Unit 5: Acid-Base Calculations Lesson 1: Kw, Ka, and Kb Remember to provide notes handout!

Review: Ions and Acid-Base Theory Compare [H3O+] to [OH-] (using <, > or =) for A) a neutral solution B) an acidic solution C) a basic solution

Kw The ionization of water can be written as either H2O + 59kJ H+ + OH- or 2 H2O + 59kJ H3O+ + OH- Write the equilibrium expression for each equation above. The equilibrium constant for this reaction is a special value called Kw. At 25°C, Kw = 1.00x10-14.

Equilibrium Shifts and Kw What happens to Kw when water is heated? When it’s cooled? What happens to the water ionization equilibrium when acid is added? When base is added?

Kw Calculations What is [H3O+] and [OH-] in 0.0010 M HCl? What is [H3O+] and [OH-] in 4.0 M NaOH? I do, we do - [H3O+] = [HCl] b/c strong acid, then solve for [OH-]. – 10 min

Brain Break: Find as many words as you can using the letters shown, always using the middle letter. What’s the 9-letter word?

Ka When a weak acid is added to water, an acid ionization equilibrium forms. E.g. CH3COOH + H2O CH3COO- + H3O+ It has an acid ionization constant, Ka. Write the equilibrium expression for this reaction. NB: assume concentrations are low enough that [H2O] remains constant

Kb When a weak base is added to water, a base ionization equilibrium forms. E.g. NH3 + H2O NH4+ + OH- It has a base ionization constant, Kb. Write the equilibrium expression for this reaction. NB: assume concentrations are low enough that [H2O] remains constant

Acid and Base Strengths Fill in the blanks: The greater the value of Ka, the __________ the acid. The greater the value of Kb, the __________ the base.

Practice Pg. 128 #31-34 15 min