1. All cations except act as __________ in aqueous solutions, e.g., weak acids Al 3+ (aq) + 3 H 2 O(l) Al(OH) 3 (aq) + 3 H + (aq) -- the cations do NOT affect pH pH Most cations free-up H + ions.

2. Predicting pH for salts derived from a... (1)...strong base and a strong acid e.g., -- NaCl; Ca(NO 3 ) 2 pH = 7 (2)...strong base and a weak acid e.g., -- NaClO; Ba(CH 3 COO) 2 pH > 7 (3)...weak base and a strong acid e.g., -- NH 4 Cl; Al(NO 3 ) 3 pH < 7 B A pH > 7 A B pH = 7 B A pH < 7

3. (4)...weak base and a weak acid e.g., -- NH 4 CH 3 COO; NH 4 CN; FeSO 3 compare K a for cation w /K b for anion; the pH goes the way of the larger KaKa KbKb KaKa KbKb KaKa KbKb

4. What related info is found in the ref. tables? K b for NH 3 = 1.8 x 10 –5 Example: Is NH 4 CN(aq) acidic or basic? But we have ______, not ____, and ______ would _____ a proton, so we need its ____. “conjugatized” K a for NH 4 + = 5.6 x 10 –10 K b is larger: NH 4 CN(aq) is basic (pH > 7). K a for HCN = 6.2 x 10 –10 (for NH 3 to gain a proton)(for HCN to lose a proton) And we have ____, not ______, and ____ would _____ a proton, so we need its ____. “conjugatized” K b for CN – = 1.6 x 10 –5 NH 4 + NH 3 NH 4 + lose K a CN – HCN gain K b CN –

5. Acid-Base Behavior and Chemical Structure Three Factors Affecting Acid Strength 1. To transfer H +, acid must have the polarity... H–X -- ionic hydrides don’t -- C–H bonds don’t As polarity increases, acid strength generally increases. BUT... 2....if H–X bond is too strong… acid is weak 3. Stable conjugate bases (e.g., NO 3 – and Cl – ) usually indicate a... strong acid. (e.g., ) HF (They’re nonpolar.) (NaH, ) Na–H

6. For binary acids: (1) Down a group, bond strength is the determining factor....charge separation ___, so bond strength ___ and acid strength ___ HCl HBr HI weaker stronger (2) Across a period, polarity governs....polarity ___ and acid strength ___ inc. binary acid strength FON ClSP BrSe I H 2 O HF weaker stronger