An Acid-Base Titration


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:
• 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:
CVS brand
Mass of one dose
20.0 g
21.0 g
18.0 g
18.3 g
17.5 g
mL NaOH used in back-titration
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 ? AlCl3 + H20
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.

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