Definition of pH scale in Chemistry

Definition of pH scale in Chemistry. Interested in learning about the pH scale? This guide explains how pH works and provides examples of common acids, bases and everyday items that have a pH level.


The pH scale is a measure of how acidic or basic a substance is. It’s used to categorize substances and calculate their levels of acidity or alkalinity. Understanding the pH scale can be beneficial for different sectors, including food and beverage manufacturers, water purification engineers and medical professionals.

What is the pH Scale?
The pH scale is a numerical scale used to measure how acidic or basic a substance is. It ranges from 0 to 14; substances with a pH lower than 7 are considered acidic, while those with a pH higher than 7 are considered basic or alkaline. A neutral pH of 7 means that the substance has equal parts acid and base, neither of which can react with water.

Understanding Acids and Bases.
Acids are compounds that split into hydrogen ions (H+) in water, while bases can release hydroxide ions (OH-) into a solution. For example, vinegar is an acid and baking soda is a base. The stronger the acid or base is, the greater the variation in pH levels. Some everyday items, such as lemon juice (2-3) and bleach (13), have very strong acids or bases respectively.

Examples of Common Substances With pH Levels.
Acids, bases and neutral substances may be classified by their pH level, with numbers ranging from 0-14. Examples of common substances include baking soda (8.2 – 9.6), coffee (5-6), and blood (7.35-7.45). In addition to these three categories, some substances are more specific: tomatoes have a pH of 4-4.3, honey is close to being neutral at pH 3-4, and ethanol is a very strong base with a pH level of 11-13.

Importance of Monitoring pH Levels.
Knowing the pH level of a substance can be important for many reasons. For example, it helps to differentiate between an acid and base so that proper safety precautions can be taken when handling certain materials, as well as to determine the suitability of certain products for particular applications. In addition, measuring changes in pH over time can signal shifts in environmental or chemical conditions and alert the need for further investigation.

Interpreting a pH Meter Reading.
Knowing how to read a pH meter is essential for understanding the pH level of a solution. A pH meter usually consists of two main parts – an electrode and measuring instrument. The electrode is inserted into a sample and sends electrical signals to the meter, which then displays the corresponding pH reading. Generally, lower pH readings indicate acidic solutions while higher readings indicate bases or alkaline solutions. Anything in between indicates neutrality. It is important to use the right calibration standards when measuring a solution’s pH level in order to get accurate readings.

The pH scale in Chemistry represent values with specific color.

The pH is the degree of acidity or basicity of a chemical substance in aqueous systems.

pH scale
pH scale


In simple terms pH is the power of hydrogen ion or hydronium ion concentration.

It can be calculated by :

The pH scale by Equation

pH = – log10[H+] or 

pH = – log10[H3O+

[ ] square bracket represents the concentration in mol/dm3

Example: If a sample of an acid is found to have[ H+]=1X10-4

Than pH = – log10[1X10-4]

pH = -[-4 log 10]

pH= 4

H+ Concentration Formula

If you want to find out [ H+] than you can use the following formula:

H+ concentration = 10-pH

Few questions: 1. What is pH scale?

2. How can you check the acidity of water?

3. Can you differentiate between acid rainwater and pure water? Write the process for this experiment.

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