Vidaara.orgClass 10 · Chemistry
CodeVID-C10-01-T3-01
Assignment — Oxidation, Reduction & Everyday Effects
Name: ____________________
Roll No.: __________
Date: ____________
General Instructions
- All questions are compulsory.
- Section A carries 1 mark each, Section B 2 marks, Section C 3 marks and Section D 5 marks.
- Show all working for Sections B, C and D. Only final answers are given at the end — for full solutions, raise your doubts with your teacher.
Section A — Multiple Choice Questions
5 × 1 = 5 marks
1.
Gain of oxygen by a substance is called:
- A.reduction
- B.oxidation
- C.corrosion
- D.displacement
2.
In CuO + H2 → Cu + H2O, the oxidising agent is:
- A.H2
- B.Cu
- C.CuO
- D.H2O
3.
The reddish-brown substance formed when iron rusts is mainly:
- A.iron sulphide
- B.hydrated iron(III) oxide
- C.iron carbonate
- D.iron chloride
4.
Stainless steel resists corrosion because iron is alloyed with:
- A.copper and tin
- B.chromium and nickel
- C.lead and zinc
- D.carbon only
5.
Antioxidants are added to food packets to prevent:
- A.rusting
- B.rancidity
- C.combustion
- D.neutralisation
Section B — Short Answer (2 marks)
3 × 2 = 6 marks
6.
Define oxidation and reduction in terms of oxygen and hydrogen.
7.
In ZnO + C → Zn + CO, name the substance oxidised and the substance reduced.
8.
State two methods of preventing the rusting of iron.
Section C — Short Answer (3 marks)
2 × 3 = 6 marks
9.
What is rancidity? Explain three ways in which food manufacturers prevent it.
10.
Explain why the reaction CuO + H2 → Cu + H2O is a redox reaction.
Section D — Long Answer (5 marks)
1 × 5 = 5 marks
11.
Define corrosion. Describe the conditions needed for the rusting of iron, state two harmful effects of corrosion, and explain two methods used to prevent it.
Answer Key
Section A — Multiple Choice Questions
- (B) oxidation
- (C) CuO
- (B) hydrated iron(III) oxide
- (B) chromium and nickel
- (B) rancidity
Section B — Short Answer (2 marks)
- Oxidation is the gain of oxygen or loss of hydrogen by a substance; reduction is the loss of oxygen or gain of hydrogen.
- Carbon is oxidised to CO (gains oxygen); zinc oxide is reduced to zinc (loses oxygen).
- Any two of: painting, oiling/greasing, galvanisation (zinc coating), electroplating, or alloying to make stainless steel.
Section C — Short Answer (3 marks)
- Rancidity is the oxidation of fats and oils in food, producing a bad smell and taste. It is prevented by adding antioxidants, by packing food in air-tight containers, and by flushing packets with nitrogen (or refrigerating the food) so that oxygen cannot reach it.
- CuO loses oxygen and is reduced to Cu, while H₂ gains oxygen and is oxidised to H₂O. Since oxidation and reduction occur together in the same reaction, it is a redox reaction.
Section D — Long Answer (5 marks)
- Corrosion is the slow eating away of a metal by air, moisture or chemicals on its surface; the rusting of iron is its commonest form. Conditions for rusting: both oxygen (from air) and water (moisture) must act on the iron together; removing either prevents rust. Harmful effects: it weakens structures such as bridges, railings and car bodies, and causes large economic losses by destroying useful metal articles. Prevention: (1) galvanisation — coating iron with a layer of zinc, which keeps out air and moisture and corrodes preferentially; (2) painting, oiling or greasing the surface to form a barrier; alloying to make stainless steel is another effective method.
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