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IN-DEPTH ONLINE LAB INVESTIGATION: ACID-BASE TITRATIONSwww.sasinschools.comQuick Launch #9Can you......□give the Arrhenius and Brønsted–Lowry definitions for acids and bases?□remember acid-base nomenclature?□describe reactions of acids and bases in aqueous solutions?□calculate and explain the concept of pH?□describe the dissociation processes that occur in aqueous solutions for acids and bases (strong and weak)?□write a complete balanced equation, ionic equation, and net ionic equation for a chemical reaction that occurs in aqueous solution?□use a scientific/graphing calculator to perform calculations involving logarithms?□interpret graphical representations of data?What is a titration?What purpose does itserve?Watch this video!! http://www.dvaction.org/parentdetail.php?id=37Click on “Quicktime movie (download)”
BACKGROUND READING.....TitrationsSuppose that you were to dispense 0.500 M sodium hydroxide (NaOH) from a buret into an Erlenmeyer flask containing 50.0 mL of hydrochloric acid (HCl). Not only would a neutralization reaction occur, but careful measurements would enable you to determine the concentration of the HCl solution. Such an analysis, termed a titration, is used to determine the unknown concentration of an acid or base by reacting it with a known concentration of acid or base. During the titration process, as the acid and base neutralize one another, a point is reached (the equivalence point) where the moles of H+and OH-ions in the solution are equal. After the equivalence point is reached, continued addition of acid or base creates an excess of H+or OH-ions in the solution. IndicatorsHow would you be able to recognize the equivalence point? An indicatoris a substance that changes color due to the presence of excess acid or base. If an appropriate indicator is added to the Erlenmeyer flask before the titration begins, it will change color after the equivalence point, in response to the excess H+or OH-ions. The indicator signals the endpointof the titration. Choice of IndicatorsIt is important to note that each indicator has a specific pH range over which it changes color. Thus, each titration must use an indicator that changes color near the equivalence point pH (which can be estimated for each type of titration). For example, bromthymol blue could be used as an indicator for a titration whose equivalence point pH is 6.3, whereas phenolphthalein might act as the indicator for a titration whose equivalence point pH is 9.0. You will explore three types of titrations, using the ChemScope—titration of a strong acid with a strong base, titration of a weak acid with a strong base, and titration of a weak base with a strong acid.