Conductimetric Titration
Aqueous sulfuric acid and barium hydroxide both conduct electricity; distilled water does not. As barium hydroxide solution is added to sulfuric acid, conductivity decreases until it reaches zero at the equivalence point. As excess barium hydroxide is added, the conductivity gradually increases.
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Keywords
acids and bases, electrical conductivity, electrolytes, evidence of a chemical reaction, precipitation, stoichiometry, titration
Multimedia
Introduction
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movie (39 seconds, 2.4 MB)
A sulfuric acid solution's conductivity is tested. After rinsing
the electrodes, water's conductivity is tested. A barium hydroxide
solution is also tested for conductivity.
The conductivity device is used to constantly monitor the dilute sulfuric acid solution's conductivity throughout this simple titration.
Demonstration
_Play
movie (1 minute 18 seconds, 4.6 MB)
As barium hydroxide is slowly added to the acid, hydrogen ions
from the acid react with hydroxide ions from the base to form
neutral water molecules. Sulfate ions from the acid react with
barium ions from the base to form insoluble barium sulfate. The
solution's conductivity gradually decreases, as indicated by the
decrease in the noise generated by the device, and eventually by
the dimming of the lights. The decrease in conductivity of the
solution results from a decrease in the concentration of ions.
Since neither the water nor the barium sulfate generates free ions
in solution, the conductivity approaches zero. Once all of the
acid is used up, addition of barium hydroxide again results in an
increase in concentration of ions in solution, so the conductivity
begins to rise.
Discussion
Information on the conductivity testing device used in the demonstration can be obtained from the Institute for Chemical Education, Department of Chemistry, University of Wisconsin - Madison.
Additional still images for this topic
Demonstration Notes: Warnings, Safety Information, etc.
Exam and Quiz Questions
1. Which solution is the better conductor, sulfuric acid or barium hydroxide?
2. Write a balanced net ionic equation for the reaction of aqueous sulfuric acid with aqueous barium hydroxide. Explain why the conductivity drops as barium hydroxide is added to the sulfuric acid solution.
3. As more barium hydroxide is added, the conductivity decreases almost to zero, but then begins to increase. Why?
4. What ions were present in the solution at the beginning of the demonstration? What ions were present at the equivalence point? What ions were present at the end?