1. Basic Chemistry Copyright © 2011 Pearson Education, Inc. 1 Chapter 14 Acids and Bases 14.3 Strengths of Acids and Bases Acids produce hydrogen ions in aqueous solution.

2. Basic Chemistry Copyright © 2011 Pearson Education, Inc. A final thought A Peanuts cartoon showed one of the others (Linus?) asking the awful Lucy why the sky was blue. The conversation went something like this: Linus: "Why is the sky blue?" Lucy: "BECAUSE IT ISN'T GREEN!" Linus: "Oh... I thought the reason would be much more complicated than that." Make of that what you will! 2

3. Basic Chemistry Copyright © 2011 Pearson Education, Inc. 3 A strong acid ionizes (100%) in aqueous solutions. HCl(g) + H 2 O(l) H 3 O + (aq) + Cl - (aq) A weak acid dissociates only slightly in water to form an aqueous solution containing mostly molecules of acid and a few ions. H 2 CO 3 (aq) + H 2 O(l) H 3 O + (aq) + HCO 3 − (aq) Strengths of Acids

4. Basic Chemistry Copyright © 2011 Pearson Education, Inc. 4 Strong and Weak Acids In solution, hydrochloric acid, HCl, a strong acid, dissociates 100% acetic acid, CH 3  COOH, a weak acid, contains mostly molecules and a few ions

5. Basic Chemistry Copyright © 2011 Pearson Education, Inc. 5 Strong acids make up six of all the acids have weak conjugate bases Strong Acids

6. Basic Chemistry Copyright © 2011 Pearson Education, Inc. 6 Weak acids make up most of the acids have strong conjugate bases Weak Acids

7. Basic Chemistry Copyright © 2011 Pearson Education, Inc. 7 Strong Bases Strong bases are formed from metals of Groups 1A (1) and 2A (2) include LiOH, NaOH, KOH, and Ba(OH) 2 dissociate 100% in water KOH(s) K + (aq) + OH − (aq) Bases in household products are used to remove grease and to open drains.

8. Basic Chemistry Copyright © 2011 Pearson Education, Inc. 8 Weak Bases Weak bases are poor acceptors of protons dissociate only slightly in water produce only a few ions in water are used in household products such as cleaners NH 3 (g) + H 2 O(l) NH 4 + (aq) + OH − (aq)

9. Basic Chemistry Copyright © 2011 Pearson Education, Inc. 9 Learning Check Identify each of the following as a strong or weak acid or base: A. HBr B. HNO 2 C. NaOH D. H 2 SO 4 E. Cu(OH) 2

10. Basic Chemistry Copyright © 2011 Pearson Education, Inc. 10 Solution A. HBrstrong acid B. HNO 2 weak acid C. NaOHstrong base D. H 2 SO 4 strong acid E. Cu(OH) 2 weak base

11. Basic Chemistry Copyright © 2011 Pearson Education, Inc. 11 Learning Check A. Identify the stronger acid in each pair. 1. HNO 2 or H 2 S 2. HCO 3 - or HBr 3. H 3 PO 4 or H 3 O + B. Identify the stronger base in each pair. 1. NO 3 - or F - 2. CO 3 2- or NO 2 - 3. OH - or H 2 O

12. Basic Chemistry Copyright © 2011 Pearson Education, Inc. 12 Solution A. Identify the stronger acid in each pair. 1. HNO 2 2. HBr 3. H 3 O + B. Identify the stronger base in each pair. 1. F - 2. CO 3 2- 3. OH -

13. Basic Chemistry Copyright © 2011 Pearson Education, Inc. http://www.chemguide.co.uk/index.html#top http://www.chemguide.co.uk/inorganic/group7/acid ityhx.html The values for TxdS (needed to calculate G) for the four reactions at a temp of 298 K are: TxdS (kJ mol -1 ) HF-29 HCl-13 HBr-4 H-I+4 13 The values for T x dS (needed to calculate dG) for the four reactions at a temperature of 298 K are:

14. Basic Chemistry Copyright © 2011 Pearson Education, Inc. However, the terms involving the hydrogen will be the same for every hydrogen halide. So if we are just trying to draw comparisons, we only need to look at the terms shown in red in the diagram. bond enthalpy of HX (kJ mol -1 ) electron affinity of X (kJ mol -1 ) hydration enthalpy of X - (kJ mol -1 ) sum of these (kJ mol -1 ) HF+562-328-506-272 HCl+431-349-364-282 HBr+366-324-335-293 HI+299-295-293 -289If you compare the total HF and HCl values, there is virtually no difference. 14 However, the terms involving the hydrogen will be the same for every hydrogen halide. So if we are just trying to draw comparisons, we only need to look at the terms shown in red in the diagram. If you compare the total HF and HCl values, there is virtually no difference.

15. Basic Chemistry Copyright © 2011 Pearson Education, Inc. Putting all this together, what is the effect on the free energy change, and therefore the value of the equilibrium constant for the reaction? H (kJ mol -1 ) TS (kJ mol -1 ) G (kJ mol -1 ) K a (mol dm -3 ) HF-13-29+161.6 x 10 -3 HCl-59-13-461.2 x 10 8 HBr-63-4-592.2 x 10 10 HI-57+4-615.0 x 10 10 15 Putting all this together, what is the effect on the free energy change, and therefore the value of the equilibrium constant for the reaction?