Class 10 Metallurgy Mock Test (ICSE)

Topics in Metallurgy

• Occurrence of metals
• Activity series
• Extraction of aluminium
• Alloys and their uses
• Corrosion

Metallurgy practice questions with answers

1. Q1Multiple choice·1 mark
   During the electrolytic extraction of aluminium by Hall-Heroult's process, cryolite is added to alumina primarily to:

   1. (a)Act as a chemical reducing agent
   2. (b)Increase the chemical purity of bauxite
   3. (c)Lower the fusion temperature of the mixture
   4. (d)Prevent the graphite anode from burning away
   Show answer and step marks

   1. Correct option: (c) Lower the fusion temperature of the mixture+1

   Answer: (c)
2. Q2Multiple choice·1 mark
   The alloy of copper consisting of copper and zinc, which is commonly used for making hardware and decorative items, is:

   1. (a)Bronze
   2. (b)Duralumin
   3. (c)Brass
   4. (d)Invar
   Show answer and step marks

   1. Correct option: (c) Brass+1

   Answer: (c)
3. Q3Multiple choice·1 mark
   Which of the following is a chief oxide ore of aluminium?

   1. (a)Calamine
   2. (b)Galena
   3. (c)Bauxite
   4. (d)Iron pyrites
   Show answer and step marks

   1. Correct option: (c) Bauxite+1

   Answer: (c)
4. Q4Short answer·2 marks
   State two distinct methods used for the prevention of rusting of iron, briefly explaining how each method works.
   Show answer and step marks

   1. First method, any one of: galvanisation (coating with zinc); painting; oiling or greasing; electroplating or tinning; alloying (e.g. stainless steel); sacrificial protection with a more reactive metal such as magnesium; or any other valid method.+0.5
   2. How the first method works, the matching one of: a coating (paint, oil, grease, zinc or tin) keeps moisture and oxygen away from the iron; a more reactive metal (zinc, magnesium) corrodes in preference to iron; alloying makes the iron itself resist rusting; or the working of any other valid method.+0.5
   3. Second method, a different one from the same list.+0.5
   4. How the second method works, the matching mechanism from the same list.+0.5

   Answer: Any two of: galvanisation (zinc coat shuts out air and moisture and corrodes in preference to iron), painting, oiling or greasing (a barrier against air and moisture), electroplating or tinning (a protective metal coat), alloying such as stainless steel, sacrificial protection with magnesium.
5. Q5Short answer·2 marks
   State the two essential conditions required for the rusting of iron and name the process used to prevent it by coating iron with a layer of zinc.
   Show answer and step marks

   1. First condition: presence of moisture (water).+0.5
   2. Second condition: presence of oxygen (air).+0.5
   3. Process: Galvanisation.+1

   Answer: Conditions: Moisture and oxygen; Process: Galvanization
6. Q6Long answer·4 marks
   (a) Define metals found in the native state. Name one metal that occurs predominantly in the native state and one metal that occurs as a sulphide ore. (b) What is the difference between a mineral and an ore? Give a reason why all ores are minerals, but all minerals are not ores.
   Show answer and step marks

   1. (a) Metals found in the uncombined or free state in nature due to their least reactive (chemically inactive) nature are called native state metals.+1
   2. (a) Native metal, any one of: gold ($\text{Au}$); platinum ($\text{Pt}$); or any other valid metal found mainly in the free state.+0.5
   3. (a) Metal occurring as a sulphide ore, any one of: zinc (zinc blende, $\text{ZnS}$); lead (galena, $\text{PbS}$); mercury (cinnabar, $\text{HgS}$); copper (copper glance, $\text{Cu}_2\text{S}$); or any other valid metal.+0.5
   4. (b) Minerals are naturally occurring compounds of metals obtained from the earth's crust. Ores are those minerals from which metals can be extracted profitably and conveniently.+1
   5. (b) All ores are minerals because every ore is a naturally occurring compound of a metal, but all minerals are not ores because a metal cannot be extracted profitably from every mineral.+1

   Answer: (a) Native metals occur free (uncombined) in nature because they are unreactive; e.g. gold; zinc occurs as the sulphide ore zinc blende (ZnS). (b) A mineral is a naturally occurring metal compound; an ore is a mineral from which the metal can be extracted profitably. Every ore is a mineral, but a metal cannot be extracted profitably from every mineral, so not all minerals are ores.

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