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QJEEM07Ch39e7: JEE Main 2007 Chemistry - Class 11 JEEM07Ch39e7 Solution: The pK a of a weak acid (HA) is 4.5. The pOH of an aqueous…

The pK_a of a weak acid (HA) is 4.5. The pOH of an aqueous buffered solution of HA in which 50% of the acid is ionized is :

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For acidic buffer

pH = p{K_a} + \log \left[ {{{salt} \over {acid}}} \right]

\,\,\,pH = p{K_a} + \log {{\left[ {{A^ - }} \right]} \over {\left[ {HA} \right]}}

Given

p{K_a} = 4.5\,\,

and acid is

50\%

ionised.

\left[ {HA} \right] = \left[ {{A^ - }} \right]\,\,\,

(when acid is

50\%

ionised)

\therefore

\,\,\,pH = p{K_a} + \log \,1

\therefore

\,\,\,pH = p{K_a} = 4.5

pOH = 14 - pH

= 14 - 4.5

= 9.5