Metals and Non-metals NCERT Solution, study material, CBSE Notes

NCERT Solution: Metals and Non-metals

A metal M does not liberate hydrogen from acids but reacts with oxygen to give a black colour product. Identify M and black coloured product and also explain the reaction of M with oxygen

Copper does not react with acids. But copper gives black coloured copper oxide when it reacts with oxygen. Hence, M is copper and black coloured product is copper oxide.

2Cu + O₂ → CuO

An element forms an oxide A2O3 which is acidic in nature. Identify A as a metal or non-metal.

Oxides of non-metals are acidic in nature. Hence, A is a non-metal.

A solution of CuSO₄ was kept in an iron pot. After few days the iron pot was found to have a number of holes in it. Explain the reason in terms of reactivity. Write the equation of the reaction involved.

Iron is more reactive than copper. Due to this, iron displaced copper from copper sulphate to form iron sulphate. A portion of the iron pot got dissolved in this process and caused holes in it. Following equation is involved in this reaction:

CuSO₄+ Fe →FeSO₄ + Cu

A non-metal A which is the largest constituent of air, when heated with H2 in 1: 3 ratio in the presence of catalyst (Fe) gives a gas B. On heating with O₂ it gives an oxide C. If this oxide is passed into water in the presence of air it gives an acid D which acts as a strong oxidising agent.

(a) Identify A, B, C and D

Ans. A is nitrogen; because nitrogen is the largest constituent of air. B is ammonia, C is nitrogen dioxide and D is nitric acid (nitric acid is a strong oxidizing agent). When nitrogen is heated with hydrogen in the presence of a catalyst, following reaction takes place:

N₂ + 3 H₂→ 2NH₃

When nitrogen is heated with oxygen, we get nitrogen dioxide.

N₂ + O₂ → 2NO₂

When nitrogen dioxide is treated with water, we get nitric acid

NO₂+ H₂O → HNO₃

(b) To which group of periodic table does this non-metal belong?

Ans. This non-metal belongs to Group 15.

Give the steps involved in the extraction of metals of low and medium reactivity from their respective sulphide ores.

During extraction of metals of low and medium reactivity, a respective sulphide ore is first heated in air. This helps in obtaining oxide of metal. It is easier to extract a metal from its oxide rather than from its sulphide. Hence, this step is used. Mercury is a metal of low reactivity. Mercury sulphide (cinnabar) is heated in air. Mercury sulphide gets oxidized to produce mercury oxide.

2HgS +3O₂ → 2HgO + 2SO₂
After that, mercury oxide is reduced to obtain mercury.
2HgO → 2Hg + O₂

Zinc is a metal of medium reactivity. It is found as zinc blende (ZnS).
Zinc blende is roasted to obtain zinc oxide. After that, zinc oxide is reduced to obtain pure zinc.

2ZnS + 3O₂ → ZnO + 2SO₂

After that, mercury oxide is reduced to obtain mercury.
ZnO + C → Zn + CO

Explain the following

(a) Reactivity of Al decreases if it is dipped in HNO₃.
Ans. Nitric acid is a strong oxidizing agent. Due to this, when aluminium is dipped in nitric acid, a layer of aluminium oxide is deposited on aluminium. As a result; reactivity of aluminium decreases when it is dipped in nitric acid.

(b) Carbon cannot reduce the oxides of Na or Mg
Ans. Sodium and magnesium are highly reactive metals. Hence, they have higher affinity to oxygen than to carbon. Due to this, carbon fails to reduce the oxides of sodium or magnesium.

(c) NaCl is not a conductor of electricity in solid state whereas it does conduct electricity in aqueous solution as well as in molten state
Ans. NaCl is an ionic compound. Ionic compounds do not conduct electricity in solid state. But ionic compounds are good conductors of electricity in molten state and in aqueous solution.

(d) Iron articles are galvanised.
Ans. Iron has a tendency to react with atmospheric moisture. This process is called rusting and leads to corrosion of iron. Iron articles are galvanized to prevent rusting of iron.

(e) Metals like Na, K, Ca and Mg are never found in their free state in nature.
Ans. Na, K, Ca and Mg are highly reactive metals. They can easily form compound with most of the elements. Due to this, these metals are not found in their free state in nature.

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

(a) Roasting of copper (1) sulphide
Ans. 2Cu₂S + 3O₂ → 2Cu₂O + 2SO₂

(b) Reduction of copper (1) oxide with copper (1) sulphide.
2Cu₂O + Cu₂S → 6Cu + SO₂

(c) Electrolytic refining
Ans. At cathode: Cu²⁺ + 2e^- → Cu

(ii) Draw a neat and well labelled diagram for electrolytic refining of copper

Fig. 3.2 Electrolytic refining of copper. The electrolyte is a solution of acidified copper sulphate. The anode is impure copper, whereas, the cathode is a strip of pure copper. On passing electric current, pure copper is deposited on the cathode.

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

X is sodium, Y is magnesium and Z is iron.

X is sodium, Y is magnesium and Z is iron.
2Na + H₂O → 2NaOH + H₂
Mg + H₂O → Mg(OH)2 + H₂
3Fe + H₂O → Fe₃O₄ +4 H₂
Their sequence in reactivity series is as follows:
Fe < Mg < Na.