Description
I need help in my lab report for my envirornmental engineering report. the lab consist of the calibration data, and strong and weak acid titration. there an excel work need to be finish first. I already collect the data for each section. so in the excel sheet that attached has three sheets on it: one for the calibration question, second for strong acid titration and the last one for the weak acid titration. I also attached the instruction for the lab assignment. I already start working on the calibration data in the first sheet in the excel sheet . please correct if there any issues with the calculation.
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CIVE 6373 (Experimental Methods) Laboratory 2: pH, pKa, and Titrations
CHEMICALS:
Deionized (DI) water, for rinsing
pH standards (pH 1.68, 4.01, 7.00, 10.01, 12.46), for calibration
Sodium hydroxide, NaOH (1 M), to use as the titrant
Hydrochloric acid (unknown concentration), sample to be titrated
Weak acid (unknown identity and concentration), sample to be titrated
EQUIPMENT:
Stir bars, stir plate
Glass scintillation vials (20 mL)
Pipettor and pipet tips (10-100 L)
pH probe (various models)
pH meter (various models)
PROCEDURE:
Data records
1. Record the laboratory temperature.
2. Record the manufacturer and model number of the pH probe.
3. Record the manufacturer and model number of the pH meter.
Calibration of the pH probe
1. Set the pH meter to the voltage setting.
2. Measure and record the voltage response for each of the five pH calibration standards.
(Your lab notebook page should already have your calculated theoretical values listed in a
table record the actual measured values in a column next to the theoretical values.)
3. Using your measured data, make a rough estimate of the mV reading that would correspond
to pH 11 (approximately halfway between the pH 10 and pH 12.46 standards). Record it
on your lab note sheet.
Acid base titration
Titrations will be performed on the unknown HCl sample (strong acid strong base titration) and
the unknown weak acid sample (weak acid strong base titration). The procedure below is the
same for both types of samples. A table of NaOH volume increments will be provided in the lab.
1. Prepare a glass vial with a clean stirbar. Add 10 mL of the HCl sample to the vial.
2. Rinse the pH probe thoroughly with DI water. Blot with a Kimwipe to remove excess
water. Keep the pH meter set to report raw voltage readings.
3. Measure and record the initial mV reading (with 0 mL of base added).
4. Add the 1 M NaOH in the increments provided to you. Allow the pH probe to stabilize
after each addition, and record the volume of base added and the mV reading. Continue
until the mV reading reaches the value corresponding to pH 11, as determined above.
5. Rinse the pH probe thoroughly with DI water.
6. Titrate the weak acid solution, making sure to record the volume of base added and the
mV reading.
Page 2 of 5
CIVE 6373 (Experimental Methods) Laboratory 2: pH, pKa, and Titrations
Shutdown procedure: Rinse the pH probe thoroughly with DI water. Store the pH probe in the
bottle of storage solution. Discard the titrated samples (in the glass vials) in the provided waste
container.
DATA ANALYSIS AND REPORTING:
Data and Observations: Attach a copy of the data sheets from your lab notebook.
Results and Data Analysis: For all of the following analyses, please use Excel to organize your
data and perform calculations. Your spreadsheet should be well organized, with units labeled
wherever relevant. Final results/answers should be typed into the Word document template
provided on Canvas with this lab, saved as a PDF, and uploaded onto Canvas along with your lab
notebook sheets and Excel spreadsheet.
Data Analysis and Results
1. For the calibration data:
a. Compute the theoretical (expected) slope using the Nernst equation. This should
already have been completed on your pre-lab assignment, but you should make
corrections as needed using the actual (measured) laboratory temperature.
b. Plot the calibration curve. Determine and report the slope and intercept.
c. Calculate the % error for the experimental slope relative to the theoretical slope.
2. For the strong acid titration:
Prepare the following table in your Excel spreadsheet:
Raw data
Volume of pH probe
1 M NaOH reading
(mV)
added ( L)
0
V1 [replace
with data]
V2 [replace
with data]
[Fill in
data]
[Fill in
data]
[Fill in
data]
Vi [replace
with data]
[Fill in
data]
Vb,1 =
Vb,0 + V1
Vb,2 =
Vb,1 + V2
Processed data
Step 2a:
Step 2b:
pH
Vb,avg
[Report the
units]
pH0 [replace [Leave empty]
with results]
pH1 [replace (Vb,0 + Vb,1)/2
with results]
pH2 [replace (Vb,1 + Vb,2)/2
with results]
Vb,i =
Vb,i-1 + Vi
pHi [replace
with results]
Step 2a:
Cumulative
volume of
NaOH ( L)
Vb,0 = 0
(Vb,i-1 + Vb,i)/2
Step 2b:
pH/ V
[Report the
units]
[Leave empty]
(pH1
pH0)/V1
(pH2
pH1)/V2
(pHi
pHi 1)/Vi
a. As shown in the table columns above for Step 2a, compute the total (cumulative)
volume of NaOH, Vb, added up to each data point. Use the calibration curve to
convert the probe reading (mV) to the pH. Plot the titration curve in Excel as the
pH vs. Vb. Visually estimate the equivalence point, Ve, for the titration curve (i.e.,
where the titration curve has the steepest slope), and label it on the plot.
b. Another method to identify the steepest slope for the equivalence point can be to
compute the first derivative (slope) between each two data points. First, compute
Page 3 of 5
CIVE 6373 (Experimental Methods) Laboratory 2: pH, pKa, and Titrations
the average cumulative volume of base, Vb,avg, that was added between each two
data points, as shown in the table above for Step 2b. Then, estimate the slope as
pH/ V between each two consecutive titration points. Plot pH/ V vs. Vb,avg,
and estimate Ve as the volume of base corresponding to the maximum pH/ V on
the graph.
c. Based on the estimated Ve from the first derivative plot, calculate the concentration
of HCl in the unknown sample.
3. For the weak acid titration:
a. Perform all the data analysis in Step 2 above the same way as for the strong acid to
identify the equivalence point, Ve, and the concentration of weak acid in the
unknown sample.
b. In addition, also estimate pKa as follows:
The pKa is equal to the pH when the molar concentration of the acid (HA) and
conjugate base (A-) are equivalent. You can assume that the initial sample started
with only the acid form. Hence, determine and report the pKa for each titration as
the pH at the halfway point from Vb = 0 to Ve (i.e., the pH corresponding to Ve/2)
c. Charts of various functional groups and their typical approximate pKa values can
be found online, for example:
https://cactus.utahtech.edu/smblack/chem2310/summary_pages/pKa_chart.pdf
Based on the pKa value that you determined, which of the following acidic
functional groups is most likely to be present in the sample that you titrated?
Hydrofluoric acid; Carboxylic acid; Carbonic acid; Hydrogen sulfide; Protonated
Amines; Amides
Discussion Questions
1. Consider the data analysis approach used to find the equivalence point. If your pH probe
is functioning correctly (i.e., the voltage response is linear with pH across the entire pH
range), but it was not calibrated using the pH standards before use, would your calculated
acid concentrations still be accurate using this method? Why or why not?
2. Consider the data analysis approach used to find the pKa. If your pH probe is functioning
correctly (i.e., the voltage response is linear with pH across the entire pH range) but it was
not calibrated using the pH standards before use, would your calculated pKa still be
accurate using this method? Why or why not?
3. Weak acids or bases are used for their buffering capability, where the buffer range is taken
approximately as the pKa ± 1. What range of pH is the buffer range for the weak acid
in the lab? Use your strong acid titration data to estimate and report the total volume of 1
M NaOH that was required to increase the pH from the lower to the upper end of the pH
range you determined. Do the same for the weak acid titration data. (For example, if pKa
= 7 for the weak acid, compute the volume of NaOH needed to increase the pH from pH 6
to pH 8 for the strong acid acid, and compare to the moles of NaOH needed to increase the
pH from pH 6 to pH 8 for the weak acid). Discuss whether it matches your expectations
for a buffered vs. non-buffered sample.
Page 4 of 5
CIVE 6373 (Experimental Methods) Laboratory 2: pH, pKa, and Titrations
4. Instead of a potentiometric titration, colorimetric titrations can be performed to determine
that is added to the sample. For strong acid titrations, phenolphthalein is often used, as
shown in the lecture demo. The transition from colorless to pink occurs around pH 8.0 to
9.6 for phenolphthalein. However, this transition is beyond the equivalence point at pH 7
for a strong acid. How is it possible to obtain an accurate acid concentration when
titrating strong acids using this method, even though the color transition is not at the
equivalence point? (Note: Your answer should not
Page 5 of 5
Given
Slope
E˚(T)
0.05817
0.40719
Pre-Lab
PH
E(T) (V)
1.68
0.3094644
4.01
0.1739283
7
0.00
10.01
-0.1750917
12.46
-0.3176082
Slope
-0.05817
Intercept
0.40719
% error
-3.0358295
PH
1.68
4.01
7
10.01
11
12.46
Lab
E (measured) (MV) E (measured) (V)
275.8
0.2758
144.5
0.1445
-28.2
-0.0282
-191.8
-0.1918
-230
-0.23
-347.6
-0.3476
Slope
-0.056404058
Intercept
0.371051886
0.4
0.3
y = -0.0582x + 0.4072
R² = 1
T(T) “V”
0.2
0.1
0
0
2
4
6
8
10
12
14
12
14
-0.1
-0.2
-0.3
E(T) (V)
-0.4
PH
0.4
E(T) measured “V”
0.3
y = -0.0564x + 0.3711
R² = 0.9977
0.2
0.1
0
0
2
4
6
8
10
-0.1
-0.2
-0.3
-0.4
E (measured) (V)
PH
14
Strong NaOH added
Volume added (uL) mV reading
0
335.2
200
313.7
200
317.5
200
309
200
302.4
200
275.5
200
260.8
200
228.5
20
222.7
20
175.2
20
-243
20
-276.6
Weak NaOH added
Volume added (uL) mV reading
0
209
100
166.4
100
127.3
100
118.6
100
110.9
100
100.7
100
92.6
100
82.3
100
69.4
100
48.5
20
40.3
20
35.5
20
20.3
20
9.9
20
-31
20
-258.4
20
-280.5
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