Relation Between Normality and Molarity, Formula, Differences, Examples

Anand Classes Study Material and Notes to learn the relationship between Normality (N) and Molarity (M) with formulas, key differences, and solved examples. Understand Normality vs Molarity for Class 11 CBSE Chemistry, JEE, and NEET exams, including calculation methods and practical applications.

Q1: What is the Relationship Between Normality and Molarity ?

Normality (N) and Molarity (M) are both measures of the concentration of a solution. However, normality considers the reactive capacity (n-factor) of a substance, while molarity only considers the number of moles of solute per liter of solution.

The relationship between Normality (N) and Molarity (M) is given by: $$N = M \times \text{n-factor}$$

where:

• N = Normality (equivalents per liter)
• M = Molarity (moles per liter)
• n-factor = The number of H⁺ ions (for acids), OH^– ions (for bases), or electrons transferred (for redox reactions) per mole of solute.

Q2: How Does n-factor Differ for Acids, Bases, and Redox Compounds?

Q3: Can You Give Examples Showing the Relationship Between Normality and Molarity?

Example 1: For Acids

Let’s consider H₂SO₄ (Sulfuric acid), which releases 2 H⁺ ions per molecule.

• Given: 1 M solution of H₂SO₄
• n-factor = 2 (since it releases 2 H⁺ ions)
• Using the formula: $N = M \times n$
• $N = 1 \times 2 = 2N\:$ So, a 1 M solution of H₂SO₄ is actually 2 N.

Example 2: For Bases

Consider Ca(OH)₂ (Calcium Hydroxide), which releases 2 OH^– ions per molecule.

• Given: 0.5 M solution of Ca(OH)₂
• n-factor = 2 (since it releases 2 OH^– ions)
• Using the formula: $N = 0.5 \times 2 = 1 N\:$ So, a 0.5 M solution of Ca(OH)₂ is actually 1 N.

Example 3: For Redox Reactions

Consider Fe²⁺ → Fe³⁺, where 1 electron is lost per ion.

• Given: 0.1 M Fe²⁺ solution
• n-factor = 1 (since Fe²⁺ loses 1 electron)
• Using the formula: $N = 0.1 \times 1 = 0.1 N\:$ So, a 0.1 M Fe²⁺ solution is also 0.1 N.

Q4: When Are Normality and Molarity the Same?

For substances where n-factor = 1, normality and molarity are the same. Examples:

• HCl (Hydrochloric Acid) → n-factor = 1
  • 1 M HCl = 1 N HCl
• NaOH (Sodium Hydroxide) → n-factor = 1
  • 1 M NaOH = 1 N NaOH
• AgNO₃ (Silver Nitrate) in Redox Reactions → n-factor = 1
  • 1 M AgNO₃ = 1 N AgNO₃

Q5: Why is Normality Used Instead of Molarity?

• Titrations & Neutralization Reactions: Since acids and bases react based on equivalents, normality gives a direct ratio.
• Redox Reactions: Electron transfer depends on n-factor, making normality more accurate.
• Complex Reactions: In precipitation reactions and salt reactions, normality simplifies calculations.

Normality (N) vs. Molarity (M) – Understanding the Key Difference

Both Normality (N) and Molarity (M) measure the concentration of a solution, but they serve different purposes:

• Molarity (M): Counts the number of moles of solute per liter of solution.
• Normality (N): Takes into account the reactive capacity of a substance in a given reaction by considering the n-factor (equivalents).

Therefore,

✅ Molarity (M) tells us the number of molecules present.
✅ Normality (N) tells us how reactive those molecules are in a given reaction!

This is why normality is crucial in titrations, redox reactions, and complex chemical processes where the actual reactive capacity of a solution matters. 🎯

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