Unit 13

Question 1

Corrosion (DEFINITION)

Answer 1

the deterioration of a metal caused by chemical interaction with oxygen, moisture or other substances in the environment

Question 2

Conditions for rusting to happen

Answer 2

Both oxygen and water are needed

Question 3

Factors that speed up the process of rusting

Answer 3

1. Presence of ionic substance
   The rusting process speed up if water present contains ionic substances like NaCl.

Question 4

EXAM TYPE: Outline an experiment, with explanation, to show that both air and water are necessary for rusting to occur.

Answer 4

My Ans:
Tube A contains anhydrous calcium chloride which absorbs moisture from the air inside the tube. The iron nail is exposed to only dry air.
Tube B contains distilled water which is boiled to drive away any dissolved oxygen. The layer of oil on the water surface prevents oxygen from dissolving into the water. The iron nail is exposed to only water.
The iron nail in the tube C is exposed to air (oxygen) and water.
—> After several days, the iron nails in tubes A and B show no signs of rusting, but the iron nail in tube C has rust on it.
- the experimental results show that both air (oxygen) water are needed for iron to rust.

Question 5

EXAM TYPE: Explain why further corrosion in iron but not aluminium.

Question 6

Chemical Nature of Rusting

Answer 6

Iron (III) oxide Fe2O3·xH2O

Question 7

Rust indicator

Answer 7

A mixture of
- potassium hexacyanoferrate (III)
- phenolphthalein

Question 8

Rust indicator

Answer 8

A mixture of
- potassium hexacyanoferrate (III)
- phenolphthalein