Bell Work - Augusta County Public Schools

Bell Work - Augusta County Public Schools

Buffers and Kas 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. It relies on Le Chtelier's principle to absorb the excess OH- or H+ ions 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. Weak Acids and Bases

Weak acids and bases only partially ionize. Therefore, they reach equilibrium. Since they reach equilibrium, they have equilibrium constants. These constants are called acid-ionization constants 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 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. 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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