Chapter 13Acids and Bases

What are acids and Bases?

A. Properties of Acids

-tastes sour

-conducts electricity

-turn blue litmus paper red

-reacts with bases to form water and salts

-have pH less than 7

Naming Acids

Two Types of Acids

a. Binary Acid

-contains only H and one other element

Naming Binary Acids

1. Name begins with prefix hydro-

2. Root of second element follows hydro and ends with the suffix -ic

Examples of Binary Acids

Hydrofluoric acid HF

Hydrochloric acid HCl

Hydrobromic acid HBr

Hydrosulfuric acid H2S

Acids cont.

b. Oxyacid

- acid that contains H, O, and a third element,usually a nonmetal

Naming Oxyacids

1. Root of the anion plus the suffix –ic followed by the word acid

Examples of Oxyacids

Acetic acid acetate

Carbonic acid carbonate

Nitric acid nitrate

Phosphoric acid phosphate

Sulfuric acid sulfate

Properties of Bases

- tastes bitter- Feels slippery- Turns red litmus paper blue- Reacts with acids to form water and

salts- Have a pH greater than 7

Bases cont.

Naming Bases

- Element name followed by hydroxide

- There are a few exceptions:

Ammonia NH3

Aniline C6H5NH2

Acid-Base Theories

Arrhenius Acids and Bases

1. Arrhenius Acid

acids in water produce H+ ions

HNO3(aq) H+(aq) + NO3-

2. Arrhenius Base

bases in water produce OH-

KOH(s) K+(aq) + OH-(aq)

Cont.

Bronsted-Lowry Acids and Bases-Acids are proton(H+) donors

H2CO3(aq)+H2O(l)H3O+(aq)+HCO3-(aq)

(acid) (base) (C.A.) (C.B.)-Bases are proton acceptor

NH3(aq) + H2O(l) NH4+(aq) + OH-(aq)

base acid C.A. C.B.Conjugate acid- ion formed when a base has accepted a

H+ Conjugate base- ion formed when an acid has donated a

H+

How are weak acids and bases compared?

Acid-dissociation constant(Ka)- ratio of concentrations of the products to the

reactants for a weak acid- Example

CH3COOH(aq) + H2O(l) CH3COO-(aq) + H3O+(aq)

Ka= [CH3COO-] [H3O+] [CH3COOH]

Cont.

Base-dissociation constant(Kb)

-ratio of concentrations of the products to the reactants for a weak base

NH3(aq) +H2O(l) NH4+(aq) + OH-(aq)

Kb= [NH4+] [OH-]

[NH3]

The pH scale

Is the negative of the common logarithm of the hydronium ion concentration

Ranges from 0-14

We use the following equation:

pH= -log[H3O+]

Self-Ionization Constant of Water

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

Kw= [H3O+] [OH-]

Kw = 1.00 x 10-14 at 25° C

Determining [H3O+] and [OH-] with Kw

Example

What is [OH-] in a 3.00x 10-5 M solution of HCl?

HCl(g) + H2O(l) H3O+(aq) +Cl-(aq)

2H20(l) H3O+(aq) + OH-(aq)

What do we know?

Kw= 1.00 x 10-14

[H3O+]= 3.00 x 10-5

Using Logarithms in pH calculations

1. Calculating pH from [H3O+]

pH= -log [H3O+]

2. Calculating [H3O+] from pH

[H3O+] = 10-pH

Examples of pH

What is the pH of a .00010 M solution of HNO3, a strong acid?

[HNO3]= .00010 M or 1.0 x 10-4 M

pH= -log[1.0 x10-4]

pH= 4.00

Examples cont.

What is the pH of a .0136 M solution of KOH, a strong base?

[OH-]= .0136 M

Kw= 1.00 x 10-14

Kw= [H3O+][OH-]

pOH= -log[OH-]

pH + pOH = 14

Calculating [H3O+] and [OH-] from pH

What are the concentrations of the hydronium and hydroxide ions in a sample of rain that has a pH of 5.05?

[H3O+] = 10-5.05

= 8.9 x 10-6 MSince pH + pOH = 14 pOH= 8.95 so

[OH-] = 10-8.95

= 1.1 x 10-9 M

Calculating Ka/Kb for a weak acid or base

A vinegar sample is found to have .837 M CH3COOH. Its hydronium concentration is found to be 3.86 x 10-3 mol/L. Calculate Ka for acetic acid.

What do we know?

[CH3COOH]= .837 M

[H3O+]= 3.86 x 10-3 M

CH3COOH(aq)+ H2O(l)H3O+(aq)+CH3COO-(aq)

Neutralization and Titrations

Neutralization Reaction- a reaction between an acid and a

hydroxide base that results in a salt and water

HCl + NaOH NaCl + H2O

Titrations

Titrations- a procedure in which a solution of known

concentration is used to determine the concentration of a second unknown solution

Equivalence Point

- the point at which a neutralization reaction is complete

Titrations cont.

How do we know when the equivalence point has been reached?You use an indicatorA substance that changes its color as it reacts with either an acid or baseThe instant the indicator changes color is called the End Point

Common indicators are red cabbage juice, litmus, bromthymol blue, and phenolphthalein

Titration Calculations

Suppose that in the titration of 40. mL of vinegar, 20.mL of .50 M NaOH were needed to reach the equivalence point. What is the molarity of the acetic acid in the vinegar?

NaOH(aq)+CH3COOH(aq)NaCH3COO(aq) + H2O(l)

What do we know?Volume of NaOH= 20. Ml[NaOH]= .50 MVolume of vinegar = 40. ml