Table of Contents Chapter 19 Acids and Bases

Table of Contents Chapter 19: Acids and Bases 19. 3: What is p. H?

Acids and Bases: Basic Concepts Starter • 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!

Acids and Bases: Basic Concepts The ion product constant for water • Self-ionization of water: H 2 O(l) 2 H 2 O(l) H+(aq) + OH-(aq) H 3 O+(aq) + OH-(aq) Kw =[H+][OH-] = 1. 0 x 10– 14 • Just “plug and chug” to solve for concentrations of either ion

Acids and Bases: Basic Concepts The ion product constant for water • 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. [OH-] = 1. 0 x 10 -9 M, acidic 1. [H+] = 1. 0 x 10 -5 M [OH-] = 1. 0 x 10 -1 M, basic 2. [H+] = 1. 0 x 10 -13 M [H+] = 1. 0 x 10 -7 M, neutral 3. [OH-] = 1. 0 x 10 -7 M [H+] = 1. 0 x 10 -11 M, basic 4. [OH-] = 1. 0 x 10 -3 M

Acids and Bases: Basic Concepts Measuring p. H • p. H measures acidity. • Indicators turn different colors at different p. Hs. • p. H meters measure the exact p. H of a solution.

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

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

Acids and Bases: Basic Concepts The p. H Scale [H+] – 11 = 1 x 10 M – 4 [H 3 O+ ] = 1 x 10 M [H 3 O+ ] – 4 = 1. 1 x 10 M p. H =11 p. H = 4 p. H = 3. 96

Acids and Bases: Additional Concepts p. H and p. OH • p. H scale: show acidity • p. OH scale: shows basicity

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

Acids and Bases: Additional Concepts CALCULATING p. H and p. OH from [H+] Ex 5) If a carbonated soft drink has a hydrogen ion – 4 concentration of 7. 3 x 10 M, what are the p. H and p. OH of the soft drink? Known: [H+] Calculate p. H

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

Practice calculating p. H and p. OH • Calculate the p. H and p. OH of aqueous solutions having the following ion concentrations. Ex 6) [OH-] = 1. 0 x 10 -6 M p. OH = 6. 00, p. H = 8. 00 Ex 7) [OH-] = 6. 5 x 10 -4 M p. OH = 3. 19, p. H = 10. 81 Ex 8) [H+] = 3. 6 x 10 -9 M p. H = 8. 44, p. OH = 5. 56 Ex 9) [H+-] = 0. 025 M p. H = 1. 60, p. OH = 12. 40

p. H + p. OH = 14 p. H p. OH p. H=-log[H+] p. OH=-log[OH-] [H+] 1. 0 x 10 -14 = [H+][OH-]

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

Acids and Bases: Additional Concepts [H+] – Calculating and [OH ] from p. H Ex 10) What are [H+] and [OH–] in a solution with a p. H of 9. 70? • Find [H+]. + [H ] = -p. H 10 = 10 -9. 70 – 10 + [H ] = 2. 0 x 10 M

Acids and Bases: Additional Concepts [H+] – Calculating and [OH ] from p. H – + Ex 10) What are [H ] and [OH ] in a solution with a p. H of 9. 70? • Determine p. OH

Acids and Bases: Additional Concepts [H+] – Calculating and [OH ] from p. H – + Ex 10) What are [H ] and [OH ] in a solution with a p. H of 9. 70? – • Find [OH ] = -p. OH 10 = 10 -4. 30 As expected, [OH–] > [H+] in this basic solution.

Practice finding ion concentrations • The p. H is given for three solutions. Calculate [H+] and [OH-] in each solution. +] =4. 3 x 10 -3 M [H 11. p. H = 2. 37 [OH-]=2. 3 x 10 -12 M 12. p. H = 11. 05 [H+] = 8. 9 x 10 -12 M [OH-]=1. 1 x 10 -3 M 13. p. H = 6. 50 [H+] =3. 2 x 10 -7 M [OH-]=3. 2 x 10 -8 M

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

Practice calculating p. H of SA & SB • Calculate the p. H of the following solutions. 1) 1. 0 mol/L HI 2) 0. 050 mol/L HNO 3 3) 1. 0 M KOH 4) 2. 4 x 10 -5 M Mg(OH)2 p. H = 0. 00 p. H = 1. 30 p. H = 14. 00 p. H = 9. 68

p. H + p. OH = 14 p. H p. OH p. H=-log[H+] p. OH=-log[OH-] [H+]=10 -p. H [H+] [OH-]=10 -p. OH 1. 0 x 10 -14 = [H+][OH-]