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Biology LibreTexts

3: H2O dissociation, pH, Weak Acids and Bases

Reading & Problems: Acid-Base section of handout book, LNC p. 58 -63, p. 71 prob. 2-11; Segel p. 91 prob. 5 (except “i”), 8, p. 92, prob. 24

I. Dissociation of water

Water dissociates to a very small extent. The concentrations of H+ and OH- in pure water are 10-7 M (this is one molecule dissociating among 5 X 108).

II. pH


A. Brönsted acids (proton donor or OH- acceptor) and bases (proton acceptor or OH-donor)


B. Strong acids and bases completely dissociate in water (HA –> A- + H+ , BOH –> B+ OH- completely)


C. Weak acids and bases - dissociation incomplete, [H+] determined by an equilibrium equation.


D. Buffers - mixtures of conjugate acid and conjugate base at ±1 pH unit from pH = pKa. Resistant to changes in pH in response to small additions of H+ or OH-.


Some take home information

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