Ontario Virtual High School Acid Base Titration Chemistry Lab Report

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Assignment: Acid-Base Titration
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Assignment: Acid-Base Titration
A titration is a common laboratory method used in analytical chemistry to determine
the concentration of certain acids or bases during the production of certain biofuels,
pharmaceutical drugs, and many other commercial products. In this assignment,
you will perform an acid-base titration of an unknown acid.
Instructions
Your task is to conduct an acid-base titration. In this experiment, you will use the
simulation from ChemCollective to determine the molar concentration of a weak
monoprotic acid using a strong base of known volume and concentration.
Select the link to open the Unknown Acid and Base simulation in another browser
window.
 ChemCollective: Unknown Acid and Base
1. Select the File in the upper left corner to open the assignment. Choose Load an
Assignment from the drop down list.
2. In the Assignment list, select Acids and Bases. Scroll down to the Unknown Acid
and Base Problem, and select the arrow to the right of the title. This will take you
to the lab.
Step 1: Setting Up The Work Bench
Open the simulation on your browser and navigate to the Unknown Acid and Base
Problem. The following steps are required to set-up the lab work bench.
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Assignment: Acid-Base Titration
1. In the Stockroom there are three tabs: Solutions, Glassware, and Tools. Select
the Solutions tab. In the list of solutions, select the Unknown Acid 0.1 L. This will
place 100.00 mL of the unknown acid in an Erlenmeyer flask on the lab
workbench. Return to the Stockroom.
2. In the Solutions list, select Indicators. Choose the Phenolphthalein Indicator
Solution from the list. The indicator will turn pink when you have passed the end
point.
3. Select and hold the bottle of Phenolphthalein and move it over the top of the
flask containing the unknown acid. A measurement box will appear. Add 5.00 mL
of indicator solution to the flask containing the unknown acid. Right click on the
indicator bottle, and choose Remove to take it from the workbench. Return to the
Stockroom.
4. In the Solutions list, choose a Strong Base from the list of solutions. Make note of
the type of base, the volume, and the molar concentration. Return to the
Stockroom.
5. In the Glassware list, select Other. from the drop down list, choose the 50.00 mL
burette. This will place it on the lab work bench.
6. Select and hold the flask containing the base, and move it over the top of the
burette. A measurement box will appear. Add 50.00 mL of the base to the
burette. Record the initial burette reading.
Step 2: Conducting Your Experiment
1. Select and hold the burette containing the base, and move it over the top of the
flask containing the unknown acid. A measurement box will appear. Begin by
adding the base to the unknown acid at 5.00 mL increments (watch the pH
readings in the panel at the left). Record each increment of base added to the
unknown acid, along with the corresponding pH.
 As you approach the colour change, reduce the amount of base to 1.00 mL
increments, then 0.50 mL increments. Note: you can use even smaller
increments to get more precise results.
2. Once you have identified the endpoint, repeat the procedure but go past the
endpoint. Continue adding base at your selected increment until the pH is
approximately 11.
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Assignment: Acid-Base Titration
Note
Refer to the “Planning an Investigation” page in the Scientific Skills and
Formatting module to help you set-up your test.
Step 3: Graphing and Analyzing Your Results
1. Use your data to calculate the concentration (i.e. molar concentration) of the
unknown acid.
2. Graph your titration curve. Place the volume of base on the x-axis and the pH of
the unknown acid solution on the y-axis.
3. Find the equivalence point on your graph, and use the volume at this point to
calculate the concentration of the unknown acid.
 When the colour of the solution changes to pink, you have passed the
endpoint. However, this gives you a good idea where the endpoint is: it is the
volume just before the solution changes colour.
4. In your discussion, comment on the two ways of calculating the acid
concentration. Also include a description of how the number of moles of base
affected the pH of the unknown solution.
Step 4: Communicating Your Results
1. Once you have completed your test(s), communicate your results in a lab report.
2. Your lab report should include the following sections: purpose/objective,
materials, procedure, observations, results, discussion, and conclusion. Note:
there is no testable question/hypothesis for this experiment. In its place, simply
report the purpose or objective of the test.
Note
Refer to the “Formal Lab Report” page in the Scientific Skills and Formatting
module to help you write your report.
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Assignment: Acid-Base Titration
Assessment Details
Your submission should include the following:

Your report

Your titration curve

The equivalence point for your titration

All in-text citations and a reference list for sources used in your final report
Upload your submissions to the Assignment: Acid-Base Titration Dropbox.
Submit this assignment to the dropbox. This assignment will be evaluated for a grade that will
contribute to your overall final grade in this course.
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Acid-Base Titration
Tala Naksho
SCH4U j26+
Sheilds, Jennifer
May 18, 2022
TITLE: ACID-BASE TITRATION
2
OBJECTIVES
To determine the molar concentration of a weak monoprotic acid using a strong base of known
volume and concentration.
MATERIALS USED
1.
Burette.
2.
Conical flask.
3.
Dropper.
4.
0.1L of 0.1M NaOH
5.
0.2L of unknown acid X.
6.
Phenolphthalein indicator.
PROCEDURE
The burette was filled with 0.05L of 0.1M NaOH and the initial burette reading value taken. 0.1L
of acid X was poured into a conical flask. Five mils of phenolphthalein indicator were then
added to acid X in the conical flask. From the burette, NaOH was added to the conical flask in
steps of five mils until a pH of 7 was reached. The NaOH was now reduced to steps of 0.1mils
until a color change was observed. This was taken as the end point. The final burette reading was
taken after the color change was observed.
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Again, the burette was filled with 0.05L of 0.1M NaOH. 0.1L of acid X was poured into a
conical flask. Five mils of phenolphthalein indicator were then added to acid X in the conical
flask. From the burette, NaOH was added in steps of five mils into the conical flask until around
40 mils near the endpoint. The corresponding value of contents in the conical flask was recorded
after every addition of NaOH. The NaOH was reduced to steps of 2mils until a pH of around
11.5 was achieved. The corresponding values of pH were recorded after every addition of NaOH.
These values were recorded in table 1.
OBSERVATION
At the end point, the contents of the conical flask changed from colorless to pink.
RESULTS
Initial Burette Reading
= 2mL
Final Burette Reading
= 44.1mL
Volume of NaOH used
= 42.1mL
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Table 1: Volume of NaOH versus pH
VOLUME OF NaOH USED
pH OF THE SOLUTION
0
3.3
5
4.34
10
4.7
15
4.95
20
5.16
25
5.37
30
5.6
35
5.9
40
6.5
42
8.74
44
11.11
46
11.41
48
11.58
50
11.7
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ANALYSIS
A graph of pH against volume of NaOH used was plotted using the values in table 1. The value
of volume at the equivalence point (point with the steepest slope) (Jordan, J., & Dumbaugh, W.
H.,1959) was read off from the graph. This was equivalent to the volume of NaOH required for
neutralization to occur.
Volume of NaOH used
= 42mL
To calculate the molarity of X, first a balanced chemical equation is written.
HX(aq) + NaOH(aq)
NaX(aq) + H2O(l)
The mole ratio of HX:NaOH = 1:1
NaOH has a molar mass of 40.
𝑁𝑢𝑚𝑏𝑒𝑟 𝑜𝑓 𝑁𝑎𝑂𝐻 𝑚𝑜𝑙𝑒𝑠 =
𝑇𝑖𝑡𝑒𝑟 𝑣𝑎𝑙𝑢𝑒
×𝑀𝑜𝑙𝑎𝑟𝑖𝑡𝑦
1000
Using the titer value of 42.1mL;
42.1
𝑁𝑢𝑚𝑏𝑒𝑟 𝑜𝑓 𝑁𝑎𝑂𝐻 𝑚𝑜𝑙𝑒𝑠 = 1000 ×0. 1 = 0. 00421 𝑚𝑜𝑙𝑒𝑠
𝑁𝑢𝑚𝑏𝑒𝑟 𝑜𝑓 𝑚𝑜𝑙𝑒𝑠
But; 𝑀𝑜𝑙𝑎𝑟𝑖𝑡𝑦 = 𝑉𝑜𝑙𝑢𝑚𝑒 𝑜𝑓 𝑋 𝑢𝑠𝑒𝑑 ×1000
𝑀𝑜𝑙𝑎𝑟𝑖𝑡𝑦 𝑜𝑓 𝑋 =
0.00421
×1000 = 0. 0421𝑀
100
Using the value of 42mL from the graph;
42
𝑁𝑢𝑚𝑏𝑒𝑟 𝑜𝑓 𝑁𝑎𝑂𝐻 𝑚𝑜𝑙𝑒𝑠 = 1000 ×0. 1 = 0. 0042 𝑚𝑜𝑙𝑒𝑠
𝑀𝑜𝑙𝑎𝑟𝑖𝑡𝑦 𝑜𝑓 𝑋 =
DISCUSSION
0.0042
×1000 = 0. 042𝑀
100
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The molarity obtained for acid X from using direct titration was 0.0421M. Using the graph, the
molarity value was 0.042M. The value from graphical analysis was lower but more accurate
since it gives a better estimate of volume for the end point. The direct titration fails to provide an
accurate value since the color change occurs after the end point. The graphical value accounts for
this.
From the titration curve, as the volume of NaOH increased, (number of moles increased) the pH
of the weak acid reduced. This is because as moles of the base increase, some of the acid is
neutralized hence the number of hydrogen ions reduces leading to a lower pH.
CONCLUSION
An acid-base titration is simply a neutralization reaction. (Sheppard, 2006) Using either and
indicator or a titration curve gives us a good estimate of volume in neutralization at the end point
(neutralization point), hence molarity of an unknown base or acid can be calculated easily using
molarity formulas, and balanced chemical equations.
References
Jordan, J., & Dumbaugh, W. H. (1959). Thermometric Titration of Weak Monoprotic
Acids. Analytical Chemistry, 31(2), 210-213.
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Sheppard, K. (2006). High school students’ understanding of titrations and related acid-base
phenomena. Chemistry Education Research and Practice, 7(1),
32-45.