Acids and Bases

19.1 IntroductionDr. Michael J Passow

Acids and Bases

• Acids and bases (alkalis) are some of the most important compounds, industrially and internally (biochemically)

• Common acids include carbonic acid in sodas, citric acids in fruits, acetic acid in vinegar, and hydrochloric acid in your stomach

• Bases are commonly found in such substances as soaps, cleaning fluids, milk, and blood

Properties of Acids and Bases

Acids• Sour taste• React with some metals to

product hydrogen gas (H2)• Some carbonates react with

acids to release CO2

• Causes blue litmus paper to turn pink

• Solutions conduct electricity

Bases• Bitter taste• Slippery feel• Causes pink litmus paper to

turn blue (“blue = base”)• Solutions conduct electricity

Neutral –neither acid nor base

Ion in Solution

Water decomposes in “hydronium ions” H3O+ (aq) and “hydroxide ions” OH-(aq)

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

Simplified version of “self-ionization”:H2O(l) H+(aq) + OH-(aq)

(“Pure water” is always neutral, and very rare.)

Types of Acids and Bases

Arrhenius

• Acid contains H and ionizes to form H+ in solutions

HCl(g) H+ + Cl-

• Base contains OH and dissociates to produce OH- in solutions

NaOH Na+ + OH-

Bronsted-Lowry

• Acid donates H+ (hydrogen-ion donor)

• Base accepts H+ (hydrogen-ion donor)

HX + H2O H3O+ + X-

acid base

Conjugate Acids and Bases

Conjugate acids• Produced when a base

accepts a H+ from an acid

Conjugate bases • What results when an acid

donates a H+ to a base

HX + H2O H3O+ + X-

(acid) (base) (conjugate acid) (conjugate base)

NH3 + H2O NH4+ + OH-

(base) (acid) (conjugate acid) (conjugate base)

(H2O and other substances that can act as both acids and bases are said to be amphoteric)

Carbonic acid and carbonates

• CO2, O2, and H2O in air may form carbonic acid H2CO3.

• When this “acid rain” encounters carbonates (limestones, marbles, cement), it may dissolve the substance

• When liquid evaporates, deposits may form

• Stalactites hang tightly• Stalagmites grow up

mightily