Ch17_AB_1

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

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Unformatted text preview: 1 The Chemistry of Acids and Bases 2 Strong and Weak Acids/Bases Strong and Weak Acids/Bases 3 HNO3, HCl, H2SO4 and HClO4 are among the only known strong acids. • Generally divide acids and bases into STRONG or WEAK ones. STRONG ACID: HNO3(aq) + H 2O(liq) ---> H3O+(aq) + NO3-(aq) H—Cl H—Cl HNO3 is about 100% dissociated in water. Cl-Cl H2O H2O H3O+ H3O+ Chapter 17 Strong and Weak Acids/Bases • Weak acids are much less than 100% ionized in water. One of the best known is acetic acid = One CH3CO2H = HOAc CH HOAc(aq) + H2O(liq) ¸ OAc-(aq) + H 3O+(aq) 4 Strong and Weak Acids/Bases • Strong Base: 100% dissociated in water. ammonia NH3(aq) + H2O(liq) ¸ NH 4+(aq) + OH-(aq) Other common strong bases include KOH and Ca(OH) 2 Page 1 6 Strong and Weak Acids/Bases One of the best known weak bases is NaOH(aq) ---> Na+(aq) + OH-(aq ) NaOH Ca(OH) 2 (slaked lime) Ca(OH) 5 • Weak base: less than 100% ionized in water CaO (lime) + H2O --> OAc- = CH3CO2- = acetate ion Hydronium ion CaO 7 ACID-BASE THEORIES • The most general theory for common aqueous acids and bases is the BRØNSTED - LOWRY theory BRØNSTED theory ACID-BASE THEORIES 8 ACID-BASE THEORIES The Brønsted definition means NH 3 is a BASE in water — and water is itself an ACID ACID NH3 + H 2O Base Acid H+ • ACIDS DONATE IONS • BASES ACCEPT H + IONS 9 NH3 is a BASE in water — and water is itself BASE an ACID an ACID NH4+ + OHAcid Base NH4+ + OHAcid Base NH3 + H 2O Base Acid NH3 / NH4+ is a conjugate NH conjugate by the gain or loss of H + pair — related Every acid has a conjugate base and vice-versa. 10 ACID-BASE THEORIES A strong acid is 100% dissociated. HNO3(aq) + H2O(liq) ¸ H3O+(aq) + NO3-(aq) base base acid weak B weak Notice that every A-B reaction has two acids and two bases! 12 ACID-BASE THEORIES BASE Therefore, a STRONG ACID —a good H + Therefore, STRONG donor—must have a WEAK CONJUGATE donor—must WEAK BASE—a poor H+ acceptor. STRONG A 11 HNO3 + H 2O STRONG ACID ACID H3O+ + NO3WEAK BASE We know from experiment that HNO 3 is a strong acid. 1. It is a stronger acid than H 3O+ 2. H2O is a stronger base than NO 3- Page 2 ACID-BASE THEORIES Acetic acid is only 0.42% ionized when [ HOAc] = 1.0 M. It is a WEAK ACID 1.0 WEAK HOAc WEAK A + H2O base base ¸ H3O+ acid + OAc- STRONG B STRONG Because [H 3O+] is small, this must mean 1. H3O+ is a stronger acid than HOAc 2. OAc- is a stronger base than H 2O 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 14 15 ACID-BASE THEORIES Predicting the direction of an acid-base reaction. ACID1 + BASE 2 ACID2 STRONG STRONG STRONG 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. Page 3 Reactions always go from the stronger A-B pair to the weaker A-B pair. + BASE1 weak Use Table 17.3 ...
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This note was uploaded on 10/19/2011 for the course CHM 2210 taught by Professor Mcquade during the Fall '08 term at FSU.

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