1. Acid Base Equilibria Chapter 16 part II

2. Write the Dissociation Reaction for the following: A. HCl A. HCl B. Acetic Acid B. Acetic Acid C. Ammonium ion C. Ammonium ion D. C 6 H 5 NH 4 + D. C 6 H 5 NH 4 + E. [Al(H 2 O) 6 ] 3+ E. [Al(H 2 O) 6 ] 3+

3. Answers A. HCl  H + + Cl- A. HCl  H + + Cl- B. HC 2 H 3 O 2  H + + C 2 H 3 O 2 - B. HC 2 H 3 O 2  H + + C 2 H 3 O 2 - C. NH 4 +  H + + NH 3 C. NH 4 +  H + + NH 3 D. C 6 H 5 NH 4 +  H + + C 6 H 5 NH 3 + D. C 6 H 5 NH 4 +  H + + C 6 H 5 NH 3 + E. [Al(H 2 O) 6 ] 3+  H + + [Al(H 2 O) 5 OH] 2+ E. [Al(H 2 O) 6 ] 3+  H + + [Al(H 2 O) 5 OH] 2+ What about their Ka? What about their Ka?

4. Acid Strength Strength is defined by the equilibrium position of its ionization. Strength is defined by the equilibrium position of its ionization. Strong acids almost completely dissociate. Strong acids almost completely dissociate. That is because strong acids have WEAK conjugate bases that do not compete effectively for the H+ ion. That is because strong acids have WEAK conjugate bases that do not compete effectively for the H+ ion.

5. Weak Acids Weak acids do not completely dissociate. In fact most of a weak acid remains completely intact in solution. The minority of the weak acid ionizes. The reason is that weak acids have STRONG conjugate bases that have high affinity for the proton. The weaker the acid, the stronger the conjugate base.

6. Vocabulary Monoprotic acids Monoprotic acids Have only one proton to donate. Have only one proton to donate. They may have more than one hydrogen in the chemical formula, but only one is an acidic hydrogen. They may have more than one hydrogen in the chemical formula, but only one is an acidic hydrogen. HCl HCl HNO 3 HNO 3 HC 2 H 3 O 2 HC 2 H 3 O 2

7. Diprotic Acids These have two acidic hydrogens. These have two acidic hydrogens. H 2 SO 4 H 2 SO 4 H 2 S H 2 S Triprotic Acids Triprotic Acids Have three acidic hydrogens. Have three acidic hydrogens. H 3 PO 4 H 3 PO 4 H 3 P H 3 P

8. Oxyacids Acids in which the acidic hydrogen is bound to oxygen. Acids in which the acidic hydrogen is bound to oxygen. H 2 SO 4 H 2 SO 4 Organic Acids aka Organic Acids aka Carboxylic Acids are a type of oxyacid. Carboxylic Acids are a type of oxyacid.

9. Oxyacids The –COOH group can share the negative charge between two oxygens as a resonance structure. These tend to be weak acids; they do not fully ionize. The –COOH group can share the negative charge between two oxygens as a resonance structure. These tend to be weak acids; they do not fully ionize.

10. Table: Describing Acids StrongWeak Ka Value Largesmall Equilibrium position Far to right Far to left Equilibrium [H+] to [HA] [H+]>>[HA][H+]<<[HA] Strength of conjugate base Weak A- is weaker than H 2 O Strong A- is stronger than H 2 O

11. What are the strong Acids? Hickle Hickle Hibber Hibber Hi Hi Hicolo Hicolo HeNo HeNo He So Fine He So Fine

12. Question What is the relative strength of these conjugate bases? What is the relative strength of these conjugate bases? Weak: H 2 O, F-, Cl-, NO 2 -, CN- Weak: H 2 O, F-, Cl-, NO 2 -, CN- Find the Ka and arrange. Find the Ka and arrange. KaAcid KaAcid 7.2 X 10 -4 HF 7.2 X 10 -4 HF 4.0 X 10 -4 HNO 2 4.0 X 10 -4 HNO 2 6.2X 10 -10 HCN 6.2X 10 -10 HCN

13. Answer H 2 O is a stronger base than the conjugate H 2 O is a stronger base than the conjugate base of a strong acid. base of a strong acid. Therefore: Therefore: Weakest Cl- < H 2 O < F- < NO 2 - < CN- strongest Weakest Cl- < H 2 O < F- < NO 2 - < CN- strongest How did we pick the others? How did we pick the others? Read the Ka. Read the Ka.

14. Water Is a substance that can act as both an acid and base is called an amphoteric substance. Is a substance that can act as both an acid and base is called an amphoteric substance. Not only is water an amphoteric substance, it can also auto-ionize. Not only is water an amphoteric substance, it can also auto-ionize. It can ionize with itself to form a hydroxide ion and a hydronium ion. It can ionize with itself to form a hydroxide ion and a hydronium ion.

15. Is water the only compound capable of auto-ionization? No. No. In Solution ammonia ionizes to form ammonium and hydroxide. In Solution ammonia ionizes to form ammonium and hydroxide.

16. Kw of Water From the auto- ionization expression of water we get the equilibrium constant expression. 2 H 2 O  H 3 O + + OH- Kw= [H 3 O + ][OH-] Why not H 2 O? Kw= [H + ][OH-]

17. Kw is the ion-product Kw is aka dissociation constant of water Kw is aka dissociation constant of water It has been found experimentally that at 25 °C, It has been found experimentally that at 25 °C, [H + ]=[OH-] and they both equal 1X10 -7 M [H + ]=[OH-] and they both equal 1X10 -7 M Since Kw= [H + ][OH-] = [1X10 -7 M] 2 Since Kw= [H + ][OH-] = [1X10 -7 M] 2 Then Kw = 1X 10 -14. Then Kw = 1X 10 -14.