Total Dissolved Solids
Experiment
24
Experiment 24
Acid-Base Titration
Experiment 9: Acid-Base Titration
(original “Exp10” adapted by Kelemu Woldegiorgis)
With added video link and virtual data
A titration is a process used to determine the volume of a solution needed to react with a given amount of another substance. In this experiment, you will titrate hydrochloric acid solution, HCl, with a basic sodium hydroxide solution, NaOH. The concentration of the NaOH solution is given and you will determine the unknown concentration of the HCl. Hydrogen ions from the HCl react with hydroxide ions from the NaOH in a one-to-one ratio to produce water in the overall reaction:
H+(aq) + Cl–(aq) + Na+(aq) +OH–(aq) H2O(l) + Na+(aq) + Cl–(aq)
When an HCl solution is titrated with an NaOH solution, the pH of the acidic solution is initially low. As base is added, the change in pH is quite gradual until close to the equivalence point, when equimolar amounts of acid and base have been mixed. Near the equivalence point, the pH increases very rapidly, as shown in Figure 1. The change in pH then becomes more gradual again, before leveling off with the addition of excess base.
In this experiment, you will use a computer to monitor pH as you titrate. The region of most rapid pH change will then be used to determine the equivalence point. The volume of NaOH titrant used at the equivalence point will be used to determine the molarity of the HCl.
Figure 1
MATERIALS
Power Macintosh or Windows PC
wash bottle
Vernier computer interface
50-mL buret
Logger Pro
ring stand
Vernier pH Senso
2 utility clamps
HCl solution, unknown concentration
10-mL pipet
0.100 M NaOH solution
pipet bulb or pump
magnetic sti
er (if available)
250-mL beake
sti
ing ba
distilled wate
PROCEDURE
1. Obtain and wear goggles.
2. Use a pipet bulb (or pipet pump) to pipet 10 mL of the HCl solution into a 250-mL beaker. Add 50 mL of distilled water. CAUTION: Handle the hydrochloric acid with care. It can cause painful burns if it comes in contact with the skin.
3. Place the beaker on a magnetic sti
er and add a sti
ing bar. If no magnetic sti
er is available, you need to stir with a sti
ing rod during the titration.
Figure 2
4. Use a utility clamp to suspend a pH Sensor on a ring stand as shown in Figure 2. Position the pH Sensor in the HCl solution and adjust its position so that it is not struck by the sti
ing bar.
5. Obtain a 50-mL buret and rinse the buret with a few mL of the ~0.1 M NaOH solution. Use a utility clamp to attach the buret to the ring stand as shown in Figure 2. Fill the buret a little above the 0.00-mL level of the buret with ~0.1 M NaOH solution. Drain a small amount of NaOH solution so it fills the buret tip and leaves the NaOH at the 0.00-mL level of the buret. Record the precise concentration of the NaOH solution in your data table. Dispose of the waste solution from this step as directed by your teacher. CAUTION: Sodium hydroxide solution is caustic. Avoid spilling it on your skin or clothing.
6. Prepare the computer for data collection by opening the file in the Experiment 24 folder of Chemistry with Computers. The vertical axis has pH scaled from 0 to 14 pH units. The horizontal axis has volume scaled from 0 to 25 mL. Check to see that the Meter window shows a pH value between 2 and 3.
7. Before adding NaOH titrant, click and monitor pH for 5-10 seconds. Once the displayed pH reading has stabilized, click . In the edit box, type “0” (for 0 mL added). Press the ENTER key to store the first data pair for this experiment.
8. You are now ready to begin the titration. This process goes faster if one person manipulates and reads the buret while another person operates the computer and enters volumes.
a.
Add the next increment of NaOH titrant (enough to raise the pH about 0.15 units). When the pH stabilizes, again click . In the edit box, type the cu
ent buret reading, to the nearest 0.01 mL. Press ENTER. You have now saved the second data pair for the experiment.
. Continue adding NaOH solution in increments that raise the pH by about 0.15 units and enter the buret reading after each increment.
c. When a pH value of approximately 3.5 is reached, change to a one-drop increment. Enter a new buret reading after each increment. Note: It is important that all increment volumes in this part of the titration be equal; that is, one-drop increments.
d. After a pH value of approximately 10 is reached, again add larger increments that raise the pH by about 0.15 pH units, and enter the buret level after each increment.
e. Continue adding NaOH solution until the pH value remains constant.
9. When you have finished collecting data, click . Dispose of the beaker contents as directed by your teacher.
10. Print a copy of the Table window. Enter your name(s) and the number of copies of the table.
11. Print a copy of the Graph window. Enter your name(s) and the number of copies of the graph.
12. If time permits, repeat the procedure.
PROCESSING THE DATA
1. Use your graph and data table to determine the volume of NaOH titrant used in each trial. Examine the data to find the largest increase in pH values upon the addition of 1 drop of NaOH solution. Find and record the NaOH volume just before this jump.
2. Find and record the NaOH volume after the drop producing the largest pH increase was added.
3. Determine the volume of NaOH added at the equivalence point. To do this, add the two NaOH values determined above and divide by two.
4. Calculate the number of moles of NaOH used.
5. See the equation for the neutralization reaction given in the introduction. Determine the number of moles of HCl used.
6. Recall that you pipeted out 10.0 mL of the unknown HCl solution for each titration. Calculate the HCl concentration.
7. If you did two titrations, determine the average [HCl] in mol/L. View the video:
Lab Experiment #15: Volumetric Analysis - pH Titration.
•Ali Hayek Mar 1, 2015
https:
www.youtube.com/watch?v=eJHD6RwmbAc
virtual data: titration data attached:
DATA TABLE
Concentration of NaOH
0.10 M
NaOH volume added before the largest pH increase
mL
NaOH volume added after the largest pH increase
mL
Volume of NaOH added at equivalence point
mL
Moles NaOH
mol
Moles HCl
mol
Concentration of HCl
mol/L
Chemistry with Computers 24 -
24 - Chemistry with Computers
Chemistry with Computers 24 -
Collect
Collect
Keep
Keep
Keep
Keep
Stop
Stop
⎯ → ⎯
⎯ → ⎯
Volume NaOH (mL)
pH
Volume NaOH (mL)
pH
ETK 64 - Quiz 1 - Spring 96 Name:
CHM114 – Summer 2021 Assignment 4 (Ch 17, 18, & 19 Tro) Sheet 1 of 2
Name______________
No collaboration! Due Monday, 8/2/21.
You must show your calculations.
XXXXXXXXXX%) Chapter 17, Neutralization of acid lake with calcium ca
onate:
How miuch limestone, CaCO3, completely neutralizes a 4.3 billion liter lake with a pH of 5.5?
2.) (20%) Chapter 17, White wine, greater acidty than red wine:
Find the [H3O+] in a Sauvignon Blanc with a pH of 3.23 and a Cabernet Sauvignon with a ph of XXXXXXXXXXHow many times more acidic is the Sauvignon Blanc?
3.) (20%) Chapter 18, Calculate the pH of a buffer solution made up of 150 mL of 0.25 M HF with 225 mL of 0.30 M NaF.
CHM114 – Summer 2021 Assignment 4 (Ch 17, 18, & 19 Tro XXXXXXXXXXSheet 2 of 2
Name______________
4.) (20%) Chapter 18, Ksp:
Write a balanced equation and expression of Ksp for the dissolution of PbCl2
5.) (20%) Chapter 20: Which processes are driven by a decrease in the entropy of the system?
a) The condensation of water vape
) The sublimation of dry ice
c) The freezing of wate
d) The melting of ice