Suggested Answers to In-Text Activities and Unit-End Exercises

New 21st Century Chemistry

Suggested answers to in-text activities and unit-end exercises Topic 1 Unit 4

I n-text activities Library Search & Presentation (page 65) 1 Metal Name of ore Extraction method Aluminium bauxite electrolysis of the molten ore Copper copper pyrite heating the ore alone Lead galena heating the ore alone and then with carbon Iron haematite heating the ore with carbon Mercury cinnabar heating the ore alone

2 Aluminium is difficult to extract. It is extracted by electrolysis, which is an expensive method.

Discussion (page 71) Advantages • A new road is built for delivering the limestone. This also improves the transportation of the town. • The company provides jobs for local people. • There would be tax income for the town. • There is a new village hall built by big donations from the company. • The availability of limestone may lead to the development of other industries and hence the prosperity of the town. Disadvantages • The rock dug from the ground becomes waste. This causes pollution problems. • The blasting and the heavy traffic cause sound pollution. • Consumption of energy may lead to greenhouse effect.

Checkpoint (page 72) 1 a) Calcium hydroxide b) i) Heating calcium carbonate ii) Adding dilute hydrochloric acid to calcium carbonate iii) Adding water to calcium oxide

2 a) Use flame test. Both compounds give a brick-red flame. b) Add dilute hydrochloric acid to both compounds. Effervescence occurs for calcium carbonate.

There is no observable change for calcium hydroxide.

Unit-end exercise s (pages 7 5 - 80 ) 1

3 a) False Most metals exist as compounds in the Earth’s crust. b) False Sodium is extracted by electrolyzing its molten ore. c) True d) True e) False Marble is harder than limestone.

5 C

6 A Calcium carbonate is insoluble in water.

7 A carbon dioxide + calcium hydroxide  calcium carbonate + water

8 D

9 D

10 D 11 a) • Extracting iron from iron ore • As a material for the construction of road and buildings any one • To neutralize acidity in soil and water • To neutralize sulphur dioxide in flue gas from power stations • Making glass b) Earth movements may cause chalk to sink. Higher pressure and heat cause the chalk to turn into much harder limestone. The limestone deposit may stay below the Earth for a long time. Higher temperature and pressure may turn the limestone into marble.

12 a) i) Carbon dioxide ii) The gas turns limewater milky. b) i) Add water to calcium oxide. ii) calcium oxide + water  calcium hydroxide c) i) Add dilute hydrochloric acid to calcium carbonate. ii) Effervescence occurs. / Calcium carbonate dissolves in the dilute acid. iii) calcium carbonate + dilute hydrochloric acid  calcium chloride + water + carbon dioxide

13 a) Process 1 – filtration Process 2 – distillation b) Process 1

Process 2

c) Calcium carbonate

14 Carry out flame test to show the presence of calcium in the sample. A sample containing calcium will give a brick-red flame. Add dilute hydrochloric acid to the sample. A carbonate reacts with dilute hydrochloric acid to give carbon dioxide gas. The gas will turn limewater milky. The carbon dioxide gas can also be tested with a hydrogen carbonate indicator (which will change from red to yellow).