Metallurgy
Short Questions
1. What is metallurgy?
Answer : Metallurgy is the science and technology of extracting metals from their ores and purifying them for use.
2. What are the physical states of metals at room temperature?
Answer : Most metals are solid, except mercury and gallium, which are liquid.
3. Which property allows metals to be drawn into wires?
Answer : Ductility allows metals to be drawn into wires.
4. What is the property of metals that produces a sound when struck?
Answer : Sonority is the property that produces a sound when metals are struck.
5. Which nonmetal is lustrous?
Answer : Iodine is a lustrous nonmetal.
6. Which nonmetal is the hardest natural substance?
Answer : Diamond, an allotrope of carbon, is the hardest natural substance.
7. What are electropositive elements?
Answer : Metals are electropositive elements as they lose electrons to form positively charged ions.
8. Which metals react with cold water to liberate hydrogen gas?
Answer : Sodium and potassium react with cold water to liberate hydrogen gas.
9. What is the reactivity series of metals?
Answer : It is the arrangement of metals in decreasing order of their reactivity.
10. Which metal is more reactive, iron or copper?
Answer : Iron is more reactive than copper, as it displaces copper from copper sulphate solution.
11. What are electronegative elements?
Answer : Nonmetals are electronegative elements as they gain electrons to form negatively charged ions.
12. What is an ionic compound?
Answer : An ionic compound is formed by the electrostatic attraction between cations and anions.
13. Why do ionic compounds have high melting points?
Answer : Strong electrostatic forces between ions require large energy to break, resulting in high melting points.
14. What are ores?
Answer : Ores are minerals from which metals can be extracted economically.
15. What is gangue?
Answer : Gangue is the impurities like soil, sand, and rocky substances present in ores.
16. What is the purpose of concentration of ores?
Answer : Concentration of ores separates gangue to increase the metal compound’s concentration.
17. Which method concentrates sulphide ores like zinc blende?
Answer : Froth floatation method concentrates sulphide ores like zinc blende.
18. What is roasting in metallurgy?
Answer : Roasting is heating sulphide ores in air to convert them into oxides.
19. What is corrosion?
Answer : Corrosion is the deterioration of metals due to reactions with environmental factors like moisture and oxygen.
20. What is galvanizing?
Answer : Galvanizing is coating iron or steel with a thin layer of zinc to prevent corrosion.
Long Questions
1. Explain the physical properties of metals with examples.
Answer : Metals are generally solid, lustrous, ductile, malleable, and good conductors of heat and electricity. For example, copper is ductile and used for wires, while tungsten has a high melting point (3422°C). Exceptions include soft alkali metals like sodium and liquid metals like mercury.
2. Describe the physical properties of nonmetals with exceptions.
Answer : Nonmetals are often gases or brittle solids, non-lustrous, and poor conductors of heat and electricity. Exceptions include iodine, which is lustrous, and diamond, which is extremely hard. Graphite, another carbon allotrope, is a good conductor of electricity.
3. How do metals react with oxygen, and what is the nature of the products?
Answer : Metals react with oxygen to form metal oxides, which are often basic. For example, sodium forms sodium oxide (Na₂O), which reacts with water to form alkali (NaOH). Magnesium forms magnesium oxide (MgO), which produces magnesium hydroxide with water.
4. Explain the reaction of metals with water, including variations in reactivity.
Answer : Highly reactive metals like sodium and potassium react vigorously with cold water, liberating hydrogen gas. Calcium reacts slowly with cold water, while metals like aluminium and iron react only with steam. Less reactive metals like gold and copper do not react with water.
5. What is the significance of the reactivity series in metallurgy?
Answer : The reactivity series ranks metals by their ability to displace others from salt solutions, guiding extraction methods. Highly reactive metals like sodium require electrolytic reduction, while less reactive ones like copper are extracted by heating. It helps predict reactions and choose suitable reducing agents.
6. Describe the formation and properties of ionic compounds.
Answer : Ionic compounds form when metals lose electrons to nonmetals, creating oppositely charged ions held by electrostatic forces. They are crystalline, hard, brittle, and have high melting points due to strong ionic bonds. They conduct electricity in molten or aqueous states as ions become mobile.
7. How is bauxite concentrated using Bayer’s process?
Answer : In Bayer’s process, bauxite is ground and heated with concentrated sodium hydroxide to form soluble sodium aluminate. Insoluble impurities like iron oxide are filtered out, and the solution is diluted to precipitate aluminium hydroxide. The precipitate is calcined at 1000°C to obtain pure alumina.
8. Explain the electrolytic reduction of alumina to extract aluminium.
Answer : Alumina is mixed with cryolite and fluorspar to lower its melting point and electrolyzed in a steel tank with a graphite cathode. Aluminium ions are reduced to molten aluminium at the cathode, while oxygen is liberated at the anode, forming carbon dioxide. The molten aluminium is collected from the tank’s bottom.
9. What is the froth floatation method, and how is it used in metallurgy?
Answer : Froth floatation separates sulphide ores by exploiting their hydrophobic properties, wetting them with oil while gangue is wetted by water. Air is blown through a mixture of ore, water, and oil, forming froth that carries sulphide particles to the surface. This method concentrates ores like zinc blende and copper pyrite.
10. How are moderately reactive metals extracted from their ores?
Answer : Moderately reactive metals like zinc and iron occur as sulphides or carbonates, which are converted to oxides by roasting or calcination. The oxides are then reduced using carbon or reactive metals like aluminium. For example, zinc oxide is reduced with carbon to produce zinc.
11. Describe the process of corrosion and its effects on iron and copper.
Answer : Corrosion is the reaction of metals with environmental factors, forming compounds like rust (Fe₂O₃·H₂O) on iron and copper carbonate (CuCO₃) on copper. Rusting weakens iron structures, causing financial loss, while copper’s green patina affects its appearance. Both reduce the metal’s durability and aesthetic value.
12. Explain methods to prevent corrosion of metals.
Answer : Corrosion is prevented by coating metals with paint, oil, or non-corrosive metals like zinc (galvanizing) or tin (tinning). Electroplating applies a less reactive metal layer, and alloying, like stainless steel, reduces corrosion intensity. Anodization forms a protective oxide layer on metals like aluminium.
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