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Question 890006
JEE Chemistry · Hard

Surface Chemistry: JEE Main MCQ

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JEE MainHardQuestion 890006

Question

Coagulation of a negatively charged colloid is best done by:
  1. A
    Al³⁺ (highest valence cation coagulates most effectively — Hardy-Schulze rule)
    Correct
  2. B
    Na⁺
  3. C
    Ca²⁺
  4. D
    Cl⁻ (anion)

Correct answer

Al³⁺ (highest valence cation coagulates most effectively — Hardy-Schulze rule)

Explanation

Hardy-Schulze rule: for coagulating a negatively charged colloid, cations are needed. Higher the valence of the cation, greater the coagulating power. Al³⁺ > Ca²⁺ > Na⁺ (in terms of coagulating power). Alum (Al₂(SO₄)₃) is used to purify water (coagulates negatively charged clay/silt colloids).

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