Citric acid vs. Hydrochloric acid Concentration and Conductivity

Ask which is "stronger" 0.05 M HCl(aq) or 0.10M citric acid?  Test each solution using a conductivity test.  Even though the concentration of citric acid is twice the concentration of HCl, the citric acid solution lights up the light bulb dimly.  The 0.05M HCl solution lights up the light bulb brightly.

Curriculum Notes 

Citric acid solution partially dissociates, meaning that only a few H+ and C6H5O73- ions are present in solution.  Citric acid stays mostly together as H3C6H5O7 molecules in aqueous solution.  Citric acid solution is a weak acid and is classified as a weak electrolyte.

The HCl solution dissociates 100% in water, meaning that all of the HCl reacts with water to form H3O+ ions and Cl- ions. A HCl solution is a strong acid and is classified as a strong electrolyte.

The concentration of an acid solution has NOTHING to do with the classification of a solution as a “strong acid” or “weak acid”.

© Copyright 2012 Email: Randy Sullivan, University of Oregon Chemistry Department and UO Libraries Interactive Media Group