Acids and Bases

Unit 10

1

Properties of Acids and Bases

2

Acids Bases

•Taste Sour •Taste Bitter

•Turns Litmus Dye Red •Turns Litmus Dye Blue

•Reacts with Metals to give H2 (g) •Do Not React with Metals

•Reacts with CaCO3 to give CO2 (g) •Do Not React with CaCO2

•Electrolyte •Electrolyte

•Neutralized by Bases •Neutralized by Acids

Arrhenius Definition of Acids

and Bases

3

http://en.wikipedia.org/wiki/Svante_Arrhenius

Acids dissolve in water to

produce H+1 ions.

• HCl (aq) → H+(aq) + Cl – (aq)

Bases dissolve in water to

produce OH-1 ions.

•NaOH (aq) → Na+ (aq) + OH – (aq)

Arrhenius Definition of Acids

and Bases

Common Acids

Nitric Acid (HNO3)

• HNO3 (aq)→ H+(aq) + NO3

-(aq)

Sulfuric Acid (H2SO4)

• H2SO4 (aq) → 2H+ (aq)+ SO4

2-(aq)

Acetic Acid (HC2H3O2)

• HC2H3O2 (aq) → H+ (aq)+ C2H3O2

-(aq)

Common Bases

Potassium Hydroxide KOH

• KOH (s) → K + (aq) + OH - (aq)

Magnesium Hydroxide Mg(OH)2

• Mg(OH)2 (s) → Mg 2+ (aq) + 2 OH – (aq)

Calcium Hydroxide Ca(OH)2

• Ca(OH)2 (s) → Ca 2+ (aq) + 2 OH – (aq)

4

Neutralization Reactions(Arrhenius Theory)

Acids and base neutralize one another to form

water and a salt. (Salt = ionic cmpd)

e.g.

HCl (aq) + NaOH (aq) → HOH (l) + NaCl (aq)

H2SO4 (aq) + 2 KOH (aq) → 2 HOH (l) + 2 KCl (aq)

2 HNO3 (aq) + Mg(OH)2 (aq) → 2 HOH (l) + 2 Mg(NO3)2 (aq)

5

Naming Acids

Acids are ionic compounds. To name acids

look up the name of the anion in the acid.

a) Anion ends in ―ide‖

Acid Name = ―Hydro‖ + root of anion + ―ic‖ Acid

b) Anion ends in ―ite‖

Acid Name = Root of anion + ―ous‖ Acid

c) Anion ends in ―ate‖

Acid Name = Root of anion + ―ic‖ Acid

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7

Naming Acids Practice

HF . . . .

HBr . . .

HI . . . . .

H2SO3 . .

H2SO4 . .

HClO3 . .

HClO2 . .

H2CrO4 .

H2C2O4 .

HNO2 .

HNO3 . .

HCl . . .

Anion = Fluoride . . . . . . . . .

Anion = Bromide . . . . . . . . .

Anion = Iodide . . . . . . . . . .

Anion = Sulfite . . . . . . . . . .

Anion = Sulfate . . . . . . . . . .

Anion = Chlorate . . . . . . . .

Anion = Chlorite . . . . . . . . .

Anion = Chromate . . . . . . .

Anion = Oxalate . . . . . . . . .

Anion = Nitrite . . . . . . . . . .

Anion = Nitrate . . . . . . . . . .

Anion = Chloride . . . . . . . .

Hydrofluoric Acid

Hydrobromic Acid

Hydroiodic Acid

Sulfurous Acid

Sulfuric Acid

Chloric Acid

Chlorous Acid

Chromic Acid

Oxalic Acid

Nitrous Acid

Nitric Acid

Hydrochloric Acid

Acid/Base Titrations

An acid/base titration is when acid and base

are reacted with one another until they

reach the end point or equivalence point.

The end (equivalence) point occurs when

the # of moles of acid = the # of moles of

base.

The equivalence point is usually signaled

when a dye, referred to as an indicator,

changes color.

8

Acid/Base Titrations

9

You will titrate HCl with NaOH. You will use

a HCl solution of known concentration to

find the concentration of a the base:

HCl (aq) + NaOH (aq) → H2O (l) + NaCl (aq)

Known Volume

and Known

[HCl]

Known Volume

and Unknown

[NaOH]

Acid/Base Titrations

Use burets to deliver precise

volumes of acid and base.

Burets can measure to the nearest

0.01 mL.

10

http://en.wikipedia.org/

wiki/Image:Burette.svg

Images from :

http://www.csudh.edu/oliver/demos/b

uretuse/buretuse.htm

Acid/Base Titrations

In our lab, the

equivalence

point occurs

when the

phenolphthalei

n turns from

clear to pink.

11

Images from:

http://www.chemistry.w

ustl.edu/~courses/gen

chem/Labs/AcidBase/

phph.htm

Not enough

base added.

Too much

base

added.

Just

right.

Kw- A special Equilibrium Constant

Water molecules ionize to a very small

degree:

H2O (l) ↔ H+(aq) + OH-

(aq)

The equilibrium constant for the reaction is:

Keq = [H+][OH-]

This equilibrium constant is so common that

it is referred to as the dissociation constant

of water and is given the symbol, Kw.

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[H+] and [OH-] in Pure Water

The concentration of H+ and OH- in pure water

are both 1 x 10 -7 M. The Kw in pure water is:

Kw = [H+] x [OH-] = [1 x 10 -7 M] x [1 x 10 -7 M]

= 1 x 10 -14

In all aqueous solutions:

[H+][OH-] = 1 x 10 -14

13

Calculations of H+ and OH- in

Aqueous SolutionsIf you know the concentration of H+ in

solution, you can always find the

concentration of OH-.

e.g. Find the [OH-] in a 0.25 M solution of HCl.

Ans: 1 x10-14 = [0.25 M][OH-] ; [OH-] = 4.0x10 -14 M

In the same way, you can find [H+] from [OH-].14

pH Scale

pH is a convenient way to express the

amount of acid or base in a solution

without having to use exponents.

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pH from [H+] [H+] from pH

pH = - log [H+] [H+] = 10 -pH

Find the pH of a 0.010 M solution

of HCl.

Find the [H+] of a solution with

pH = 3.5.

Ans: pH = -log [0.010M] = 2.00 Ans: 10 -3.5 = 0.0032 M

Examples:

pH Scale

16Image Source is http://www.ltbenvironmentalproject.com/content.aspx?id=20

[H+], [OH-], pH, and pOH

These four relationships will allow you to

solve any problems involving [H+], [OH-],

pH, and pOH:

1. [H+] x [OH-] = 1 x 10-14

2. pH + pOH = 14

3. pH = -log [H+]

4. pOH = -log [OH-]

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Brønsted Lowry Theory

The Brønsted-Lowry Theory of acids and

bases is broader than the Arrhenius

theory. According to the B-L theory:

Acids –- donate H+ ions

Bases—accept H+ ions

This theory broadens the definition of a base

beyond substances that contain the OH –

ion.

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B-L Theory of Acids and Bases

Examples of B-L Acid/Base Reactions:

HCl (aq) + OH- (aq) ↔ Cl – (aq) + HOH (aq)

NH3 (aq) + HNO3 (aq) ↔ NH4+

(aq) + NO3-

(aq)

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Acid (H+ donor)

Acid (H+ donor)

Base (H+ Acceptor)

Base (H+ Acceptor)

Conjugate Acids/Bases

According to B-L Theory, acids become

bases after they have donated an H+.

The difference between an acid and its

conjugate base is simply an H+. . .

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Acid Conjugate Base

HCl Cl -

HSO4- SO4

2-

H2SO4 HSO4-

NH4 + NH3

Strong and Weak Acids

Strong acids ionize 100% while weak acids

ionize less than 10% in water.

Strong Acid: HCl (aq) H + (aq) + Cl – (aq)

Weak Acid: HF (aq) H + (aq) + Cl – (aq)

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100%

2.5%~

Weak Acids: KAs

The strength of a weak acids can be

expressed by its equilibrium constant KA:

HA ↔ H+ + A- KA =

The larger the equilibrium constant, the

stronger the acid.

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[HA]

]][A[H

KAs of AcidsAcid Ionization Reaction KA Expression KA Value

HCl HCl ↔ H+ + Cl- Very Large

HNO3 HNO3 ↔ H+ + NO3- Very Large

H2SO4 H2SO4 ↔ 2 H+ + SO42- Large

HSO4-1 HSO4

-1 ↔ H+ + SO42- 1.3 x 10 -2

HF HF ↔ H+ + F - 6.7 x 10 -4

HC2H3O2 HC2H3O2 ↔ H+ + C2H3O2- 1.8 x 10 -5

H2S H2S ↔ H+ + HS - 1.0 x 10 -7

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[HCl]

]][Cl[H

][HNO

]][NO[H

3

3

]SO[H

]][HSO[H

42

4

][HSO

]][SO[H-

4

4

[HF]

]][F[H

][HS

]][HS[H

2

]OH[HC

]OH][C[H

232

232

Strong Vs. Concentrated

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Str

ong, C

oncentr

ate

dS

trong, D

ilute

Weak, D

ilute

Weak, C

oncentr

ate

d

Predicting Direction of Rxn

To predict the direction of a B-L acid-base

rxn, compare the KAs of the acids.

The reaction will proceed away from the

strongest acid:

HSO4- + HF ↔ H2SO4 + F –

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

6.7 x 10 -4 Large

25

Predicting Rxn Direction

Predict the direction of the following

reactions:

NO2- + H2SO3 ↔ HNO2 + HSO3

-

1.7 x 10 -2 5.1 x 10 -4

HC2H3O2 + Cl- ↔ C2H3O2- + HCl

1.8 x 10 -5 Very Large

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Acids and Bases

The End