Grade 10 Q&A: Chapter 8: Metallurgy

Concept Questions

Q1: What is 'metallurgy'?

Answer: Metallurgy is the science and technology dealing with the properties of metals and their production and purification from ores.

Q2: Name two physical properties of metals.

Answer: Two physical properties of metals are malleability (can be hammered into thin sheets) and ductility (can be drawn into wires).

Q3: What is the 'reactivity series' of metals?

Answer: The reactivity series is a list of metals arranged in decreasing order of their reactivity, with the most reactive metals at the top and the least reactive at the bottom.

Q4: What are 'minerals'?

Answer: Minerals are naturally occurring chemical substances found in the Earth's crust, often in the form of compounds, from which metals can be extracted.

Q5: What is an 'ore'?

Answer: An ore is a mineral from which a metal can be extracted profitably and conveniently.

Q6: What is 'gangue' (or matrix)?

Answer: Gangue (or matrix) refers to the unwanted impurities like sand, rocky materials, and earthy substances present in an ore.

Q7: What is 'concentration of ore'?

Answer: Concentration of ore is the process of removing unwanted impurities (gangue) from the ore before the extraction of the metal.

Q8: Name two methods for the concentration of ores.

Answer: Two methods for the concentration of ores are gravitation separation method (e.g., Wilfley table method) and magnetic separation method.

Q9: What is 'roasting' in metallurgy?

Answer: Roasting is the process of heating a concentrated ore (typically a sulfide ore) strongly in the presence of air (oxygen) to convert it into its oxide form, releasing sulfur dioxide gas.

Q10: What is 'calcination' in metallurgy?

Answer: Calcination is the process of heating a concentrated ore (typically a carbonate or hydrated oxide ore) strongly in the absence or limited supply of air to remove volatile impurities like carbon dioxide or water.

Q11: What is 'smelting'?

Answer: Smelting is a process of extracting a metal from its ore by heating it to a high temperature in the presence of a reducing agent (like carbon), often with a flux, to obtain the molten metal.

Q12: What is 'refining of metals'?

Answer: Refining of metals is the process of purifying the crude metal extracted from its ore to obtain a high degree of purity.

Q13: What is 'corrosion'?

Answer: Corrosion is the process of slow degradation of metals due to the reaction of atmospheric gases and moisture with the metal surface, forming undesirable compounds (e.g., rust on iron).

Q14: What is the chemical formula for rust?

Answer: The chemical formula for rust is Fe₂O₃·nH₂O (hydrated iron(III) oxide).

Q15: Name two methods to prevent corrosion.

Answer: Two methods to prevent corrosion are painting and greasing/oiling.

Q16: What is an 'alloy'?

Answer: An alloy is a homogeneous mixture of two or more metals, or a metal and a non-metal, prepared by melting the components together.

Application-Based Questions

Q17: Explain why highly reactive metals cannot be extracted by reduction with carbon.

Answer: Highly reactive metals (like sodium, potassium, calcium, magnesium, aluminum) have a very strong affinity for oxygen and are more reactive than carbon. Therefore, carbon cannot reduce their oxides to the pure metal. These metals are typically extracted by electrolytic reduction of their molten chlorides or oxides.

Q18: Describe the process of 'electrolytic refining' of copper.

Answer: In electrolytic refining of copper, impure copper is made the anode, a thin strip of pure copper is made the cathode, and an acidified solution of copper sulfate is used as the electrolyte. When current is passed, pure copper from the anode dissolves into the electrolyte and deposits onto the cathode, while impurities settle down as anode mud or dissolve in the electrolyte.

Q19: How does 'galvanizing' prevent rusting of iron?

Answer: Galvanizing prevents rusting of iron by coating the iron object with a thin layer of zinc. Zinc is more reactive than iron, so it acts as a sacrificial metal. If the coating is scratched, zinc corrodes preferentially, protecting the iron underneath. This is called cathodic protection.

Q20: Why is 'froth flotation method' specifically used for sulfide ores?

Answer: The froth flotation method is specifically used for sulfide ores because sulfide ores are preferentially wetted by oil (pine oil) and hydrophobic, while gangue particles are wetted by water and hydrophilic. When air is blown through a mixture of powdered ore, water, and oil, the sulfide ore particles adhere to the froth (foam) and float to the surface, while the gangue sinks.

Q21: Give an example of an alloy and mention its uses.

Answer: An example of an alloy is Brass. It is an alloy of copper (Cu) and zinc (Zn). It is used for making utensils, decorative articles, and musical instruments due to its strength, corrosion resistance, and attractive appearance.

Higher-Order Thinking Questions

Q22: Discuss the environmental impact of various metallurgical processes.

Answer: Metallurgical processes can have significant environmental impacts: 1. Mining: Causes habitat destruction, soil erosion, and water pollution (acid mine drainage). 2. Air Pollution: Roasting of sulfide ores releases sulfur dioxide (SO₂), contributing to acid rain. Smelting processes release particulate matter and other gaseous pollutants. 3. Water Pollution: Effluents from refining processes can contain heavy metals and toxic chemicals, polluting water bodies. 4. Waste Generation: Production of large amounts of solid waste (slag, tailings) that require proper disposal. 5. Energy Consumption: Many metallurgical processes are energy-intensive, contributing to greenhouse gas emissions if fossil fuels are used. Sustainable metallurgy aims to minimize these impacts through cleaner technologies, recycling, and waste treatment.

Q23: Explain the concept of 'sacrificial protection' in preventing corrosion, with an example.

Answer: Sacrificial protection is a method of corrosion prevention where a more reactive metal is deliberately connected to the metal to be protected. The more reactive metal (the 'sacrificial anode') corrodes preferentially, thereby protecting the less reactive metal. For example, in galvanizing, iron is coated with zinc. Since zinc is more reactive than iron, if the coating is damaged, zinc will oxidize (corrode) instead of iron, protecting the iron object from rusting. Another example is attaching magnesium blocks to steel pipelines or ship hulls.

Q24: How does the position of a metal in the reactivity series determine its method of extraction from its ore?

Answer: The position of a metal in the reactivity series is crucial in determining its extraction method: 1. Highly Reactive Metals (top of series, e.g., K, Na, Ca, Mg, Al): These metals are very stable in their compound forms (oxides, chlorides) and cannot be reduced by common reducing agents like carbon. They are extracted by electrolytic reduction of their molten salts. 2. Moderately Reactive Metals (middle of series, e.g., Zn, Fe, Pb, Cu): These metals are found as carbonates or sulfides. Their ores are first converted to oxides by calcination or roasting, respectively. The metal oxides are then reduced to crude metal using a reducing agent like carbon (coke) or sometimes more reactive metals. 3. Less Reactive Metals (bottom of series, e.g., Ag, Au, Pt): These metals are often found in free state or as easily reducible compounds (e.g., sulfide ores). They can be extracted by simple heating (roasting) or by displacement reactions with more reactive metals, or are found in native form.

Q25: Discuss the importance of 'alloys' in modern engineering and technology.

Answer: Alloys are of immense importance in modern engineering and technology because they possess properties superior to those of their constituent pure metals. 1. Enhanced Strength and Hardness: Alloys like steel (iron + carbon) are much stronger and harder than pure iron, making them suitable for construction, tools, and machinery. 2. Improved Corrosion Resistance: Stainless steel (iron + chromium + nickel) is highly resistant to rust, crucial for kitchenware, medical instruments, and chemical plants. 3. Specific Properties: Alloys can be designed for specific applications, e.g., duralumin (Al, Cu, Mg, Mn) is lightweight and strong, ideal for aircraft. Nichrome (Ni, Cr) has high electrical resistance and melting point, used in heating elements. 4. Lower Melting Point: Solder (lead + tin) has a low melting point, useful for joining metals. 5. Aesthetics: Alloys like brass and bronze are used for decorative purposes. Without alloys, many modern technologies and structures would not be possible.

Q26: What is 'anodizing' and how does it protect aluminum from corrosion?

Answer: Anodizing is an electrolytic process used to increase the thickness of the natural oxide layer on the surface of metal parts, typically aluminum. In this process, the aluminum object is made the anode in an electrolytic cell containing an acid electrolyte. When current is passed, oxygen gas is released at the anode, which reacts with the aluminum to form a thick, hard, porous, and highly corrosion-resistant aluminum oxide layer. This oxide layer acts as a protective barrier, preventing further corrosion of the aluminum underneath. It can also be dyed for decorative purposes.

Q27: Describe the 'magnetic separation method' for concentrating ores. When is it used?

Answer: The magnetic separation method is used for concentrating ores when either the ore particles or the gangue particles are magnetic. The finely crushed ore is passed over a conveyor belt that moves over a magnetic roller. The magnetic particles are attracted by the roller and fall in a separate heap closer to the roller, while the non-magnetic particles fall in a heap further away. This method is commonly used for concentrating magnetic ores like magnetite (iron ore) or for removing magnetic impurities from non-magnetic ores.

Q28: Why is it important to remove gangue from the ore before extracting the metal?

Answer: It is important to remove gangue from the ore before extracting the metal for several reasons: 1. Increased Efficiency: Removing gangue increases the concentration of the desired metal in the ore, making subsequent extraction processes more efficient and economical. 2. Reduced Cost: Less gangue means less material to heat and process, reducing energy consumption and overall production costs. 3. Purity of Metal: Impurities in the gangue can react with the metal during extraction, leading to a less pure final product or forming undesirable byproducts. 4. Environmental Impact: Reducing the volume of material processed minimizes the amount of waste generated and the environmental impact of the extraction process.

Q29: What is 'amalgamation' and for which metals is it primarily used in extraction?

Answer: Amalgamation is a metallurgical process primarily used for the extraction of noble metals like gold (Au) and silver (Ag). In this method, the crushed ore containing the noble metal is mixed with mercury. The noble metal dissolves in mercury to form an alloy called an 'amalgam'. The amalgam is then heated, causing the mercury to vaporize (which is then condensed and reused), leaving behind the pure gold or silver. This method is effective because gold and silver readily form amalgams with mercury, while gangue does not.

References

1. MSBSHSE Class 10 Science and Technology Textbook Part 1 (2021-22 English) - Chapter 8: Metallurgy
2. Maharashtra State Board 10th Standard Science Syllabus 2025-26
3. Balbharati Science and Technology Part 1 Textbook
4. Shaalaa.com Balbharati solutions for Science and Technology 1