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Strength of an Acid and Base pH Scale

Grade 10
May 4, 2023

In this article, we’ll learn about the strength of an acid and base pH scale, but first, understand the acid and base. Let’s begin

Acid and Base 

Acid is a substance that is sour in taste, and the base is a substance that is bitter in taste. Examples of acids are acetic acid and citric acid, as in lemon. Some examples of the bases are Sodium bicarbonate, Ammonia hydroxide.

Identification of Acids & Bases

A simple method to identify acid or base is by using litmus paper. Red litmus turns blue with the base, and blue litmus turns red with acid. With the help of litmus paper and the procedure, we can easily find whether the solution is acidic or not.


Universal Indicator

A universal indicator is a combination of various solutions that exhibit a wide range of colors to identify acids & bases with a wide range of pH values called a pH scale. The pH scale is a scale of values ranging from 0 to 14 measuring hydrogen ion concentration in a solution.

pH values:

pH values range from 0 to 14 values.


Importance of pH values:

pH values provide information about hydrogen ion concentration in a given solution, which helps in knowing a substance’s acidic and basic strength.

Hydrogen ion Concentration:

H+ is said to be a hydrogen ion or proton. The amount of H+ in a given solution decides the nature of the solution as either acidic or basic. An acid produces more H+ ions in water. On the other hand, a base produces less number of H+ ions or more OH ions in water.

Strength of Acid and Base pH Scale

Strength of an Acid

Substances which show less pH values are acidic. Substances ranging in pH values from 0 to 7 are acidic. Acidic substances with pH values ranging from (0 to 3) are highly acidic and are called strong acids.

Examples: Hydrochloric acids(HCl), Sulphuric acid(H2SO4)

Weak Acids:

Acidic substances with pH values ranging from (4 to 7) are slightly acidic and are called weak acids.


Examples:  Acetic acids (CH3COOH), Oxalic acid(C2H2O4)

Strength of Base

Substances which show more pH values are basic. For example, substances ranging in pH values from 7 to 14 are basic.

Strong Bases:

Basic substances with pH values ranging from (11 to 14) are highly basic and called strong bases.

Examples:  Sodium hydroxide(NaOH), Magnesium hydroxide (Mg(OH)2

Weak Bases:

Basic substances with pH values ranging from (7  to 10) are slightly basic and are called weak bases.

Examples: Ammonia (NH)3, Aluminum hydroxide (Al(OH)3)

Neutral solutions

Solutions or substances with a pH value of exactly 7 are considered neutral substances.

Example: Pure water

Activity for Comparison

Consider the following different materials available around you.

  1. Saliva before a meal
  2. Saliva after a meal
  3. Cool drink
  4. Carrot juice
  5. Coffee
  6. Tomato juice
  7. Tap water
  8. NaOH or soap
  9. HCl or gastric juice
  10. Lemon juice


  • Collect these materials and try to test the pH of each substance with the litmus papers (blue or red) and note the colors.
  • Match the colors obtained with colors of the pH scale and note the approximate pH values.
  • Observe the range of pH and find the nature of the substances.


  • Electrolytes are substances that split into ions in the water.
  • Substances that split completely and easily in water are strong electrolytes like HCl, NaOH, etc., including acids and bases.
Acid and Base pH Scale


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