4 a. 168 dm3 b. 12 dm3 c. 0.024 dm3 (24 cm3) 5 a. 12 dm3 b. 2.4 dm3 6 a. 12 dm3 b. 12 dm3 7 a. 12 dm3


EDUCATALYST 4

b. 6 dm3

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1 a. 1 mole b. 1 mole 2 a. 2 mol / dm3

b. 1.5 mol / dm3

3 a. 0.5 dm3 (500 cm3)

b. 0.005 dm3 (5 cm3) 4 a. 20 g

b. 0.5 g

5 a. 0.5 moles per litre b. 0.25 moles per litre


EDUCATALYST 5

PAGE 81 1 a. 4 b. 4 2 found by experiment 3 FeS 4 SO3

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1 MgCl2 2 AlF3 3 The empirical formula gives the simplest ratio in which atoms combine; the molecular formula gives the exact numbers of atoms in the molecule. They may be the same, for example for CH4. 4 CH 5 C2H4


EDUCATALYST 6

6 a. C7H16 b. C7H16 7 P4O6

PAGE 85 1 a. The actual amount obtained, given as a % of the theoretical amount (which is calculated from the equation) b. The mass of pure substance in the product, given as a % of the total mass of the product 2 76.7% 3 63% 4 172 g 5 88%


EDUCATALYST 7

PAGE 86 Extended 1 a. iron(III) oxide + carbon monoxide →iron + carbon dioxide b. 160 c. 2000 moles d. 2 moles e. 4000 moles f. 224 kg 2 a. calcium carbonate → calcium oxide + carbon dioxide b. 0.5 moles c. i. 11.2 g ii. 8.8 g iii. 4.8 dm3 or 4800 cm3


EDUCATALYST 8

3 a. i. 4 moles ii. 19 moles b. 4.75 moles c. 114 dm3 d. 227 g e. 502.2 dm3 f. A small amount of liquid produces a very large volume of gas. This creates a massive pressure wave, which causes damage.

PAGE 87 Extended 4 a. 0.5 moles b. 25 cm3


EDUCATALYST 9

c. i. 75 cm3 ii. 50 cm3 5 a. 1.4 g b. 0.025 moles c. 0.025 moles d. Fe + H2SO4 → FeSO4 + H2; Fe2+ e. 0.6 dm3 6 a. 106.5 g b. 3 moles c. 1 mole d. AlCl3 e. 0.1 mol / dm3


EDUCATALYST 10

7 a. 45.5 cm3 b. 41.7 cm3 c. 62.5 cm3 8 a. P2O3 b. 41.3 g c. P4O10 d. It could be P4O6 to match the other oxide (or P2O3). 9 a. Zn3P2 b. 24.1% 10 a. 64 g b. 4 moles c. 2 moles


EDUCATALYST 11

d. MnO2 e. 632.2g 11 The missing molecular formulae are: a. N2H4 b. C2N2 c. N2O4

d. C6H12O6 12 a. carbon and hydrogen b. CH2 c. A is C3H6 and B is C6H12. 13 a. 217 g b. 20.1 g of mercury, 1.6 g of oxygen c. 94.5 %


EDUCATALYST 12

14 a. 0.0521 moles b. 4.375 g c. 87.5%

CHAPTER 6 PAGE 73

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