How many grams of NaOH is to be added to one litre of 1 M H.CO, to get a HCO3-/C03-2 buffer of maximum capacity ?
Answers
Answer:
HA
(
a
q
)
+
OH
−
(
a
q
)
→
A
−
(
a
q
)
+
H
2
O
(
l
)
The number of moles of weak acid and of conjugate base present in the buffer before the addition of the strong base is given by
moles HA
=
moles A
−
=
0.1 moles
10
3
mL
⋅
100
mL
moles HA = moles A
−
=
0.01 moles
Now, if you take
x
to be the number of moles of sodium hydroxide added to the buffer, you can say that after the reaction is complete, the resulting solution will contain
(
0.01
−
x
)
moles HA
The reaction will consume
x
moles of the weak acid.
(
0.01
+
x
)
moles A
−
The reaction will produce
x
moles of the conjugate base.
As you know, the
pH
of a weak acid-conjugate base buffer can be calculated using the Henderson - Hasselbalch equation.
pH
=
p
K
a
+
log
(
[
A
−
]
[
HA
]
)
Assuming that the volume of the buffer does not change upon the addition of the strong base, you can say that the volume of the solution after the strong base is added is equal to
100 mL
.