Chem1202PReviewCh17

Chem1202PReviewCh17 - Chemistry 1202 Review/Preview Chapter...

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Chemistry 1202 Review/Preview Chapter Seventeen Review Guide Dr. Saundra McGuire Spring 2007 Director, Center for Academic Success Adj. Prof., Dept. of Chemistry Additional Aspects of Aqueous Equilibria I. The Common Ion Effect The addition of a common ion to a weak acid or base solution shifts the equilibrium in the direction of the undissociated species and changes the pH of the solution. This is the same result as would be predicted by LeChatelier's principle. This phenomenon is generally known as the common ion effect, and is defined as the shift in equilibrium caused by the addition of a compound having an ion in common with the dissolved substances. (See pages 722 – 724 of the text.) II. Buffered Solutions Buffer solutions are solutions that resist a change in pH when acid or base is added. A. Buffer solutions are made from a weak acid and its salt or a weak base and its salt B. The Henderson-Hasselbach Equation can be used to calculate the pH of buffered solutions: pH = pK a + log [base]/[acid] C. Buffer Capacity Buffer solutions can resist a change in pH after the addition of base or acid. The effective buffer region is one in which the pH of the solution is within one unit of the pK a of the weak acid to be used. Effective buffer region: pK a + 1. The optimal pH of a buffer solution is equal to the pK a of the acid. See section 17.2 of the text for a more detailed discussion of buffer solutions.
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Chem1202PReviewCh17 - Chemistry 1202 Review/Preview Chapter...

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