Acid – Base Theory
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Acid – Base Theory. Definitions:. Arrhenius: An acid is a substance that increases the H + (or H 3 O + ) concentration in an aqueous solution. HCl + H 2 O  H 3 O + + Cl -. HCl  H + + Cl -. A base is a substance that increases the OH - concentration

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Definitions:

Arrhenius:

An acid is a substance that increases the H+ (or H3O+) concentration in an aqueous solution.

HCl + H 2O  H3O+ + Cl-

HCl  H+ + Cl-

A base is a substance that increases the OH- concentration

in an aqueous solution.

NaOH(s)  Na+ + OH-

What about Na2CO3 ????


Bronsted-Lowry:

HCl(aq) + NaOH(aq) → HOH + NaCl

Acid = a proton donor in a RXN

Base = a proton acceptor in a RXN


Lewis:

An acid is an electron pair acceptor

H+

acid

..

H:O:H

..

A base is an electron pair donor

water

..

:O:H-

..


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 

HOH + KCl

HCl + Ca(OH)2

2

2HOH + CaCl2

Require equal numbers


1. Ba(OH)2 + H3PO4

2. HC2H3O2 + NaOH

3. H2SO4 + KOH

4. H2CO3 + NaOH

5. Na2CO3 + HCl 


6. NH4OH + H2SO4

7. NH3 + HCl 

Give a definition of an acid:

An acid is a proton donor (H+)

Give a definition of a base:

A base is a proton acceptor


Conjugate acids and Conjugate bases

HCl + KOH 

HOH + KCl

acid

base

conj. base

conj. acid

Na2CO3 + 2HCl  H2CO3 + 2NaCl

acid

conj. base

base

conj. acid

Na2CO3 + 2HCl  H2O + CO2(g) + 2NaCl

acid

conj. acid

base

conj. base


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:

100% ionized (completely dissociated) in water.

HCl + H2O  H3O+ + Cl-

Strong Acids:

Perchloric HClO4

Chloric, HClO3

Hydrobromic, HBr

Hydrochloric, HCl

Hydroiodic, HI

Nitric, HNO3

Sulfuric, H2SO4


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, and

Ba(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

HCl

HCl

HCl

(H2O)

ADD WATER to MOLECULAR ACID


Strong Acids:

Cl-

H3O+

(H2O)

Cl-

H3O+

H3O+

Cl-

Cl-

H3O+

H3O+

Cl-

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


Weak Acid Ionization:

HC2H3O2

HC2H3O2

(H2O)

HC2H3O2

HC2H3O2

HC2H3O2

Add water to MOLECULES of WEAK Acid


Weak Acid Ionization:

HC2H3O2

HC2H3O2

H30+ C2H3O2-

HC2H3O2

(H2O)

HC2H3O2

H30+ C2H3O2-

HC2H3O2

HC2H3O2

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.

This gives rise to an Equilbrium expression, Ka


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