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JEE Advanced levelOne or more correct optionsDifficulty 3 of 3ie157

1.0 L of a buffer contains 0.20 mol HA and 0.10 mol NaA (, ). Select the correct statements (volume changes may be ignored).

  1. AThe pH of the buffer is 4.50
  2. BDiluting it to 10 L leaves the pH unchanged (ideal behaviour)
  3. CAdding 0.05 mol NaOH gives a solution of pH 4.80
  4. DAdding 0.10 mol HCl gives a solution whose pH is

Answer: A, B, C

pH = 4.80 + log(0.10/0.20) = 4.499 (a true). Dilution keeps the ratio (b true). 0.05 mol NaOH gives HA = 0.15, A- = 0.15 so pH = pKa (c true). 0.10 mol HCl uses up all 0.10 mol A-, leaving HA = 0.30 mol and excess nothing of salt: buffer destroyed, formula not applicable (d false).
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