Problem 19 - A Complete Resource Book in Chemistry for JEE Main

Question

Normality of \(0.04 \mathrm{M} \mathrm{H}_{2} \mathrm{SO}_{4}\) is (a) \(0.02 \mathrm{~N}\) (b) \(0.01 \mathrm{~N}\) (c) \(0.04 \mathrm{~N}\) (d) \(0.08 \mathrm{~N}\)

Step-by-Step Solution

Answer

The normality of 0.04 M H₂SO₄ is 0.08 N (option d).

Step 1: Understand Normality

Normality is a measure of concentration equivalent to molarity multiplied by the number of equivalents per mole of solute. For acids, the number of equivalents is determined by the number of H⁺ ions the acid can provide. H₂SO₄ is a diprotic acid, meaning it can provide 2 H⁺ ions per molecule.

Step 2: Calculate the Number of Equivalents

For H₂SO₄, each molecule can provide 2 H⁺ ions. Therefore, the number of equivalents per mole is 2.

Step 3: Use the Normality Formula

The formula for normality ( N) in relation to molarity ( M) is N = M imes ext{number of equivalents}. Here, the molarity ( M) is 0.04 M and the number of equivalents is 2.

Step 4: Perform the Calculation

Using the formula, calculate the normality: N = 0.04 imes 2 = 0.08 N.

Step 5: Select the Correct Answer

Compare the calculated normality with the given options: (a) 0.02 N, (b) 0.01 N, (c) 0.04 N, (d) 0.08 N. The calculated normality is 0.08 N, which matches option (d).

Key Concepts

Molarity

Molarity is a key concept in chemistry to describe the concentration of a chemical solution. It tells us how many moles of a solute are present in one liter of solution. Molarity is usually denoted by the letter 'M'.
To calculate molarity, we use the formula:

• M = \( \frac{\text{moles of solute}}{\text{liters of solution}} \)

The solute is the substance dissolved in the liquid, creating a solution. Molarity helps us understand how strong or weak a solution is. This is important in experiments and industrial processes, where precise chemical reactions are crucial.
For example, if you have 0.04 moles of sulfuric acid \((\text{H}_2\text{SO}_4)\) in one liter of solution, you say the solution is 0.04 M. Understanding molarity paves the way for learning about other concentration measures like normality.

Diprotic Acid

A diprotic acid is a type of acid that can donate two protons or hydrogen ions \((\text{H}^+)\) per molecule when dissolved in water. Sulfuric acid \((\text{H}_2\text{SO}_4)\) is a classic example of a diprotic acid.

• In the first ionization step, \(\text{H}_2\text{SO}_4\) releases one \(\text{H}^+\) ion, forming \(\text{HSO}_4^-\).
• In the second step, \(\text{HSO}_4^-\) can release another \(\text{H}^+\) ion to form \(\text{SO}_4^{2-}\).

This means that each molecule of a diprotic acid like sulfuric acid can contribute two hydrogen ions, making it significant in stoichiometry calculations such as normality.
Such acids are essential for understanding and calculating equivalent weight and normality, as they introduce more hydrogen ions taking part in acid-base reactions.

Chemical Concentration

Chemical concentration is a fundamental concept in chemistry that refers to the abundance of a solute in a given volume of solvent. It tells us how much solute is present in a mixture, providing insights into its properties and how it might react.
Concentration can be expressed in various ways:

• **Molarity** - defined as moles of solute per liter of solution.
• **Normality** - defined in terms of equivalent amounts, considering the reacting capacity of molecules.
• **Mass percent, volume percent,** and **mole fraction** are other common methods.

It's essential to choose the right form of concentration depending on what you're investigating. For instance, molarity or normality might be preferred in reactions as they relate directly to the amounts of substances reacting with each other.

Equivalent Weight

Equivalent weight is a concept used in chemistry to compare the mass of one substance that will combine with or displace a fixed amount of another substance. It is particularly useful in reactions involving acids and bases.
To calculate the equivalent weight of an acid, you divide its molar mass by the number of hydrogen ions, \(\text{H}^+\), it can donate. This number is called the valency factor.

• For sulfuric acid \((\text{H}_2\text{SO}_4)\), the molar mass is about 98 grams per mole and it has a valency factor of 2 (since it releases 2 hydrogen ions). Thus its equivalent weight is \(\frac{98}{2} = 49\) grams per equivalent.

Understanding equivalent weight helps in calculating normality, as normality relates to the number of equivalents of solute present in the solution. This ensures precise measurements in chemical reactions, especially in titration and solution formulation.