Ch17_AB_1 - 1 2 The Chemistry of Acids and Bases Strong and...

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Unformatted text preview: 1 2 The Chemistry of Acids and Bases Strong and Weak Acids/Bases • Generally divide acids and bases into STRONG or WEAK ones. STRONG ACID: HNO3(aq) + H 2O(liq) ---> aq) O(liq) H3O+(aq) + NO3-(aq) aq) aq) HNO3 is about 100% dissociated in water. is Strong and Weak Acids/Bases HNO3, HCl, H2SO4 and HClO4 are among the only known strong acids. 3 H—Cl H—Cl Cl-Cl H2O H2O H3O+ H3O+ Chapter 17 Hydronium ion Strong and Weak Acids/Bases • Weak acids are much less than 100% ionized in water. One of the best known is acetic acid = CH3CO2H = HOAc HOAc(aq) + H2O(liq) HOAc( aq) O(liq) OAc-(aq) + H 3O+(aq) aq) aq) OAc- = CH3CO2- = acetate ion CH acetate ¸ 4 Strong and Weak Acids/Bases • Strong Base: 100% dissociated in water. NaOH(aq) ---> Na+(aq) + OH-(aq) NaOH( aq) aq) aq) Other common strong bases include KOH and Ca(OH) 2 CaO (lime) + H2O --> Ca(OH) 2 (slaked lime) (slaked CaO 5 6 Strong and Weak Acids/Bases • Weak base: less than 100% ionized in water One of the best known weak bases is ammonia NH3(aq) + H2O(liq) ¸ NH 4+(aq) + OH-(aq) aq) O(liq) NH aq) aq) Page 1 7 ACID-BASE THEORIES • The most general theory for common aqueous acids and bases is the BRØNSTED - LOWRY theory theory ACID-BASE THEORIES The Brønsted definition means NH 3 is a is BASE in water — and water is itself an ACID 8 9 ACID-BASE THEORIES NH3 is a BASE in water — and water is itself is an ACID • ACIDS DONATE IONS IONS • BASES ACCEPT H + IONS IONS H+ NH3 + H 2O Base Acid NH4+ + OHAcid Base NH3 + H 2O Base Acid NH4+ + OHAcid Base NH3 / NH4+ is a conjugate NH is conjugate by the gain or loss of H + pair — related related Every acid has a conjugate base and vice-versa. 10 11 12 ACID-BASE THEORIES A strong acid is 100% dissociated. Therefore, a STRONG ACID—a good H + ACID—a donor—must have a WEAK CONJUGATE BASE—a poor H+ acceptor. BASE—a acceptor. HNO3(aq) + H2O(liq) ¸ H3O+(aq) + NO3-(aq) aq) O(liq) aq) aq) STRONG A base acid weak B ACID-BASE THEORIES BASE ACID ACID-BASE THEORIES Acetic acid is only 0.42% ionized when [ HOAc] = HOAc] 1.0 M. It is a WEAK ACID HOAc WEAK A 1. 2. + H2O base ¸ H3O+ acid + OAcOAc STRONG B HNO3 + H 2O STRONG ACID H3O+ + NO3WEAK BASE Notice that every A-B reaction has two acids and two bases! We know from experiment that HNO 3 is a is strong acid. 1. It is a stronger acid than H 3O+ 2. H2O is a stronger base than NO 3- Because [H 3O+] is small, this must mean H3O+ is a stronger acid than HOAc is OAc- is a stronger base than H 2O is Page 2 Acid-Base Reactions • Now we can describe • Now we can describe reactions of acids with reactions of acids with bases and the direction bases and the direction of such reaction. of such reaction. • Consider the acid HF • Consider the acid HF reacting with the base reacting with the base NH3.. NH3 • HF + NH3 --> NH4+ + F-• HF + NH3 --> NH4+ + F 13 Predicting the Direction of Acid-Base Reactions Based on experiment, we can put acids and bases on a chart — Table 17.3 (page 794) ACIDS ACIDS STRONG STRONG weak weak CONJUGATE BASES CONJUGATE BASES weak weak STRONG STRONG 14 15 ACID-BASE THEORIES Predicting the direction of an acid-base reaction. ACID1 + BASE 2 STRONG ACID2 + BASE1 weak Use chart to predict the direction of reactions between any A-B pair. Reactions always go from the stronger A-B pair to the weaker A-B pair. Reactions always go from the stronger A-B pair to the weaker A-B pair. Use Table 17.3 Page 3 ...
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This note was uploaded on 01/11/2011 for the course ENGINEERIN MAE 107 taught by Professor Pozikrizdis during the Fall '08 term at San Diego.

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