1. Due: Acid WS Today: 1.Bases 2.pOH 3.Relationship between pOH and pH HW Base & pOH WS

2. Properties of Bases  Bases are proton (hydrogen ion, H + ) acceptors or produce OH- in solution  Bases have a pH greater than 7  Bases taste bitter  Bases effect indicators  Red litmus turns blue  Phenolphthalein turns purple  Solutions of bases feel slippery  Bases neutralize acids

3. Bases are Proton (H + ion) Acceptors  Sodium hydroxide (lye), NaOH  Potassium hydroxide, KOH  Magnesium hydroxide, Mg(OH) 2  Calcium hydroxide (lime), Ca(OH) 2 OH - (hydroxide) in base combines with H + in acids to form water H + + OH -  H 2 O

4. © 2009, Prentice-Hall, Inc. Strong Bases Strong bases are the soluble hydroxides, which are the alkali metal and heavier alkaline earth metal hydroxides (Ca 2+, Sr 2+, and Ba 2+ ). Again, these substances dissociate completely in aqueous solution.

5. © 2009, Prentice-Hall, Inc. Weak Bases Bases react with water to produce hydroxide ion.

6. © 2009, Prentice-Hall, Inc. Weak Bases The equilibrium constant expression for this reaction is NH 3 (aq)  NH 4 + + OH - [ NH 4 + ] [OH - ] [ NH 3 ] K b = where K b is the base-dissociation constant.

7. Self-Ionization of Water H 2 O   H 3 O + + OH - Set Up the Equilibrium Expression for water [H 3 O + ][OH - ] [H 2 O] K w = Kw = [H 3 O + ][OH - ] = 1 x 10 -14

8. K w – Ionization Constant for Water What is the concentration of hydronium & hydroxide? [H 3 O + ] = 1 x 10 -7 mol/L [OH - ] = 1 x 10 -7 mol/L pH = 7 pOH = 7

9. pH + pOH = 14

11. © 2009, Prentice-Hall, Inc. Sample Exercise 16.9 Calculating the pH of a Strong Base What is the pH of (a) a 0.028 M solution of NaOH, (b) a 0.0011 M solution of Ca(OH) 2 ? What is the concentration of a solution of (a) KOH for which the pH is 11.89; (b) Ca(OH) 2 for which the pH is 11.68? Answers: (a) 7.8 × 10 –3 M, (b) 2.4 ×10 –3 M Practice Exercise Solution Analyze: We are asked to calculate the pH of two solutions of strong bases. Plan: We can calculate each pH by either of two equivalent methods. First, we could use Equation 16.16 to calculate [H + ] and then use Equation 16.17 to calculate the pH. Alternatively, we could use [OH – ] to calculate pOH and then use Equation 16.20 to calculate the pH. Solve: (a) NaOH dissociates in water to give one OH – ion per formula unit. Therefore, the OH – concentration for the solution in (a) equals the stated concentration of NaOH, namely 0.028 M. (b) Ca(OH) 2 is a strong base that dissociates in water to give two OH – ions per formula unit. Thus, the concentration of OH – (aq) for the solution in part (b) is 2 × (0.0011 M) = 0.0022 M