Chapter 16 Outline

Chapter 16 Outline - Joseph Chapter 16 Outline: Acid-Base...

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Joseph Chapter 16 Outline: Acid-Base Equilibria Acids and bases were tirst recognized by the properties of their aqueous soJutions. For example, acids turn litmus red, whereas bases turn litmus blue. Arrhenius recognized lhat lhe properties of acidic solutions are due to H+(aq) ions and lhose of basic solutions are due to OH- (aq) ions. The Arrhenius concept of acids and bases, while useful, has limitations. For one thing, it is restricted to aqueous solutions. In 1923 the Danish chemist Johannes Brønsted (1879-1947) and the English chemist Thomas Lowry (1874-1936) proposed a more general definition of acids and bases. Their concept is based on the fact that acid-base reactions involve the transfer of H + ions from one substance to another. The H + Ion in Water An H + ion is simply a proton with no surrounding valence electron. This small, positively charged particle interacts strongly with the nonbonding electron pairs of water molecules to form hydrated hydrogen ions. For example, the interaction of a proton with one water molecule forms the hydronium ion, H 3 O + (aq) : When a proton is transferred from HCl to H 2 O, HCl acts as the acid and H 2 O acts as the base. Brønsted and Lowry proposed that acids and bases be defined in terms of their ability to transfer protons. According to their definition, an acid is a substance (molecule or ion) that can transfer a proton to another substance. Likewise, a base is a substance that can accept a proton. In these terms, when HCl dissolves in water, HCl acts as a Brønsted-Lowry acid (it donates a proton to H 2 O), and H 2 O acts as a Brønsted-Lowry base (it accepts a proton from HCl). In the forward reaction HX donates a proton to H
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Chapter 16 Outline - Joseph Chapter 16 Outline: Acid-Base...

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