Lesson 6 Lab: Titrations and Natural Acid/Base Indicators
Begin by viewing the following Thinkwell videos
15.1.7 CIA Demonstration: Titrations
11.2.2 CIA Demonstration: Natural Acid-Base Indicators
(NOTE: The second video is sort of a supplement to the first, and shows how this applies to your daily life. Feel free to try some of the things listed in the video, but be sure to report back to the class regarding the results of your experiments!)
After you watch the above video, answer the questions below in sufficient detail:
(a) (1 pts.) In YOUR OWN WORDS, what is a titration? What type of reaction is it? Be detailed and specific in order to receive credit.
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(b) (1 pts.) What is the BALANCED chemical reaction for the titration performed in this lab demonstration? What does this balanced equation tell us that is so important with respect to this particular lab exercise, and how do you mathematically use this information in this lab?
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(c) (1 pts.) What is the name of the special piece of glassware used in this titration exercise? Why use it as opposed to, say, a graduated pipette--what is special about the glassware used here? How is it SPECIFICALLY used in this lab?
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(d) (2 pts.) In a titration, assuming it is carried out just like the one in this lab exercise, how do you determine the number of moles of base used? Explain in detail, showing all work.
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(e) (2 pts.) In a titration, assuming it is carried out just like the one in this lab exercise, how do you determine the number of moles of acid used? How do you then use this information to determine the concentration of the acid? Explain in detail, showing all work.
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(f) (1 pts.) In this titration example, how do you know when the reaction is complete? What is used (be specific), and how does it work? What is the official name (Dr. Yee mentions this) of the end of this reaction? Be sure to address all questions to receive credit.
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(g) (2 pts.) How does the hydrogen ion (H+) [or the hydronium ion (H3O+)] and the hydroxide ion (OH-) fit into all of this? What is their role in this reaction? In the case of this particular example that you watched, where would each of these ions have come from? Be specific, and be sure to address all questions to receive credit.
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(h) (2 pts.) Suppose I wanted to calculate the pH of the acid used in this titration. How (explain) can I use the results from this experiment to do this? What would the pH be in this case? Show all work.
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(i) (2 pts.) Throughout the video there were various suggestions that came up that were useful tips for you to remember that would help make sure your titration was a successful one. Dr. Yee mentions a few, but there were also some that came up within the images on the screen. What were at least 2 tips mentioned here for carrying out a successful titration?
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(j) (1 pts.) In the second video listed above, red cabbage was demonstrated as a natural indicator, and the hydrangea flower was also mentioned. Do some research (include references) and find and discuss another natural acid/base indicator that was not mentioned in the video and what it looks like under different conditions that allows it to be an indicator.
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(k) Suppose your instructor handed you a bottle of hydrochloric acid of unknown concentration. The chemistry department was considering using it for a summer program for elementary students to test rock samples to see if they contain limestone. However, they don’t want to give it to the kids if it is too strong, and noone in the department was willing to drop some on their skin, and all the graduate students and TA’s were already guinea pigs in other experiments, and the department did not want to compromise the data from that research in any way. So, the task falls to you, the eager undergraduate student.
(2 pts.) First, explain, using a balanced chemical equation, and then describing/discussing it, how hydrochloric acid could test for the presence of limestone. What specific reaction would be taking place, and what easily noticeable phenomenon would you be looking for when doing this test? Why?
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[ii] (3 pts.) Suppose you take a 35.00 mL sample of this acid solution. You then titrate it with a 0.1477 M sodium hydroxide solution. A volume of 29.15 mL of potassium hydroxide was required to complete the titration. What is the concentration of this unknown hydrochloric acid solution?
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