Acids and Bases

Properties of Acids/Bases

Acids are substances which…

Bases are substances which…

Properties of Acids and Bases Acids: Sour taste React with active

metals to produce hydrogen gas

Neutralize bases Change the color of

indicators Conduct electricity

Bases: Bitter taste Slippery feel Neutralize acids Change the color of

indicators Conduct electricity

Arrhenius Acid/Base Theory Acids are substances

that produce H+ (H3O+) ions in solution.

HCl H+ + Cl-

Bases produce OH- ions in solution.

NaOH Na++ OH-

Acid Nomenclature The presence of O in an acid molecule

determines how the acid is named. Acids without O use the prefix “hydro” and

the suffix “ic.” HCl is hydrochloric acid. Acids with O use a suffix ending of “ous”

or “ic” depending on the amount of O present.

H2SO4 = sulfuric acid; H2SO3 = sulfurous acid.

Name the following acids:

HBr

H2CO3

H3PO4

H2Se

HCN

H2C2O4

Strong Acids and Strong Bases Strong acids ionize completely when

placed in water. There are six strong acids, all the rest are

weak acids. HCl, HBr, HI, HNO3, H2SO4, HClO4

Strong bases dissociate completely when placed in water.

Strong bases include all elements in group I and heavy group 2 elements.

Brønsted-Lowry Acids and Bases Acids are substances capable of donating

a proton. Bases are capable of accepting a proton. B/L theory is applicable to reactions that

do not occur in water. Can include gas phase reactions NH3(g) + H2O(l) NH4

+(aq)+ OH- (aq)

HBr(aq) + H2O(l) H3O+(aq) + Br-(aq)

CO32-(aq) + H2O(l) HCO3

-(aq) + OH-(aq)

HSO4-(aq) + HCO3

-(aq) SO42-(aq) + H2CO3(aq)

HCHO2(aq)+ PO43-(aq) CHO2

-(aq) + HPO4

- (aq)

Identify the conjugate acid-base pairs in thefollowing reactions:

H2SO3(aq)+H2O(l) HSO3-(aq) + H3O+ (aq)

HPO42-(aq)+H2O(l) H2PO4

-(aq) + OH-(aq)

HSeO3-(aq)+H2O(l) H3O+(aq) + SeO3

2-(aq)

Lewis Acids and Bases According to Lewis, an acid is an electron

pair acceptor. Acids generally have incomplete octets. A base is an electron pair donor. Bases will have lone pairs. NH3 + BF3 H3NBF3

Strengths of Acids and Bases Strong acids ionize completely. HCl H+ + Cl-

Strong acids produce the maximum number of ions in solution so they are good conductors of electricity.

Strong bases dissociate completely. NaOH Na+ + OH-

Strong bases produce the maximum number of hydroxide ions in solution.

Weak acids produce an equilibrium mixture of molecules and ions in solution.

Because an equilibrium is established, anequilibrium expression or Ka can be writtenfor a weak acid.

HCOOH H+ + HCOO-

Ka = [H+][HCOO-] [HCOOH]

Determine the equilibrium constant for a 0.15 M solution of acetic acid if the H+

concentration is 1.45 x 10-6M.

The Ka for hydrofluoric acid is 6.8 x 10-4. Determine the [H+] of a 0.500 M solution.

Table of Acid and Base Dissociation Constants  

Weak Acids

Name Chemical Formula KA

Acetic acid HC2H3O2 1.8010-5

Acetylsalicylic acid HC9H7O4 3.210-4

Benzoic acid HC7H5O2 6.010-5

Chloroacetic acid ClCH2COOH 1.4010-3

Formic acid HCOOH 1.7710-4

Hydrocyanic acid HCN 4.0010-10

Hypochlorous acid HOCl 4.0010-8

Hydrofluoric acid HF 7.2010-4

Hypoiodous acid HOI 2.3010-11

Lactic Acid HC3H5O3 1.5×10-4

Nicotinic acid HC6H4NO2 1.4010-5

Nitrous Acid HNO2 4.510-4

Weak Bases

Name Chemical Formula KB

Ammonia NH3 1.8010-5

Diethylamine (CH3CH2)2NH 8.610-4

Methylamine CH3NH2 4.210-4

Pyridine C5H5N 1.5×10-9

Quinoline C9H7N 6.310-8

Trimethylamine (CH3)3N 7.4×10-5

Carbonic = 4.3 x 10-7

Sulfurous = 1.7 x 10-2

Phosphoric = 7.5 x 10-3

Phosphorous = 1.58 x 10-2

Hydrosulfuric = 9.5 x 10-8

Autoionization of Water Protons transfer from

one water molecule to another.

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

Kw = [H+] [OH-]

Kw = 1.0 x 10-14

The product of [H+] [OH-] must always equal 1.0 x 10-14

Determine the [OH-] if the [H+] = 2.5 x 10-5M.

Calculate the [H+] if the [OH-] is 6.5 x 10-8M.

The Ka for phosphoric acid is 7.08 x 10-3. Write the equilibrium expression for phosphoricacid and determine the hydrogen ion concentration of a 0.145 M solution.

pH The amount of H+ ions in solution can be

expressed quantitatively using a logarithmic scale.

pH = -log[H+]; pOH = -log[OH-] At 298 K pH values range from 0-14. pH + pOH = 14 A solution is considered acidic if its pH <7. A solution is considered basic if its pH >7. At a pH of 7 [H+] = [OH-] and the solution

is considered to be neutral.

[H+] [OH-] pH pOH

6.5 x 10-3

7.8 x 10-8

10.56

Complete the following table:

Determine the pH of the following solutions:

1.0 M HI

0.050 M HNO3

1.5 M KOH

0.0075 M Ba(OH)2

2.5 M HCl

0.0045 M NaOH

pH + pOH =14

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

Determine the Ka of a 0.10 M solution of formic acid with a pH of 2.37.

Determine the pH of a 0.50 M solution ofacetic acid. The Ka for acetic acid is 1.8 x 10-5.

Neutralization Reactions Occur between acids and bases. Produce a salt and water. The pH of the resulting salt depends on

the nature of the acid and the base. HNO3 + CsOH H2O + CsNO3

Determine the pH of a 0.450 M solution ofsulfurous acid. The Ka of sulfurous acid is 1.7 x 10-2.

Write equations for the following reactions.Predict the pH of the salt formed in each case.

Hydrobromic acid + calcium hydroxide

Sulfuric acid + potassium hydroxide

Acetic acid + ammonium hydroxide

Titration Method for determining the concentration

of a solution by neutralization. A solution of known concentration is

reacted with a set volume of another solution of unknown molarity.

Titration proceeds until the equivalence point is reached.

The equivalence point is where moles of H+ ions = moles of OH- ions.

Titration Procedure:

1. A measured volume of acid or base is placed in a beaker.

2. A buret is filled with a solution of known concentration.

3. A pH meter or indicator is used to signalthe endpoint of the procedure.

An indicator or pH meter is used to signal the end of the titration.

Titration problems can be solved by relatingmoles of acid to moles of base using the formula for Molarity:

Molarity = moles liter of solution

At the equivalence point:

moles of acid =moles of base or

MAVA = MBVB

What is the molarity of a solution of KOH if30.0 mL of the solution is titrated with 26.5 mL of 0.250 M HBr solution?

What volume of 0.590 M HCl is needed toneutralize 55.00 mL of 0.125 M NaOH?

Determine the concentration of 35.0 mL of sulfuric acid solution that is titrated with45.0 mL of 0.150 M KOH.