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Home , Alnico, Amalgam (chemistry), Duralumin, Magnalium

CHAPTER 7 METALLURGY EXERCISE 7D Question 1: Explain the following: (a) is used to cover so as to prevent rusting of iron. Why? (b) In construction work, why is the of – used rather than pure aluminium? Solution 1 (a) Zinc is more electropositive than iron, gets oxidized and saves iron. Also zinc forms protective layer of ZnO on iron. This layer is sticky and impervious in nature and protects the iron metal underneath from rusting. (b) In construction work, the alloy of aluminium–duralumin is used rather than pure aluminium because of the following reasons: a) Duralumin is lighter and strong, but aluminium is light and not strong. b)Duralumin is unaffected by moist air, while aluminium gets affected by moist air. c) Duralumin is corrosion-resistant, while aluminium can undergo corrosion.

Question 2: What is an alloy? How do properties of an alloy differ from its constituents? Solution 2 Alloy is a homogeneous mixture of two or more or of one or more metals with certain non-metallic elements. The properties of alloys are often greatly different from those of the components. For example: a) is too soft to be used without small percentage of . b) A low percentage of molybdenum improves the toughness and wear resistance of steel. c) Bell metal is more sonorous than copper or . d) an alloy of aluminium, and can lift 60 times its own mass. e) These added elements improve hardness, wear resistance, toughness and other properties.

Q 3: Both Brass and bronze contain copper as major constituents. Name other elements in these alloys. Solution 3: The other element in Brass is Zinc. The other elements in Bronze are Tin and Zinc. Q 4: Name an alloy of: (a) Aluminium used in aircraft construction. (b) used in electrical wiring or electrical work in joining metals. (c) Copper in electrical appliances or household vessels. (d) Zinc used in simple voltaic cells.

Solution 4: (a) Duralumin (b) Solder (c) Brass (d) Zinc Question 5: What is amalgam? State its use with an example. Solution 5: An alloy of with a number of metals such as , zinc, gold and is known as amalgam. Dental amalgam is a mixture of mercury and a silver tin alloy. Q 6 (a) State two properties of brass that render it more useful for some purposes than its components. (b) A metal which forms a liquid alloy at ordinary temperature.

Solution 6: (a) Two properties of brass that make it more useful than its components are: (i) It is malleable and ductile. (ii) It resists corrosion. (iii) Can be easily cast. (b) A metal which forms a liquid alloy at ordinary temperature is sodium.(). Question 7: Name the constituents of: (a) Duralumin (b) Solder (c) Bronze (d) Brass Solution 7: The constituents of (a) Duralumin are aluminium (95%), copper (4%), (0.5%) and (0.5%). (b) Solder are lead (50%) and tin (50%). (c) Bronze are copper (80%), tin (18%) and zinc (2%). (d) Constituents of brass: 60–70% Cu and 40–30% Zn Question 8: Name the following: (a) A metal which is liquid at room temperature. (b) A metal which is always present in the amalgam. (c) The compound formed by the reaction between calcium oxide and silica. (d) A compound which is added to lower the fusion temperature of the electrolytic bath in the extraction of aluminium. (e) Name an allotrope of a non-metal that allows electricity to pass through it.

Solution 8: (a) Mercury (b) Mercury metal is always present in the amalgam. c) (d) Cryolite (e) Graphite

Q 9: (a) Brass is an alloy of: (i) Copper and tin (ii) Copper and zinc (iii) Zinc and lead (iv) Lead and tin (b) Steel is an alloy of iron and: (i) Nickel (ii) Zinc (iii) Carbon (iv) Aluminium Solution 9: (ii) Copper and zinc (iii) Carbon Question 10: Name the alloy used for the following purposes: (a) Making electric circuits (b) Making medals (c) Making parts of watches (d) Surgical instruments (e) Aircraft Solution 10: (a) Making electric circuits: Nichrome (b) Making medals: Bronze (c) Making parts of watches: Brass (d) Surgical instruments: Stainless steel (e) Aircraft: Duralumin and