4: Rocks and Minerals

Question 1

What is the name of the ore containing aluminium oxide?

Answer 1

Bauxite

Question 2

What is the name of the ore containing mercury sulphide?

Answer 2

Cinnabar

Question 3

What is the name of the ore containing iron oxide?

Answer 3

Haematite

Question 4

What is the name of the ore containing copper carbonate?

Answer 4

Malachite

Question 5

List two metal compounds from which the metal can be separated through heating the ore alone.

Answer 5

Mercury sulphide and silver oxide

Question 6

What is limestone?

Answer 6

Limestone is one of the most common types of rock found on the surface of the Earth. It is a rock composed largely of the mineral calcite, which is composed of calcium carbonate.

Question 7

List 5 usages of limestone.

Answer 7

1. For construction of buildings and roads
2. Making glass
3. Neutralising sulphur dioxide in flue gas from power stations
4. Making cement
5. Neutralising acidity in soil and lakes

Question 8

List 2 usages of quicklime.

Answer 8

1. Making steel from iron
2. Neutralising acidity in soil

Question 9

List 2 usages of slaked lime.

Answer 9

1. Neutralising acidity in soil and lakes
2. Making bleaching powder

Question 10

What is the word equation for the reaction from limestone to quicklime?

Answer 10

Calcium carbonate ^heat -> calcium oxide + carbon dioxide

Question 11

What is the word equation for the reaction from quicklime to slaked lime and limewater?

Answer 11

Calcium oxide + water -> calcium hydroxide

Question 12

What is the word equation for the reaction from clear limewater to milky limewater?

Answer 12

Calcium hydroxide + carbon dioxide -> calcium carbonate + water

Question 13

What is the word equation for the reaction of limewater turning from milky to clear?

Answer 13

Calcium carbonate + water + carbon dioxide -> calcium hydrogencarbonate

Question 14

What is the word equation for the reaction between hydrochloric acid and limestone?

Answer 14

Calcium carbonate + dilute hydrochloric acid -> calcium chloride + water + carbon dioxide

Question 15

Why does the size of limestone chips shrink when dilute hydrochloric acid is added to them?

Answer 15

Calcium carbonate reacts with dilute hydrochloric acid to produce calcium chloride, which is soluble in water. Therefore, the size of calcium carbonate appears to shrink.

Question 16

What is the definition of effervescence?

Answer 16

Bubbling / fizzing

Question 17

What is the test for metal carbonate?

Answer 17

1. Add the solid into some dilute acid.
2. Stopper the tube immediately with a stopper connected with a delivery tube. Put the other end of the delivery tube into a test tube of limewater.
3. Observe if there is any colour change for the limewater.
   If the solid is a metal carbonate, there should be effervescence and the limewater will turn from colourless to milky.

Question 18

What is the relationship between chalk, limestone, and marble?

Answer 18

Chalk is formed when calcium carbonate from the shells of sea creatures sink to the bottom and receive pressure and heat.
Higher pressure and heat causes chalk to turn into much harder limestone.
If buried limestone in an active part of Earth’s crust suffers huge increases in pressure and temperature, it turns into marble.
Among the three rocks, chalk is the softest while marble is the hardest.

Question 19

What is weathering?

Answer 19

Weathering is the process where rock is dissolved, worn away or broken down into smaller and smaller pieces. Once the rock has been weakened and broken up by weathering, it is ready for erosion. Erosion happens when weathered rock materials are moved to another place by ice, water, wind, or gravity.

Question 20

How are limestone caves formed?

Answer 20

1. When rain falls, rainwater absorbs carbon dioxide in the air to form carbonic acid
   water + carbon dioxide -> carbonic acid
2. The acid in the rainwater reacts with calcium carbonate in the limestone to produce calcium hydrogencarbonate solution, and thus dissolves the limestone.
   calcium carbonate + carbonic acid -> calcium hydrogencarbonate
3. Rainwater slowly dissolves the limestone along the cracks in the rock. Over millions of years, underground limestone caves are formed.

Question 21

What is the procedure of the chloride test?

Answer 21

1. Dissolve the sample in water.
2. Add excess dilute nitric acid.
3. Add an aqueous solution of silver nitrate.
   A white precipitate will be produced if the solid sample is a chloride.