Introduction to Acids & Bases

Packet #19

Introduction• Acids are group of ionic

compounds with unique properties and are found everywhere• Cause lemons to be sour• Allows for digestion of food in

the stomach• Dissolve one’s tooth enamel

to cause cavities• Eighty billion pounds of

sulfuric acid, H2SO4, is used every year in the United States to help manufacture

• Detergents• Batteries• Plastics• Pharmaceuticals• Storage batteries• Metals

Introduction II

• Acids were first recognized as substances that taste sour.

• While bases, sometimes called alkalis, are characterized by their bitter taste and slippery feel.

Introduction III

• Svante Arrhenius was the first person to recognize the essential nature of acids and bases.

Introduction IV

• Arrhenius postulated that: • Acids produce

hydrogen ions (H+) in an aqueous solution

• Bases produce hydroxide ions (OH-) in an aqueous solution.

• The limitation of Arrhenius’ concept was that OH- was the only base that could be produced.

• HCl(g) H+(aq) + Cl-(aq)

• NaOH(s) Na+(aq) + OH-

(aq)

• Top reaction• The product produced is

hydrochloric acid.• Both products are in the aqueous

form

• Bottom reaction• The bottom reaction occurs

when sodium hydroxide, is placed in water.

• Produces a strong base as the solution.

H2

O

H2

O

Introduction VBronsted-Lowry

• In the Bronsted-Lowry model: -• An acid is a proton

(H+) donor• A base is a proton

(H+) acceptor• This results in the

formation of a new acid, called the conjugate acid, and a new base called the conjugate base.

Introduction VIBronsted-Lowry Acids & Bases

• HA(aq) + H2O(l) H3O+(aq) + A-(aq)• Acid + Base Conjugate acid + Conjugate Base• Example

• HCl(aq) + H2O(l) H3O+(aq) + Cl-(aq)

• HCl(aq) and Cl- become the acid-conjugate base pair

• H2O(aq) and H3O+(aq) become the base-acid conjugate base pair.

• A conjugate acid-base pair consists of two substances relate to each other by the donating and accepting of a single proton.

Examples

• Which of the following represent conjugate acid-base pairs?a. HF, F-

b. NH4+, NH3

c. HCl, H2O

d. A & B are correcte. B & C are correctf. A & C are correctg. All of the above are correcth. None of the above is correct

Introduction VII

• A third theory of acids and bases was propose by Gilbert Lewis (1875 – 1946)

• Lewis proposed that an acid accepts a pair of electrons during a chemical reaction while a base donates a pair of electrons.• Much more general

than Arrhenius theory or the Bronsted-Lowry theory.

Introduction VIIILewis Acids & Bases

NAMING ACIDS

Naming Acids I

• Acids• Compounds that are proton (H+) donors.

• Formulas usually begin with ‘H’.

• The general formula for acids is HnX

• X represents the anion

• Examples:• HCl (aq) – hydrochloric acid

• HNO3 – nitric acid

• H2SO4 – sulfuric acid

Naming Acids II

• Remember• The general formula for acids is HnX

• Follow these three rules when attempting to name acids

Rule #1 {Monoatomic anions}Remember HnX

• When the name of the anion (X) ends with –ide• The acid begins with the prefix hydro- AND

the stem of the anion has the suffix –ic. • The word acid follows.

• Example• X = Cl- = chloride• Therefore the acid’s molecular formula is HCl

• Remember from previous lecture on ions• The name of the acid becomes hydrochloric

acid.

Rule #2 {Polyatomic ions}Remember HnX

• When the anion name ends in –ite.• The acid name is the stem of the anion with

the suffix –ous. • The word acid follows.

• Example• Name the acid H2SO3

• What is the name of the polyatomic anion?• Sulfite

• What is the name of the acid?• Sulfurous acid

Rule #3 {Polyatomic anions}Remember HnX

• When the anion ends in the name –ate• The acid name is the stem of the anion with

the suffix –ic.• The word acid follows.

• Example• HNO3

• What is the polyatomic ion?• X = NO3 = nitrate

• Therefore the acid’s name is nitric acid.

NAMING BASES

Naming Bases I

• Bases are named in the same way as other ionic compounds.• The name of the cation followed by the name

of the anion.• Example

• NaOH• Sodium hydroxide

• Al(OH)3

• Aluminum hydroxide

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