Danny
Name: ______________________________
General Chemistry II, Spring 2021
.
Data Sheet I
Part II: Titration of a Weak Acid
Unknown number
#2
________________
[NaOH], $
0.200
M
________________
initial
Volume (mL)
pH
-
3.02
pH
Midpoint
3.25mL
4.76
EQP
6.5mL
8.69
Part III: Identifying an Unknown Diprotic Acid
I
Unknown number
________________
Mass of sample
________________
0.0953g
initial pH
Volume (mL)
pH
1st Midpoint
1.89mL
2.21
1st EQP
3.79mL
2.91
2nd Midpoint
5.68mL
3.84
2nd EQP
7.57mL
8.04
'-
I -90
8
General Chemistry II, Spring 2021
Data Sheet II
9
General Chemistry II, Spring 2021
Data Sheet III
I
RBI
10
General Chemistry II, Spring 2021
Name: ______________________________
Post-Laboratory Questions
1.
(5 points) Determine the concentration of the weak acid in Part II.
2
Unknown # ______
(0.200174-0065-1)=0.26
(o -005L)
2.
(5 points) Determine the pKa of the acid in Part II and compare it to the actual value.
pKa
Experimental
Actual
3.
M
pKa
=
=
4.76
4.75
(2 points) Why is the EQP of the titration in Part II at a pH > 7? (one sentence)
Because we're titrating
there's
resulting
to
going
in
a
be
a
more
pH > 7
weak
OH
acid ,
-
meaning
than
Hzot
,
.
11
General Chemistry II, Spring 2021
4.
(4 points) Determine the molar mass of the unknown diprotic acid.
1
Unknown # ______
( 0.200
M
)(O
.
00757L )
-2
0-095392
7-57×10
5.
-
4
not
=
126
=
7-57×10-4
mot
glmol
(4 points) Determine the pKa values of the unknown diprotic acid.
pKa 1=2.21
pka 2=3.84
6.
(4 points) Using your results and Table 1, identify the diprotic acid.
oxakc Aced
7.
(2 points) During the titration in Part III, what was the primary species of your unknown diprotic acid at pH 5? Use
your titration curve from Part III to answer this question. Hint: Figure 4 shows the primary species in solution at
different points of a titration of H2SO3.
C. 042
-
12
General Chemistry II, Spring 2021
8.
In another lab, students were asked to titrate solutions of NH3(aq) with standardized HCl(aq) solutions.
a. (2 points) Sketch the curve for this titration.
¥¥¥py
pit
Volume
of
HCl
b. (2 points) Is the equivalence point at a pH = 7, > 7 or < 7? Explain (one sentence).
egp
of
is
a
weak
the
conjugate acid
because the
>
present
is
base
solution
in
.
c. (4 points) Explain how to determine the Kb of NH3 using the titration curve.
By
finding
the
of
volume
find
by
2
where
,
Pkb
can
fand
the
14
-
pKa
raise
the
,
the
point
equivalence IS
new
nrcdpotnt
volume
ill
at
be
pkatpkb
use
so
,
-
divide
the
the
pH= pKa
=
midpoint
and
pH To
midpoint
the
From
there
pkg
to
Kb
value
,
lopkb
.
.
-44
.
you
to
.
13