Vidaara.orgClass 10 · Chemistry
CodeVID-C10-03-T3-01
Assignment — Extraction of Metals & Corrosion
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.
- Write balanced equations wherever asked. 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.
The earthy impurity present in an ore is called:
- A.flux
- B.slag
- C.gangue
- D.ore
2.
Roasting is carried out on which type of ore?
- A.oxide
- B.sulphide
- C.carbonate
- D.chloride
3.
Which metal is extracted by electrolysis of its molten oxide?
- A.copper
- B.iron
- C.aluminium
- D.zinc
4.
Rust is chemically:
- A.FeO
- B.Fe₂O₃·xH₂O
- C.Fe₃O₄
- D.FeS
5.
Brass is an alloy of copper and:
- A.tin
- B.zinc
- C.nickel
- D.carbon
Section B — Short Answer (2 marks)
3 × 2 = 6 marks
6.
Write the equation for the reduction of zinc oxide with carbon.
7.
Why does silver not occur in the free state as commonly as gold, yet both are found native?
8.
State two methods used to prevent the rusting of iron.
Section C — Short Answer (3 marks)
2 × 3 = 6 marks
9.
Explain why highly reactive, moderately reactive and least reactive metals need different extraction methods.
10.
Describe the process of electrolytic refining of copper.
Section D — Long Answer (5 marks)
1 × 5 = 5 marks
11.
Trace the extraction of zinc from zinc blende (ZnS): enrichment, roasting, reduction and refining, writing the equations. Then explain what corrosion is and how alloying helps.
Answer Key
Section A — Multiple Choice Questions
- (C) gangue
- (B) sulphide
- (C) aluminium
- (B) Fe₂O₃·xH₂O
- (B) zinc
Section B — Short Answer (2 marks)
- ZnO + C → Zn + CO (carbon reduces the oxide to the metal).
- Both silver and gold are very low in the reactivity series, so they occur native; however silver is slightly more reactive than gold, so it is also found in combined form such as sulphides and tarnishes to Ag₂S.
- Painting/oiling/greasing the surface, and galvanisation (coating with zinc); tin- and chromium-plating and alloying are also used.
Section C — Short Answer (3 marks)
- Highly reactive metals (K, Na, Ca, Mg, Al) hold their compounds so strongly that only electrolysis frees them. Moderately reactive metals (Zn, Fe, Pb, Cu) are converted to oxides by roasting/calcination and then reduced by carbon. Least reactive metals (e.g. Hg) can be obtained by heating their oxides alone (2HgO → 2Hg + O₂).
- The impure copper is made the anode, a thin strip of pure copper the cathode, and copper sulphate solution the electrolyte. On passing current, copper dissolves from the anode and pure copper deposits on the cathode; impurities settle as anode mud.
Section D — Long Answer (5 marks)
- Enrichment of zinc blende is done by froth flotation. Roasting: 2ZnS + 3O₂ → 2ZnO + 2SO₂. Reduction of the oxide with carbon: ZnO + C → Zn + CO. The crude zinc is purified by electrolytic refining. Corrosion is the slow eating away of a metal by air and moisture (rusting of iron gives Fe₂O₃·xH₂O). Alloying (e.g. making stainless steel from iron, chromium and nickel) changes the surface chemistry and physical properties so the metal resists corrosion and is harder and stronger.
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