Chapter 19: Acids and Bases Table of Contents 19.3: What is pH?

Starter Acids and Bases: Basic Concepts Define Arrhenius and Brønsted-Lowry acids and bases What is the difference between weak and strong acids and bases? What are some characteristics of acids? bases? Today, you’ll need a scientific/graphing calculator!

The ion product constant for water Acids and Bases: Basic Concepts Self-ionization of water: K w = H 2 O (l) H + (aq) + OH - (aq) Just “plug and chug” to solve for concentrations of either ion 2H 2 O (l) H 3 O + (aq) + OH - (aq) [H + ][OH - ]= 1.0x10 –14

The ion product constant for water Acids and Bases: Basic Concepts When [H + ] > [OH - ], the solution is acidic When [H + ] < [OH - ], the solution is basic When [H + ] = [OH - ], the solution is neutral

Practice finding [H+] & [OH-] The concentration of either the H + ion or OH - ion is given. For each solution, calculate [H + ] or [OH - ]. State whether the solution is acidic, basic, or neutral. 1. [H + ] = 1.0x10 -5 M 2. [H + ] = 1.0x M 3. [OH - ] = 1.0x10 -7 M 4. [OH - ] = 1.0x10 -3 M [OH - ] = 1.0x10 -9 M, acidic [OH - ] = 1.0x10 -1 M, basic [H + ] = 1.0x10 -7 M, neutral [H + ] = 1.0x M, basic

Measuring pH Acids and Bases: Basic Concepts pH measures acidity. pH meters measure the exact pH of a solution. Indicators turn different colors at different pHs.

pH: A mathematical scale Measures concentration of hydronium (H 3 O + ) ions in a solution Range: 0 to 14 The pH Scale Acids and Bases: Basic Concepts

pH = 7 is neutral. Interpreting the pH Scale Acids and Bases: Basic Concepts pH < 7 is acidic. lower number = more acidic, less basic pH > 7 is basic. higher number = more basic, less acidic.

The pH Scale Acids and Bases: Basic Concepts [H + ] = 1x10 –11 M [H 3 O + ] = 1x10 –4 M pH =11 pH = 4 [H 3 O + ] = 1.1x10 –4 MpH = 3.96

Acids and Bases: Additional Concepts pH and pOH pH scale: show acidity pOH scale: shows basicity

Acids and Bases: Additional Concepts Relationship between pH and pOH The pH and pOH values for a solution may be determined if either [H + ] or [OH – ] is known.

Acids and Bases: Additional Concepts CALCULATING pH and pOH from [H + ] Ex5) If a carbonated soft drink has a hydrogen ion concentration of 7.3 x 10 –4 M, what are the pH and pOH of the soft drink? Known: [H + ]Calculate pH

Acids and Bases: Additional Concepts CALCULATING pH and pOH from [H + ] The carbonated soft drink is acidic.

Practice calculating pH and pOH Calculate the pH and pOH of aqueous solutions having the following ion concentrations. Ex6) [OH - ] = 1.0x10 -6 M Ex7) [OH - ] = 6.5x10 -4 M Ex8) [H + ] = 3.6x10 -9 M Ex9) [H +- ] = M pOH = 6.00, pH = 8.00 pOH = 3.19, pH = pH = 8.44, pOH = 5.56 pH = 1.60, pOH = 12.40

pHpOH [H + ][OH - ] 1.0x = [H + ][OH - ] pH + pOH = 14 pH=-log[H + ] pOH=-log[OH - ]

Acids and Bases: Additional Concepts CALCLUATING ion concentrations from pH [H + ] = 10 -pH [OH - ] = 10 -pOH

Acids and Bases: Additional Concepts Calculating [H + ] and [OH – ] from pH Ex10) What are [H + ] and [OH – ] in a solution with a pH of 9.70? Find [H + ]. [H + ] = 2.0 x 10 –10 M [H + ] = 10 -pH =

Acids and Bases: Additional Concepts Calculating [H + ] and [OH – ] from pH Determine pOH Ex10) What are [H + ] and [OH – ] in a solution with a pH of 9.70?

Acids and Bases: Additional Concepts Calculating [H + ] and [OH – ] from pH Find [OH – ] As expected, [OH–] > [H+] in this basic solution. [OH - ] = 10 -pOH = Ex10) What are [H + ] and [OH – ] in a solution with a pH of 9.70?

Practice finding ion concentrations The pH is given for three solutions. Calculate [H + ] and [OH - ] in each solution. 11. pH = pH = pH = 6.50 [H + ] =4.3x10 -3 M [OH - ]=2.3x M [H + ] = 8.9x M [OH - ]=1.1x10 -3 M [H + ] =3.2x10 -7 M [OH - ]=3.2x10 -8 M

Acids and Bases: Additional Concepts CALCLUATING pH of strong acids and bases Mg(OH) 2(aq) → Mg 2+ (aq) + 2OH – (aq) HCl (aq) → H + (aq) + Cl – (aq) Remember, strong acids and bases completely break into their ions in water For every HCl molecule, 1 H + ion is produced. So, [H + ] = [HCl] For every Mg(OH) 2 molecule, 2 OH - ions are produced. So, [Mg(OH) 2 ] = 2[OH - ]

Practice calculating pH of SA & SB Calculate the pH of the following solutions. 1) 1.0 mol/L HI 2) mol/L HNO 3 3) 1.0 M KOH 4) 2.4x10 -5 M Mg(OH) 2 pH = 0.00 pH = 1.30 pH = pH = 9.68

pHpOH [H + ][OH - ] 1.0x = [H + ][OH - ] pH + pOH = 14 pH=-log[H + ] pOH=-log[OH - ] [H + ]=10 -pH [OH - ]=10 -pOH