Alloys - UNSOLVED PRACTICE SET

Q7. Define an alloy. Give two reasons why alloys are made. Write the composition of brass and bronze.

Q8. Why is pure gold (24 carat) not suitable for making jewellery? How does alloying with copper or silver make it suitable?

Q9. Your school bell is made of bronze, not pure copper. Explain why bronze is preferred over pure copper for making bells, using the properties of alloys.

Q10. What is amalgam? Give one example. Why is mercury used in dental amalgam?

Q11. Write the composition and uses of: (i) Stainless steel, (ii) Solder, (iii) Duralumin, (iv) Brass.

Q12. Why are alloys generally harder and more corrosion-resistant than pure metals? Explain in terms of the arrangement of atoms in alloys.

Q13. Define alloy and explain why alloys are made. Describe the composition, properties, and uses of: (i) brass, (ii) bronze, (iii) stainless steel, and (iv) duralumin. Why are alloys generally harder and more corrosion-resistant than pure metals? Explain with reference to the arrangement of atoms in alloys.

Q14. A student is given samples of pure copper, brass, and bronze. She is asked to compare their properties.

(a) How can she test the hardness of each sample?

(b) Predict which sample will be the hardest and which will be the softest.

(c) Which sample will be most resistant to corrosion? Why?

(d) Which sample will produce the best sound when struck? Why are bells made of bronze and not brass?

(e) If the student wants to make a musical instrument, which alloy should she choose and why?

(f) Why is pure copper used for electrical wiring despite brass being harder?

Q15. "Alloys have shaped human civilization from the Bronze Age to the modern era, and India has a rich tradition of metalworking." Discuss this statement by explaining: (i) the historical significance of bronze in the Indus Valley Civilization, (ii) why stainless steel revolutionized kitchenware and medical instruments, (iii) the use of duralumin in the Indian aerospace industry, and (iv) why alloying is essential for making materials suitable for specific applications.

Q16. A jewellery manufacturer in India makes 22-carat gold ornaments.

(a) Calculate the percentage of pure gold in 22-carat gold.

(b) If a necklace weighs 100 g, calculate the mass of pure gold and the mass of other metals (copper/silver) in it.

(c) If pure gold costs ₹5,500 per gram and copper costs ₹500 per gram, calculate the cost of materials for the 100 g necklace.

(d) Why do jewellers add copper to gold rather than silver for making red gold?

(e) If the manufacturer makes 1000 necklaces per month, calculate the annual requirement of pure gold in kilograms.

(f) 18-carat gold contains 75% gold. If a customer wants a 50 g ring in 18-carat gold, calculate the mass of pure gold in it.

Q17. An aircraft manufacturer uses duralumin (an alloy of aluminium) for making aircraft parts.

(a) Duralumin contains 95% aluminium, 4% copper, 0.5% magnesium, and 0.5% manganese. If an aircraft wing requires 500 kg of duralumin, calculate the mass of each metal needed.

(b) Pure aluminium has a density of 2.7 g/cm³ and duralumin has a density of 2.8 g/cm³. If a part has a volume of 10,000 cm³, calculate its mass in pure aluminium and in duralumin.

(c) Why is duralumin preferred over pure aluminium for aircraft despite being slightly denser?

(d) If the aircraft manufacturer produces 50 aircraft per year, and each aircraft requires 2000 kg of duralumin, calculate the annual copper requirement for duralumin production.

(e) The HAL (Hindustan Aeronautics Limited) in India manufactures aircraft. Why is duralumin particularly suitable for Indian weather conditions?

Q18. A steel manufacturing company in India produces various types of steel for different applications.

(a) Mild steel contains 0.1-0.2% carbon. If a batch of 1000 kg of mild steel contains 0.15% carbon, calculate the mass of carbon and iron.

(b) High-carbon steel contains 0.6-1.5% carbon. If a cutting tool requires 2 kg of steel with 1.2% carbon, calculate the mass of carbon in the tool.

(c) Stainless steel contains 18% chromium and 8% nickel. If a kitchen sink requires 5 kg of stainless steel, calculate the mass of chromium and nickel.

(d) Why is stainless steel preferred over mild steel for kitchen utensils and medical instruments?

(e) The TISCO (Tata Iron and Steel Company) in Jamshedpur is one of India's largest steel producers. Why is the steel industry called the backbone of Indian industry?

(f) If India produces 100 million tonnes of steel annually, and the average carbon content is 0.5%, calculate the total mass of carbon used in steel production.