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EEJ MAIN Chemistry QUESTION #7168
Question 1
Which of the following salt solutions is the most efficient for the coagulation of an arsenious sulphide sol?
  • $BaCl_{2}$
  • $AlCl_{3}$✔️
  • $NaCl$
  • $Na_{2}SO_{4}$
Correct Answer Explanation
For a negatively charged sol like arsenious sulphide, the cation with the highest positive charge will be the most effective coagulant (Hardy-Schulze Rule). Comparing the cations:
  • $Na^{+}$ from $NaCl$ and $Na_{2}SO_{4}$ (+1)
  • $Ba^{2+}$ from $BaCl_{2}$ (+2)
  • $Al^{3+}$ from $AlCl_{3}$ (+3)
$AlCl_{3}$ is the most effective.