CBSE Class 10 Science Chapter 1: Chemical Reactions and Equations NCERT Solutions

Let's analyze the given reaction: $2\; \backslash text\{PbO\}\_\{(s)\}\; +\; \backslash text\{C\}\_\{(s)\}\; \backslash longrightarrow\; 2\; \backslash text\{Pb\}\_\{(s)\}\; +\; \backslash text\{CO\}\_\{2(g)\}$

Oxidation is the gain of oxygen or loss of electrons, while reduction is the loss of oxygen or gain of electrons.

In this reaction:

• Lead oxide (PbO) loses oxygen to form lead (Pb). Therefore, lead oxide is getting reduced. This means statement (d) is correct.
• Carbon (C) gains oxygen to form carbon dioxide (CO2). Therefore, carbon is getting oxidised. This means statement (c) is correct.
• Since lead oxide is reduced, statement (a) 'Lead is getting reduced' is incorrect because it is the compound (lead oxide) that is reduced, not just the element lead in isolation.
• Since carbon is oxidised to carbon dioxide, statement (b) 'Carbon dioxide is getting oxidised' is incorrect. Carbon dioxide is the product of oxidation, not the substance being oxidised.

The incorrect statements are (a) and (b).

Therefore, the correct option is (i) (a) and (b).

In the given reaction, $Fe\_2O\_3\; +\; 2Al\; \backslash longrightarrow\; Al\_2O\_3\; +\; 2Fe$, Aluminium (Al) is a more reactive metal than Iron (Fe). Aluminium displaces Iron from its oxide (Iron(III) oxide).

A reaction in which a more reactive element displaces a less reactive element from its compound is called a displacement reaction.

Therefore, the given reaction is an example of a displacement reaction.

The correct option is (d).

When a metal reacts with an acid, it typically produces a salt and hydrogen gas. Iron (Fe) is a reactive metal that reacts with dilute hydrochloric acid (HCl).

The reaction is as follows:

$$Fe\_\{(s)\}\; +\; 2HCl\_\{(aq)\}\; \backslash longrightarrow\; FeCl\_\{2(aq)\}\; +\; H\_2\; \backslash uparrow$$

In this reaction, iron reacts with hydrochloric acid to form iron(II) chloride (an iron salt) and hydrogen gas. The hydrogen gas is released as bubbles.

Therefore, hydrogen gas and iron chloride are produced.

The correct answer is (a).

A balanced chemical equation is a representation of a chemical reaction where the number of atoms of each element is the same on both the reactant side and the product side of the equation. This ensures that the total mass is conserved during the reaction.

Chemical equations should be balanced to adhere to the Law of Conservation of Mass. This fundamental law states that mass can neither be created nor destroyed in a chemical reaction. Therefore, the total mass of the reactants must be equal to the total mass of the products. Balancing the equation ensures that the number of atoms of each element involved in the reaction remains constant throughout the process.

We will translate each statement into a chemical equation and then balance it.

(a) Hydrogen gas combines with nitrogen to form ammonia.

The reactants are hydrogen gas ($H\_2$) and nitrogen gas ($N\_2$). The product is ammonia ($NH\_3$).

Unbalanced equation: $H\_\{2(g)\}\; +\; N\_\{2(g)\}\; \backslash longrightarrow\; NH\_\{3(g)\}$

To balance this equation, we need 6 hydrogen atoms and 2 nitrogen atoms on both sides.

Balanced equation: $$3H\_\{2(g)\}\; +\; N\_\{2(g)\}\; \backslash longrightarrow\; 2NH\_\{3(g)\}$$

(b) Hydrogen sulphide gas burns in air to give water and sulphur dioxide.

Burning in air means reacting with oxygen ($O\_2$). The reactants are hydrogen sulphide ($H\_2S$) and oxygen ($O\_2$). The products are water ($H\_2O$) and sulphur dioxide ($SO\_2$).

Unbalanced equation: $H\_2S\_\{(g)\}\; +\; O\_\{2(g)\}\; \backslash longrightarrow\; H\_2O\_\{(l)\}\; +\; SO\_\{2(g)\}$

To balance this equation, we need 2 hydrogen atoms, 2 sulphur atoms, and 6 oxygen atoms on both sides.

Balanced equation: $$2H\_2S\_\{(g)\}\; +\; 3O\_\{2(g)\}\; \backslash longrightarrow\; 2H\_2O\_\{(l)\}\; +\; 2SO\_\{2(g)\}$$

(c) Barium chloride reacts with aluminium sulphate to give aluminium chloride and a precipitate of barium sulphate.

The reactants are barium chloride ($BaCl\_2$) and aluminium sulphate ($Al\_2(SO\_4)\_3$). The products are aluminium chloride ($AlCl\_3$) and barium sulphate ($BaSO\_4$).

Unbalanced equation: $BaCl\_\{2(aq)\}\; +\; Al\_2(SO\_4)\_\{3(aq)\}\; \backslash longrightarrow\; AlCl\_\{3(aq)\}\; +\; BaSO\_\{4(s)\}$

To balance this equation, we need 3 barium atoms, 6 chloride ions, 2 aluminium atoms, and 3 sulphate groups on both sides.

Balanced equation: $$3BaCl\_\{2(aq)\}\; +\; Al\_2(SO\_4)\_\{3(aq)\}\; \backslash longrightarrow\; 2AlCl\_\{3(aq)\}\; +\; 3BaSO\_\{4(s)\}$$

(d) Potassium metal reacts with water to give potassium hydroxide and hydrogen gas.

The reactants are potassium metal ($K$) and water ($H\_2O$). The products are potassium hydroxide ($KOH$) and hydrogen gas ($H\_2$).

Unbalanced equation: $K\_\{(s)\}\; +\; H\_2O\_\{(l)\}\; \backslash longrightarrow\; KOH\_\{(aq)\}\; +\; H\_\{2(g)\}$

To balance this equation, we need 2 potassium atoms, 4 hydrogen atoms, and 2 oxygen atoms on both sides.

Balanced equation: $$2K\_\{(s)\}\; +\; 2H\_2O\_\{(l)\}\; \backslash longrightarrow\; 2KOH\_\{(aq)\}\; +\; H\_\{2(g)\}$$