Take the weak acid vinegar, substitute three chlorine atoms for the three hydrogen atoms, and remarkably, the new acid is 10,000 times more powerful! Acids vary greatly in their strength—their ability to ionize or produce H+ ions when dissolved in water. In this demonstration, the effect of electron-withdrawing groups on the strength of weak acids is shown by preparing half-neutralized solutions of a series of chlorinated acetic acids and then using indicators to compare their resulting pH values. Unique demonstration provides a colorful lesson in recognizing and identifying trends or patterns in chemical properties. Excellent review of pKa determinations! Teacher Demonstration Notes, along with both a reproducible student worksheet and answer sheet are included. Enough materials are included to perform the demonstration seven times.
Concepts: Acid strength, weak acid, conjugate base, equilibrium constant and inductive effect.
Time Required: 20 minutes
Chemicals Provided: Acetic acid solution, chloroacetic acid solution, trichloroacetic acid solution, sodium hydroxide solution, phenolphthalein indicator solution, orange IV indicator solution, bromphenol blue indicator solution, methyl red indicator solution, universal indicator solution, disposable Petri dishes, disposable pipets.
Additional ResourcesNo Additional Resources at the time.
Flinn Catalog/Reference Manual Page 343
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