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Pookie Answer 2

Written by

abhishekinbh

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Class 10 CBSE Science

Metals and Non-metals · Questions 64 and 65

Question 64

(A) Write the name of two metals of moderate reactivity. Which one of the two is more reactive? How can this fact be demonstrated experimentally in a school laboratory?
(B) Some metals of moderate reactivity are also found in the Earth’s crust in the form of their carbonates. Name the processes involved in the extraction of metal from them, giving chemical equations for the reactions that occur.

Part (A)

Two metals of moderate reactivity: Iron (Fe) and Copper (Cu). Iron is more reactive than copper.

Laboratory demonstration (displacement reaction):

  1. Take two test tubes, each containing about 5 mL of copper sulphate solution (blue).
  2. Place a clean iron nail in one test tube and a clean copper strip in the other.
  3. Leave them undisturbed for 20 to 30 minutes and observe.

The iron nail becomes coated with a reddish-brown deposit of copper, and the blue colour of the solution fades to pale green. This happens because iron displaces copper from its salt solution. Copper strip shows no change, which confirms that copper is less reactive.

\( \mathrm{Fe_{(s)} + CuSO_{4(aq)} \rightarrow FeSO_{4(aq)} + Cu_{(s)}} \)

Part (B)

Metals of moderate reactivity found as carbonates, such as zinc (calamine, ZnCO₃), are extracted in two main steps.

  1. Calcination: The carbonate ore is heated strongly in limited air, which decomposes it into the metal oxide and carbon dioxide.
    \( \mathrm{ZnCO_{3(s)} \xrightarrow{\Delta} ZnO_{(s)} + CO_{2(g)}} \)
  2. Reduction: The metal oxide is reduced to the metal by heating it with carbon (coke), which acts as the reducing agent.
    \( \mathrm{ZnO_{(s)} + C_{(s)} \xrightarrow{\Delta} Zn_{(s)} + CO_{(g)}} \)

Calcination removes volatile impurities and carbon dioxide. Reduction converts the oxide to the free metal.

Question 65

Some metals of low and medium reactivity are extracted from their sulphide ores. What are the steps involved in the extraction of such metals?

Metals of low and medium reactivity, such as zinc (ZnS) and copper (Cu₂S), are extracted from sulphide ores in the following steps.

  1. Concentration (Ore dressing): The ore is crushed and purified. Froth flotation is the usual method for sulphide ores, because the sulphide particles stick to the froth while the gangue (earthy impurities) sinks.
  2. Roasting: The concentrated sulphide ore is heated strongly in excess air. This converts the sulphide into the metal oxide and releases sulphur dioxide.
    \( \mathrm{2ZnS_{(s)} + 3O_{2(g)} \xrightarrow{\Delta} 2ZnO_{(s)} + 2SO_{2(g)}} \)
  3. Reduction: The metal oxide is reduced to the metal using carbon (coke) as the reducing agent.
    \( \mathrm{ZnO_{(s)} + C_{(s)} \xrightarrow{\Delta} Zn_{(s)} + CO_{(g)}} \)
  4. Refining: The impure metal is purified, most commonly by electrolytic refining.

Note: For copper, which is less reactive, the metal can sometimes be obtained directly from the roasted sulphide without carbon. This is called self-reduction.
\( \mathrm{Cu_2S + 2Cu_2O \rightarrow 6Cu + SO_2} \)

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