Titration Laboratory Essay
* 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 blue, Methyl orange, Bromothymol blue, and Phenolphthalein. Thymol blue changes from red to yellow at a pH of 1.2–2.8 and from yellow to blue at a pH of 8.0–9.6. Methyl orange changes from red to yellow at a pH of 3.2-4.4. Phenolphthalein changes from white to pink at a pH of 8.2-10.0. Bromothymol blue changes from yellow to blue at a pH of 6.0-7.6. In my case, I used Bromothymol blue for all because the equivalence point for a strong acid being titrated by a strong base is at a point near the neutral position.
6. (a) Why is it important for the buret to be clean before using? How do you clean a buret? It is important to clean the buret thoroughly before using it because it will help for the buret to perform better and will minimize or even prevent error in the experiment. (b) Why are air bubbles in the buret tip a possible source of error in a titration experiment? How do you remove air bubbles from the buret tip?
Air bubbles in the buret tip can cause error in a titration experiment because it can cause the reader to read an inaccurate value of the volume in the buret. One can remove air bubbles by draining several milliliters of the titrant into a waste beaker.
7. Predict the products of these reactions.
(a) HNO3 (aq) +KOH (aq) KNO3 (aq) + H2O (l)
(b) HCl (aq) + Ca (OH) 2(aq) CaCl2 (aq) + 2H2O (l)
(c) NH3 (aq) + H2SO4 (aq) HSO4- (aq) + NH4+ (aq)
8. For the reactions (a) and (b) in question 8, how many moles of the base are required to neutralize one mole of the acid? How many mL of 0.100 M base are required to neutralize 10.00 mL of 0.100 M acid? (a) It takes 10.0mL of the 0.100M base to neutralize the 10.0mL of the 0.100M acid because the mole ratio is 1 to 1. (b) It takes 5.00mL of the 0.100M base to neutralize the 10.0mL of the 0.100M acid because the mole ratio is 2 to 1. 9. A student weighs 0.347 g of KHP on a laboratory balance. The KHP was titrated with NaOH and the concentration of the NaOH determined to be 0.110 M. For the second titration, the student correctly diluted 6 M HCl from the reagent shelf using a graduated cylinder to obtain approximately 0.6 M HCl. This solution was titrated with the original NaOH solution. The student calculated the concentration of NaOH from the experiment to be 0.099 M. In which experiment should the student be more confident of the concentration of the NaOH solution? Why?
The student should consider strongly the first experiment, even though he/she correctly diluted the HCl concentration, because he/she has more significant figures to by; therefore, making the concentration of NaOH much more exact than that of the 6 M HCl experiment. 10. A student needed to standardize a solution of NaOH which was approximately 0.04 M. The student weighed out 0.237 g of KHP. The student carefully prepared the titration setup, but after 25 mL of NaOH was added, no observable change had taken place. What is the procedural error in this experiment?
The student forgot to calculate how of the NaOH he/she was going to add. By seeing the calculations (0.237g) / (204.227g/mol) x (1/1) =0.00116mol NaOH
0.00116 mol / (0.04 mol/L) = 0.029 L = 29mL NaOH
The student should have added at least 29mL of NaOH in order to reach the equivalence point and, therefore, be able to see a change. 11. A student is given a dilute solution of a strong base and a solution of a weak base of unknown concentration. If each solution is titrated with a standard solution of HCl (aq); (a) what would the student observe in each titration? (b) How would you distinguish between the two different solutions? (a) The student would observe that, for the titration with the strong base, he/she would have seen a change at an equivalence point near the point of neutral position on the pH scale. However, on the titration of the weak base the change would occur at a much smaller equivalence point because of the strong acid acting upon the weak base, (b) In order to distinguish between the two solutions, we must look at their equivalence points. The solution with the strong will have a higher equivalence point than that of the solution with the weak base.
* The laboratory was done, for the first time in our history of the class, virtually on a computer at home. * This experiment was materials free since all we had to do was calculate and time the amounts of substances we were going to add digitally. * I observed that when adding a strong base to a strong acid, the equivalence point was at a near neutral position. The same thing happened when adding a weak base to a weak acid. * I also observed that when adding a weak base to a strong acid, the equivalence point was lower than 7. * I also viewed that when adding a strong base to a weak acid, the equivalence point, was higher than 7. * Because of the laboratory being virtual, there was basically little to no human error in the experiment. * Also, there was no equipment error since there were no real materials and, therefore, there couldn’t have been any flawed materials
for the job. Conclusion
In this laboratory, we worked with the titration of an acid with a base. First of all, titration is a procedure for determining the amount of one substance by carefully adding a measured volume of a solution with known concentration of another substance until the reaction of both is complete. We also worked with the equivalence point in a titration, which is the point in a titration when a stoichiometric amount of reactant has been added.
The objective of this laboratory was to recreate and understand what titration is. We were able to accomplish this by virtually choosing substances, acids or bases, to add to other substances until they reached an equivalence point. Here, we had the option to react strong bases with strong acids, weak bases with strong acids, strong bases with weak acids, and weak bases with weak acids. Then, we had to choose which indicator was the most suitable for each experiment in order to obtain the correct equivalence points. In both, strong base with strong acid and weak base with weak acid, the equivalence point was near the neutral position of the pH scale. In the reaction of a weak base with a strong acid, the equivalence point was lower than 7. Consequently, the equivalence point of the reaction of a strong base with a weak acid was at a point higher than 7.
In this type of experiment, there is very little room for any kind of error because all of the materials are basically perfect, meaning they had no flaws or uncleanliness that could have affected the results of the laboratory. Also, human error in this type of laboratory is very minimum since all we had to do was determine how much we were going to add of a substance and actually try to stop the titration at the equivalence point. We actually had the option to repeat the titration again if something went wrong, a factor that prevents errors in this experiment. In conclusion, I believe that the stated hypothesis was proven since we were able to 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. From this lab, I learned about the effects on the equivalence point in a titration of adding a strong or weak base to a strong of weak acid. I also learned that choosing the correct indicator for an experiment plays an important role in the determination of the equivalence point. Finally, I learned that patience is key when doing a titration because of the exact volume that needs to be added in order to reach the equivalence point.