Acid-base titrations Lab Report

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Marquette University *

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1001

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Chemistry

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Feb 20, 2024

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CHEM 1001 ACID-BASE TITRATIONS Laboratory Report NAME : Liam Cedeno Agosto DATE : 3/21/23 SECTION : 403 TA : Audrey Vice A. Goals/Purpose of Experiment ( 2 Points, ~50 words ) : The purpose of this experiment was to understand acid-base neutralization reactions, which is one of the characteristic reactions in aqueous solutions as well as develop problem solving ability through qualitative determination of an analyte in solution. And to achieve this, we were to learn titration using an acid-base indicator to find the concentration of an unknown acid or base. B. Theory/Introduction ( 6 Points, ~100 words ) : For this lab, a technique called titration was used. This method is used to determine the quality of an analyte solution. This technique involves the reaction between a titrant that is dispensed through a buret, and an analyte, which is a solution taken in an Erlenmeyer flask. For this experiment, acid-base titration was used. This is one of the most commonly used titrations in chemistry C. Procedure summary ( 5 Points, ~100 words ) : This experiment consisted of two parts. For part 1, first we were to weigh around 100 mg of Crotonic acid using a weighing boat, mass was recorded in grams up to 3 decimals places. The mg of Crotonic Acid were transferred to a 125 mL Erlenmeyer flask and about 30 mL of water were added. Then, about 1 to 2 drops of the phenolphthalein indicator were added. NaOH was then added in increments using a buret, this was to be done until there was a pink color that signaled the endpoint of the titration. This was to be done 2 times. For part two, we were given an unknown acetic solution to use, then we were to take about 50 mL of said acetic solution into a 50 mL Erlenmeyer flask. From there, we were to wash our pipet with water and rinse with about 1-2 mL of the given acetic solution. Then we were to take 10 mL of the acetic solution and pour it into a 125 mL Erlenmeyer flask. 1-2 drops of the phenolphthalein were added into the flask, and the same steps from part were followed four times, five if there were any errors in previous trials.

D. Results and Calculations: ( 12 Points ) : Part 1: Titration with Crotonic acid Table 1: Molarity of Crotonic Acid Trial 1 Trial 2 Mass of Crotonic acid (mg) 102 mg 101 mg Number of moles of Crotonic acid 0.00184 mol 0.001173 mol Initial buret reading (mL) 15.5 mL 11.63 mL Final buret reading (mL) 30.48 mL 29.18 mL Volume of NaOH used: Final – Initial buret reading (mL) 14.98 mL 17.55 mL Molarity of NaOH (M) 0.122 M 0.06683 M Average molarity of NaOH (M) 0.09441 M Part 2: Titration with acetic acid of unknown strength Table 2: Molarity of Acetic Acid Trial 1 Trial 2 Trial 3 Trial 4 Trial 5 Volume of Acetic acid (mL) 10 mL 10 mL 10 mL 10 mL Initial buret reading (mL) 19.5 mL 27.11 mL 9.37 mL 20.97 mL Final buret reading (mL) 27.11 mL 38.91 mL 20.97 mL 30.82 mL Volume of NaOH used (mL) 7.61 mL 11.8 mL 11.6 mL 9.85 mL Molarity of Acetic Acid (M) 0.071846 M 0.1114 M 0.1095 M 0.09299 M

Use Excel for the following three calculations. Average molarity of unknown acetic acid solution = 0.096434 Standard deviation = 0.018358762 Relative standard deviation = 19.03764407 Demonstrated Calculations: Show one calculation for: Molarity of NaOH solution = 0.00184 mol/0.1498 L= 0.122 M Molarity of unknown Acetic acid solution = 0.09441(11.8) = M2(10) = 0.1114 M E. Discussion ( 10 Points ) : Please write your answers underneath each question. 1. During the cleanup, you found an unlabeled beaker with a colorless solution. How will you determine if the solution is an acid or base? ( 1 point ) I would add a few mL of NaOH, if the solution turns pink in any way, or stays pink, I would know it was a base, same if the solution stayed clear the whole time, I would then know the solution was acidic. 2. What is the difference between a strong acid and a weak acid? Give one example of each. ( 2 points ) A strong acid fully dissolves in water, so the change is irreversible once it disassociates, whereas a weak acid only dissolves a percentage amount in water, therefore the change is reversible. An example of a strong acid would be hydrochloric acid, and an example of a weak acid would be acetic acid. 3. What is the role of the indicator in this titration? If you forgot to add the indicator at the beginning of the titration, can you still add it after adding a few mL of the base? Explain your answer. ( 2 points )

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The purpose of the indicator was to show when the solution became basic, and it allowed me to know when I had reached my equivalence point once the solution turned pink. Since it was solely an indicator of how basic the solution was, it would make no large difference if the indicator wasn ’ t added at the beginning, which I did myself in one of my trials. I just went back and added the drops after having added a couple mL of the NaOh, it still reacted the way it would ’ ve otherwise. 4. Give an example of an acid-base neutralization reaction other than what you learned in this lab indicating the four components involved (acid, base, salt, water). ( 2 points ) You can create an acid-base neutralization reaction of table salt and water with hydrogen chloride and sodium hydroxide. HCl + NaOH → H2O + NaCl 5. Can you comment on the accuracy and precision of your results? Explain. ( 2 points ) I think that I was very precise with my procedure and results, I followed the same steps indicated for each trial. However, because of a slightly off trial in part 1 that I didn’t repeat , my overall results were skewed, and my percent error was high. 6. Discuss the possible sources of error in your experiment. ( 1 point ) My second trial in part 1 was very off. The solution was hot pink instead of light pink due to having added too much of the NaOH and I didn’t redo the trial due to lack of time and the area already being cleaned up by the time I went back to do my calculations, which is where the error was more prominent . I’m certain that having let the buret drip too much of the NaOH during that trial was the biggest error in my experiment. F. Conclusions ( 5 Points, ~100-150 words ) : In conclusion, I ’ m certain I was successful in the sense of having a much better understanding of acids and bases through the use of titrations. Due to my large percent error and the fact that the solutions were a concentrated pink by the end, I ’ m aware that my first couple of trials were not the best titration practices. However, from those trials, I was able to consistently perform my trials for part 2 where the solution was a light pink or just pink. Both my errors and my successful trials allowed me to have a better understanding of how to do proper titrations.