Short Answer

pH is a scale used to measure how acidic or basic a solution is. It tells us the concentration of hydrogen ions (H⁺) present in the solution. A lower pH value means stronger acidity, and a higher pH value means stronger basicity. Pure water has a pH of 7, which is considered neutral.

The pH scale usually ranges from 0 to 14. Substances like lemon juice and vinegar have low pH, showing acidity, while substances like soap and baking soda have high pH, showing basic nature. pH is widely used in science, health, agriculture, and industry to check acidity levels.

Detailed Explanation :

pH

The term pH stands for “potential of hydrogen” or “power of hydrogen.” It is a numerical scale used to determine whether a solution is acidic, basic, or neutral. The pH of a solution depends on the number of hydrogen ions (H⁺) present. The more hydrogen ions present, the more acidic the solution becomes. The fewer hydrogen ions present, the more basic the solution is.

The pH scale is one of the most important tools in chemistry because it helps us understand chemical reactions, solution behaviour, and environmental conditions. It is used in laboratories, industries, medicine, agriculture, and many everyday applications.

Meaning of pH

pH is defined as the negative logarithm of the hydrogen ion concentration in a solution.
Mathematically:

pH = –log [H⁺]

This means:

• A solution with a high concentration of H⁺ ions will have a low pH (acidic).
• A solution with a low concentration of H⁺ ions will have a high pH (basic).

Because the pH is based on a logarithmic scale, each step on the pH scale represents a tenfold change in acidity. For example, a solution with pH 3 is ten times more acidic than a solution with pH 4.

The pH Scale

The pH scale ranges from 0 to 14:

• pH < 7 → acidic solution
• pH = 7 → neutral solution
• pH > 7 → basic solution

Examples:

• Stomach acid: pH around 1–2
• Lemon juice: pH about 2
• Pure water: pH 7
• Baking soda: pH 8–9
• Soapy water: pH 12

This scale helps classify common substances easily.

Importance of pH

The pH value is used in many fields:

1. Human Body

The human body maintains a stable pH in blood (around 7.4). Even slight changes can affect body functions. Stomach acid has a low pH to help digestion.

2. Agriculture

Soil pH affects plant growth. Some plants prefer acidic soil, while others grow better in alkaline soil. Farmers check soil pH to improve crop yield.

3. Environment

Aquatic life depends on stable pH levels. Acid rain lowers the pH of water bodies, harming fish and plants.

4. Industry

Industries check pH during manufacturing of medicines, cosmetics, soaps, food items, and chemicals.

5. Household Products

Cleaning agents, shampoos, and skincare products are designed based on pH to make them safe and effective.

How pH Is Measured

There are several methods to measure pH:

1. pH Paper or Litmus Paper

This paper changes colour when dipped in a solution. The colour is compared with a standard scale to determine pH.

2. pH Meter

A digital device that gives accurate pH readings using an electrode.

3. Natural Indicators

Substances like turmeric, red cabbage, and beetroot show colour changes in acidic or basic solutions.

Factors Affecting pH

Several factors can change the pH of a solution:

1. Temperature

pH can change with temperature because ionisation varies.

2. Dilution

Adding water affects hydrogen ion concentration, slightly changing pH.

3. Chemical Reactions

Acid–base reactions can increase or decrease pH.

4. Dissolved Gases

Gases like CO₂ can form carbonic acid in water, lowering pH.

Role of pH in Everyday Life

pH affects many things in our daily routine:

• Shampoo pH protects hair.
• Toothpaste is basic to neutralise acids in the mouth.
• Swimming pools must be kept at a safe pH.
• Cooking (like curd formation) depends on pH changes.
• Food preservation often requires controlling acidity.

Thus, the pH scale is essential for daily living and scientific understanding.

Conclusion

pH is a measure of how acidic or basic a solution is, determined by the concentration of hydrogen ions. The pH scale ranges from 0 to 14, with lower values representing acids, higher values representing bases, and 7 indicating neutrality. pH is a key concept in chemistry and plays an important role in biology, agriculture, industry, and environmental science. Understanding pH helps us control chemical reactions and maintain safe and healthy conditions in daily life.