chapter 19: acids and bases table of contents 19.3: what is ph?

Chapter 19: Acids and Bases

Table of ContentsTable of Contents

19.3: What is pH?

Starter

Acids and Bases: Basic ConceptsAcids and Bases: Basic ConceptsAcids and Bases: Basic ConceptsAcids 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


• Self-ionization of water:

Kw =

H2O(l) H+(aq) + OH-

(aq)

• Just “plug and chug” to solve for concentrations of either ion

2H2O(l) H3O+(aq) + OH-

(aq)

[H+][OH-] = 1.0x10–14

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+] & Practice finding [H+] & [OH-][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+] = 1.0x10-5M2. [H+] = 1.0x10-13M3. [OH-] = 1.0x10-7M4. [OH-] = 1.0x10-3M

[OH-] = 1.0x10-9M, acidic[OH-] = 1.0x10-1M, basic[H+] = 1.0x10-7M, neutral[H+] = 1.0x10-11M, basic

Measuring pH


• 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 (H3O+) ions in a solution

• Range: 0 to 14

The pH Scale


• pH = 7 is neutral. Interpreting the pH Scale


• pH < 7 is acidic. lower number = more acidic, less basic

• pH > 7 is basic. higher number = more basic, less acidic.

The pH Scale


[H+] = 1x10–11M

[H3O+] = 1x10–4M

pH =11

pH = 4

[H3O+] = 1.1x10–4M pH = 3.96

Acids and Bases: Additional ConceptsAcids and Bases: Additional Concepts Acids and Bases: Additional ConceptsAcids and Bases: Additional Concepts

pH and pOH

• pH scale: show acidity

• pOH scale: shows basicity


Relationship between pH and pOH

• The pH and pOH values for a solution may be determined if either [H+] or [OH–] is known.


CALCULATING pH and pOH from [H+]

Ex5) If a carbonated soft drink has a hydrogen ion concentration of 7.3 x 10–4M, what are the pH and pOH of the soft drink?

Known: [H+] Calculate pH


CALCULATING pH and pOH from [H+]

The carbonated soft drink is acidic.

Practice calculating Practice calculating pH and pOHpH and pOH

• Calculate the pH and pOH of aqueous solutions having the following ion concentrations.

Ex6) [OH-] = 1.0x10-6MEx7) [OH-] = 6.5x10-4MEx8) [H+] = 3.6x10-9MEx9) [H+-] = 0.025 M

pOH = 6.00, pH = 8.00pOH = 3.19, pH = 10.81pH = 8.44, pOH = 5.56pH = 1.60, pOH = 12.40

pH pOH

[H+] [OH-]1.0x10-14 = [H+][OH-]

pH + pOH = 14

pH=-log[H+]

pOH=-log[OH-]


CALCLUATING ion concentrations from pH

[H+] = 10-pH

[OH-] = 10-pOH


Calculating [H+] and [OH–] from pHEx10) 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

= 10-9.70


Calculating [H+] and [OH–] from pH

• Determine pOH

Ex10) What are [H+] and [OH–] in a solution with a pH of 9.70?


Calculating [H+] and [OH–] from pH

• Find [OH–]

As expected, [OH–] > [H+] in this basic solution.

[OH-] = 10-pOH

= 10-4.30

Ex10) What are [H+] and [OH–] in a solution with a pH of 9.70?

Practice finding ion Practice finding ion concentrationsconcentrations

• The pH is given for three solutions. Calculate [H+] and [OH-] in each solution.

11. pH = 2.37

12. pH = 11.05

13. pH = 6.50

[H+] =4.3x10-3 M[OH-]=2.3x10-12 M

[H+] = 8.9x10-12 M[OH-]=1.1x10-3 M

[H+] =3.2x10-7 M[OH-]=3.2x10-8 M


CALCLUATING pH of strong acids and bases

Mg(OH)2(aq)→ Mg2+(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 Practice calculating pH of SA & SB pH of SA & SB

• Calculate the pH of the following solutions.

1) 1.0 mol/L HI2) 0.050 mol/L HNO3

3) 1.0 M KOH4) 2.4x10-5 M Mg(OH)2

pH = 0.00pH = 1.30pH = 14.00pH = 9.68

pH pOH

[H+] [OH-]1.0x10-14 = [H+][OH-]

pH + pOH = 14

pH=-log[H+]pOH=-log[OH-]

[H+]=10-pH [OH-]=10-pOH

chapter 19: acids and bases table of contents 19.3: what is ph?

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