Reactivity Series - UNSOLVED PRACTICE SET

Q7. Write the reactivity series of metals (from most reactive to least reactive) including K, Na, Ca, Mg, Al, Zn, Fe, Pb, H, Cu, Ag, Au.

Q8. Why can potassium displace hydrogen from cold water but iron cannot? Explain using the reactivity series.

Q9. Your school has an iron gate that is rusting, while the brass (copper-zinc alloy) nameplate remains shiny. Explain why iron rusts but copper and zinc in brass do not, using the reactivity series.

Q10. What happens when zinc granules are added to copper sulphate solution? Write the balanced chemical equation and explain the observation in terms of the reactivity series.

Q11. Why is gold found in nature in the free state (native state) while sodium is never found free in nature? Explain using the reactivity series.

Q12. A student adds iron filings to a solution of copper sulphate. What colour change will she observe? Write the chemical equation and explain which metal is more reactive.

Q13. Define the reactivity series of metals. Write the complete series from most reactive to least reactive. Explain how the reactivity series helps in predicting: (i) displacement reactions, (ii) reactions with water and acids, (iii) extraction of metals from their ores, and (iv) the tendency of metals to corrode.

Q14. A student is given four metals: A, B, C, and D. She performs the following experiments:

Metal A reacts vigorously with cold water.

Metal B reacts with steam but not with cold water.

Metal C displaces iron from iron sulphate solution.

Metal D does not react with dilute acids or water.

(a) Arrange the metals A, B, C, and D in order of decreasing reactivity.

(b) Identify which metal could be: sodium, zinc, copper, or magnesium.

(c) Write a chemical equation showing metal C displacing iron from iron sulphate.

(d) If metal D is gold, explain why it is found in native state.

(e) Design an experiment to determine the exact position of metal C in the reactivity series.

Q15. "The reactivity series is not just a list — it is a practical tool that guides chemists, engineers, and even jewellers." Discuss this statement by explaining: (i) how the reactivity series helps in choosing the right metal for specific applications, (ii) its role in the extraction of metals from their ores, (iii) why highly reactive metals are used as reducing agents, and (iv) how understanding the reactivity series helps in preventing corrosion of metals used in Indian infrastructure.

Q16. A chemistry laboratory tests the reactivity of metals by measuring the rate of hydrogen gas production:

Table

Metal Mass (g) Time to Produce 100 mL H₂ (s)

Mg 0.24 30

Al 0.18 45

Zn 0.65 120

Fe 0.56 180

(a) Calculate the rate of hydrogen production (mL/s) for each metal.

(b) Arrange the metals in order of decreasing rate of reaction. Does this match the reactivity series?

(c) Calculate the number of moles of each metal used. (Atomic masses: Mg = 24, Al = 27, Zn = 65, Fe = 56)

(d) If 0.5 g of each metal is used, predict which metal would produce the most hydrogen and which would produce the least.

(e) Copper does not produce any hydrogen with dilute HCl. How long would it take copper to produce 100 mL of H₂? Explain.

Q17. A metal extraction company uses the reactivity series to choose extraction methods:

(a) For a metal M that is high in the reactivity series (above carbon), which extraction method is used? Why can't carbon be used as a reducing agent?

(b) For a metal N that is moderate in the reactivity series (below carbon but above hydrogen), which extraction method is used? Write a general equation.

(c) For a metal P that is low in the reactivity series (below hydrogen), which extraction method is used? Why is chemical reduction unnecessary?

(d) If the company extracts 100 kg of aluminium daily by electrolysis, and the process requires 15 kWh of electricity per kg, calculate the daily electricity consumption.

(e) If electricity costs ₹8 per kWh, calculate the daily electricity cost for aluminium extraction. Why is aluminium expensive despite being abundant in nature?

Q18. In India, the reactivity of metals affects their use in various sectors:

(a) Railway tracks are made of steel (iron alloy). If 1000 km of track contains 500 tonnes of iron per km, and the track needs replacement every 20 years due to corrosion, calculate the total iron requirement for 1000 km over 60 years.

(b) To prevent corrosion, the Railways galvanizes the tracks. If galvanization adds 2% zinc by mass, calculate the mass of zinc needed for 500 tonnes of track.

(c) Zinc is more reactive than iron. Explain how zinc protects iron even if the coating is scratched.

(d) Copper wires are used for electrical transmission. If copper is less reactive than hydrogen, why does it not corrode easily in air?

(e) Gold is used for coating connectors in electronic devices. If gold costs ₹5,000 per gram, and a device needs 0.01 g of gold plating, calculate the cost. Why is gold used despite its high cost?