[student8607]

I'm trying to figure out how to determine how to do the calculations....

• Calculate the number of moles of H⁺ per gram of antacid that the tablet should have neutralized: 2HCl + CaCO₃    CaCl₂ +  H₂CO₃

[student8607]

I might have gotten it 
The label said 500mg of CaCO3 per tablet (the active ingredient)

1.284 is the average mass of the tablets.

so

500mg x 1 g  x    1 mole x  2 moles H+      x  1 tablet         = 0.00778 moles/gram
            1000mg  100g      1 mole CaCO3      1.284 grams

Does that sound right?

It is comparable to the 0.00863 moles/gram that did neutralize

[student8607]

Last question:

•   Calculate mg of CaCO3 per gram of tablet for class chart:

0.00863moles H+ x  1 mole CaCO3 x 100g CaCO3 x 1000mg x 1 tablet = 336.1
                           2 moles H+        1 mol            1 g         1.284g


0.00863 is the average number of moles of H+ there were neutralized.

1.284 is the average mass of the tablets.


DOES THIS LOOK RIGHT ALSO?

[ARGOS++]

Dear student8607;

Both results are correct.  (Units?)

Good Luck!
                    ARGOS⁺⁺

[student8607]

Great.

And would it be correct to say that the effectiveness of an antacid depends on how much active ingredient is present?

[ARGOS++]

Dear student8607;

It depends, how you define effectiveness.
It can be one factor, but you may think about, that it can be very dangerous, if a tablet contains three or four times the "Nominal Content" (You may think about an Asthma tablet or so!).

Effectiveness can also be defined: How fast the tablet releases from pain, and that depends on how fast the tablet releases the active ingredient in the stomach.       

Good Luck!
                    ARGOS⁺⁺

[student8607]

OK. Thanks for your *delete me*

[ARGOS++]

Dear student8607;

You 're welcome!   ─   Soon again.

Good Luck!
                    ARGOS⁺⁺

[student8607]

Soon again.

Sooner than I had hoped.  One last question.

I am to explain why the absorption of CO₂ from the air will cause the red endpoint color of titration to fade back to clear within a few minutes.

I'm told: You may find it helpful to begin thinking about this question by asking what is formed when CO2 and H2O react with each other.

I Googled it and some results said they make natural gas.

[nj_bartel]

http://en.wikipedia.org/wiki/Carbonic_acid

[ARGOS++]

Dear student8607;

Do I’m right if I assume that you are talking about titration with phenolphthalein?
In this case study what CO₂ from air is forming in water on:

http://scifun.chem.wisc.edu/chemweek/pdf/CarbonDioxide.pdf

Good Luck!
                    ARGOS⁺⁺

[student8607]

Dear student8607;

Do I’m right if I assume that you are talking about titration with phenolphthalein?
In this case study what CO₂ from air is forming in water on:

http://scifun.chem.wisc.edu/chemweek/pdf/CarbonDioxide.pdf

Good Luck!
                    ARGOS⁺⁺

Yes we used PHN. My fault for not including that.

Let me read over this and see what I can come up with.

[ARGOS++]

Dear student8607;

In this case: Why are you telling from red back to clear?
But the effect is still the same for BTB anyway, but not so strong/fast!

Good Luck!
                    ARGOS⁺⁺

[student8607]

So I got:
CO2 + H2O ⇌ H2CO3        (a weak acid)

With this reaction, however, most of the carbon dioxide is not transformed into carbonic acid and stays as CO2. And, without a catalyst it takes a long time to reach equilibrium.

But I'm not sure where to go from here?

[ARGOS++]

Dear student8607;

You are right!
The weak acid is driving the pH slowly back to lower pH and that’s going faster, as more far from the equilibrium the actual pH is.
For PHN it needs very very small amount of H₂CO₃; if you have not over-titrated.

Good Luck!
                    ARGOS⁺⁺