Class 10 Science

Metals and Non-metals

NCERT Exemplar Problems

Long Answer

Part 2

Question 62: Given below are the steps for extraction of copper from its ore. Write the reaction involved.

(a) Roasting of copper (1) sulphide

Answer: 2Cu2S + 3O2 ⇨ 2Cu2O + 2SO2

(b) Reduction of copper (1) oxide with copper (1) sulphide.

Answer: 2Cu2O + Cu2S ⇨ 6Cu + SO2

(c) Electrolytic refining

Answer: At cathode: Cu2+ + 2e ⇨ Cu

Question 63: Draw a neat and well labelled diagram for electrolytic refining of copper

electrolytic refining of copper

Question 64: Of the three metals X, Y and Z. X reacts with cold water, Y with hot water and Z with steam only. Identify X, Y and Z and also arrange them in order of increasing reactivity.

Answer: X can be sodium or calcium, Y is magnesium and Z is iron.

As X can react with cold water, it is the most reactive one, followed by Y which does not react with cold water but reacts with hot water. Z is least reactive because it does not react with cold or hot water but with steam. Order in reactivity series: Na > Mg > Fe

Question 65: An element A burns with golden flame in air. It reacts with another element B, atomic number 17 to give a product C. An aqueous solution of product C on electrolysis gives a compound D and liberates hydrogen. Identify A, B, C and D. Also write down the equations for the reactions involved.

Answer: A is sodium (burns with golden flame), B is chlorine (atomic number 17), C is sodium chloride and D is sodium hydroxide.

When sodium reacts with chlorine, it gives sodium chloride.

Na + Cl ⇨ NaCl

Electrolysis of sodium chloride gives sodium hydroxide.

2NaCl + 2H2O ⇨ 2NaOH + Cl2 + H2

Question 66: Two ores A and B were taken. On heating; ore A gives CO2 whereas, ore B gives SO2. What steps will you take to convert them into metals?

Answer: Carbon dioxide is evolved when a carbonate ore is heated. A carbonate ore should be subjected to calcination which will give metal oxide. For example; zinc carbonate should be subjected to calcinations to get zinc oxide.

ZnCO3 ⇨ ZnO + CO2

When a sulphide ore is heated, it produces sulphur dioxide. This ore should be roasted to obtain metal oxide. For example; zinc sulphide should be roasted to obtain zinc oxide.

2ZnS + 3O2 ⇨ 2ZnO + 2SO2

After any of the above steps, zinc oxide should be reduced to obtain zinc.

ZnO + C ⇨ Zn + CO