Ainun dan winda

By : Ainun Jariah
Winda Hayati

*
For centuries people had known that vinegar, lemon
juice,apple and many other food items taste sour. But they didn’t
know that their sourness comes from their specific acids. The term
acid comes from the Latin word “acere” ,which means sour. In the
17thcentury,the English Chemist Robert Boyle grouped substances as
either acids or bases, but he couldn’t explain their behavior. The
first logical definition wouldn’t be coined until 200 years later.

In this presentation ,we will focus on acid-base reactions in
aqueous solutions. such solutions play important roles in our daily
lives.

The Authors

Supplementary
Introduction Contents Material Questions

Glossary References

Content
1. Acid-Base Theories
1.a. The Arrhenius Acid-Base Theory
1.b. The BrФnsted-Lowry Acid-Base Theory
1.c. The Lewis Theory
1.d. General Properties of Acids
1.e. General Properties of Bases
2. Ionization of Water
3. The pH Scale
4. Strength of Acids and Bases
4.a. Acid Strength
4.b. Base Strength
5. Neutralization
Supplementary

Glossary References


1.a. The Arrhenius Acid-Base Theory
In 1884, Swedish chemist Svante
Arrhenius defined acids as compounds
that produce H+ ions in aqueous
solutions,and base as compounds that
produce OH-- ions in aqueous solutions.
For example,HCL and are HNO3 Arrhenius
acids.
HCL(aq) ------------→ Cl - (aq) + H+ (aq)
HNO3 (aq) ---------- → NO 3- (aq) + H+ (aq)
Supplementary

Glossary References


NaOH and Ba(OH)2 are example of
Arrhenius bases. These bases
release OH-- ions in aqueous media.
NaOH(aq) ------------→ Na
+(aq) + OH - (aq)

Ba(OH)2 (aq) ----------→ Ba
2+(aq) + 2OH - (aq)

In water, the H+ ion of acid is
attracted to a water(H2O) molecule
to produce hydronium ion (H3O+ )
Supplementary

Glossary References


• The Arrhenius acid-base theory is
insufficient to explain the acidic
or basic properties of some
substances,such as SO2 and NH3
since these don’t have H + and
OH- ions in their structures. For
these molecules,another theory
must be applied,since the
Arrhenius acid-base theory can
only be applied to aqueous
solutions.
Supplementary

Glossary References

1.Acid-Base Theories
1.b. The The BrФnsted-Lowry Acid-Base Theory
In 1923,Johannes BrФnsted and his English counterpart Thomas Lowry
independently developed a more general acid-base theory. According to the
BrФnsted-Lowry model,an acid is a proton donor and a base is a proton acceptor.
Each proton donor(acid) has its pair(conjugate) proton acceptor base.
For example: Conjugate acid-
base pair

NH3 H2O NH4+ OH-
(Base 1) (Acid 2) (Acid 1) (Base 2)

Conjugate acid-
base pair

Supplementary

Glossary References

Example
H2S (g) + H2O (l) ↔ H3O+ (aq) + HS- (aq)
find the conjugate acid-base pairs for the above
reaction.
Solution:
H2S give H+ (proton) to H2O (proton accceptor), so it
is an acid. In the same way, H2O accepts one H+
(proton) from H2S (proton donor). Thus it is a
base.
Supplementary

Glossary References

Example
conjugate acid-base pair

H2S (g) + H2O (l) ↔ H3O+ (aq) + HS- (aq)
acid 1 base 2 acid 2 base 1

conjugate acid-base pair

Supplementary

Glossary References

NH3 and NH4+ form a conjugate acid-base pair,where NH3 is the conjugate base of
NH4 (NH4+ is the conjugate acid of NH3). Similarly, H2O and OH- are conjugates of
each other.

A model of Acid-Base reaction between NH3 and H2O

H
N O N O
H H H H H H H
H H

Supplementary

Glossary References

1.c. The Lewis Acid-Base Theory
in 1923, American chemist,Gilbert N.Lewis definited acid and base considered to
chemical bond theory. According to Lewis opinion that acid is compound that
accept the pair of free electron. And base is compound that donor the pair of free
electron.
the example of The Lewis Acid-Base theory:

F F

B F F B F
F
F F

Supplementary

Glossary References

1.d. General Properties of Acids
The General properties of Acids can be summarized as:
1.The aqueous solutions of acids conduct electricity
2. Acids change the color of litmus paper to red
3. Acids have a sour taste (such as vinegar and lemon)
4. Acids are corrosive substances.
5. Acids react with active metals and produce hydrogen gas.
For example:
2Al(s) + 3H2SO4(aq) → Al2(SO4)3 (aq) + 3H2(g)
Zn(s) + 2HCl(aq) → ZnCl2(aq) + H2 (g)

Supplementary

Glossary References

6. Acids react with bases to produce salt and water,this reaction is called a
neutralization reaction.
For example:
NaOH(aq) + HCl(aq) → NaCl(aq) + H2O(l)
7.Inert metals (Cu,Hg,Ag,Pt,Au) do not react with binary acids(HCl,HBr,…).
Cu,Hg,and Ag can react with strong
oxyacid such as HNO3 and H2SO4.
For example:
3Cu(s) + 8HNO3(aq) →(dilute) → 3Cu(NO3)2 (aq) + 2NO (g) + 4H2O(l)
8. Acids react with carbonate salts of metal.
For example:
MgCO3(s) + 2HCl(aq) → MgCl2(aq) + CO2(g) + H2O(l)

Supplementary

Glossary References

1.e. General Properties of Bases
The General properties of Bases can be summarized as:
1.The aqueous solutions of Bases conduct electricity
2. Bases change the color of litmus paper to blue
3. Bases have a bitter taste
4. Strong bases are corrosive
5. Basic solutions cause slippery skin
6. Bases do not react with most metals. However, strong bases(KOH,NaOH)
react with amphoteric metals such as aluminium(Al), zink(Zn),and produce
hydrogen gas.
For example:
2Al(s) + 6NaOH(aq) → 2Na3AlO3(aq) + H2(g)
Zn(s) + 2NaOH(aq) → Na2ZnO2(aq) + H2 (g)

Supplementary

Glossary References

Some molecules and ions act as acids or bases depending on the conditions
of the reaction are called amphoteric.
A water molecule acts as an acid when it donates a proton, and acts as a
base when it accepts a proton, as given below:
H2O(l) +H2O(l) ↔ H3O+(aq) + OH-(aq)

H
O O O O
H H H H H H H

Supplementary

Glossary References

The equilibrium sconstan expression for the reaction is:

Kw = [H3O+ ] [OH-]

Kw is the equilibrium constant used in equations to refer to ionization of water.
Kw= 1,0 . 10-14 at 250C
[H3O+ ] = [OH-] for the neutral medium. Then,
1 . 10-14 = [H3O+ ] 2
1. 10-7 = [H3O+ ]
[H3O+ ] = [OH-] = 1. 10-7 M

Supplementary

Glossary References

3. The pH Scale
The acidity or basicity of a solution can be described in terms of its H3O+ or OH- ion
concentrations.
These concentrations are usually small. For example,H3O+ ion concentration is 1.10-7 M
in the neutral solution. Thus,the concentration of H3O+ is generally expressed as
the negative logarithm. This is known as pH. From now on, for simplicity H+ will be
used instead of H3O+

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

In a similar,the way negative logarithm of [OH-] is pOH

pOH= -log[OH-] and [OH-] = 10-pOH

Supplementary

Glossary References

For pure water at 250C,
[H+] = 1. 10-7 [OH-] = 1. 10-7
pH = - log (1. 10-7) pOH = - log (1. 10-7)
pH = 7 pOH = 7
Since [H+] [OH-] = 1. 10-14 a

pH + pOH = 14

The pH value of a solution gives an idea about the condition of a solution as follows:
If pH < 7,0 Solution is acidic
If pH = 7,0 solution is neutral
If pH > 7,0 Solution is basic

Supplementary

Glossary References

pH is measured by using a pH meter. A pH meter translates H+ion
concentrations in solutioninto an electrical signal that is converted into a digital
display

H+ CONCENTRATION, [H+] in mol/L
100 10-1 10-2 10-3 10-4 10-5 10-6 10-7 10-8 10-9 10-10 10-11 10-12 10-13 10-14

0 1 2 3 4 5 6 7 8 9 10 11 12 13 14

pH scale
pure water baking powder
Acid in stomach vinegar coffe rain water blood soap household
lemon juice tomato bread milk sea water amonnia
juice

Supplementary

Glossary References

A less accurate way to mesure pH is to use indicators. An indicator is a
compound such as phenolphthalein or methyl orange, that is changes color
reversibility at different pH values. For exampe, phenolphthalein is a colourless
substance in any solution with a pH value smaller than 8,3 it turns red-violet in
solution with a pH value greater than 8,3.

Indicator Acidic Basic
Phenolphthalein Colorless Red-violet
Methyl orange Red Orange-yellow
Litmus Red Blue

Supplementary

Glossary References

Example

Supplementary

Glossary References

4.a. Acid Strength
Acids are classified as strong and weak, depending upon theirdegree of ionization in
water. A weak acidionizes in water reversibly to form H3O+ions. A weak acid is a weak
electrolyte and its aqueous solution does not conduct electricity well. The dissociation
reaction occurs to very small extent; usually,fewer than 1 percent of the HA molecules are
ionized. The ionized of a weak acid is shown as follows:
HA(aq) + H2O(l) ↔H3O+(aq) + A-(aq)
weak acid conjugate base
The dissociation constant Ka,of a given acid iswritten as ;

Ka=[H3O+] [A-] / [HA]
Ka refers to the acid dissociation constant which is measure of an acid’s strength. Some
references call Ka the acid ionization constant
If Ka < 10-3, acid is generally said to be weak
If Ka = 1 to 10-3, acid is accepted as moderate
If Ka > 1 acid is strong.

Supplementary

Glossary References

Some Ka values of acids are given in Table below.

Name of acid Formula Ka
Hydrochloric acid HCL 1.107
Nitric acid HNO3 1.103
Sulfuric acid H2SO4 22
Oxalic acid (COOH)2 6,5 .10-2
Phosphoric acid H3PO4 7,5 . 10-3
Lictic acid C2H5OCOOH 1,38 .10-4
Formic acid HCOOH 1,8.10-4
Nitrous acid HNO2 4. 10-4
Hydroflouric acid HF 7,2 .10-4
Acetic acid CH3COOH 1,8 . 10-5
Supplementary

Glossary References

4.2 Base Strength

The dissociation of a weak base in water is illustrated as follows ;
B(aq) + H2O(l)↔ BH+(aq) + OH-(aq)
The equilibrium expression for the above weak base is

Kb= [BH+] [OH-] / [B]

Kb is the base dissociation constant or base
ionization constant, that measure a base’s strength.

Supplementary

Glossary References

Some Kb values of bases are given in Table
below.
Name of base Formula Kb
Potassium hydroxide KOH 158,5
Sodium hydroxide NaOH 10
Methylamine CH3NH2 4,38 . 10-4
Ethylamine C2H5NH2 5,6 . 10-4
Ammonia NH3 1,8 . 10-5
Pyridine C5H5N 1,7 . 10-9
Aniline C6H5NH2 3,8 . 10-10

Supplementary

Glossary References

4.c. Relationship between Ka and Kb

Dissociation constants of weak acids and bases
can be determined in the laboratory. However, it
is easy to find the Ka or Kb values of acids or
bases by using a simple mathematical
expression between Ka and Kb of conjugate acid-
base. The multiplication of Ka and Kb of
conjugate acid-base is Kw.
Supplementary

Glossary References

Kw = Ka . Kb = Kb . Ka = 1 . 10-14

For example NH4+ - NH3 is a conjugate acid base.
I. NH3 + H2O ↔ NH4+ + OH- K1 = Kb of NH3
II. NH4+ + H2O ↔ NH3 + H3O+ K2 = Ka of NH4+
2H2O ↔ H3O+ + OH- Kw = K1 . K2

Supplementary

Glossary References

Example
What is the Ka value of NH4+ if the Kb of NH3 is
1.8 x 10-5 ?

Solution:
NH3 + H2O ↔ NH4+ + OH-
NH4+ is the conjugate acid of NH3
Kb for NH3 is 1,8 x 10-5

Supplementary

Glossary References

5. Neutralization
The reaction of an acid and a base solution to form salt
and water is called a neutralization reaction. Indeed,a
neutralization reaction is a reaction hydrogen(H+) ions and
hydroxide(OH-) ions to form water. In neutralization,all H+ and
OH- ions coming from acid and bases turn into H2O. The
reaction between HCl(aq) and NaOH(aq) is an example of a
neutralization reaction.
HCl(aq) + NaOH(aq) → NaCl(aq) + H2O(l)
The net ionic equation for this reaction is
H+(aq) + OH- (aq)→ H2O (l)

Supplementary

Glossary References

The nature of the particular acid and base involved in a reaction determines the
acidity or basicity of the resulting solution.
1 .Neutralization of a strong acid and strong base gives a neutral solution.
HCl(aq) + NaOH(aq) → NaCl(aq) + H2O(l)
The resulting NaCl salt is neutral
2. Neutralization of a strong acid and a weak base gives a acidic solution.
HCl(aq) + NH3(aq) → NH4Cl(aq) + H2O(l)
NH4Cl is called acidic salt
3. Neutralization of a weak acid and a strong base gives a basic solution.
CH3COOH(aq) + NaOH(aq) → CH3COONa(aq) + H2O(l)
CH3COONa is called basic salt
4. Neutralization of a weak acid and a weak base gives a complex type of acid-base
solution. If weak acid and weak base have the same strength,the solution is
neutral. If the strength of an acid and base are not equal,the solution will be either
acidic or basic,depending on the strength of either.

Supplementary

Glossary References

Supplementary Questions
1. Find the conjugate acid-base pairs for the
following reaction.
a. CO32- + H2O ↔ HCO3- + OH-
b. HF + H2O ↔ H3O+ + F-
c. NH3 + H2O ↔ NH4+ + OH-
d. HSO4- + HCl ↔ H2SO4 + Cl-

Supplementary

Glossary References

2. What is the pH of a solution prepared by
dissolving 0.8 g NaOH in water to make 200
mL solution ?
3. How many moles of HCl are found in 500 mL
of HCl solution, whit a pH of 3 ?
4. How many millilitres of 0.01 M NaOH are
required to neutralize 50 mL of 0.02 M HCl ?

Supplementary

Glossary References

5.

I II
after mixing the solutions, what would be
the pH of the final solution ?

Supplementary

Glossary References

Glossary
Acid : A substance that produces hydrogen ions
in solution. A proton donor substance.
Acid dissociation constans (Ka) : The equilibrium
constant for weak acids.
Aqueous solutions : solutions in which water is
the solvent.
Arrhenius concept : A concept stating that acids
produce hydrogen ions and bases produc
hydroxide ions in aqueous solution.
Supplementary

Glossary References

Glossary
Base : A substance that produces hydroxide ions
in aqueous solution. A proton acceptor substance
Base dissociation constans (Kb) : the equilibrium
constans for the reaction of a base with water to
produce the conjugate acid and hydroxide ion.
Chemical bond : The force, or energy, that holds
atoms together in a compound.
Supplementary

Glossary References

Glossary
Conjugate acid : The specie formed when a
proton is added to a base.
Conjugat acid-base pair : two species related to
each other by donating and accepting of a single
proton.
Conjugat base : What remains of an acid
molecule after a proton is lost.
Supplementary

Glossary References

Glossary
Equilibrium : The position where the rate of
forwad and reverse reaction becomes equal.
Indicator : A chemical that changes color and is
used to mark the end-point of a titration.
Ion-product constant (Kw) : the equilibrium
constant for water.
Lewis acid : An electron-pair acceptor
Supplementary

Glossary References

Glossary

Supplementary

Glossary References

Glossary
Polyprotic acid : an acid with more than one
acidic proton. It dissociates in a stepwise
manner, one proton at a time.
Salt brige : A U-shaped tube containing an
electrolyte that connects the two compartments
of a galvanic cell without extensive mixing of the
different solutions.

Supplementary

Glossary References

Glossary
Solution : A homogeneous mixture.
Strong base : A metal hydroxide salt that
completely dissociates into its ions in water.
Weak acid : An acid that dissociates only slightly
in aqueous solution.
Weak base : A base that reacts with water to
produce hydroxide ions to only a slight extent
ain aqueous solution.
Supplementary

Glossary References

References
• Nazli, Ayhan., Lise 2 kimya Ders Kitab.
Textbook of Chemistry for Lycee 2. Zambak
Publishing, Istanbul : 2006
• McDuell B., A Level Chemistry. Letts
Education, UK : 2000
• Earl B., Wilford L.D.R., IGCSE Chemistry.
Hodder Murray, Dubai : 2005

Supplementary

Glossary References

References
• Ratcliff B., Eccles H., and others, AS Level and
A level Chemistry. Cambridge University
Press, UK : 2005
• Oxtoby, D.W., Nachtrieb, N.H., Principals of
Modern Chemistry. 3rd Ed., Saunders Collage
Publising, USA : 1996

Supplementary

Glossary References

References
• Sevenair, J.P., Burkett, A.R., Introductory
Chemistry. Investigating the Molecular
Nature of Matter. WBC Publishers, USA :1997
• Prescott, C.N., Chemistry A Course for “0”
Level. Times Media Privat Limited, Singapore :
2000

Supplementary

Glossary References

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