1. Strength of Acids and Bases: Chemistry 12◊ Chapter 14

2. Key Idea: The strength of an acid is determined by the extent to which it ionizes (its percent ionization) NOT the concentration of the acid (the concentration of its hydronium ions or its ability to react with a metal)

3. Strong Acid: A strong acid that nearly completely dissociates All molecules of the acid break up to form the ions soluble in water

5. Weak Acid: An acid that only slightly dissociates in a water solution Only a small percent of acid molecules donate their hydrogen and most remain the same. The majority of acids are weak! Example: CH 3 COOH

7. Comparing: A strong acid essentially ionizes 100%. HCl (g) + H 2 O (l)  H 3 O + (aq) + Cl - (aq) 0.10 mol 0.10 mol0.10 mol ( few molecules)(many ions) A weak acid ionizes very little CH 3 COOH (l) + H 2 O (l)  H 3 O + (aq) + CH 3 COO - (aq) 0.10 mol << 0.10 mol << 0.10 mol (many molecules)(few ions) CH 3 COOH has 5% ionization at 25  C

9. Strong and Weak Bases: A strong base almost completely dissociates into its ions All oxides and hydroxides of group 1 and 2 are strong bases. Ex: NaOH Weak bases dissociate only slightly in water Most bases are weak Example: NH 3 (1% ionization) NH 3(g) + H 2 O (l)  NH 4 + (aq) + OH - (aq) 0.10 mol << 0.10 mol << 0.10 mol

10. Electrolytes: Strong acids and bases are strong electrolytes and weak acids and bases are weak electrolytes Why? The more ionization (ions in the solution) the greater the conductivity Strong acids have lots of charged ions and weak acids have very, very few ions

11. Experimentally: Distinguishing strong acids from weak acids and strong bases from weak bases: We must compare a strong acid to a weak acid of equal concentration Therefore, we could compare by: a) use a conductivity apparatus test (light bulb will be brighter for a strong acid). b) react the two acids with a metal like magnesium (stronger acid will react faster, more bubbling as H 2 is formed) c) measure the pH of the solutions using a pH meter or indicators (strong acid has a lower pH)

12. H + A - H + A - HA A - H + A - H + A – H + A - H + A - H + A - HA H + A - H + A - H + A - H + HA HA HA HA HA H + A - HA HA HA HA H + A – HA H + A – HA HA H + A - H + A - H + A - H + A - HA A - H + A - H + A - H + A - H + A - H + A - HA H + A - H + A - H + A - A - H + A - H + A - H + A - H + A - H + H + A - H + A - H + A - HA H + A - A - H + A - H + A - H + A - H + A – H + A - H + A - H + A - H + A - H + A - H + A - H + A - H + A - H + A - HA A - H + A - H + A - H + A - H + HA HA H + A - HA HA HA HA HA HA HA HA H + A - H + A - HA HA HA HA HA HA HA H + A - HA HA HA HA HA HA H + A - HA HA H + A - HA HA HA HA HA HA HA HA H + A - HA HA H + A - HA HA HA HA HA HA HA H + A - HA HA HA DILUTE CONCENTRATED STRONG WEAK STRONG ACIDS Dissociate nearly 100% HA H 1+ + A - WEAK ACIDS Dissociate very little HA H 1+ + A - Concentration vs Strength:

13. Comparing Strengths: Data booklet (2 nd last page) Figure 14.12 in text page 563

15. Strengths Of Conjugate Acid-Base Pairs: The stronger an acid, the weaker is its conjugate base. The stronger a base, the weaker is its conjugate acid. An acid-base reaction is favoured in the direction from the stronger member to the weaker member of each conjugate acid-base pair.

16. The stronger acid and stronger base form the weaker acid and the weaker base, so the direction proceeds in that direction (left) Reactants are favoured in this reaction. Weak baseweak acid

17. Try it: Pg 564 # 10, 11