An Overview of the Weak Acids

Acids form an essential topic in chemistry. Students go through different types of acids, including strong acids and weak acids. A strong acid is one that dissociates completely when dissolved in water, while a weak acid doesn’t wholly dissociate in water. Some of the common weak acid examples are malic acid, carboxylic acid, etc.

Let us have an overview of the weak acids and the common examples. We’ll cover the properties of a weak acid, acid dissociation constant Ka, and its relation to the primary weak acids. Let us start with the definition of weak acid.

What is a weak acid?

Common words like strong, weak, concentrated, and dilute are used with the acids in chemistry. While concentrated and dilute are different terms based on the concentration of acid or its purity, strong or weak acid is based on its acidity.

A weak acid is an acid that doesn’t get completely dissociated in the water. Hence, it is opposite to the strong acid, which gets 100% dissociated in water. A simple example of a weak acid is ethanoic acid. The chemical reaction of ethanoic acid is

CH3COOH + H2O  ⇌ CH3COO– + H30–

At any time, only 1% of the ethanoic acid gets dissociated in the water while the others remain as the ethanoic molecules only. It reacts with water to release ethanoate ions and hydroxonium ions. Some of the weak acids are hydrogen fluoride or other organic acids. The lower the value of the pKa or dissociation constant, the stronger is the acid, while the higher the value of the pKa, the weaker is the acid.

Properties of weak acid

The key properties of the weak acid are:

• These acids never dissociate completely in water.
• The weak acids react with strong bases to form the conjugate base of the weak acid. There is an equilibrium between the conjugate base thus formed and the weak acid in water.
• It is easy to distinguish a strong acid and a weak acid based on the acid dissociation equilibrium in non-aqueous solvents and the estimated pKa values of the water.
• Ka or dissociation constant is used to determine the pH value of the weak acid solution.
• A weak acid has a highly strong conjugate base.
• Both forward and reverse reactions are possible for the ionisation of the weak acid.
• The weak nature of the weak acid depends on the electronegativity and the size of the atom bonded to the hydrogen atom in the acid.
• Weak acids are important in chemistry to prepare buffer solutions using weak bases.
• The majority of all acids are weak in nature.
• It is estimated that only 1% of the weak acid solution dissociates in water in 0.1 moles per litre of the solution.
• The higher the value of the Ka, the weaker the acid is. The values of Ka for some weak acids are  

• The higher the value of the pKa, the weaker the acid is. The values of pKa for some weak acids are  

Weak acid examples

Some of the common weak acids are:

• Formic acid or HCOOH
• Acetic acid or CH3COOH
• Trichloroacetic acid or CCl3COOH
• Hydrofluoric acid or HF
• Hydrocyanic acid or HCN
• Hydrogen sulphide or H2S
• Water or H2O
• Conjugate acids of weak bases like NH4+

Conclusion

Hence, it is easy to understand all about the properties of the weak acid. It is an acid that can’t get fully dissociated in water and hence remains weak from other counterparts. Different factors like electronegativity and molecular constituents define the acidity of weak acids. 

Some of the weak acid examples are malic acid, carboxylic acid, etc. These acids exist in nature, and malic acid is responsible for the tart flavour in apples and other fruits. Further, all organic acids are weak acids while hydrogen fluoride is the weak inorganic acid.