1.
The initial concentration of the H
3
PO
4
solution is 0.048 M.
2.
The pK
a1
is 2.25, the pK
a2
is 7.25, the K
a1
is 5.62 x 10
-3
, and the K
a2
is 5.62 x 10
-8
for H
3
PO
4
.
3.
The H
3
PO
4
concentrations in my soft drink (SodaStream Dr. Pete) are 2.88 x 10
-3
M for the
first equivalence point and 5.75 x 10
-3
for the second equivalence point.
D.
Evidence
1.
The pH of the solution before adding any NaOH was low because H
3
PO
4
is acidic. In my
notebook I wrote down that the initial pH of the H
3
PO
4
solution was 1.17. If you take the
negative log of what I found to be the initial concentration of H3PO4 you get 1.31875, or 1.3
when considering significant figures. This shows that the initial concentration that I
experimentally found gives a pH fairly close to what the initial pH was.
2.
The K
a
values that I got from my experiment are fairly close to those given in the book, and
the pH values derived from those K
a
values are even more similar when compared. This
means that the pK
a
values are more accurate than the K
a
values, but they are both still fairly
close to the values provided by my book.
3.
When I average the two equivalence concentrations that I obtained for my soft drink I get
4.32 x 10
-3
M. The negative log of this concentration gives me a value of 2.3645, or 2.4 when
accounting for significant figures, which is the pH. I didn’t write down the initial pH, but on
my titration curve the initial pH of my soft drink is above 2.00 pH by a bit and appears to be
somewhere close to 2.5. This shows that the initial concentration that I experimentally found
gives a pH fairly close to what the initial pH appears to be on the graph in my notebook.

E.

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- Winter '20
- Chemistry, pH, Pk, Soft drink, SodaStream Cherry Cola