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JEE MainChemistryIonic Equilibrium

A student aims to prepare a basic buffer solution of a weak base B and its conjugate acid salt BHCl having a pH of 10.0 . The required concentration ratio of the salt to the base, [ BHCl ] [ B ] , to make this buffer is (Given: K_b( B ) = 2.0 10⁻⁵ , 2 = 0.3 )

Options

  1. A0.5
  2. B0.2
  3. C2.0
  4. D5.0

Correct answer

B. 0.2

Step-by-step solution

For a basic buffer, the Henderson-Hasselbalch equation is given by: pOH = p K_b + ( [ Salt ] [ Base ] ) First, calculate the pOH of the buffer: pOH = 14 - pH = 14 - 10.0 = 4.0 Next, calculate the p K_b of the weak base: p K_b = - (K_b) = - (2.0 10⁻⁵) = 5 - 2 = 5 - 0.3 = 4.7 Substitute these values into the Henderson-Hasselbalch equation: 4.0 = 4.7 + ( [ BHCl ] [ B ] ) ( [ BHCl ] [ B ] ) = 4.0 - 4.7 = -0.7 We know that 5 = ( 10 2 ) = 1 - 2 = 1 - 0.3 = 0.7 . Therefore, -0.7 = - 5 = ( 1 5 ) = (0.2) . Taking the antilo

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