Equivalent weight is a concept commonly used in chemistry to determine the equivalent quantity of a substance involved in a given chemical reaction. It is particularly useful when dealing with reactions involving metals in different valency states. When considering a divalent metal, the equivalent weight calculation becomes important as the metal ion has a valency of 2.

In this article, we will delve into the details of calculating the equivalent weight of a divalent metal. We will discuss the concept of equivalent weight, provide a step-by-step guide on how to determine the equivalent weight of a divalent metal, and explore some practical examples to enhance understanding.

Understanding Equivalent Weight:

The equivalent weight of a substance is the mass of that substance which supplies one mole of the reacting species in a chemical reaction. It is the amount of substance that will combine with or displace 1.008 grams of hydrogen, 8 grams of oxygen, or 35.5 grams of chlorine. Equivalent weight is crucial for determining the stoichiometry of chemical reactions, especially in the context of redox reactions where electrons are transferred.

When dealing with metals, the concept of equivalent weight becomes significant as metals can exhibit different valency states. In the case of a divalent metal, such as calcium (Ca^2+), magnesium (Mg^2+), or iron (Fe^2+), the valency of the metal ion is 2. This means that each ion of the metal carries a charge of +2.

Calculating Equivalent Weight of Divalent Metal:

To calculate the equivalent weight of a divalent metal, you can follow these steps:

Step 1: Determine the Atomic Mass of the Metal:

Find the atomic mass of the metal from the periodic table. For example, the atomic mass of calcium (Ca) is 40.08 g/mol.

Step 2: Identify the Valency of the Metal Ion:

Since we are dealing with a divalent metal, the valency of the metal ion is 2. This means each ion carries a charge of +2.

Step 3: Calculate the Equivalent Weight:

The equivalent weight formula for a divalent metal is:
[ Equivalent Weight = Atomic Mass / Valency ]

Using the example of calcium (Ca):
[ Equivalent Weight of Calcium = 40.08 g/mol / 2 = 20.04 g/mol ]

Practical Examples:

Let’s apply the concept to a few practical examples:

1. Calculating Equivalent Weight of Magnesium (Mg^2+):
2. Atomic Mass of Magnesium = 24.31 g/mol
3. Valency = 2

4. Equivalent Weight of Magnesium = 24.31 g/mol / 2 = 12.16 g/mol

5. Calculating Equivalent Weight of Iron (Fe^2+):

6. Atomic Mass of Iron = 55.85 g/mol
7. Valency = 2
8. Equivalent Weight of Iron = 55.85 g/mol / 2 = 27.93 g/mol

These examples demonstrate how the equivalent weight of a divalent metal is determined based on its atomic mass and valency.

Frequently Asked Questions (FAQs):

1. Why is Equivalent Weight Important in Chemistry?

• Equivalent weight is crucial for determining the stoichiometry of chemical reactions, especially in redox reactions where electrons are transferred. It helps in calculating the amount of substances involved in a reaction.

2. How is Equivalent Weight Different from Molecular Weight?

• Molecular weight is the sum of the atomic weights of all atoms in a molecule, while equivalent weight is the mass that supplies one mole of the reacting species. Equivalent weight takes into account the valency of the substance.

3. Can the Valency of a Metal Ion Change in Different Compounds?

• Yes, the valency of a metal ion can vary in different compounds. For example, iron can exist as Fe^2+ in some compounds and Fe^3+ in others, leading to different equivalent weights.

4. How is Equivalent Weight Used in Titrations?

• In titrations, equivalent weight is utilized to determine the concentration of a solution based on the volume of another solution of known concentration that reacts completely with it. It helps in calculating the molarity of the unknown solution.

5. What is the Significance of Divalent Metal Ions in Biological Systems?

• Divalent metal ions play crucial roles in biological systems as cofactors for enzymes, signaling molecules, and structural components. Examples include calcium in muscle contraction and zinc in enzyme catalysis.

In conclusion, understanding how to calculate the equivalent weight of a divalent metal is essential for various applications in chemistry. By following the steps outlined in this article and practicing with practical examples, you can master this concept and apply it in chemical reactions and analyses.