Question

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 isn't anywhere 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 Tums Mylanta CVS brand Rennies
Mass of one dose antacid
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 24.4mL

1. Which is the strongest antacid, on a single-dose basis? Which is the weakest? Explain and show your calculations.
The number of moles of NaOH required = 0.05mol/L x volume
For Maalox: moles of NaOH = 0.05mol/L x 24.1mL = 1.205mmol
Tums: moles of NaOH = 0.05mol/L x 22.4mL = 1.120mmol
Mylanta = 0.05mol/L x 20.0mL = 1.000mmol
CVS brand = 0.05mol/L x 19.9mL = 0.995mmol
Rennies = 0.05mol/L x 24.4mL = 1.220mmol
The strongest acid is the one that required the least amount of NaOH in order to neutralize the excess acid.This means that on a single dose basis, CVS brand is the strongest antacid, whilst Rennies is the weakest.

2. Which are the strongest and weakest, on a by-weight (mass) basis?
For Maalox = 2.795 mmol
Tums = 2.880 mmol
Mylanta = 3.000 mmol
CVS brand = 3.005 mmol
Rennies = 2.780 mmol
To calculate which is the best antacid on a weight basis find how much acid 1g of the antacid is able to neutralize by dividing the values listed above by the number of grams in a single dose:
For Maalox = 2.795mmol/20.0g = 0.1398mmol/g
Tums = 2.880mmol/21.0g = 0.1371mmol/g
Mylanta = 3.000mmol/18.0g = 0.1667mmol/g
CVS brand = 3.005mmol/18.3g = 0.1642mmol/g
Rennies = 2.780mmol/17.5g = 0.15886mmol/g
Mylanta is the strongest antacid on a by-weight basis, while the weakest antacid was Tums.

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?

The pH of this solution when neutral would be pH7. An indicator with a color change around this pH is required for this experiment. Bromothymol blue changes color around pH 6.0-7.6 from yellow to blue and so this indicator can be used for this experiment.


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?

Sulfuric acid would affect the results because one mole of sulfuric acid used; two moles of protons are present in the solution: H2SO4 --> H+ + HSO4(-) ---> 2H+ + SO4(2-) Therefore in using H2SO4, you need to account for there being twice as many hydrogen ions present in 1 mole of acid, than are present in 1 mole of HCl. To neutralize sulfuric acid vs. hydrochloric takes two times as much base. The effect on the calculations would be minimal. It simply would have taken a lot more extra base to reach the equivalence point.


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
Al(OH)3 + 3HCl ---> AlCl3 + 3H2O


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 the major findings from your tests and let them know generally how you performed your tests.

The following antacids were tested and the amount of NaOH required to neutralize is shown: Maalox (24.1 mL); Tums (22.4 mL); Mylanta (20.0 mL); CVS brand (19.9 mL); Rennies (24.4 mL). I learned on a single-dose basis that CVS brand is the strongest antacid, while Rennies is the weakest. Based on weight of the tablets, Mylanta is the strongest, and Tums is the weakest.

This is the project along with my answers, but something isn't feeling right.

 

 

So I was further researching this and found this online with completly different answers from mine:

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 isn't anywhere 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	Tums	Mylanta	CVS brand	Rennies
Mass of one dose antacid	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 à AlCl₃ + H₂0

1. 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 the major findings from your tests and let them know generally how you performed your tests.

Did I do some of the calculations wrong?

 

 

 

First, technically, this is NOT a back-titration, as you are adding base (antacid) to acid, and then adding MORE base to the acid until you reach the equivalence point. A back-titration would involve going past the equivalence point with base and then "back titrating" with acid until equivalence was reached.

 

Second, in each case, we are reacting the antacid and base with .040L (the 40mL) of 0.1M HCl, and molarity times volume gives moles as follows: (.040L HCl)*(0.1 mol HCl/L HCl) = .004 mol HCl.

So in all cases, to get to the equivalence point in this reaction of a strong acid with a strong base, we need to have .004 mol of base to fully react in a 1:1 ratio with the acid that's present. Thus, the combination of antacid and base that is added will add up to .004 mol.

 

1. Since we're adding the antacid first, and then adding the same .05 M NaOH to get to equivalence, whichever antacid neutralizes the most base (ie- is the strongest) will require the LEAST amount of extra base to reach equivalence. So that's the CVS brand, at .0199L (for simplicity, all volumes will be expressed in L, even though the chart is in mL). The weakest would require the MOST extra base, which is the Rennies, at .0244L. There are really no calculations necessary, however, let's work it out since they're asked for...

(.0199L NaOH)*(.05 mol NaOH/L NaOH) = .000995 mol NaOH

.004 mol base required - .000995 mol from NaOH = .003005 mol base from CVS antacid

(.0244L NaOH)*(.05 mol NaOH/L NaOH) = .00122 mol NaOH

.004 mol base required - .00122 mol from NaOH = .002780 mol base from Rennies antacid

All other volumes lie between these two, so it is confirmed that CVS is the strongest (most basic), and Rennies is the weakest (least basic).

 

2. Now we have to calculate how much base is in each tablet, per gram of pill. We already have the amount of base in moles for the two above, so we can start with them. Dividing number of moles of base in the pill (above) by the mass in grams from the chart gives us "mol base/g pill" which is what we're looking for:

CVS

(.003005 mol base)/(18.3g pill) = .0001642 mol base

Rennies

(.00278 mol base)/(17.5g pill) = .0001588 mol base

Maalox

.004 - (.0241*.05) = .00195 mol base

.00195 mol base / 20.0g = .0000975 mol base/pill Maalox

Tums

.004 - (.0224*.05) = .00288 mol base

.00288 mol base / 21.0g = .0001371 mol base/pill Tums

Mylanta

.004 - (.0200*.05) = .003 mol base

.003 mol base / 18.0g = .0001666 mol base/pill Mylanta

So, the strongest per gram is Mylanta (just barely, over CVS and Rennies), and the weakest is Maalox.

 

3. Again, it's for either a titration or a back-titration that an INDICATOR is often used to visualize a change in pH. A common indicator used in strong acid-strong base titrations where the equivalence point is near pH 7 is phenolphthalein.

 

4. The issue with using .1M H₂SO₄ instead of HCl is that sulfuric acid is diprotic, meaning it can donate two protons per molecule of acid. To FULLY neutralize sulfuric acid vs. hydrochloric takes two times as much base. The effect on the calculations would be minimal, however. It simply would have taken a lot more extra base to reach the equivalence point.

 

5. Al(OH)3 + 3HCl à AlCl₃ + 3H₂O

There must be the same number of each atom on the left and right sides of the equation. (I always start with the heaviest element and work to the lightest... just seems to work best. Here, Al is already balanced at the start, so we move to the Cl, and then back to the Al if necessary, which it wasn't, then to the O, and by that point, the H had worked themselves out.)

 

6. The strength of 5 common antacids was examined on a per dose and per gram basis by addition to 40 mL of dilute acid (1.M HCl) followed by titration with dilute base (.05M NaOH) to the equivalence point. The difference between the amount of base added and the initial amount of acid gave the neutralization power of the antacid. Per dose, CVS brand had the most acid-neutralizing power, while Rennies had the least. Per gram, Mylanta was the strongest and Maalox was the weakest. (84 words)