Acid – Base Theory

Definitions:

Arrhenius: An acid is a substance that increases the H+ (or H3O+)

concentration in an aqueous solution.

HCl + H 2O H3O+ + Cl-

A base is a substance that increases the OH- concentrationin an aqueous solution.

HCl H+ + Cl-

NaOH(s) Na+ + OH-

Acid/Base reactions:

Produce water and a salt (and sometimes carbon dioxide).

Hint: concentrate on the water first. Remember, water has the formula HOH.

Complete and balance the following:

HCl + KOH

HCl + Ca(OH)2

HOH + KCl

2

Require equal numbers

2HOH + CaCl2

1. Ba(OH)2 + H3PO4

2. HC2H3O2 + NaOH

3. H2SO4 + KOH

4. H2CO3 + NaOH

5. NH4OH + H2SO4 6. NH3 + HCl

Conjugate acids and Conjugate bases

HCl + KOH HOH + KClacid base conj. acid conj. base

Na2CO3 + 2HCl H2CO3 + 2NaCl base acid conj. acid conj. base

Na2CO3 + 2HCl H2O + CO2(g) + 2NaCl conj. baseconj. acidacidbase

NH3 + HCl NH4+ + Cl-

What is a strong Acid?

An Acid that is 100% ionized in water.

Strong Acids:100% ionized (completely dissociated) in water.

HCl + H2O H3O+ + Cl-

often written as:

HCl H+ + Cl-

Strong Acids:Perchloric HClO4

Chloric, HClO3

Hydrobromic, HBrHydrochloric, HClHydroiodic, HINitric, HNO3

Sulfuric, H2SO4

Strong Acids:100% ionized (completely dissociated) in water.

HCl + H2O H3O+ + Cl-

What is a strong Base?

A base that is completely dissociated in water (highly soluble).

NaOH(s) Na+ + OH-

Strong Bases:

Group 1A metal hydroxides(LiOH, NaOH, KOH,RbOH, CsOH)

Heavy Group 2A metal hydroxides[Ca(OH)2, Sr(OH)2, andBa(OH)2]

Strong Acids:100% ionized (completely dissociated) in water.

HCl + H2O H3O+ + Cl-

Note the “one way arrow”.

Weak Acids:Only a small % (dissociated) in water.

HC2H3O2 + H2O H3O+ + C2H3O2

-

Note the “2-way” arrow.

Why are they different?

Strong Acids:

HCl HCl HClHCl HCl

ADD WATER to MOLECULAR ACID

(H2O)

Strong Acids:

(H2O)H3O+

H3O+

H3O+

H3O+

H3O+

Cl-

Cl-

Cl-

Cl-

Cl-

Note: No HCl molecules remain in solution, all have been ionized in water.

HC2H3O2

HC2H3O2

HC2H3O2

HC

2H3O

2

HC2H3O2

(H2O)

Weak Acid Ionization:

Add water to MOLECULES of WEAK Acid

HC2H3O2

HC2H3O2

HC2H3O2

HC

2H3O

2

HC2H3O2

H30

+ C2H3O2-

(H2O)

Weak Acid Ionization:

Note: At any given time only a small portion of the acid molecules are ionized and since reactions are running in BOTH directions the mixture composition stays the same.

H30+ C2H3O2

-HC2H3O2