Chapter 8, Problem 96A

Interpretation Introduction

Interpretation: The three indicators of chemical change need to be listed.

Concept Introduction: A chemical change takes place when one or more new substances are formed. In the formation of a new substance, a change in color can be observed.

Explanation of Solution

The three indicators of chemical change are as follows:

1. Change in color.
2. Formation of a precipitate or gas.
3. Change in odor or temperature.

A chemical change takes place when one or more new substances are formed. In the formation of a new substance, a change in color can be observed. Also, there is the possibility of the formation of a precipitate or gas. When a new substance is formed, there could be a change in odor or temperature.

The examples of reactions showing the change in color, formation of a precipitate or gas, and change in odor or temperature are as follows:

Change in color: When iron solid reacts with a blue color solution of copper sulfate, solid copper and a pale green solution of ferrous sulfate are formed. Thus, the blue color changes to pale green.

The reaction is represented as follows:

  $\text{Fe}\left(s\right)+CuS{O}_4\left(aq\right)\rightleftharpoons {\text{FeSO}}_{\text{4}}\left(aq\right)+\text{Cu}\left(s\right)$

Formation of a precipitate: When potassium chloride reacts with silver nitrate, solid silver chloride is formed. Here, silver chloride formed is insoluble in water and precipitates out in the reaction.

Change in odor or temperature: The example is the chemical decomposition of the egg. This causes eggs to smell like rotten eggs thus, a change in odor takes place.