1. Intersection 11 11/12/05 Reading: 16.8 (p794-800) 17.2 (p 828-836)

2. Equilibrium Representations

3. Water Projects…Now What?

4. Outline Strong vs. Weak Acids and Bases Which H’s are acidic? Which groups are basic? Periodic Trends and Acid Strength What affects the pH of a solution? Polyprotic acids Concept Questions Acid/Base Titration: A Closer Look

5. Strong vs. Weak A

6. Vocabulary Strong (16 definitions): Weak (10 definitions): Favorable reaction.. ionizing freely in solution ionizing only slightly in solution Strong Reaction exothermic spontaneous product favored goes to completion A

7. Strong Acids An acid that dissociates completely (the equilibrium is shifted all of the way to its conjugate base and hydronium ion) is said to be a strong acid. HCl (aq) + H 2 O (l) → H 3 O + (aq) + Cl - (aq) acid conj. base An acid that does not dissociate completely (an equilibrium is established in solution between the acid, its conjugate base, and hydronium ion) is said to be a weak acid. HClO 2(aq) + H 2 O (l) ↔ H 3 O + (aq) + ClO 2 - ( aq) acid conj base K a = ([H 3 O + ][ClO 2 - ]) / [HClO 2 ] A

8. Strong Bases A base that dissociates completely (the equilibrium is shifted all of the way to its conjugate acid and hydroxide) is said to be a strong base. NaOH (aq) + H 2 O (l) → OH - (aq) + Na + (aq) + H 2 O (l) base conj. acid A base that does not dissociate completely (an equilibrium is established in solution between the base, its conjugate acid, and hydroxide) is said to be a weak base. (CH 3 ) 3 N (aq) + H 2 O (l) ↔ (CH 3 ) 3 NH + (aq) + OH - (aq) base conj. acid K b = ([(CH 3 ) 3 NH + ][OH - ]) / [(CH 3 ) 3 N] A

9. Strong Acid Weak Acid A

10. There are six strongly dissociating acids: HCl HNO 3 HBr HClO 4 HI H 2 SO 4 There are also five bases that dissociate completely in solution (strong): LiOH Ca(OH) 2 NaOH Ba(OH) 2 KOH You should commit the strong acids and bases to memory. Appendix F in your text book lists K a and K b values for many weakly dissociating acids and bases. A

11. Problem 1 Trimethylamine (CH 3 ) 3 N has a K b of 6.5 x10 -5. Write out its chemical reaction with water: What is the [OH - ] of a 0.010 M solution of triethylamine? What is the pOH? What is the pH? M

12. Which H’s are acidic? What groups are basic? M

13. What kinds of hydrogen atoms (protons) are acidic? H-halogen (HF, HCl, HBr, HI) H2OH2O H 2 S (K a1 = 8.9x10 -8 ) Oxoacids (H-polyatomic ions) (H 2 CO 3, HNO 3, etc.) HCN M

14. Organic Acids RCOOH M

15. Bases OH R 3 N M

16. Periodic Trends and Acid Strength A

17. Groups 7 and Period 2 Acid strength: HI > HBr > HCl> HF HF>H 2 O >> H 3 N >>> CH 4 A

18. Oxoacids I HOY + H 2 O H 3 O + + OY - Since a negatively charged ion must be formed, it will be most stable when Y is an atom that is most effective at attracting electron density to itself, thereby stabilizing the negative charge. So the more electronegative atom as Y, yields a stronger acid Acid strength: HOI < HOBr < HOCl Y = I, Br, Cl A

19. Oxoacids II What trend do you see and why? NameHypochlorousChlorousChloricPerchloric FormulaHOClHOClOHOClO 2 HOClO 3 Experimental K a 3.2 x10 -8 1.3 x10 -2 1x10 2 2 x10 7 A

20. What affects the pH? M

21. Question 1 How could you change the pH of a solution of acetic acid (CH 3 COOH)? M

22. Question 2 Apatite, Ca 5 (PO 4 ) 3 OH is the mineral in teeth. Ca 5 (PO 4 ) 3 OH(s) 5 Ca +2 (aq) + 3PO 4 -4 (aq) + OH - (aq) Sour milk contains lactic acid. Not removing sour milk from the teeth of young children can lead to tooth decay. Use chemical principles to explain why. M

23. Can salts affect the pH of a solution? Ca(OH) 2 Na(CH 3 COO) NH 4 Cl NaNO 3 K sp = 7.9x10 -6 K b NH3 = 1.8 x10 -5 K a CH3COOH = 1.8 x10 -5 NH 4 + + H 2 O NH 3 + H 3 O + NaH 2 PO 4 Na 2 HPO 4 M

24. Name ions found in salts that would not affect the pH: M

25. Question 3 A carbonated beverage is left open to the atmosphere. Will the pH change? CO 2 (aq) + H 2 O(l) ↔ H 2 CO 3 (aq) H 2 CO 3 + H 2 O(l) ↔ H 3 O + + HCO 3 ¯ K a1 = 4.2 × 10 -7 HCO 3 ¯ + H 2 O(l) ↔ H + + CO 3 2 ¯ K a2 = 4.8 × 10 -11 M