1. AP Chem Acids/Bases Thursday, April 12, 2012

2. May 17, 20152 When asked to give conjugate base or acid of a species, remember: Conjugate acid is simply the parent substance plus one proton (H + ) Conjugate base is simply the parent substance minus one proton (H +)

3. May 17, 20153 What is the conjugate base of each acid? HClO 4 – minus one H + ClO 4 - H 2 S – minus one H + HS – PH 4 + – minus one H + PH 3 Why the change in overall Charge? Losing +1 charge = more negative charge (actually a reduction taking place)

4. May 17, 20154 What is the conjugate acid of each base? CN - – plus one H + HCN SO 4 2- – plus one H + HSO 4 -1 H 2 O – plus one H + H 3 O + Gaining +1 causes the charge to become more positive (oxidation happening)

5. May 17, 20155 Relative Strengths of Acids and Bases Some acids are better proton donors that others. STRONG acids completely transfer their protons to water, creating completely dissociated ions in solution. Their conjugate bases have a negligible tendency to protonate (gain a proton) in aqueous solution.

6. May 17, 20156 Weak Acids only partly dissociate in water.

7. May 17, 20157 Inverse Relationship between strength of acid and conjugate bases The stronger an acid, the weaker its conjugate base. The stronger the base, the weaker its conjugate acid. Reactions involving strong species go nearly to completion; little or no reverse reaction. Keq is very large.

8. May 17, 20158 Page 618

9. May 17, 20159 Strong Acids and Bases Called strong because they are STRONG ELECTROLYTES, existing entirely as ions in aqueous solutions. Seven most common strong acids (memorize these) – HCl, HBr, HI, HNO 3, HClO 3, HClO 4 (monoprotic) and H 2 SO 4 (diprotic)

10. May 17, 201510 http://cwx.prenhall.com/petruc ci/medialib/media_portfolio/te xt_images/016_STRONGWEAK. MOV

11. May 17, 201511 There are also relatively few strong bases. Includes soluble hydroxides (there aren’t many) – Group IA (alkali metals) LiOH, NaOH, KOH, RbOH, CsOH – Heavier members of Group IIA (alkaline earth metals) Ca(OH) 2, Sr(OH) 2,, Ba(OH) 2 Completely ionize in water.

12. May 17, 201512

13. May 17, 201513 Stronger Acid Stronger Base Weaker Base Weaker acid Chemical Change Proton Transfer

14. May 17, 201514 Predicting Acid-Base Reactions The stronger acid will always transfer a proton to the stronger base. The weaker acid and base are more stable – less reactive. The stronger acid will always transfer a proton to the stronger base, yielding the weaker acid and base as favored species at equilibrium.

15. May 17, 201515 In every acid-base reaction, equilibrium favors transfer of proton to the stronger base. Which direction (forward or reverse) is most likely?? HCl (g) + H 2 O (l)  H 3 O + (aq) + Cl - (aq) A B CA CB H 2 O is a stronger base than Cl - (check the table), so H 2 O acquires the proton from HCl. HC 2 H 3 O 2 (g) + H 2 O(l)  H 3 O + (aq) + C 2 H 3 O 2 - (aq) A B CA CB C 2 H 3 O 2 - is a stronger base than H 2 O. Therefore, acetate, C 2 H 3 O - gains (or abstracts) the proton from H 3 O +.

16. May 17, 201516 Predict whether the equilibrium lies forward or reverse: HSO 4 - (aq) + CO 3 2- (aq)  SO 4 2- (aq) + HCO 3 - (aq) A B CB CA – Find the relative strengths of the two bases CO 3 2- is a stronger base than SO 4 -2 CO 3 2- will get the proton preferentially to become HCO 3 -. Equilibrium will lie to the right (forward) Another approach: Examine Acid and CA HSO 4 - is a stronger acid than HCO 3 - ; gives up a proton while the weaker one keeps its proton. (forward)

17. May 17, 201517 Key to remember The reaction favors – Consumption of the stronger acid and stronger base and – Formation of the weaker acid and weaker base

18. May 17, 201518 Predict whether the equilibrium lies predominately to the left or right. HPO 4 2- (aq) + H 2 O(l)  H 2 PO 4 - (aq) + OH - (aq) B A CA CB OH - is a stronger base than HPO 4 2- – Reverse NH 4 + (aq) + OH - (aq)  NH 3 (aq) + H 2 O (l) A B CB CA OH - is a stronger base than NH 3 – Forward.

19. May 17, 201519 Write the net ionic equation for the reaction between hydrofluoric acid, HF, and the sulfite ion, SO 3 2-, and predict which side will be favored at equilibrium.

20. May 17, 201520 HF(aq) + SO 3 2- (aq)  F - (aq) + HSO 3 1- (aq) A B CB CA Refer to the acid-base strength table and identify strength. – HF is stronger acid than HSO 3 - – SO 3 2- is stronger base than F - Equilibrium favors the side with the weaker acid and base. Forward reaction favored. “The weak shall inherit the test tube.”