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JEE MainChemistryIonic Equilibrium

A student needs to prepare a buffer solution of pH = 5.04 by adding 0.2 M NaOH solution to 100 mL of 0.3 M acetic acid. The volume of the NaOH solution required to be added is: (Given: pK _ a of acetic acid = 4.74 , 2 = 0.30 )

Options

  1. A300 mL
  2. B50 mL
  3. C75 mL
  4. D100 mL

Correct answer

D. 100 mL

Step-by-step solution

Initial millimoles of acetic acid = 100 0.3 = 30 mmol . Let V mL of 0.2 M NaOH be added. The millimoles of NaOH added = 0.2V . The added NaOH reacts completely with acetic acid to form sodium acetate: CH ₃ COOH + NaOH CH ₃ COONa + H ₂ O Millimoles of salt ( CH ₃ COONa ) formed = 0.2V Millimoles of acid ( CH ₃ COOH ) remaining = 30 - 0.2V Using the Henderson-Hasselbalch equation: pH = pK _ a + ( [ Salt ] [ Acid ] ) 5.04 = 4.74 + ( 0.2V 30 - 0.2V ) 0.30 = ( 0.2V 30 - 0.2V ) Since 2 = 0.30 , we have: 0.2V 30 - 0.2V =

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