1. ACIDS AND BASES Ionization of Water

2. Describe the relationship between the hydronium and hydroxide ion concentrations in water Include: the ion product of water, K w Additional KEY Terms

3. Water is amphoteric HA + H 2 O (l) H 3 O + (aq) + A¯ (aq) or B + H 2 O (l) BH + (aq) + OH¯ (aq) H+H+ H+H+

4. Water also dissociates into ions - self-ionization Water particles collide - ions form H 2 O (l) H + (aq) + OH¯ (aq) H 2 O (l) + H 2 O (l) H 3 O + (aq) + OH¯ (aq)

5. ion product for water, K w K W = [H 3 O + ][OH¯] K W = [H + ][OH¯] H 2 O (l) H + (aq) + OH¯ (aq) Water reaches equilibrium with its ions

6. Like all constants, the value of K w varies with temperature. Water is neutral - these ions must be a 1:1 ratio K w = [H + ][OH - ] = 1.00 x 10 -14 [H + ] = [OH - ] = 1.00 x 10 -7 M At room temperature:

7. Like any reversible reaction, Le Chatelier's applies: Add a SB – increase [OH - ] decrease [H + ] OH - H2OH2O H+H+ + K w = [H + ][OH - ] = 1.00 x 10 -14 Add a SA – increase [H + ] decrease [OH - ] This means that H + and OH¯ are BOTH present in any solution - whether they are acidic or basic.

8. If 2.5 moles of hydrochloric acid is dissolved in 5.0 L of water, what is the [hydroxide ions]? Since HCl is a strong acid (100% dissociation): [H + ] = 0.50 M 5.0 L = 0.50 mol/L 2.5 mol n V M= HCl (s) H + (aq) + Cl¯ (aq)

9. [OH - ] = 2.0 x 10 -14 M K w = [H 3 O + ] [OH - ] 1.0 x 10 -14 = [0.50 [OH - ] + 1.0 x 10 -7 ]] H 2 O (l) H + (aq) + OH¯ (aq) How does the addition of HCl affect WATER’s equilibrium? Amount contributed by self-ionization of water

10. 0.40 g of NaOH is dissolved in water to make a solution with a volume of 1.0 L. What is the hydronium ion concentration in this solution? NaOH = 40.0 g/mol 0.40 g 1 L 40.0 g 1 mol = 0.010 M NaOH (s) Na + (aq) + OH¯ (aq) Since NaOH is a strong base(100% dissociation): [OH - ] = 0.010 M

11. [H + ] = 1.0 x 10 -12 M K w = [OH - ] [H 3 O + ] 1.0 x 10 -14 = [0.010 [H 3 O + ] + 1.0 x 10 -7 ]] How does addition of NaOH affect WATER’s equilibrium?

12. H 2 O (l) H + (aq) + OH¯ (aq) K W = [H + ][OH¯] = 1.00 x 10 -14 Add a SA – increase [H + ] decrease [OH - ] Add a SB – increase [OH - ] decrease [H + ]

13. CAN YOU / HAVE YOU? Describe the relationship between the hydronium and hydroxide ion concentrations in water Include: the ion product of water, K w Additional KEY Terms