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99 Percentile Qs Bank for JEE MainChemistryIonic Equilibrium

How much of 0.3 M N H 4 O H should be mixed with 30 mL of 0.2 M solution of N H 4 C l to give buffer solution of pH 8.65? (Given: pK b of NH 3 = 4.75 )

Options

  1. A2 mL
  2. B3 mL
  3. C5 mL
  4. D7 mL

Correct answer

C. 5 mL

Step-by-step solution

It is a basic buffer p H = 8.65 , pOH = 14 – 8.65 = 5.35 p O H = p K b + l o g [ N ⊕ H 4 ] [ N H 4 O H ] 5.35 = 4.75 + log [ N ⊕ H 4 ] [ N H 4 O H ] [ N ⊕ H 4 ] [ N H 4 O H ] = antilog (5.35 – 4.75) = antilog (0.6) ≈ 4.0 So [ N ⊕ H 4 ] [ N H 4 O H ] = 30 × 0.2 0.3 × V ≈ 4.0 So V = 5 mL.

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