[Peppersrule]

Hello!

In doing an experiment to analyze the amount of acid (HCl)  consumed by various antacid brands, we reacted a known amount and concentration of HCl with a measured sample of antacid and the amount of acid left over was titrated with a known amount and concentration of NaOH in order to find the amount of HCl consumed by the antacid. The basic constituent of the antacid was Mg(OH)2.

One of the calculations involved is to find the amount of base in the antacid sample, and the scaling this up to find the moles of Mg(OH)2 in the entire tablet (of known mass). How should I calculate this?

So far I know: moles of HCl consumed by NaOH; moles and hence mass of Mg(OH)2 that was required to consume HCl. But how do I proceed to find the amount of antacid base?

Your help will be much appreciated!

[Borek]

Describe the titration procedure.

General ways of dealing with the titration calculation are described here:

http://www.titrations.info/titration-calculation
http://www.titrations.info/back-titration

but from what you posted it is no clear to me where the problem lies. I feel like it is the scaling to the whole table that poses a problem - and this depends on the procedure followed.

[Peppersrule]

An antacid tablet is weighed and found to be 0.5749 g. It is grounded into fine powder and a sample of 0.1006 g is reacted with 25.0 mL of 0.1003 M HCl. Solution then heated to remove CO2. 6 drops of bromophenol indicator added to the HCl and antacid solution. This solution was then titrated with 0.1002 M NaOH. (Volume used turned out to be 7.30 mL).

Yes, my problem lies in scaling to find the amount of base in the whole tablet; I've found the the amount in the 0.1006 g sample.

Thank you

[Peppersrule]

Alright. So this is how I proceeded from the links you provided:

% base in antacid of the 0.1006 g sample = (mass of antacid base reacted/the mass of sample)*100 = 51.48016103 %

Then to "scale it up"  to find the mass of antacid base in the entire tablet:

(51.48016103 % * mass of tablet)/100 = mass of base in tablet:
(51.48016103 % * 0.5749 g)/100 = 0.2959447 g = 296 mg

The mass listed in antacid info package said that each tablet contained 311 mg of antacid base.

This shows me the calculation was reasonable. Is this correct?
 

[billnotgatez]

Out of curiosity does the package info state the weight of each tablet.
Just a curiosity question.

[Borek]

(51.48016103 % * mass of tablet)/100 = mass of base in tablet:
(51.48016103 % * 0.5749 g)/100 = 0.2959447 g = 296 mg

Looks OK, although I would take slightly different route - you know tablet was 0.5749 g, and you took 0.1006 g of that. That means to scale amount of the base to the mass of the tablet you need to multiply it by 0.5749/0.1006 - which is "how many 0.1006 g samples are in the 0.5749 g tablet". But the final result will be the same.

Please don't abuse significant digits - while it is correct to use all digits in calculations, when you report intermediate results, report them rounded down (so not 51.48016103%, but just 51.5%, although you should use 51.48016103 in calcualtions).