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Equilibrium — Chemistry STD 11 Science — Question

Gujarat BoardEnglish MediumSTD 11 ScienceChemistryEquilibrium3 Marks
Question
A certain buffer is made by mixing sodium formate and formic acid in water. With the help of equations explain how this buffer neutralizes addition of a small amount of an acid or a base?
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Answer

$\text{HCOONa}\xrightarrow{\ \ \ \ \ \ \ \ \ \ }\text{HCOO}^-+\text{Na}^+$
$\text{HCOOH}\rightleftharpoons\text{HCOO}^-+\text{H}^+$
$\mathrm{HCOO}^{-}$is common ion in the above acidic buffer. When small amount of $\mathrm{H}^{+}$ions is added, these $\mathrm{H}^{+}$ions combine with $\mathrm{HCOO}^{-}$which are in excess to form HCOOH back and $\left[\mathrm{H}^{+}\right]$remains practically same, so pH remains constant. When small amount of $\mathrm{OH}^{-}$ions are added, $\mathrm{OH}^{-}$ions will take up ${\mathrm{H}^{+}}$and association of HCOOH will increase so as to maintain concentration of $\mathrm{H}^{+}$ions. So, pH is not affected.

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