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A certain amount of PCl ₃ is completely hydrolyzed in excess of water. The resulting acidic mixture requires exactly 15 moles of Ca(OH) ₂ for complete neutralization. The number of moles of PCl ₃ initially taken is

Options

  1. A5
  2. B3
  3. C10
  4. D6

Correct answer

D. 6

Step-by-step solution

The hydrolysis reaction of PCl ₃ is: PCl ₃ + 3 H ₂ O H ₃ PO ₃ + 3 HCl Let x be the number of moles of PCl ₃ taken. Moles of H ₃ PO ₃ formed = x Moles of HCl formed = 3x H ₃ PO ₃ is a dibasic acid, so it furnishes 2 H ^+ ions per molecule. HCl is a monobasic acid, furnishing 1 H ^+ ion per molecule. Total moles of H ^+ furnished = 2x + 3x = 5x Moles of OH ^- furnished by 15 moles of Ca(OH) ₂ = 15 2 = 30 For complete neutralization: Moles of H ^+ = Moles of OH ^- 5x = 30 x = 6 Answer: 6

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