Project #2408 - Indigestion and Titration: An Acid-Base Titration

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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.

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.

Subject Science
Due By (Pacific Time) 02/19/2013 09:00 pm
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