Ask A Scientist Chemistry Archive

name         Suzie
status       other
grade        9-12
location     N/A

Question -   I was just curious if back titration method is a method 
that is more appropriate for analysing the antacid tablets than a 
standard titration techniques?
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Suzie,

Think of why a back-titration was needed in the first place, or why you 
couldn't expect good results from directly titrating an antacid tablet. In 
your experience, when you were asked to do a direct titration, in what 
state were the substances analyzed? Is an antacid tablet completely 
soluble? What is an antacid tablet definitely soluble in? You can then 
generalize your conclusions to other situations where a back-titration may 
be more effective then a direct titration.

Roberto Gregorious
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I am sure that there are procedures for each. The advantage of the "back
titration" is the entire antacid can be reacted completely with excess
standardized HCl and then "back titrated" with standardized KOH (not NaOH
because NaOH absorbs CO2 from the atmosphere and causes errors, where KOH
does not). Both certified pre-standardized HCl and KOH are available
commercially so that reduces some of the manipulation required.

Vince Calder
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