Higher the amount of acid or base used to produce a definite change of pH in a buffer solution, higher will be its buffer capacity.Buffer capacity is maximum under the following conditions.

[Salt] = [Acid] for acid buffer solution and [Salt] = [Base] for basic buffer solution.p^H of a buffer lies in the range of ${\mathrm{p}}^{{\mathrm{k}}_{\mathrm{a}}}\pm 1$. Any buffer solution can be used as buffer up to two units depending on ${\mathrm{p}}^{{\mathrm{k}}_{\mathrm{a}}}$ or ${\mathrm{p}}^{{\mathrm{k}}_{\mathrm{b}}}$ values. When p^H = ${\mathrm{p}}^{{\mathrm{k}}_{\mathrm{a}}}$ or ${\mathrm{p}}^{{\mathrm{k}}_{\mathrm{b}}}$ solution is said to be efficient buffer.

For preparing a buffer solution of pH = 7.0, which of the buffer system will be selected?

• A

  ${\mathrm{H}}_3{\mathrm{PO}}_4,{\mathrm{H}}_2{\mathrm{PO}}_4^{-}$

• B

  ${\mathrm{H}}_2{\mathrm{PO}}_4^{-},{\mathrm{HPO}}_4^{2-}$

• C

  ${\mathrm{HPO}}_4^{2-},{\mathrm{PO}}_4^{3-}$

• D

  ${\mathrm{H}}_3{\mathrm{PO}}_4,{\mathrm{PO}}_4^{3-}$

A buffer of acetic acid $\left({\mathrm{pK}}_{\mathrm{a}}\approx 4.8\right)$with sodium acetate will be, when CH₃COOH and CH₃COONa are present in equivalent amounts has pH limits equal to:

• A

  0 to 4.8

• B

  3.8 to 5.8

• C

  4.3 to 5.3

• D

  4.8

Buffer capacity is maximum when

• A

  one mole of NH₄CI is added to two moles of NH₄OH

• B

  one mole of NH₄CI is added to one mole of NH₄OH

• C

  one mole of NH₄CI is added to one mole of NaOH

• D

  one mole of NaCl is added to one mole of NaOH

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