Chapter 15 - Acid-Base Equilibria There are several...

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Acid-Base Equilibria There are several different ways to classify acids and bases: (1) Arrhenius: An acid increases the concentration of hydronium ions (H 3 O + ) when dissolved in water A base increases the concentration of hydroxide ions (OH - ) when dissolved in water
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Brønsted-Lowry Acids and Bases A Brønsted-Lowry acid is a substance that can donate a hydrogen io A Brønsted-Lowry base is a substance that can accept a hydrogen io → ¬  + - 3 2 3 3 ( ) + H O(l) H O (aq) + CH COO (aq) Acid Base Acid Base CH COOH aq We say that CH 3 COOH and CH 3 COO - form a conjugate acid- base pair, where CH 3 COO - is the conjugate base of CH 3 COOH Similarly, H 3 O + and H 2 O form a conjugate acid-base pair
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Brønsted-Lowry Acids and Bases → ¬  + - 3 2 4 ( ) + H O(l) NH (aq) + OH (aq) Base Acid Acid Base NH aq Some molecules and ions can function as either acids or bases depending on the conditions; these are called amphoteric. The most common example is water → ¬  + - 3 2 3 3 ( ) + H O(l) H O (aq) + CH COO (aq) Acid Base Acid Base CH COOH aq Another example is the hydrogen carbonate ion - → ¬  + 2- 3 2 3 3 ( ) + H O(l) H O (aq) + CO (aq) Acid Base Acid Base HCO aq - → ¬  - 3 2 2 3 ( ) + H O(l) H CO (aq) + OH (aq) Base Acid Acid Base HCO aq
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Lewis Acids and Bases Lewis base is any species that donates a lone pair of electrons (e.g. Lewis acid is any species that accepts a lone pair of electrons (e.g. H Lewis Acid Lewis Base Coordinate covalent bond
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Oxides of the Non-Metals The oxides of most non-metals are acidic: → → → → + - 2 5 2 3 3 + 2- 3 2 2 4 4 N O (s) + H O(l) 2 HNO (aq) 2H (aq) + 2 NO (aq) SO (g) + H O(l) H SO (aq) 2H (aq) + SO (aq) Silicon trioxide is weakly acidic, evidenced by the fact that H 2 SiO 3 dissolves in strong bases - 2- 2 3 3 2 H SiO (s) + 2OH (aq) SiO (aq) + 2H O(l)
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Oxides of the Metals Oxides of the Group I and II metals are basic: 2+ - 2 CaO(s) + H O(l) Ca (aq) + 2OH (aq) Metal oxides from the middle groups of the periodic table (III, IV and V) lie on the border of being acidic and basic. As a result, some of these oxides are amphoteric (exhibit both acidic and basic character). + 3+ 2 3 3 2 - - 2 3 2 4 Acting as an acid: Al O (s) + 6H O (l) 2Al (aq) + 9 H O(l) Acting as a base: Al O (s) + 2OH (aq) + 3H O(l) 2 Al(OH) (aq)
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Oxide Character of the Main-Group Elements
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Reactions between Oxides Reactions between metal and non-metal oxides can be classified as reactions between Lewis acids and Lewis bases 2 3 CaO(s) + CO (g) CaCO (s) O 2- donates electron pair Accepts electron pair 3 4 MgO(s) + SO (g) MgSO (s) Metal oxide (base) Non-metal oxide (acid)
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Properties of Acids and Bases in Water Water is unique amongst all molecules because it can: (1) Stabilize polar and ionic solutes through its substantial dipole moment (2) Participate directly in acid-base reactions Reactions in water are integral to all biological processes and the survival of living organisms Of the various definitions of acids and bases the Brønsted- Lowry definitions are most useful.
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Chapter 15 - Acid-Base Equilibria There are several...

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