Calculate The Equivalent Weight Molarity and Normality of The Following

Calculating equivalent weight, molarity, and normality is essential for chemistry students and professionals working with solutions. These measurements help determine the concentration and reactivity of chemical solutions, which is crucial for experiments, industrial processes, and quality control.

What is Equivalent Weight?

The equivalent weight of a substance is the mass of one mole of that substance that will react with or produce 1 mole of hydrogen ions (H⁺) or hydroxide ions (OH⁻). It's particularly important in acid-base chemistry and redox reactions.

Key Point: Equivalent weight is different from molar mass. While molar mass is based on the atomic mass of the element, equivalent weight depends on the substance's reactivity.

For example, the equivalent weight of sulfuric acid (H₂SO₄) is 49 g/mol because it can donate 2 H⁺ ions per molecule. The formula to calculate equivalent weight is:

Equivalent Weight = Molar Mass / n-factor

Where the n-factor is the number of equivalents per mole of the substance.

Molarity vs. Normality

Both molarity and normality measure the concentration of a solution, but they do so differently:

Molarity (M) is the number of moles of solute per liter of solution. It's calculated as moles of solute divided by liters of solution.
Normality (N) is the number of equivalents of solute per liter of solution. It's calculated as moles of solute multiplied by the n-factor, divided by liters of solution.

Molarity (M) = moles of solute / liters of solution Normality (N) = moles of solute × n-factor / liters of solution

For example, a 1 M solution of sulfuric acid (H₂SO₄) has a normality of 2 N because each mole of H₂SO₄ provides 2 equivalents of H⁺ ions.

How to Calculate

To calculate equivalent weight, molarity, and normality, follow these steps:

Determine the molar mass of the substance using the periodic table.
Identify the n-factor for the substance based on its reactivity.
Calculate the equivalent weight using the formula: Equivalent Weight = Molar Mass / n-factor.
For molarity, divide the moles of solute by the volume of the solution in liters.
For normality, multiply the moles of solute by the n-factor and divide by the volume of the solution in liters.

Here's an example calculation for hydrochloric acid (HCl):

Example: Calculate the equivalent weight, molarity, and normality of 10 g of HCl dissolved in 1 L of solution.

1. Molar mass of HCl = 36.46 g/mol

2. Moles of HCl = 10 g / 36.46 g/mol ≈ 0.274 mol

3. n-factor for HCl = 1 (it donates 1 H⁺ ion per molecule)

4. Equivalent weight = 36.46 g/mol / 1 = 36.46 g/eq

5. Molarity = 0.274 mol / 1 L = 0.274 M

6. Normality = 0.274 mol × 1 / 1 L = 0.274 N

Practical Applications

Understanding equivalent weight, molarity, and normality is crucial in various fields:

Chemical Industry: For precise formulation of chemicals and solutions.
Laboratory Work: To ensure accurate reactions and measurements.
Environmental Science: For analyzing water quality and pollution levels.
Medicine: In pharmaceutical formulations and drug delivery systems.

Common Mistakes

When calculating these values, avoid these common errors:

Confusing equivalent weight with molar mass.
Using the wrong n-factor for the substance.
Incorrectly measuring the volume of the solution.
Not accounting for dilution when preparing solutions.

Tip: Always double-check your calculations and verify the n-factor for each substance using reliable chemical references.

Frequently Asked Questions

What is the difference between equivalent weight and molar mass?

Molar mass is the mass of one mole of a substance based on its atomic composition, while equivalent weight depends on the substance's reactivity and is used in acid-base and redox reactions.

How do I determine the n-factor for a substance?

The n-factor is determined by the number of equivalents the substance can donate or accept in a reaction. It's typically found in chemical reference tables or textbooks.

Can molarity and normality be the same for a substance?

Yes, if the n-factor is 1 (like for hydrochloric acid), the molarity and normality will be the same. For substances with n-factors greater than 1, normality will be higher than molarity.