Titration of an Acid with a Base
Tristian Pérez Rivera
Professor Judith Martínez PhD
* The purpose of this laboratory is to recreate and understand what titration is. Hypothesis
* If the experiment works correctly, we should determine the amount of a substance by adding a carefully measured volume of a solution with known concentration until the reaction of both is complete. Materials
1. How will you know when your titration is finished?
I will know that the titration is finished when the color of the indicator changes, meaning that the equivalence point has been reached. 2. Draw and label the pH scale below with acid, base, and neutral, indicating numbers for each.
3. On the scale above, use an arrow to show where your equivalence point is located.
The equivalence point in all the trials was always near the neutral position since in all of them a strong acid and a strong base were used. 4. Show the neutralization reaction that occurs between hydrobromic acid (HBr) and lithium hydroxide (LiOH). HBr (aq) + LiOH (aq) → LiBr (aq) + H2O (l)
5. What is the concentration of 10.00 mL of HBr if it takes 5 mL of a 0.253 M LiOH solution to neutralize it?
V1= 10.0mL HBr
V2= 5.00mL LiOH
[HBr]= (0.253) (5.00)/10.0= 0.127M
Concentration of base: 0.25M
Prepare a table like the one below for your particular data. You should do 4 trials of the virtual titrations. | Trial 1| Trial 2| Trial 3| Trial 4|
Initial Buret Volume| 50.0mL| 50.0mL| 50.0mL| 50.0mL|
Final Buret Volume| 30.0mL| 30.0mL| 30.0mL| 30.0mL|
Volume of Base| 20.0mL| 20.0mL| 20.0mL| 20.0mL|
Volume of Base| 0.020L| 0.020L| 0.020L| 0.020L|
Moles of Base| 0.005mol| 0.005mol| 0.005mol| 0.005mol| Moles of Acid| 0.005mol| 0.005mol| 0.005mol| 0.005mol| Volume of Acid| 0.020L| 0.020L| 0.020L| 0.020L|
Acid Concentration| 0.25M| 0.25M| 0.25M| 0.25M|
Average Concentration| 0.25M| 0.25M| 0.25M| 0.25M|
Analysis and Post-lab:
1. How would it affect your results if you used a wet Erlenmeyer flask instead of a dry one when transferring your acid solution from the volumetric pipette?
Using a wet Erlenmeyer flask when transferring the acid solution from the volumetric pipette would affect the results because the water inside the Erlenmeyer flask affects the concentration of the solution by increasing its volume. 2. How do you tell if you have exceeded the equivalence point in your titration? You can tell that you exceeded the equivalence point in your titration when the indicator stops changing color and stays as it is. 3. Vinegar is a solution of acetic acid (CH3COOH) in water. For quality control purposes, it can be titrated using sodium hydroxide to assure a specific % composition. If 25.00 mL of acetic acid is titrated with 9.08 mL of a standardized 2.293 M sodium hydroxide solution, what is the molarity of the vinegar? What is the % composition (wt/wt %)?
V1= 25.0mL CH3COOH
V2= 9.08mL NaOH
[CH3COOH]= (2.293) (9.08)/25.0= 0.833M
VTotal= 25.0 + 9.08= 34.1mL
Moles NaOH= 0.0341*2.293= 0.0781mol
Moles CH3COOH= 0.0341*0.833= 0.0284mol
Total moles= 0.106mol
CH3COOH % = 0.284/0.106 * 100% = 26.8%
Vinegar molarity: 0.833M
Vinegar % composition: 26.8%
4. Calculate the percent error.
The percent error is 0% because we basically didn’t leave room for human error except for maybe not stopping the titration in time, but that wasn’t the case here. In all of the trials, I managed to stop the titration process exactly at the equivalence point; therefore, there was no error.
5. What indicator is used in this experiment? Describe the color change of the indicator.
In this lab, we had the option to use four different indicators. The indicators were Thymol...