Respuesta :
If the pKa of HCHOâ‚‚ is 3.74 and the pH of an HCHOâ‚‚/NaCHOâ‚‚ solution is 3.11, then the statement which is correct is [HCHOâ‚‚] > [NaCHOâ‚‚].
Buffer solution is a solution which is a mixture of weak acid and its conjugate base or vice a versa. It shows a very little change in pH when strong acid or base is added in it.
Since NaCHOâ‚‚ is a basic salt of formic acid and it acts as a buffer solution. The pH of buffer solution is calculated by the formula
pH=pKa+log([base]/[acid])
We know that HCHOâ‚‚ is an acid, where NaCHOâ‚‚ is a base. Plug all values in the formula
3.11=3.74+log([NaCHOâ‚‚]/[HCHOâ‚‚])
3.11-3.74=log([NaCHOâ‚‚]/[HCHOâ‚‚])
log([NaCHOâ‚‚]/[HCHOâ‚‚])=-0.63
Take antilog on both side
[NaCHOâ‚‚]/[HCHOâ‚‚]=10^(-0.63)
[NaCHOâ‚‚]/[HCHOâ‚‚]=0.234423
Multiply both side by [HCHOâ‚‚]
([NaCHO₂]/[HCHO₂])×[HCHO₂]=0.234423×[HCHO₂]
[NaCHO₂]=0.234423×[HCHO₂]
From the above calculation, it is observed that concentration of NaCHOâ‚‚ is less than the concentration of HCHOâ‚‚. Hence, [HCHOâ‚‚] > [NaCHOâ‚‚].
Therefore, if the pKa of HCHOâ‚‚ is 3.74 and the pH of an HCHOâ‚‚/NaCHOâ‚‚ solution is 3.11, then the statement which is correct is [HCHOâ‚‚] > [NaCHOâ‚‚]. Hence, 'option d' is correct.
To know more about buffer solution
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