Chapter 19 More about ACID-BASES

Self-Ionization of Water Two water molecules produce a hydronium ion & a hydroxide ion by the transfer of a proton. H 2 O (l) + H 2 O (l)  H 3 O + (aq) + OH - (aq) In pure water, every time you make one H 3 O + you get one OH - That is, [H 3 O + ] = [OH - ]

Hydronium Concentration Symbolized [H 3 O + ]

In Water at 25°C [H 3 O + ] = 1.0 x M And [OH - ] = 1.0 x M

IONIZATION CONSTANT OF WATER at 25°C K w = [H 3 O + ] [OH - ] K w = (1.0 x M) x (1.0 x M) = 1.0 x M 2

ION PRODUCT CONSTANT FOR WATER at 25°C K w = [H + ] [OH - ] K w = (1.0 x M) x (1.0 x M) = 1.0 x M 2

Neutral solutions Pure water is Neutral and [H 3 O + ] = [OH - ] In any solution that is neutral, [H 3 O + ] = [OH - ]

In any solution that is acidic, [H 3 O + ] > [OH - ] [H 3 O + ] > 1.0 x M

In any solution that is basic, [H 3 O + ] < [OH - ] [OH - ] > 1.0 x M [H 3 O + ] < 1.0 x M

STRONG ACIDS & BASES NEARLY COMPLETELY IONIZE OR DISSOCIATE IN AQUEOUS SOLUTION

STRONG ACID Solutions HClO 4 (aq) H 2 SO 4 (aq) HNO 3 (aq) HCl (aq) HBr (aq) HI (aq) MEMORIZE!!!

Strong Bases Group 1 Hydroxides NaOH KOH LiOH RbOH CsOH Group 2 Hydroxides Ca(OH) 2 Ba(OH) 2 Sr(OH) 2

NaOH  Na + (aq) + OH - (aq) Therefore, 1 mole of NaOH will yield 1 mole of OH - in an aqueous solution.

Ca(OH) 2  Ca 2+ (aq) + 2OH - (aq) Therefore, 1 mole of Ca(OH) 2 will yield 2 mole of OH - in an aqueous solution.

HCl  H + (aq) + Cl - (aq) Therefore, 1 mole of HCl will yield 1 mole of H + in an aqueous solution.

H 2 SO 4  2H + (aq) + SO 4 2- (aq) Therefore, 1 mole of H 2 SO 4 will yield 2 mole of H + in an aqueous solution.

For any aqueous solution at 25°C K w = [H 3 O + ] [OH - ] = 1.0 x M 2 Using this equation, if the concentration of one of the ions is known, then, the concentration of the other can be calculated.

Exercise Determine the hydronium and hydroxide ion concentrations in a solution that is 1 x M HCl. Answer: [H 3 O + ] = 1 x M [OH - ] = 1 x M

Exercise Determine the hydronium and hydroxide ion concentrations in a solution that is 1.0 x M HNO 3. Answer: [H 3 O + ] = 1.0 x M [OH - ] = 1.0 x M

Exercise Determine the hydronium and hydroxide ion concentrations in a solution that is 1.0 x M Ca(OH) 2 Answer: [H 3 O + ] = 5.0 x M [OH - ] = 2.0 x M

pH Convenient way to express numbers that tend to be very small. pH = - log[H 3 O + ] [H 3 O + ] = 1 x 10 -pH If [H 3 O + ] = 1 x then pH = 7

Figure 14.8 The pH Scale and pH Values of Some Common Substances

pOH pOH = - log[OH - ] If [OH - ] = 1 x then pOH = 7 pH + pOH = 14

Calculating pH & pOH Determine the pH & pOH of the following solutions. 1) 1 x M HCl pH = 3.0 pOH = ) 1 x M HNO 3 pH = 5.0 pOH = 9.0 3) 1 x M NaOH pH = 10.0 pOH = 4.0

Calculating the pH & pOH What is the pH of a solution if the hydronium ion conc. is 6.7 x M? pH = 3.17 What is the pH of a solution if the hydronium ion conc. is 2.5 x M? pH = 1.60 pOH = Determine the pH of a 2.0 x M Sr(OH) 2 solution. pH = 12.60

Calculating the hydronium and hydroxide ion concentrations The pH of a solution is 5.0. What is the hydronium ion concentration? 1 x M The pH of an aqueous solution is measured to be Calculate the hydronium ion and hydroxide ion concentrations. [H 3 O + ] = 3.2 x M [OH - ] = 3.2 x M

pH Calculations & the Strength of Acids and Bases For strong acids and bases, the hydronium and hydroxide ion concentrations can be directly calculated. For weak acids and bases, hydronium and hydroxide ion concentrations cannot be directly calculated because not all of the molecules are ionized.

Homework Complete worksheet