Question

100 mL of 0.06 M TRIS hydrochloride (C4H12ClNO3) is titrated with 1.0 M sodium hydroxide (NaOH). what is the pKa

Answer 1

According to the Henderson-Hasselalch equation:

TRIS-HCl + NaOH ---> TRIS + H2O + NaCl

Treat TRIS-HCl as a monoprotic acid, so there is a 1:1 molar ratio between TRIS-HCl and NaOH.

This the required answer.

Answer 2

Step-by-step explanation:

According to Henderson-Hasselbalch equation:

pH =
`pK_(a) + log(([TRIS])/([TRISH^(+)]))`

When pH = pKa = 8.

Therefore,

8 = 8 +
`log(([TRIS])/([TRISH^(+)]))`

`log(([TRIS])/([TRISH^(+)]))` = 0

`([TRIS])/([TRISH^(+)])` =
`10^0`

= 1

Hence, [TRIS] =
`[TRISH^+]`

As, fraction of amine groups converted to
`NH3^+`

=
`([TRISH^+])/(([TRISH+] + [TRIS]))`

=
`([TRISH^+])/(([TRISH+] + [TRISH^+]))`

=
`([TRISH^+])/((2[TRISH^+]))`

=
`(1)/(2)`

= 0.5

Hence, we can conclude that fraction of the amine group coverted to
`NH3^(+)` is 0.5.