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? 1. 1 2. 3. 0 4.,000 5. 1,000,000 6.,000,000 7. More than,000,000 Lecture 20 CH1 A1 (MWF 9:05 am) Monday, October 22, 2018 For today Review: Concentrations after precipitation 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 A comprehensive example A comprehensive example You are given 150 ml of a 0.20 M aqueous solution of ammonium carbonate and 150 ml of 0.40 M aqueous solution of barium iodide. These solutions are mixed and a precipitate forms NH 4 2 CO 3 2 NH 4 CO 2 3 BaI 2 Ba 2 2 I Ba 2 CO 2 3 BaCO 3 Ba 2 CO 2 3 BaCO 3 start 0.060 mol 0.030 mol 0 change 0.030 mol 0.030 mol 0.030 mol end 0.030 mol 0 0.030 mol 5 You are given 150 ml of a 0.20 M aqueous solution of ammonium carbonate and 150 ml of 0.40 M aqueous solution of barium iodide. These solutions are mixed and a precipitate forms. Write the net ionic equation for this process. What are the spectator ions for this process? What is the limiting reactant? How many moles of the solid precipitate are formed? After precipitation, what are the molarities M of each ion in solution? Is the final solution electrically neutral? 6 Copyright 2018 Dan Dill dan@bu.edu 1
A comprehensive example You are given 150 ml of a 0.20 M aqueous solution of ammonium carbonate and 150 ml of 0.40 M aqueous solution of barium iodide. These solutions are mixed and a precipitate forms. After the precipitation, the total electrical charge due to the ions remaining in solution is 0. Ionization of molecular non ionic solutes Moles of ions Moles of charge NH 4 0.060 0.060 I 0.120 0.120 Ba 2 0.030 0.060 Total 0 8 9 Ionization of molecular solutes Cl:H :OH 2 H:OH 2 Cl: Nearly complete reaction ~ 0 % theoretical yield Note: Unlike NaCl(aq), HCl(aq) does exist Strong electrolyte 11 Copyright 2018 Dan Dill dan@bu.edu 2
Ionization of molecular solutes 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 CH 3 CH 2 O:H :OH 2 H:OH 2 CH 3 CH 2 O: Almost no reaction 0 % theoretical yield Weak electrolyte 12 Non electrolyte 13 Memorize: Table 6.13: Common acids and bases Water self-ionizes, but only a very, very little HO:H :OH 2 H:OH 2 HO: Almost no reaction 0 % theoretical yield 14 Non electrolyte 16 Copyright 2018 Dan Dill dan@bu.edu 3
Water self-ionizes, but only a very, very little 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 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? 1. 1 2. 3. 0 4.,000 5. 1,000,000 6.,000,000 7. More than,000,000 Non electrolyte 17 19 Water self-ionizes, but only a very little 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 :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: 20 22 Copyright 2018 Dan Dill dan@bu.edu 4
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 25 26 TP Which solution in the diagram contains the weakest acid? TP 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 29 Response Counter 30 Copyright 2018 Dan Dill dan@bu.edu 5
Quiz Which solution in the diagram contains the most concentrated acid? 1. A 2. B 3. C 4. 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 Response Counter 32 Response Counter 33 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 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. 34 35 Copyright 2018 Dan Dill dan@bu.edu 6