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1 TP In pure water at 25, there is only a tiny, tiny amount of self ionization, ~ 7 mol/l. In pure water, how many water molecules are there for every OH ion? , ,000,000 6.,000, More than,000,000 Lecture 20 CH1 A1 (MWF 9:05 am) Monday, October 23, 2017 For today Ionization of molecular solutes Self ionization of water Acid base reactions: Competition for H Next lecture: Balancing oxidation reduction equations; Complexation as Lewis acid base reaction To memorize: Table 6.13, p 194: Common acids and bases 1 Ionization of molecular non ionic solutes Ionization of molecular solutes Cl:H :OH 2 H:OH 2 Cl: Nearly complete reaction ~ 0 % theoretical yield 3 Strong electrolyte 4 Copyright 2017 Dan Dill dan@bu.edu 1

2 Note: Unlike NaCl(aq), HCl(aq) does exist Ionization of molecular solutes CH 3 C O O:H :OH 2 H:OH 2 CH 3 C O O: Only a little reaction 0 % theoretical yield 5 Weak electrolyte 6 Ionization of molecular solutes CH 3 CH 2 O:H :OH 2 H:OH 2 CH 3 CH 2 O: Almost no reaction 0 % theoretical yield Memorize: Table 6.13: Common acids and bases Non electrolyte 7 8 Copyright 2017 Dan Dill dan@bu.edu 2

3 HO:H :OH 2 H:OH 2 HO: Almost no reaction 0 % theoretical yield HO:H :OH 2 H:OH 2 HO: In pure water at 25 C, there is only a tiny, tiny amount of self ionization, ~ 7 mol/l Non electrolyte Non electrolyte 11 HO:H :OH 2 H:OH 2 HO: In pure water at 25, there is only a tiny, tiny amount of self ionization, ~ 7 mol/l. TP In pure water at 25, there is only a tiny, tiny amount of self ionization, ~ 7 mol/l. In pure water, how many water molecules are there for every OH ion? , ,000,000 6.,000, More than,000, Copyright 2017 Dan Dill dan@bu.edu 3

4 HO:H :OH 2 H:OH 2 HO: In pure water at 25, there is only a tiny, tiny amount of self ionization, ~ 7 mol/l. H:OH 2, usually written H 3 O, is typically hydrogen bonded to several other water molecules, with the partners continually exchanging with other water molecules. Acid-base reactions: Competition for H + Brønsted Lowry model: The H source is called an acid CH 3 C O O:H aq :OH 2 H:OH 2 CH 3 C O O: The H destination is called a base HO:H :NH 3 H:NH 3 HO: Practice: Acids and bases Practice: Acids and bases HCOOH OH HCOO H 2 O NH 3 H 2 CO 3 NH 4 HCO 3 HCOOH proton source, so it is the acid OH proton destination, so it is the base NH 3 proton destination, so it is the base H 2 CO 3 proton source so it is the acid Copyright 2017 Dan Dill dan@bu.edu 4

5 Practice : Acids and bases H 2 C 4 H 4 O 6 HCO 3 HC 4 H 4 O 6 H 2 CO 3 aq Practice: Acids and bases CH 3 NH 2 H 3 O CH 3 NH 3 H 2 O H 2 C 4 H 4 O 6 proton source, so it is the acid HCO 3 proton destination, so it is the base CH 3 NH 2 proton destination, so it is the base H 3 O proton source, so it is the acid TP Which solution in the diagram contains the weakest acid? Quiz Which solution in the diagram contains the strongest acid? 1. A 2. B 3. C 4. D 1. A 2. B 3. C 4. D Copyright 2017 Dan Dill dan@bu.edu 5

6 TP Which solution in the diagram contains the most concentrated acid? TP Which is the strongest acid, solution B or solution D? 1. A 2. B 3. C 4. D 50% 50% 1. B 2. D TP HCl means 1. H ions and Cl ions surrounded by waters 2. H 3 O ions and Cl ions surrounded by waters 3. HCl molecules surrounded by waters 4. 1 and 2 are correct 5. Doesn t exist 6. None of the above Base strength Weak bases are weak electrolytes: They react only to a small extent with water HO:H :NH 2 CH 2 CH 3 H:NH 2 CH 2 CH 3 HO: Only a little reaction 0 % theoretical yield Copyright 2017 Dan Dill dan@bu.edu 6

7 Base strength Strong bases are strong electrolytes: They react nearly completely with water Na:OH Na HO: Nearly complete reaction ~ 0 % theoretical yield HO: is a strong proton acceptor Note that NaOH is a special case: There is no competition for H, only hydration of OH. 29 Copyright 2017 Dan Dill dan@bu.edu 7