The concentration of a solution may be defined as the amount of solute present in the given quantity of the solution.

The concentration of solution may be expressed in several ways as discussed below:

Mass Percentage

The mass percentage of a component in a given solution is the mass of the component per 100 g of the solution.

\[\text{Mass percentage of a component = }\frac{\text{Mass of the component in the solution}}{\text{Total mass of the solution}} × 100\]

Volume percentage

In the case of a liquid dissolved in another liquid, it is convenient to express the concentrations in volume percentage. The volume percentage is defined as the volume of the component per 100 parts by the volume of the solution.

Mass by volume percentage (w/v)

Sometimes, we express the concentrations as weight/volume. It is the mass of solute dissolved in 100 mL of the solution

Molarity of a solution

The molarity of a solution is defined as the number of moles of the solute dissolved per litre of the solution.It is represented as ′M′. Mathematically,

\[Molarity = \frac{\text{Moles of solute}}{\text{Volume of the solution (in mL)}} × 1000\]

Molarity of a solution

The molarity of a solution is defined as the number of moles of the solute dissolved per litre of the solution.

Molality of the solution

The molality of a solution is defined as the number of moles of the solute dissolved per 1000 g (or 1 kg) of the solvent.

The equivalent weight of an acid is obtained by dividing its molecular weight by its:

Basicity

The correct answer is option 2. Basicity.

Let us clarify the concept of equivalent weight and how it applies to acids.

The equivalent weight of an acid is a concept used to compare the reactivity of different acids based on the number of replaceable hydrogen ions \((H^+)\) they can donate in a chemical reaction. It is calculated as follows:

\(\text{Equivalent weight of an acid} = \frac{\text{Molecular weight of the acid}}{\text{Basicity of the acid}}\)

Basicity of an Acid

The term basicity of an acid refers to the number of hydrogen ions \((H^+)\) that one molecule of the acid can donate. For example:

Hydrochloric acid \((HCl)\) has a basicity of 1 because each molecule can donate 1 hydrogen ion.

Sulfuric acid \((H_2SO_4)\) has a basicity of 2 because each molecule can donate 2 hydrogen ions.

Phosphoric acid \((H_3PO_4)\) has a basicity of 3 because each molecule can donate 3 hydrogen ions.

Incorrect Options

1. Acidity: This term is often confused with basicity, but in the context of equivalent weight, we are specifically referring to the number of replaceable hydrogen ions, which is defined as basicity.

3. pH: This measures the hydrogen ion concentration in a solution but does not relate directly to the calculation of equivalent weight.

4. None of these: Since the correct term is basicity, this option is not applicable.

Conclusion

The equivalent weight of an acid is obtained by dividing its molecular weight by its basicity, which accurately reflects the number of replaceable hydrogen ions \((H^+)\) that the acid can donate in a reaction. Therefore, the correct answer is 2. Basicity.