Chapter 19Chapter 19

Acids, Bases, and SaltsAcids, Bases, and Salts

Anything in black letters = write it in your notes (‘knowts’)

UNIT 6 – Acids & Bases & Redox RxnsUNIT 6 – Acids & Bases & Redox Rxns

Chapter 19 – Acids, Bases, and SaltsChapter 19 – Acids, Bases, and SaltsChapter 20 – Oxidation-Reduction RxnsChapter 20 – Oxidation-Reduction Rxns

19.1 – Acid-Base Theories19.1 – Acid-Base Theories

Taste sourDissolve active metals to produce hydrogen gas

Turns litmus paper RED

BasesTaste bitterFeels slippery on skin (dissolves oils on skin)

Turns litmus paper BLUE

Have you seen the litmus paper yet??

Acids

These are experimental definitions, they do not explain (theory) how an acid is different from a base.

Svante Arrhenius (1857 – 1927)

Arrhenius defined an acid and base theoretically.

Dissociate - to split or separate from another

First, a vocal word…

ACID – substance that dissociates in water to form hydrogen ions (H+).

BASE – substance that dissociates in water to form hydroxide ions (OH-).

HCl (aq) H+ (aq) + Cl- (aq)

NaOH (aq) Na+ (aq) + OH- (aq)

Arrhenius Definition (~1887)

When an acid is placed in water, H+ ions are produced.

Hydrogen ions can also be thought of as H3O+ ions.

H3O+ = hydronium ion

HCl (aq) H+ (aq) + Cl- (aq)

HCl + H2O H3O+ + Cl-

or equivalently,

Brønsted-Lowry Definition (~1923)

ACID – donates H+

BASE – accepts H+

B-L definition covers more examples than the Arrhenius definition.

Johannes Bronstad (1879 – 1947)

Thomas Lowry (1874 – 1936)

ammonia ammonium ion

water donates a H+ and so is a B-L acid

ammonia accepts a H+ and so is a B-L base

Conjugate Acid – formed when a base accepts a H+

Conjugate Base – formed when an acid donates a H+

Amphoteric – substance that can be an acid or a base – depending on what it reacts with.

Water is amphoteric

ACIDS donate H+, BASES accept H+

label each reactant as an acid and base, label the products as conjugate acids or conjugate bases.

HNO3 + H2O H3O+ + NO3-

CH3COOH + H2O H3O+ + CH3COO-

NH3 + H2O NH4+ + OH-

H2O + CH3COO- CH3COOH + OH-

Lewis Acids and Bases (not covered)

Assignment:

Chapter 19 #52-57 (p. 684)

Acid/Base Indicators

Litmus

Acid – red, Base – blue, Neutral - colorless

Phenolphthalein

Acid – colorless, Base – pink, Neutral - colorless

Cabbage

Acid – red/pink, Base – yellow/green, Neutral – blue/purple

19.2 – Hydrogen Ions and Acidity19.2 – Hydrogen Ions and Acidity

Molarity (M) – unit used to express the concentration of a solution

Molarity = mol solute (mol)

liters of soln (L)

[H+] = ‘the hydrogen ion concentration’

anything in [brackets] means the concentration in molarity

[OH-] = ‘the hydroxide ion concentration’

Self-Ionization of WaterSelf-Ionization of Water

Water ionizes to produce a small amount of H+ and OH- ions.

H2O H+ + OH-

[H+] = [OH-] = 1 x 10-

7 M

In pure water at 25 ̊C

Ion-product constant for water (Kw)

Kw = [H+][OH-] = 1.0 x 10-14

remember…anything in [brackets] represents the concentration in molarity

A solution is acidic if [H+] > 1.0 x 10-7 M …or if the pH of the solution is below 7

pH = ‘power of the hydrogen ion’pH = -log[H+]

Just as the mole was used to simplify large numbers of atoms, pH is used to simplify small concentration

numbers

[H+] = 1 x 10-7 M

Instead of writing out numbers like these…

[H+] = 2.4 x 10-4 M

[H+] = 7.3 x 10-10 M

pH = 7.00pH = 3.62pH = 9.14

we can write number like these

We can just say “This solution has a pH of 3.62”.

Instead of saying “This solution has a hydronium ion concentration of 2.4 x 10-4 M”.

Not only is pH an easier number to talk about, pH is understood by most people, whereas molarity is not.

The pH scale is used to describe how acidic or basic (alkaline) a substance is.

Pure water has [H+] = 1.00 x 10-

7 M

pH = - log [1.00 x 10-7]

pH = 7

The pH of water would be

pH = -log[H+]

Examples

Examples

[H+] = 2.3 x 10-5 M. Calculate the pH.

pH = - log [H+]

pH = - log [2.3 x 10-5]

pH = 4.64

Examples

[H+] = 1.0 x 10-5 M. Calculate the pH.

pH = - log [H+]

pH = - log [1.0 x 10-5]

pH = 5.0

Examples

-4.2 = log [H+]

10-4.2 = 6.31 x 10-5 M = [H+]

pH = - log [H+]

10-4.2 = 10log [H+]

pH = 4.2. Calculate [H+]

Summary of pHSummary of pH

[H+] = 10-pH

pH = - log [H+]

The pH scale is used to indicate how acidic or basic a substance is.

The scale normally ranges from 0 to 14.

Acids have a pH below 7, bases are above 7.

ASSIGNMENT:

Chapter 19 #10-24 (p.655-662)

19.3 – Strengths of Acids and Bases19.3 – Strengths of Acids and Bases

Coming soon!!

19.4 – Neutralization Reactions19.4 – Neutralization Reactions

Neutralization Rxn – complete rxn of a strong base with a strong acid

A neutralization rxn will produce a salt and water.

Acid + Base Salt + H2O

HCl + NaOH NaCl + H2O

Titration – determining the concentration of an unknown solution using a solution whose concentration is known.

Equivalence Point – point where the amount of acid equals the amount of base

Standard – solution of known concentration.

End Point – point where the indicator changes color

EXAMPLE10.0 mL of 0.5 M HCl solution is added to 20.0 mL of NaOH of unknown concentration. What is the concentration of the NaOH?

HCl + NaOH NaCl + H2O0.5 M

10.0 mL 20.0 mLx M

Since the reaction of HCl and NaOH is 1:1 and twice the volume of NaOH was used, the NaOH must half as strong as HCl; [0.25 M].

EXAMPLEWhat volume of 0.10 M KOH is required to neutralize 20.0 mL of 0.20 M H2SO4 solution?

H2SO4 + 2KOH K2SO4 + 2H2O

0.20 M20.0 mL x mL

0.10 M

Always adjust if the rxn is NOT 1:1

Since KOH requires twice as many moles as H2SO4, you should double your answer.

19.5 – Salts in Solution19.5 – Salts in Solution

not covered…

Neutralization Rxn –

Acid + Base Salt + H2O

HCl + NaOH NaCl + H2O

Sulfuric acid + magnesium hydroxide

Write the balanced chemical equation for each neutralization reaction

Phosphoric acid + calcium hydroxide

Nitric acid + ammonium hydroxide

Chapter 19 Quiz Questions

1. What color will litmus paper be in an acidic solution?

3. Define an acid in terms of the Arrhenius definition.

4. What two products are always formed in an acid-base neutralization reaction?

2. What color will phenolphthalein indicator be in an basic solution?

5. A student titrated 10.0 mL of an HCl solution. The titration required 23.3 mL of 0.24M NaOH solution.

a. Which solution was the standard?

b. Which solution was more concentrated?

c. Convert the volumes to liters

d. Calculate the number of moles of NaOH that reacted.

e. Calculate the number of moles of HCl that reacted.

f. Calculate the molarity of the HCl solution.

6. Calculate the pH of solutions with the following hydrogen ion concentrations.

a. [H+] = 1.23 x 10-4M

b. [H+] = 3.42 x 10-7M

7. Calculate the hydrogen ion concentrations of solutions with the given pH.

a. pH = 3.14

b. pH = 9.2