Factors Affecting Acid Strength

You are already aware of the term acids. You have learnt about the physical and chemical properties of acids. Some simple ones are – they have a pH below 7, they turn blue litmus paper red, they have a sour taste and they react with alkalis to form salts. One interesting factor about acids is the acid strength. In this article, we will talk about acid strength and the factors which affect it.

acid strength

What is Acid Strength?

Acid strength is the measure of the ability of the acid to lose its H+ ion. It depends on several factors which we will discuss in the subsequent sections.

What are Strong and Weak Acids?

A strong acid is the one which completely ionises in a solution whereas, a weak acid only partially ionises. Strong acids are corrosive in nature and cause severe burns when they come in contact with skin. But the weak acids are only mildly corrosive and are even present in our food and body. Hydrochloric acid and sulphuric acid are examples of strong acid. Ethanoic acid, citric acid (present in citric fruits) and acetic acid (present in vinegar) are a few examples of weak acids.

Factors Affecting Acid Strength

  • It depends on the strength of the H-A bond. The weaker the bond, the lesser the energy required to break it. Hence, the acid is strong.
  • The polarity of the H-A bond affects its acid strength. If the bond is highly polar, the proton tends to leave the molecule more easily, making it a strong acid.
  • However, bond strength is more important when we consider and compare acid strengths of elements in the same group of the periodic table, using the above two factors.
  • Nevertheless, when we compare the acid strengths of elements in the same row, priority is given to the polarity of the H-A bond.
  • The atomic size of A also affects the acid strength. As the atom becomes larger, the bond gets weaker. Consequently, acid strength increases.


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Practise This Question

An ionizing solvent has