What is Acid?

Acid is a chemical substance that has a sour taste and the ability to react with certain metals to produce hydrogen gas. It is characterized by its ability to donate protons (H+) or accept electrons in a chemical reaction. Acids are also known to turn blue litmus paper red and have a pH value less than 7.

Indicators and Few Common Indicators

Indicators are substances that change color in the presence of acids or bases. They are used to determine the nature of a given substance as acidic, basic, or neutral. Some common indicators include:

1. Litmus paper: It is a commonly used indicator that turns red in the presence of an acid and blue in the presence of a base.

2. Phenolphthalein: This indicator is colorless in acidic solutions and turns pink in basic solutions.

3. Methyl orange: It is an indicator that is red in acidic solutions and yellow in basic solutions.

4. Universal indicator: This indicator is a mixture of several dyes and can show a range of colors depending on the pH of the solution.

Acids, Bases, and Salts

Acids, bases, and salts are three important categories of chemical substances. Let's understand each of them:

1. Acids:
- Acids are substances that can donate protons (H+) or accept electrons.
- They have a sour taste, turn blue litmus paper red, and have a pH value less than 7.
- Examples of common acids include hydrochloric acid (HCl), sulfuric acid (H2SO4), and acetic acid (CH3COOH).

2. Bases:
- Bases are substances that can accept protons (H+) or donate electrons.
- They have a bitter taste, turn red litmus paper blue, and have a pH value greater than 7.
- Examples of common bases include sodium hydroxide (NaOH), potassium hydroxide (KOH), and ammonia (NH3).

3. Salts:
- Salts are formed when an acid reacts with a base, resulting in the neutralization of their properties.
- They are ionic compounds composed of positive and negative ions.
- Examples of common salts include sodium chloride (NaCl), calcium carbonate (CaCO3), and potassium nitrate (KNO3).

Class 7 Science Explanation

In Class 7 Science, the concepts of acids, bases, and salts are introduced. Students learn about their properties, how they can be identified using indicators, and their importance in various chemical reactions. They also understand the pH scale and how it is used to measure the acidity or alkalinity of a substance.

The topic helps students develop a basic understanding of chemical reactions, the nature of substances, and their behavior in different environments. It lays the foundation for further studies in chemistry and provides a framework for understanding various chemical processes in daily life.

Overall, the study of acids, bases, and salts in Class 7 Science is essential for building a strong foundation in chemistry and developing scientific thinking skills.