Question

If the pka of hcho2 is 3.74 and the ph of an hcho2/nacho2 solution is 3.89, it means that

Answer 1

Hi, the question has some missing part. The complete question should be " If the
`pK_(a)` of
`HCHO_(2)` is 3.74 and the pH of an
`HCHO_(2)/NaCHO_(2)` solution is 3.89, it means that -

(a)
`[HCHO_(2)]=[NaCHO_(2)]`

(b)
`[HCHO_(2)]> [NaCHO_(2)]`

(c)
`[HCHO_(2)]< [NaCHO_(2)]`

Which of the options are true?"

Answer: Option (c) is true.

Step-by-step explanation:

`HCHO_(2)/NaCHO_(2)` is an weak acid-conjugate base buffer. Hence, in accordance with Henderson-Hasselbalch equation-

`pH=pK_(a)(HCHO_(2))+log(([CHO_(2)^(-)])/([HCHO_(2)]))`

Here, pH = 3.89,
`pK_(a)` of
`HCHO_(2)` = 3.74

So,
`3.89=3.74+log(([CHO_(2)^(-)])/([HCHO_(2)]))`

or,
`([CHO_(2)^(-)])/([HCHO_(2)])` = 1.41 (>1)

So,
`[CHO_(2)^(-)]> [HCHO_(2)]`

or,
`[NaCHO_(2)]> [HCHO_(2)]`

Hence, option (c) is correct.