Metals and Non-metals — NCERT Solutions

From the chapter:

• Mercury is the only metal mentioned as liquid at room temperature.
• Sodium is so soft that it can be cut with a knife.
• The best conductors of heat are silver and copper; choosing one example, silver.
• Lead is mentioned as a poor conductor of heat.

Malleable means a substance, especially a metal, can be beaten into thin sheets.

Ductile means a substance can be drawn into thin wires.

Sodium is kept immersed in kerosene oil because it reacts very vigorously with oxygen and water in air. Keeping it under kerosene prevents contact with air and moisture, so it does not catch fire accidentally.

(i) Iron with steam:
$$3Fe(s)+4H_2O(g)\rightarrow Fe_3O_4(s)+4H_2(g)$$

(ii) Calcium with water:
$$Ca(s)+2H_2O(l)\rightarrow Ca(OH)_2(aq)+H_2(g)$$

Potassium with water:
$$2K(s)+2H_2O(l)\rightarrow 2KOH(aq)+H_2(g)+\text{heat}$$

From the table:

• B displaces iron from iron(II) sulphate, so B is more reactive than iron.
• A displaces copper from copper(II) sulphate but does not react with iron(II) sulphate, so A is less reactive than iron but more reactive than copper.
• C displaces silver from silver nitrate but not iron, copper or zinc salts, so C is less reactive than copper but more reactive than silver.
• D does not displace any metal, so it is the least reactive.

Therefore, the most reactive metal is B and the decreasing order is B > A > C > D.

If B is added to copper(II) sulphate, it will displace copper from the solution.

When a reactive metal reacts with dilute hydrochloric acid, hydrogen gas is produced.

For iron with dilute sulphuric acid:
$$Fe(s)+H_2SO_4(aq)\rightarrow FeSO_4(aq)+H_2(g)$$

Zinc does not react with iron(II) sulphate? No — zinc is more reactive than iron, so it displaces iron from iron(II) sulphate.

Observation: the pale green solution of iron(II) sulphate changes, and iron gets deposited while zinc sulphate solution forms.

Reaction:
$$Zn(s)+FeSO_4(aq)\rightarrow ZnSO_4(aq)+Fe(s)$$

(i) Electron-dot structures:

• Sodium: Na·
• Oxygen: :O: with 6 valence electrons
• Magnesium: Mg··

(ii) Formation by transfer of electrons:

• Sodium loses 1 electron each to two oxygen-related atoms in forming sodium oxide.
• Magnesium loses 2 electrons to oxygen.

For Na₂O:

• Two sodium atoms each lose one electron.
• Oxygen gains two electrons.
• So the ions formed are 2Na⁺ and O²⁻.

For MgO:

• Magnesium loses two electrons.
• Oxygen gains two electrons.
• So the ions formed are Mg²⁺ and O²⁻.

(iii) Ions present:

• In Na₂O: Na⁺ and O²⁻
• In MgO: Mg²⁺ and O²⁻

Ionic compounds have high melting points because there is a strong electrostatic force of attraction between the oppositely charged ions. A large amount of energy is needed to overcome these forces and separate the ions.

From the chapter:

• Minerals are the elements or compounds that occur naturally in the earth's crust.
• Ores are those minerals from which a metal can be extracted profitably.
• Gangue means the unwanted impurities like soil and sand present with the ore.

The chapter says that gold and silver are found in the free state in nature. Copper is also mentioned, but the question asks for two metals, so gold and silver are correct examples.

The chapter states that obtaining metals from their compounds is a reduction process. When a metal oxide is converted into a metal, the oxygen is removed, so the process is reduction.

A more reactive metal displaces a less reactive metal from its oxide. From the reactivity order Mg > Zn > Cu:

• Mg can displace Zn from zinc oxide.
• Mg can displace Cu from copper oxide.
• Zn can displace Cu from copper oxide.
• No displacement occurs where the added metal is less reactive than the metal in the oxide.

So displacement reactions occur in:

• ZnO + Mg
• CuO + Zn
• CuO + Mg

The chapter says that silver and gold do not react with oxygen even at high temperatures, and metals like gold, silver, platinum and copper are found in the free state because the least reactive ones are not easily corroded. The commonly expected answer is gold and platinum.

A displacement reaction occurs when a more reactive metal displaces a less reactive metal from its salt solution.

From the reactivity series, copper is more reactive than silver, so copper can displace silver from AgNO₃.

• (a) Copper cannot displace sodium from NaCl.
• (b) Aluminium is more reactive than zinc, so it can displace zinc from MgCl₂? No, magnesium is not in the pair; aluminium cannot displace magnesium.
• (c) Silver is less reactive than iron, so no reaction.
• (d) Copper displaces silver from AgNO₃.

Thus, the correct pair is AgNO₃ solution and copper metal.