SC155 - INTRO TO CHEMISTRY: MATTER AND EQUILIBRIUM Indigestion and Titration: An Acid-Base Titration Imagine yourself as the Lead Analytical Chemist at Kaplan Industries. Your first big assignment is to investigate the strength of several commercial antacids for the Food and Drug Administration (FDA). They have sent five antacids to be tested with a back-titration that works as follows:
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First, each antacid tablet is mixed with 40 mL of 0.1 M HCl—this acidic solution is the same stuff that is in stomach acid, and one antacid pill is nowhere near enough to neutralize all 40 mL of the acid. So, to see how much extra help each antacid pill needs to neutralize 40 mL of 0.1 M HCL, you add 0.05 M NaOH drop-by-drop to back-titrate the solution until the pH is neutral. What this means is that, the stronger the antacid tablet, the less NaOH it will take to help bring the acid to neutral. (In other words, the stronger antacid tablets counteract more of the original HCl, leaving the solution closer to neutral before the NaOH is added.)

Here are your results: Maalox Mass of one dose antacid mL NaOH used in backtitration 20.0 g Tums 21.0 g Mylanta 18.0 g CVS brand 18.3 g Rennies 17.5 g

24.1 mL

22.4 mL

20.0 mL

19.9 mL

24.4 mL

1. Which is the strongest antacid, on a single-dose basis? Which is the weakest? Explain and show your calculations. 2. Which are the strongest and weakest, on a by-weight (mass) basis? 3. When people do back titrations, they usually watch the solution for a color change when the solution becomes neutral. What might you have used in the above experiment to get this color change to happen in the solution? At what pH would the solution have been neutral? 4. If you had walked into the lab, only to discover that you only had 0.1 M sulfuric acid available to run your tests, how might this have affected your calculations? Why? 5. In most of the antacids you tested, the active ingredient is aluminum hydroxide. Here is an unbalanced reaction that shows how this chemical neutralizes HCl (the main ingredient in stomach acid). Please provide a balanced version of this equation: Al(OH)3 + HCI  AlCl + H20 3 6. The FDA requires that all of its reports be super-brief—short enough so that they can be sent via text message to all of its lab sites across the country. As you probably know, the word limit for text messages is very small, so your goal here is to describe precisely what you did to test the antacids in fewer than 150 words. In this brief report, you should provide the FDA with the major findings from your tests and let them know generally how you performed your tests.

As you work through this mini-project, you may find it helpful to refer to the following step-by-step guide to solving the problems on page 3 below . Submitting Your Assignment Save your copy of the assignment in a location and with a name that you will remember. Be sure to use the "Save As" option to include your first and last name in the title of the document. For example, your assignment might be called Shawn_Edwards_Assignment1.doc When you are ready to submit it, click on the Dropbox and complete the steps below: • • • • • Click the link that says “Submit an Assignment.” In the "Submit to Basket" menu, select Unit 8: Mini Project. In the "Comments" field, include at least the title of your paper. Click the “Add Attachments” button. Follow the steps listed to attach your Word document.

To view your graded work, come back to the Dropbox or go to the Gradebook after your instructor has evaluated it. Click the Dropbox to access it. Make sure that you save a copy of your submitted assignment..

Help with Titratyion Mini-project

In each analysis of the various antacids, you begin with 40 mL of 0.1 M HCl. First, figure out how many moles of HCl this is. To do this, remember that M = moles / L. Therefore, you should first convert the volume from mL to L. Then, multiply volume in L by concentration in M to obtain moles of HCl. Then, an antacid is mixed with this 40 mL of 0.1 M HCl. In the process, some of the acid is neutralized. This amount is currently unknown. To figure out how much acid was neutralized by the antacid, we perform a back-titration with NaOH. This means that we will now add NaOH of a known concentration to neutralize the REMAINING acid. Since we know what the concentration of NaOH is and how much we used (note the amounts in mL, which are amounts of NaOH solution NOT amounts of antacid), we can figure out how many moles of NaOH were needed to neutralize the remaining acid. Again, the process is similar to what we did above: (1) convert volume from mL to L then (2) multiply volume of NaOH solution (in L) by the concentration of the NaOH solution (in M) to get moles of NaOH used. The number of moles NaOH used will be equal to the number of moles HCl left after treatment of the original sample with an antacid pill. So, if more HCl was left over, more NaOH was needed to neutralize it, and the antacid was weaker. If less HCl was left over, less NaOH was needed to neutralize it, and the antacid was stronger. This helps you to answer the first question. Remember that you must show your calculations to receive credit for this question. Some of this information is also useful in the second question. For the second question, you need to calculate how much acid was neutralized per gram of antacid. To do this, follow these steps: • • Calculate the moles of HCl that you started with (already done above). Calculate the moles of NaOH needed in each case to neutralize the remaining acid. Note that this is the same as the number of moles of acid leftover after the antacid has done its job. This was also already done above. Subtract the number of moles of acid remaining after treatment with each antacid from the number of moles of acid you began with. This gives you the number of moles of acid neutralized in each case. Divide the number of moles of acid neutralized in each case by that antacid's mass. This gives you the moles of acid neutralized per gram of antacid, which will allow you to judge the strongest and weakest antacids on a per weight basis.

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Notice that you never need moles of antacid itself. This is something that you cannot readily calculate with the information given. Remember that you must show your calculations to receive credit for this question as well. Number 3 relies directly on information from the video lectures. Don't over-think this question. It is meant to be simple.

For number 4, the answer lies in the molecular formula of H2SO4. When doing the back titration, will one molecule of NaOH neutralize one molecule of H2SO4? For number 5, you need to simply balance the equation. If you are rusty on balancing, see video lecture #3 in unit 3. For number 6, you need to provide a concise and precise description of what you did to solve the problems and what your major findings (i.e. most important conclusions) were. To receive full credit, you must be specific enough that another reader with your same background knowledge could reproduce what you did.