Chapter 2, Problem 76A

(a)

Interpretation Introduction

Interpretation: The observation during the given chemical change to support the fact needs to be described.

An antacid tablet was dropped into water.

Concept Introduction: When a substance changes its appearance or change in the state takes place and there is no change in its chemical composition, the change is said to be physical. On the other hand, when there is a change in the chemical composition of a substance or a new substance is formed after a chemical reaction, it is known as a chemical change.

Explanation of Solution

When the antacid tablet is dropped in water, it gets dissolved in it. Antacid tablets contain sodium bicarbonate which reacts with hydrogen ions in the water to form carbon dioxide. This carbon dioxide formation causes effervescence in water and gives a clue of chemical change.

(b)

Interpretation Introduction

Interpretation: The observation during the given chemical change to support the fact needs to be described.

A ring of scum forms around a bathtub

Concept Introduction: When a substance changes its appearance or change in the state takes place and there is no change in its chemical composition, the change is said to be physical. On the other hand, when there is a change in the chemical composition of a substance or a new substance is formed after a chemical reaction, it is known as a chemical change.

Explanation of Solution

The formation of a ring of scum around a bathtub is due to a precipitation reaction. Here, the formation of a solid that settles out of a liquid mixture cause formation of a ring of scum. Thus, the formation of precipitate shows there is a chemical change.

(c)

Interpretation Introduction

Interpretation: The observation during the given chemical change to support the fact needs to be described.

Rusting of iron

Concept Introduction: When a substance changes its appearance or change in the state takes place and there is no change in its chemical composition, the change is said to be physical. On the other hand, when there is a change in the chemical composition of a substance or a new substance is formed after a chemical reaction, it is known as a chemical change.

Explanation of Solution

Rusting of iron is due to corrosion when the iron is exposed to moisture in the air. This results in the formation of iron oxide. Here, a new substance is formed thus, it is a chemical change. Iron oxide so formed is reddish-brown and also known as rust.

(d)

Interpretation Introduction

Interpretation: The observation during the given chemical change to support the fact needs to be described.

Explosion of firecracker

Concept Introduction: When a substance changes its appearance or change in the state takes place and there is no change in its chemical composition, the change is said to be physical. On the other hand, when there is a change in the chemical composition of a substance or a new substance is formed after a chemical reaction, it is known as a chemical change.

Explanation of Solution

The explosion of a firecracker involves the production of heat, light, and sound. The explosion of the firecracker results in an exothermic redox reaction. In this reaction, a large amount of heat is released. Thus, it is a chemical change.

(e)

Interpretation Introduction

Interpretation: The observation during the given chemical change to support the fact needs to be described.

Formation of bubbles when hydrogen peroxide is poured onto an open wound.

Concept Introduction: When a substance changes its appearance or change in the state takes place and there is no change in its chemical composition, the change is said to be physical. On the other hand, when there is a change in the chemical composition of a substance or a new substance is formed after a chemical reaction, it is known as a chemical change.

Explanation of Solution

When hydrogen peroxide is poured onto an open wound, the formation of bubbles shows a chemical reaction. The bubbles are due to the release of oxygen gas. Here, oxygen gas is produced due to the breaking of hydrogen peroxide in the presence of enzyme catalyzes.

(f)

Interpretation Introduction

Interpretation: The observation during the given chemical change to support the fact needs to be described.

Cooking a hamburger.

Concept Introduction: When a substance changes its appearance or change in the state takes place and there is no change in its chemical composition, the change is said to be physical. On the other hand, when there is a change in the chemical composition of a substance or a new substance is formed after a chemical reaction, it is known as a chemical change.

Explanation of Solution

When a hamburger is cooked, a new substance is formed from raw materials. Here, new species are formed which cannot be converted back into original ingredients thus, it is a chemical change.