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IN THE NAME OF ALLAH THE MOST GRACIOUS, THE MOST MERCIFUL

CHEM 122. LEVEL-2 LECTURE# 2

CHAPTER 9 – ACIDS & BASES

Chemistry by Timberlake p.266

RCDPR

Presented by:Presented by:

Department OfDepartment OfChemistryChemistry

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Modern Concepts of Acids and BasesThree important theories of acids and bases.(1) ARRHENIUS THEORY

An acid: is a substance that contains hydrogen and ionizes in aqueous solution to give hydrogen ion.

A base: is a substance that contains hydroxyl group and gives hydroxyl ions in aqueous solution.

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Arrhenius Acids and Bases P-267

Acids produce H+ in aqueous solutions

waterHCl H+(aq) + Cl- (aq)

Bases produce OH- in aqueous solutions

water NaOH Na+(aq) + OH-

(aq)

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2) BRONSTED – LOWRY THEORY

An acid is a substance that exhibits (shows) a tendency to lose one or more protons.

A base is a substance that exhibits (shows) a tendency to gain protons.

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Bronsted-Lowry Acids P-270

Acids are hydrogen ion (H+) donorsBases are hydrogen ion (H+) acceptors

HCl + H2O H3O+ + Cl-

+ +

donor acceptor + -

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(3) LEWIS ACID – BASE THEORY

-An acid is any molecule or ion that can accept a pair of electrons and form a coordinate covalent bond.-A base is any molecule or ion that can donate a pair of electrons and form a coordinate covalent bond

- Electron pair acceptor is an acid and

electron pair donor is a base.

BF3 + :NH3 → BF3 : NH3

Acid Base

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Some Common Acids P-268

I-The name of a non-oxy acid begins with the prefix hydro- and ends

with -ic acid. In a non-oxy acid, the negative anion end in -ide.

HCl hydrochloric acid (Cl- is choride)

HBr hydrobromic acid (Br- is bromide)

II-The name of an oxy acid is named with the stem of the anion (carbonate) changed to -ic acid

HNO3 nitric acid (NO3- is nitrate)

H3PO4 phosphoric acid ( PO4- is phosphate)

H2SO4 sulfuric acid ( SO4- is sulfate)

CH3COOH acetic acid (CH3COO- is acetate)

H2CO3 carbonic acid (CO3-2 is carbonate).

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Some Common Bases P-269

NaOH sodium hydroxide

KOH potassium hydroxide

Ba(OH)2 barium hydroxide

Mg(OH)2 magnesium hydroxide

Al(OH)3 aluminum hydroxide

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Acids-Properties P-267

Produce H+ (as H3O+) ions in water

Produce a negative ion (-) too

Taste sour

Corrode metals

Are electrolytes

React with bases to form salts and

water

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Bases-Properties P-269

Produce OH- ions in water

Taste bitter, chalky

Are electrolytes

Feel soapy, slippery

React with acids to form salts and

water

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Conjugate Acids and Bases P-271

When an acid loses a proton, the residue will have the tendency to accept it back. The residue is therefore behaves as a base.

AH ⇌ H+ + B-

Acid conjugate base

An acid and base, which differ by a proton, this relationship are said to form a conjugate pair.

Thus every acid has its conjugate base and every base has its conjugate acid.

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Acid Conjugate base

NH+4 ⇌ H+ + NH3

HCO-3 ⇌ H+ + CO3

2-

CH3COOH ⇌ H+ + CH3COO-

HCl ⇌ H+ + Cl-

-Acids and bases may be ions or molecules but one of the member of conjugate pair is always an ion.

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Conjugate Acids and Bases P-271

Role of solvents in Acids and Bases : -HCl behaves as an acid in its aqueous

solution. -HCl does not behave as an acid in benzene

(it does not show its acidic properties). -This is because

“ A substance will behave as an acid only when another substance capable of accepting a proton, i.e. a base of some kind, is present.”

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-In aqueous solution of HCl, molecules of water are able to take up protons and water acts as a base.

HCl + H2O ⇌ H3O+ + Cl-

Acid I Base II Acid II Base I |

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Base I is a conjugate base of Acid I and Acid II is a conjugate acid of a Base II

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Conjugate Acids and BasesAcid I Base II Acid II Base IH2O + NH3 ⇌ NH+

4 + OH-

H2O + CH3COO- ⇌ CH3COOH + OH-

CH3COOH + NH3 ⇌ NH+4 + CH3COO-

NH3 + NH3 ⇌ NH+4 + NH-

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HF + HF ⇌ H2F+ + F-

H2O + H2O ⇌ H3O+ + OH-

-It is seen from the above example that, the strong acids have weak conjugate bases, while weak acids have strong conjugate bases.

-NH3, H2O, HF have dual character of acids & bases are called amphiprotic.

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Describe the type of solution in each of the following as:

1) acid 2) base or 3)neutral.

A. ___soda B. ___soap

C. ___coffeeD. ___ wineE. ___ water

F. ___ grapefruit

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Answer: Describe each solution as: 1) acid 2) base or 3) neutral.A. _1 _ soda

B. _2_ soapC. _1_ coffeeD. _1_ wineE. _3_ water

F. _1_ grapefruit

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Identify each as characteristic of an

A) acid or B) base

____ 1. Sour taste

____ 2. Produces OH- in aqueous solutions

____ 3. Chalky taste

____ 4. Is an electrolyte

____ 5. Produces H+ in aqueous solutions

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Answer: Identify each as a characteristic of an A) acid or B) base

_A_ 1. Sour taste

_B_ 2. Produces OH- in aqueous

solutions

_B_ 3. Chalky taste

A, B 4. Is an electrolyte

_A_ 5. Produces H+ in aqueous solutions

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Q: Give the names of the following

A. HBr (aq) 1. bromic acid

2. bromous acid

3. hydrobromic acid

B. H2CO3 1. carbonic acid

2. hydrocarbonic acid

3. carbonous acid

P-268

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Answer: A. HBr 3. hydrobromic acid

B. H2CO31. carbonic acid