Unit 4

Question 1

Ores

Answer 1

Rocks that contain minerals in concentrations high enough for economical extraction

Question 2

Panning

Answer 2

A process in which the rock or soil is placed in a shallow tray and then swirled in water. The less dense material floats alway and the denser material remains in the tray

Question 3

Calcium carbonate —> quicklime

Answer 3

Calcium carbonate is strongly heated: (thermal decomposition) (endothermic)
Calcium carbonate —> (heat) calcium oxide + carbon dioxide
CaCO3 —> CaO + CO2
—> takes place in a lime kiln

Observation:
A colourless gas is produced, which turns the limewater milky

Question 4

Calcium oxide —> slaked lime

Answer 4

The solid flakes and expands and eventually crumbles into calcium hydroxide
Calcium oxide + water —> calcium hydroxide (slaked lime)
CaO + H2O —> Ca(OH)2

Observation:
White solid dissolves

—> CaO and Ca(OH)2 are only slightly soluble. To obtain a clear solution, use filtration

Question 5

Limewater

Answer 5

Saturated / Dilute solution of calcium hydroxide
—> test for carbon dioxide ( turns from colourless to milky)

Question 6

Final stage: limewater

Answer 6

Calcium hydroxide + carbon dioxide —> calcium carbonate + water
Ca(OH)2 + CO2 —> CaCO3 + H2O

If bubbles for longer, the calcium carbonate redissolves
Calcium hydroxide + carbon dioxide(excess) + water —> calcium hydrogencarbonate (water soluble colourless solution)
Ca(OH)2 + CO2 —> Ca(HCO3)2 (aqueous solution)

Question 7

Test for carbonate

Answer 7

Metal carbonate + dilute acid —> salt+water+carbon dioxide

HCl dilute hydrochloric acid) —> metal chlorides CaCl2 (spectator ion Ca2+,Cl-)
HNO3 nitric acid —> metal nitrate Ca(NO3)2
H2SO4 sulphuric acid —> metal sulphate CaSO4

Observation:
Gas bubbles re given off / effervescence occurs
White solid dissolves
The test tube feels warm (exothermic)

Question 8

Weathering

Answer 8

A process where rock is dissolved, worn away or broken down into smaller and smaller pieces.

Question 9

Erosion (physical change)

Answer 9

Once the rock is weakened or broken down by weathering, it is ready for erosion. Erosion happens when weathered rock materials are moved to another place by wind, ice, water or gravity.

Question 10

Acid rain

Answer 10

When rainwater absorbs carbon dioxide in the air to form carbonic acid:
Water + carbon dioxide —> carbonic acid
H2O + CO2 —> H2CO3
The acid in the rainwater reacts with the calcium carbonate in the limestone to produce calcium hydrogencarbonate solution and this dissolves the limestone.

Calcium carbonate + carbonic acid —> calcium hydrogencarbonate solution (water soluble)
CaCO3 + H2CO3 —> H2(CO3)2