Combustion and rusting — KCSE Chemistry

KCSE Chemistry · 61 practice questions · 4 syllabus objectives

17 easy24 medium20 hard

What You'll Learn

Key learning outcomes for this topic, aligned to the KNEC KCSE syllabus.

Distinguish between complete and incomplete combustion and state the conditions and products of each

Describe the conditions necessary for rusting of iron and write the equation for rust formation

Describe methods of preventing rusting and explain the chemistry involved in each method

Combustion and rusting

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easySHORT ANSWER2 marks

State the chemical equation for the formation of rust from iron. (2 marks)

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Part (a) — 2 marks

4Fe + 3O2 + 6H2O → 4Fe(OH)3 (2 mks)

easySHORT ANSWER2 marks

Name two environmental conditions that promote the rusting of iron. (2 marks)

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Part (a) — 2 marks

Presence of moisture (water) (1 mk)

Presence of oxygen (air) (1 mk)

easySHORT ANSWER4 marks

State three methods of preventing rusting of iron and briefly explain the chemistry behind each method. (4 marks)

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Part (a) — 3 marks

Galvanising (zinc coating) (1 mk)

Painting (1 mk)

Oiling or greasing (1 mk)

Part (b) — 1 mark

Galvanising provides sacrificial protection as zinc corrodes preferentially, protecting iron (1 mk)

Write the chemical equation for the formation of rust from iron. (2 marks)

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