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3: H2O dissociation, pH, Weak Acids and Bases

Last updated

Jun 3, 2019
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- 2.III: Dissociation of water
- 4: Buffers, Polyprotic acids; Amphoteric Substances,

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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 = pK_a. Resistant to changes in pH in response to small additions of H⁺ or OH^-.

Some take home information

lecture 3 info.jpg

Contributors

Charles S. Gasser (Department of Molecular & Cellular Biology; UC Davis)

I. Dissociation of water

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-.