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Most Important Selected Qs for JEE AdvancedChemistryIonic Equilibrium

Paragraph: Buffer is a solution whose pH does not change significantly on addition of a small amount of acid or alkali or on dilution. Answer the following questions: Question: A weak acid HA after treatment with 12 ml of 0.1 M strong base BOH has pH =5 . At the end point, the volume of same base required is 26.6 ml . K _ a of acid is : [Given : ( 1.2 1.46 )=-0.085 ]

Options

  1. A8.2 10⁻⁶
  2. B8.2 10⁻⁵
  3. C8.2 10⁻⁴
  4. D8.2 10⁻⁷

Correct answer

A. 8.2 10⁻⁶

Step-by-step solution

array lclc & HA + BOH & & BA + H ₂ O t =0 & a 12 0.1 & 0 & 0 t = eq ( a -1.2) & 0 & 1.2 & 1.2 array Meq of HA = Meq of BOH at end point A=26.6 0.1=2.66 Meq of HA left =2.66-1.2 Now, pH = pK _ a + [ Salt ] [ Acid ] left aligned & 5=- K _ a + 1.2 (2.66-1.2) & K _ a =8.219 10⁻⁶ aligned

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