Question

The equivalent mass of an acid is equal to: (a) Molecular mass \(\times\) acidity (b) Molecular mass \(\times\) basicity (c) Molecular mass/acidity (d) Molecular mass/basicity

Short answer

The correct answer is (c) molecular mass/acidity.

Step-by-step solution

Understand Equivalent Mass of an Acid

The equivalent mass of an acid is defined as the mass of the acid that can furnish one mole of hydrogen ions (H⁺) in a reaction. It is a useful concept in titration and stoichiometry.

Identify Key Terms

Acidity refers to the number of hydrogen ions one molecule of acid can donate. Basicity, in this context, would mean the number of hydrogen ions received or neutralized by a base.

Evaluate Formula Options

Given the definitions, the equivalent mass of an acid is calculated by dividing the molecular mass by the number of moles of hydrogen ions furnished. Therefore, the formula is molecular mass divided by acidity.

Select the Correct Answer

According to the definition and evaluation in the previous steps, the correct formula for the equivalent mass of an acid is option (c) "Molecular mass/acidity."

Key concepts

Titration

Titration is a laboratory technique used to determine the concentration of an unknown solution. By adding a solution of known concentration, called the titrant, to the unknown solution in a controlled manner, you can observe the chemical reaction's endpoint.
During this process, you add the titrant slowly until the reaction reaches an endpoint, often indicated by a color change if an indicator is used.

• The titrant is the solution of known concentration, used to react with the unknown solution.
• Indicators are substances that change color at (or near) the endpoint, providing a visual cue.
• Endpoints are the points during a titration where the reaction is considered complete.

Beyond knowing specific concentrations, titrations are instrumental in understanding the reactivity and properties of acids and bases, like their acidity or basicity.

Acidity

Acidity is a measure of a substance's ability to donate protons (H⁺ ions) to a base. This concept is crucial when calculating the equivalent mass of acids.
The number of H⁺ ions an acid can donate in a chemical reaction determines the acidity. For instance, sulfuric acid (H₂SO₄) has two hydrogen ions that can donate, making its acidity 2.
Understanding acidity helps in:

• Predicting how an acid will behave in chemical reactions.
• Calculating the equivalent mass, by dividing molecular mass by the acid's acidity.

By mastering the concept of acidity, you can better predict and control chemical reactions involving acids.

Molecular Mass

Molecular mass, or molecular weight, refers to the mass of a given molecule. It is calculated as the sum of the atomic masses of all atoms in a molecule.
For example, the molecular mass of water (H₂O) is 2(1.01) + 16.00 = 18.02 g/mol. This is vital for many calculations, such as determining the equivalent mass of an acid.
Knowing the molecular mass enables you to:

• Identify how much of a substance you are dealing with by converting grams to moles.
• Calculate equivalent mass when paired with understanding of acidity.
• Understand and predict the stoichiometry in chemical reactions.

The precise calculation of molecular mass forms the foundation for various chemical formulations and reactions, connecting it intricately to both acidity and the process of titration.