Exam (elaborations)
University of Washington CHEM 152 - Lab 1 - Weak Acid Titration
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University of Washington CHEM 152 - Lab 1 - Weak Acid Titration
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Name: Alice Meng-Ju Hsieh [0734371] Section: AP Lab Partner: Chris L.EXP 1: ACID-BASE TITRATION
By signing below, you certify that you have not falsified data and that you have not plagiarized any part of this lab report.
Signature:
Total Points = 60 pts, notebook plus template
Notebook Pages (5 pts): your notebook pages will be graded for organization and completeness (Can your TA easily find and read the data he/she is looking for? Did you plot your data?)
PURPOSE AND METHOD
This section has been completed for you as an example. There is no need for you to redo this section. Do not copy this into your lab notebook for your required Purpose & Procedure section -
use this as a guide of what to include and write something in your own words.
The purpose of this lab is to determine the concentration and dissociation constant of an acetic acid (HOAc) solution. The acid solution will be titrated with ~0.10 M sodium hydroxide while a
pH meter is used to monitor the change in pH after each addition of base. The resulting titration curve (plot of pH versus volume of NaOH added) will be used to determine the equivalence
point of the titration. Using the data from the titration curve, a derivative plot will be generated, the maximum of which identifies the volume of base added to reach the equivalence point. The
volume of base added at the equivalence point, together with the concentration of the base and the volume of acid titrated, will be used to calculate the molarity of the acid according to the
following equations:
HOAc + NaOH → OAc - + H2O + Na+
Macid*Vacid = Mbase*Vbase
There are two parts to this lab:
(A) Standardization of the NaOH(aq) using potassium hydrogen phthalate (KHP). A known mass of KHP is titrated with NaOH(aq) to a phenolphthalein indicator endpoint. From the moles of
KHP and the known stoichiometry of the reaction (1:1), the concentration of NaOH is calculated.
(B) Titration of acetic acid, (HOAc) with NaOH(aq). The pH of the HOAc is measured as a function of volume of NaOH added. A plot of pH versus volume of NaOH added and a plot of
derivative (slope between adjacent points) versus volume of NaOH are used to determine the equivalence point. The equivalence point is used to calculate the concentration of HOAc and the
pH of the mixture prior to the equivalence point is used to determine the acid dissociation constant (Ka) of HOAc, pH = pKa + log[OAc-]/[HOAc] or Ka = [H+][A-]/[HA]
HELP
KHP is potassium hydrogen phthalate, see manual for structure and molar mass.
DATA, CALCULATIONS AND GRAPHS Review stoichiometry of reaction in the lab manual.
A: Standardization of NaOH using KHP Decide how many significant figures you need in the [NaOH] and format the number
accordingly [Format --> Cells --> number --> number (change to desired number of
Do not do calculations on your calculator and enter values here. Use Excel for all your decimal places].
calculations. Average =average(range of cells), excel will ignore text.
Table 1: Data for Calculation of [NaOH]
Run #1, 1 pt Run #2, 1 pt Run #3, 1 pt**
Mass of KHP 0.418 g Mass of KHP 0.443 g Mass of KHP g
Molar Mass, KHP 204.22 g/mole Molar Mass, KHP 204.22 g/mole Molar Mass, KHP g/mole
Initial buret reading 0.3 mL Initial buret reading 0.3 mL Initial buret reading mL
Final buret reading 21.5 mL Final buret reading 22.1 mL Final buret reading mL
mL Titrated 21.2 mL mL Titrated 21.8 mL mL Titrated mL
L Titrated 0.0212 L L Titrated 0.0218 L L Titrated L
[NaOH] 0.0965 M [NaOH] 0.0995 M [NaOH] M
Average [NaOH] 0.0980 M
([NaOH] will autofill in Line 240 for use in Ka calculation)
Sample calculation of [NaOH] from the titration of KHP. (6 pts)
0.418g x mol x 1 = 0.0965M
204.22g 0.0212L
**If you only performed two titrations, show the calculation that you used to determine that you did not need to
do a third titration.
Run 2: 0.443g x mol x 1 = 0.0995M
204.22g 0.0218L
| 0.0995 - 0.0965 | x 100% = 3.0% When the percent deviation is ≤ 3%,
then there's no need for third run.
[(0.0995 + 0.0965)/2]
Page 1
, B: Titration of the Acetic Acid
HOAc Volume = 25.0 mL
Table 2: Titration Data Excel Tip
Data Entry Instructions 1. For the outlined cell in column C, the formula is
Buret mL NaOH pH First In the first column, type in the buret =B70-B69. When you copy and paste this formula
readings. Your corresponding pH values go into the cells below. It will execute the formula B71-
Reading Added Value Derivative into column D (pH Value). The other B70 etc. What we really want to do is to keep the
0.4 0.0 2.848 columns, involve calculations spelled out in B69 fixed for all calculations. You can tell Excel to
the Excel tip. keep using the B72 cell number in all calculations
1.5 1.1 3.333 0.441
by putting $ before the columm and $ before the
2.5 2.1 3.637 0.304 row i.e.
3.5 3.1 3.838 0.201 =B70-$B$69
Then copy and paste
4.6 4.2 3.990 0.138
5.5 5.1 4.088 0.109 2. If you need more rows because you have more
data, use the insert
6.5 6.1 4.196 0.108 --> Insert, select rows.
7.5 7.1 4.285 0.089
3. To delete rows, highlight the rows you want to
8.5 8.1 4.373 0.088 delete, Edit, select delete rows.
9.5 9.1 4.463 0.090
4.For the Derivative, write a formula in Excel that
10.5 10.1 4.539 0.076 will calculate the slope between adjacent points.
11.5 11.1 4.613 0.074 Slope = DpH/D(mL Added)
In cell E70, type "=(D70-D69)/(C70-C69)", no $ this
12.5 12.1 4.686 0.073 time
13.5 13.1 4.765 0.079 Copy and paste into other cells
14.5 14.1 4.833 0.068 5. Format the numbers to an appropriate number
15.5 15.1 4.922 0.089 of decimal places.
16.5 16.1 5.010 0.088
17.5 17.1 5.078 0.068
18.5 18.1 5.176 0.098
19.5 19.1 5.279 0.103
20.5 20.1 5.392 0.113
20.8 20.4 5.446 0.180
21.0 21.1 5.466 0.029
21.3 21.4 5.500 0.113
21.5 21.6 5.534 0.170
21.7 21.8 5.564 0.150
22.0 22.1 5.627 0.210
22.2 22.3 5.667 0.200
22.5 22.6 5.730 0.210
22.7 22.8 5.784 0.270
23.0 23.1 5.853 0.230
23.3 23.4 5.946 0.310
23.5 23.6 5.990 0.220
23.7 23.8 6.093 0.515
24.0 24.1 6.221 0.427
24.5 24.6 6.642 0.842
25.0 25.1 10.054 6.824
25.3 25.4 10.936 2.940
25.6 25.7 11.289 1.177
26.0 26.1 11.525 0.590
26.3 26.4 11.662 0.457
27.0 27.1 11.853 0.273 8 pts
27.3 27.4 11.912 0.197
27.6 27.7 11.980 0.227
28.0 28.1 12.025 0.113
Page 2
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