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Buffers and K a ’s

Buffers and K a ’s. What are Buffers?. At times, it is essential to maintain a certain pH . To achieve this, buffers or buffer solutions are used. A solution made from a weak acid and its conjugate base that neutralizes small amounts of acids or bases added to it.

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Buffers and K a ’s

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  1. Buffers and Ka’s

  2. What are Buffers? • At times, it is essential to maintain a certain pH. • To achieve this, buffers or buffersolutions are used. • A solution made from a weak acid and its conjugate base that neutralizessmall amounts of acids or bases added to it. • It relies on Le Châtelier's principle to “absorb” the excess OH- or H+ ions

  3. Buffers are Everywhere • Buffers act as preservatives, since pH affects taste. • Phosphoric acid is added to food to buffer the pH to help maintain the taste. • Blood has a buffer system. • If the pH of blood varies to far from 7.4, sickness or even death can occur.

  4. Weak Acids and Bases • Weak acids and bases only partially ionize. Therefore, they reach equilibrium. • Since they reach equilibrium, they have equilibriumconstants. • These constants are called acid-ionizationconstants and are abbreviated Ka • As before, products go on top, reactants go on bottom, and solids and liquids are ignored. • Table 7 on page 559 lists some weak acids and their conjugate bases

  5. Helpful Hints • Weak acids will lose one H+ at a time and each loss will have a different Ka constant • This means that the [H3O+] and the other product have the same concentration. • It also means that the coefficients are one for everything in the equation. • Sometimes, the pH will be given, which will need to be changed to [H3O+] first.

  6. Example Problems • Calculate [H3O+] of a 0.150 M acetic acid solution. (Ka on page 559 is 1.75 x 10-5) • Find Ka if a 0.50 M solution of a weak acid has a hydronium ion concentration of 1.3 x 10-4. • A solution prepared by dissolving 1.0 mol of benzoic acid in water to form 1.0 L of solution has a pH of 2.1. Calculate the acid-ionization constant.

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