Acids, Bases and Indicators

Introduction

In Integrated Science, we learn about acids, bases, and indicators. Acids are substances that release hydrogen ions ($H^+$) when dissolved in water, while bases are substances that release hydroxide ions ($OH^-$) when dissolved in water. Indicators are substances that change color in the presence of acids or bases.

Acids

Acids are substances that release hydrogen ions ($H^+$) when dissolved in water. They have a pH less than 7. For example, hydrochloric acid ($HCl$) is a common acid.
Example:
Hydrochloric acid ($HCl$) + Water ($H_2O$) $\rightarrow$ Hydrogen ions ($H^+$) + Chloride ions ($Cl^-$)

Bases

Bases are substances that release hydroxide ions ($OH^-$) when dissolved in water. They have a pH greater than 7. For example, sodium hydroxide ($NaOH$) is a common base.
Example:
Sodium hydroxide ($NaOH$) + Water ($H_2O$) $\rightarrow$ Sodium ions ($Na^+$) + Hydroxide ions ($OH^-$)

Indicators

Indicators are substances that change color in the presence of acids or bases. For example, litmus paper turns red in acidic solutions and blue in basic solutions.
Example:
Litmus paper + Acid $\rightarrow$ Red color
Litmus paper + Base $\rightarrow$ Blue color

Common Mistakes

• Misidentifying substances as acids or bases based on taste
• Confusing indicators with reactants in chemical reactions

Key Points

• Acids release hydrogen ions ($H^+$), bases release hydroxide ions ($OH^-$)
• Acids have a pH less than 7, bases have a pH greater than 7
• Indicators change color in the presence of acids or bases

Practice Questions

1. What is the pH of a solution that releases hydroxide ions?
2. Explain the role of indicators in determining whether a substance is acidic or basic.
3. Identify the type of reaction that occurs when hydrochloric acid reacts with sodium hydroxide.