Molarity and Normality for NEET: Key Points, Tricks & MCQs

What NEET Asks

• Typically 1-2 questions from Solutions chapter, often involving concentration terms.
• Calculations based on Molarity, Normality, and their inter-relationship are frequently tested.
• Conceptual questions regarding temperature dependence and n-factor determination are common.

Key Points

• Molarity (M): Moles of solute per litre of solution. $M = \frac{\text{Moles of solute}}{\text{Volume of solution (L)}}$. Unit: mol L⁻¹.
• Normality (N): Gram equivalents of solute per litre of solution. $N = \frac{\text{Gram equivalents of solute}}{\text{Volume of solution (L)}}$. Unit: Eq L⁻¹.
• Equivalent Weight (EW): Molar Mass (MM) / n-factor. $EW = \frac{MM}{n}$.
• n-factor: For acids (basicity), bases (acidity), salts (total positive or negative charge), and redox reactions (change in oxidation state).
• Relationship: $N = M \times n_{factor}$.
• Molarity and Normality are temperature-dependent because they involve the volume of the solution, which changes with temperature.

Must-Know Formula / Reaction

• $N = M \times n_{factor}$
  • $N$: Normality (Eq/L)
  • $M$: Molarity (mol/L)

Common Mistakes

• Students often confuse molarity (volume of solution) with molality (mass of solvent); pay attention to the denominator.
• Don't forget to correctly identify the n-factor for different types of solutes, especially for polyprotic acids (e.g., H₃PO₄ vs H₃PO₃) and redox reagents (medium-dependent).
• Incorrectly using solution volume in mL instead of L for Molarity/Normality calculations is a common error.

Rapid Revision

Both Molarity and Normality are volume-based concentration terms, making them temperature-dependent. The 'n-factor' is key to relating them ($N=M \times n$) and is determined by the solute's nature or its role in a reaction. Always ensure volume is in litres and n-factor is correctly identified for quick, accurate calculations.