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Question 600059
JEE Chemistry · Hard

Mole Concept and Stoichiometry: Molarity vs Molality MCQ

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Molarity vs MolalityHardQuestion 600059

Question

For a dilute aqueous solution (density ≈ 1 g/mL), the relationship between molarity M and molality m is approximately:
  1. A
    M = m
  2. B
    M > m always
  3. C
    M < m always
  4. D
    M ≈ m only when the molar mass of solute is 18 g/mol
    Correct

Correct answer

M ≈ m only when the molar mass of solute is 18 g/mol

Explanation

M = m when solute molar mass = 1000/(1000/Msolute) ≈... For very dilute aqueous solutions, M ≈ m because 1 L ≈ 1 kg. More precisely: M/m = (1 − M×Ms/1000ρ) → M ≈ m for dilute solutions with ρ ≈ 1.

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