Notesale: Turn your study into money

Document Preview

Extracts from the notes are below, to see the PDF you'll receive please use the links above

---

Katarina Ong
Michael Oliver
Connor Wilson
March 18 & 25, 2014
Investigation 42: What are some properties of Cream of Tartar?
Experimental Background
A group of entrepreneurs wants to create a process for baking using no external heat
...
The
entrepreneurs have offered to pay for a satisfactory report and may continue to request service
...
0508M NaOH Solution

Buret Stand

Potassium Hydrogen Bithalate

Buret Clamp

Buffer Solutions (4
...
00 pH, to
calibrate pH probe)

Test Tube Clamp (for pH probe)

Deionized Water

pH Probe
DataLogger Software (including associated
hardware)
3 - 250mL Erlenmeyer Flasks
1 - 250mL Beaker
25mL Volumetric Pipette

Apparatus
Figure 1
...


Figure 2
...


Method
In order to provide the information the entrepreneurs asked for, the group had several
immediate goals: initially to standardize the 0
...

The first goal completed was standardization of the NaOH
...
05M NaOH solution was calculated
...
As shown in ​Figure 1​, a buret was set up on a stand in order to deliver a
measured quantity (in mL) of the NaOH solution to the known quantity of the acid
...
Three
trials were run and the associated data collected in Table 1
...
0508M for the NaOH solution
Once the standardization procedure was complete and a more precise measurement of the
concentration of the NaOH was calculated from the data collected, it was then possible to
proceed to the important part, titration of the saturated solution of unkown concentration of KHT
...
To use this stock solution, the solid KHT needed
to be removed
...
The vacuum filter was set up
(as seen in ​Figure 2​) and attached to the vacuum source
...
Then the solution was poured over the filter paper
...
In this case, the entry
was the volume of NaOH delivered, measured in mL, vs the pH probe reading
...
with a pH of 4
...
00 respectively
...
00mL of
standardized NaOH solution
...
00mL of the filtered KHT using
a 25mL volumetric pipette, and placed on a hot plate under the buret setup (the experiment was
not heated, only the stir function was utilized here)
...
The pH probe was then positioned in the 250mL beaker
such that the end of the probe was submerged in the solution
...
The “resolution” of NaOH delivered was increased to
1mL increments and then again to 1 drop increments near the half-titration point and the
equivalence point, then returning to 2mL increments to finish out the titration curve
...
Two titrations were carried out following this process
...


Data Collection

...
This was done three times to ensure accuracy, and is
seen in Table 1
...
​This table shows the data collected during the standardization of the NaOH solution
...

Test Tube #

Mass KHP (g)

NaOH used (mL)

Molarity of NaOH

1

0
...
57


...
154

16
...
0458

3

0
...
95

0
...
Test Tube 1: 0
...
2251 g KHP

×

1 mole N aOH
1 mole KHP

=

(8
...
01757 L

= 0
...

(0
...
0458+0
...
0463 M NaOH

The standardized NaOH was then titrated into 25
...
A titration curve was made, as seen in Figure 1
...
​This graph shows the relationship between the pH of Hydrogen Tartrate and the
volume of NaOH added to it
...


Data Processing
The equivalence point was found by averaging out the 2 points on either side of the vertical
portion of the graph
...
19,8
...
22,8
...
21 mL
...

N A (25
...
0463 N )(18
...
0337 M
Therefore, the concentration of Hydrogen Tartrate is 0
...

The Ksp of the saturated KHT is found using the expression:
KHT (s) ⇔

K + (aq) +

H T − (aq)

I

------

0

0

C

------

+s

+s

E

------

s

s

Therefore, the Ksp expression of the saturated Potassium Hydrogen Tartrate is:
K sp = s2
where s was found using N A V A = N B V B
...
0337, and
K sp = 0
...
14 × 10−3
The Ka of Hydrogen Tartrate was found using 3 different methods:
1) The initial point
2) The half-equivalence point
3) A random point in the buffer region

Using the Initial pH:
The pH when no base was added to the acid was 3
...

The concentration of H + ions was found to be 10−3
...
94 × 10−4 M
When the Hydrogen Tartrate dissociates, it becomes:
H T − ⇔ H + + T 2−
Using an ICE chart and the information found above, the Ka was found
...


HT −

I
C
E

0
...
0337-x

⇔

H+

0
+x
x

+

T 2−

0
+x
x

x is the concentration of H + ions found from the initial pH
...
0337−x)
(7
...
0037−(7
...
92 × 10

The half-equivalence point:

The half- equivalence point was the point at which 9
...
The pH
of this point was found using linear interpolation using the 2 points on either side of the
half-equivalence point
...
​This table shows the pH and delivered NaOH data for the two points on either side of
the half-equivalence point
...
10

3
...
11

x

9
...
87

9
...
86
9
...
10 = 3
...
86
0
...
86
0
...
01
−4

1
...
02x −
...
87
the pH at the half-equivalence point is 3
...

Therefore, 3
...
87 = K a
Ka= 1
...
00,3
...
00 is the mL of NaOH added and 3
...
00 mL of NaOH is added
...

ex​:
mmol HA = 0
...
00
mmol HA = 0
...
8425
2
...
4167
0

T 2−
0
0
...

Using the Henderson-Hasselbach equation:
pH=pKa + log( [B]
[A] )

Where B is the number of millimoles of T 2− after equilibrium is reached, and A is the number of
millimoles of HT − after equilibrium is reached
...
4167
3
...
4258
)

3
...
009)
pKa = 3
...
87
K a = 1
...

Avg
...
92×10−5 )+(1
...
35×10−4 )
3
−5

Avg
...
57 × 10

Conclusion

The purpose of this laboratory investigation was to experimentally determine the K​sp​ value of
cream of tartar (KHT), and to find the K​a​ value of the Hydrogen Tartrate anion (HT)
...
By titrating a NaOH solution of known concentration into a saturated solution of
KHT and observing changes in pH, it was possible to determine the value of K​sp​ for KHT
...
14 × 10−3
...

The average of these calculated values was found to be 9
...

The values found for K​sp and
K​a​ for KHT and HT respectively during the course of this
​
investigation were quite low at standard temperature and pressure
...
This means that the leavening
effect observed in baked goods containing cream of tartar that are exposed to heat during
baking would be much less pronounced at room temperature
...
It is unclear
whether the added time requirements for a heat-free pastry production process would outweigh
the savings in baking costs, but it may be wise to consider alternative leavening agents that
have greater reactivity at room temperature
...
00

NaOH Solution

$20
...
00

Billable Hours (6 at $100 per hour)

$600
...
00



---