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Acid-base theory

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Acid-Base

Buffer solution

Buffer solution is a solution of weak acid versus weak acid salt.or base pairs of weak
acids or means a solution of a weak base with a salt of a weak base or the acid pair of that
weak base The properties of the buffer solution are to maintain the pH of the solution with
very little change. When adding strong acids or bases a small amount goes down the
preparation. Achieved by adding a weakened acid in a weak acid salt solution or adding a
weak base to the salt solution of a weak base.

Examples of buffers are:

1.Buffer of a weak acid with a base pair of a weak acid (salt).
For example, CH3COOH / CH3COONa has a pH <7
2.Buffers of weak bases with their acidic pairs of weak bases (salts).
For example, NH3OH / NH4Cl has a pH> 7

Determination of pH of a buffer solution.

1.Acid buffer solution find the pH from the equation.

2.Base buffers can find pH as follows.

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Question

1. What is correct about buffers?
A. Solution of weak acid vs weak acid salts or weak acid base pairs.
B. A solution of a weak base to a weak base salt or an acid pair of a weak base.
C. Maintains the pH of the solution with very little change when adding a small amount
of strong acid or base to it.
D. All of the above.

Answer
D. All of the above.

2. Which of the following pairs of mixing solutions? as a buffer solution?
A. HCl with NaCl
B. HCN with KCN
c. CH3COOH with CH3COONa
D. NaOH with NaCl

Answer
c. CH3COOH with CH3COONa

3. Buffer solution contains Acetic acid solution with sodium acetate solution, which is the
same 0.1 mol / l concentration and has the same volume of 100 cm3. If Ka of acetic acid is
equal to 1.8 x 10-5 Find the pH of this buffer solution.

A. 4.77
B. 4.24
C. 4.74
D. 4.25
Answer
B. 4.24

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Because
= -log 1.8 x 10-5 + log (0.1 / 0.1 )
= 5 – log 1.8 + log 1
= 5 – 0.26
= 4.24

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ACID BASE REACTION

The acidity of a solution is the concentration of H+ (protons) [or H3O+] in
water. An acid is a substance that loses H+. A base is a substance that gains an
extra H+.

AH + B → A– + BH+

When an acid (AH) reacts with a base (B), the H+ is transferred. Water is an
amphoteric molecule that can act as an acid or a base.

HA + H2O → A– + H3O+

B + H2O → BH+ + OH–

Water can also self-ionize:

2H2O → HO– + H3O+

Because most acid/base reactions occur in water, generally water is not included
in the equations:

HA → A– + H+

B + H+ → BH+

Acid-Base Definitions

The 3 operational definitions of acids and bases include the Arrhenius, Bronsted-
Lowry, and Lewis definitions.

Arrhenius definition

According to the Arrhenius definition, acids are compounds that dissociate in
water to produce H+ ions, while bases are compounds that dissociate in water to
generate OH– ions. Examples of compounds that satisfy the Arrhenius definition
include hydrohalic acids and metal hydroxides. When these 2 groups of compounds
dissociate in water, hydrohalic acids and metal hydroxides produce H+ or OH–
ions, depending on whether the compound is a base or an acid.

Bronsted-Lowry definition

Bronsted-Lowry defines an acid as a proton donor and a base as a proton
acceptor. Water molecules donate and accept a proton, and not only participate
as a solvent, but also as a reactant.

Lewis definition

The Bronsted-Lowry definition does not explain the acidity of metal cations.
Therefore, the Lewis definition

According to the Lewis definition, an acid is an electron pair acceptor, while a
base is an electron-pair donor. The Lewis definition correctly includes the acidity
of cations. Because cations are positively charged, cations exhibit a higher
tendency to accept an electron pair. The Lewis definition is considered the most
generalized approach because the Lewis definition is more inclusive.

Acid-Base Calculation

Important quantitative concepts in acid-base calculations are pH, pOH, Kw, Ka,
and Kb:

pH: a logorithmic scale that determines how acidic or basic a solution is. A low pH
means there are more free protons and is acidic, while a higher pH means there
are more free hydroxide ions and more basic.

pOH: is related to the pH scale, but is calculated based on the hydroxide ion
concentration instead of the proton concentration. It is the opposite of the pH
scale such that a low pOH is basic and a high pOH is acidic.

Kw: this is called the water ionization constant and is known by the equation: Kw
= [H3O+][OH-]=10-14

Ka/Kb: The Ka is known as the acid dissociation constant and can be calculated
several different ways. The Kb is the base correlate of the Ka known as the base
dissociation constant.

Buffer Solutions

Buffers are solutions that resist pH changes because the buffer solution is
saturated with acidic and basic ions that can readily react with an added base or
acid, respectively. A primary requirement to produce a buffer solution is that
the acidic and basic components of the buffer system must not neutralize each
other, which can only be achieved using a weak acid or base with the conjugate.
For example, if an acetic acid-acetate buffer is considered, the two components
do not neutralize each other.

During the above ‘neutralization’ reaction, the products are still the conjugate
acid-base pair. The addition of small amounts of acid to the acetic acid-acetate
buffer system triggers a reaction with the acetate component, which contains
basic properties, producing the conjugate acid. However, if small amounts of a
base are added to the system, the acetic acid component reacts to produce the
conjugate base.

Exercise

1. Of a 0.50 M HNO3 solution and a 0.50 M HC2H3O2 solution, which
should have the higher boiling point? Explain why.
Answer HNO3 is a strong acid while HC2H3O2 is a weak acid.
HNO3 dissociates 100% and its solution contains more ions. The
more ions the solution contains the lower is its vapor pressure; the
higher temperature is required for it to boil.

2. The reaction of sulfuric acid [H2SO4(aq)] with sodium hydroxide
[NaOH(aq)] can be represented by two separate steps, with only
one hydrogen ion reacting in each step. Write the chemical equation
for each step.
Answer H2SO4 + NaOH → NaHSO4 + H2O; NaHSO4 + NaOH →
Na2SO4 + H2O

3. The reaction of aluminum hydroxide [Al(OH)3(aq)] with hydrochloric
acid [HCl(aq)] can be represented by three separate steps, with only
one hydroxide ion reacting in each step. Write the chemical equation
for each step.
Answer Al(OH)3 + HCl → Al(OH)2Cl + H2O; Al(OH)2Cl + HCl →

Al(OH)Cl2 + H2O; Al(OH)Cl2 + HCl → AlCl3 + H2O

BRØNSTED–LOWRY
ACID–BASE THEORY

DEFINITIONS OF ACIDS AND BASES introduced independently
in 1923 by the Danish
In the Bronsted–Lowry theory acids and bases are chemist Johannes
defined by the way they react with each other, which Nicolaus Bronsted and
allows for greater generality. The definition is expressed the English chemist
in terms of an equilibrium expression Thomas Martin Lowry

⇌acid + base conjugate base + conjugate acid.

With an acid, HA, the
equation can be written

symbolically as:

AQUEOUS SOLUTIONS AMPHOTERIC SUBSTANCES

Acetic acid, CH3COOH, is an The essence of Brønsted–Lowry theory is that an
acid because it donates a acid only exists as such in relation to a base, and vice
proton to water (H2O) versa.

becomes its conjugate base, Water is amphoteric as it can act as an acid or as
the acetate ion (CH3COO−). a base.
H2O is a base
In the image shown at the right one molecule of
because it accepts a proton H2O acts as a base and gains H+ to become H3O+
from CH3COOH and becomes while the other acts as an acid and loses H+ to
its conjugate acid, the become OH−.
hydronium ion, (H3O+).
the Bronsted–Lowry theory acids
The power of the Brønsted– and bases says that
Lowry theory is that, in
contrast to Arrhenius theory, An acid is a substance that can give a proton (H +) to
it does not require an acid to another substance.
dissociate. Bases are substances that can get protons (H +) from
other substances.

Miss Nutjira Phanli No.5 Class 5/5

Exercise

Bases are substances that give protons to other
substances.The explanation of this statement is

1. Boyle
2. Lewis
3. Arrhenius
4. Bronsted-Laowry
Answer 4. Bronsted-Laowry

Based on the Berinstead Lavre's theory of acid-base,
what group of substances are classified as all bases?

1. 2.

3. 4.
Answer 2.

Which of the following solutions is a mature basal
electrolyte solution?

1.Solution A changes the color of litmus paper
from red to blue. The lamp is slightly bright

2.Solution B changes the color of litmus paper
from red to blue. The lamp does not light

3.Solution C changes the color of litmus paper
from red to blue. The lamp is very bright.

4.Solution D changes the color of litmus paper
from blue to red. The lamp is very bright.

Answer 3.Solution C changes the color of litmus paper
from red to blue. The lamp is very bright.

Miss Nutjira Phanli No.5 Class 5/5

Acid-base theory

Acid-base theory; acid-base theory; Is the theory that Definition or
definition Of chemicals with acidic and base properties Generally
Important acid-base theory However, there are definitions that
relate to the determination of the polarizing properties of
molecules: acid-base. Hard-soft And the law of Fajan The
calculations involving acid-base reactions often involve the
principles of chemical equilibrium.

Acid-base test

1.The following test Which of these do you think would support the
dissolved HCl ionization theory?

A. Symptoms in which HCl is corrosive to metals
B. The reaction of HCl with AgNO3 produces a white precipitate.
C. Electrolysis is HCl (aq) and H2 is formed at the electrode.
D. The solution of HCl can change the color of litmus paper from blue to
red.

Answer

D. The solution of HCl can change the color of litmus paper from blue to
red.

2.From which molecules and ions are acid-base pairs?

A.H2SO4 and H2S2O7
B.H2SO4 and H3SO4 +
C.H2S2O7 and HS2O7-
D.H2S2O7 and H3SO4 +

Aswer

C.H2S2O7 and HS2O7
3.Bases are substances that give protons to other substances. The
explanation of this statement is
A.Boys
B.Lewis
C.Arrhenius
D.Brinstead-Laotie

Answer

D.Brinstead-Laotie

MS.PORNCHANOK RATPRAKHON NO.6 M.5/5

Acid-Base

What is an acid-base?
Acid Base in Everyday Life

Acid-base compounds are very important and involved in human daily life. First of all, it's
easy to understand what an acid-base is.
Acid solution is a solution that has a sour taste. Change litmus paper color from blue to red. Or
reacts with metals H 2 gas and salt
Base solution is a bitter solution. Change litmus paper color from red to blue. Or have a slippery
AppearanceArrhenius Concept
An acid is a compound with H and dissolves in water to H + or H3O +
Bases are OH-containing compounds and, when dissolved in water, breaks down to OH-

The limitation of this theory is The compound must be soluble in water. And cannot
explain that Why are some compounds such as NH3 bases
Bronsted-Lowry Concept
An acid is a substance that can give a proton (proton donor) to another substance.
A base is a substance that can accept a proton (proton acceptor) from another substance.

The reaction between acids and bases is the transfer of protons from the acid to the
base, such as ammonia, dissolved in water.

NH3(aq) + H2O(1) = NH4+ (aq) + OH- (aq)
base 2 ........acid 1 ........acid 2 ........base 1

In the forward reaction, NH3 receives a proton from H2O, so NH3 is a base and H2O is
an acid, but in the reverse reaction, NH4 + gives a proton to OH-, so NH4 + is an acid and OH-
is a base. The direction of the reaction depends on the strength of the base.
Lewis Concept
An acid is a substance that can receive an electron pair acceptor from another substance.
Bases are substances that can give electron pair donor to another substance.

The theory is used to describe the acid-base concept of Arrhenius and the Bronsted-
Lowry, and has the advantage that it can explain acid-bases in the event of interactions. And a
compound with a covalent bond like

OH - (aq) + CO2 (aq) HCO3- (aq)
BF3 + NH3 BF3-NH3

The acid-base question
1. What is correct about electrolyte solutions?
a. Change litmus paper color.
b. Does not change litmus paper color.
c. Can be ionized.
d. Cannot be ionized.
Answers c. Can be ionized.
2. Based on the Arrhenius theory of acid-base, what group of substances are classified as
all acids?
a. CO32- , HPO32- , Cl- , NH4+
b. KOH , H2PO4- , H3O+ , SO32-
c. NaCl , Ca(OH)2 , NO3- , NH3
d. H2O , H2CO3 , HS- , NH4+
Answers d. H2O , H2CO3 , HS- , NH4+
3. From which molecules and ions are acid-base pairs?
a. H2SO4 And H2S2O7
b. H2SO4 And H3SO4+
c. H2S2O7 And HS2O7-
d. H2S2O7 And H3SO4+
Answers c. H2S2O7 And HS2O7-

Ms.Pimnara Karuna No.7 M.5/5







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Acid-base theory

Acid-Base Theory is the theory of Definition of chemicals having acidic and base
properties. Generally Important acid-base theory Was based on the definition of the
important chemist, Arrhenius , Berinstead-Lavri and Lewis. However, there are definitions
involved in determining the molecular polarization properties of Hard-Soft Acids-Bases
(HSAB). And Fahjan's Rules. Calculations involving acid-base reactions often involve the
principles of chemical equilibrium.

Arrhenius definition

Svente Arrenius, a Swedish chemist, established the 1884 definition of an acid and base
with regard to the concentration of hydrogen ions (H +) or hydronium ions (H3O +) and hydroxides.
Oxide ions (OH−) when a substance dissolves water, stating that "acid refers to a substance that
dissolves water and then breaks up, increasing the concentration of hydrogen ions or hydronium
ions" and "bases referring to dissolved substances. The water then decomposes, increasing the
concentration of hydroxide ions. "

 Acid dissolution in water
HCl (aq) → H + (aq) + Cl− (aq)
*Disintegration in the water of the bass
NaOH (aq) → Na + (aq) + OH− (aq)

Pure water has a neutral property. Due to the disintegration on their own The auto-
dissociation of water is in the equilibrium between the concentrations of (H3O +) and (OH−), which
are the same. Therefore, the water solubility of the acidic substance as defined by Arrhenius
makes the The concentration of hydrogen ions is increased. Additionally, since hydrogen ions (H +)
are ions with only one elementary proton, Chemists call it protons. If a proton dissolves in water, it
may be denoted as (H3O +) resulting from the fusion of protons with water molecules.

 Water self-dissociation equation: H2O (l) + H2O (l) ⇌ H3O + (aq) + OH− (aq)
A major problem with Arrhenius' acid-base theory is that the acid-base pH of insoluble

substances cannot be determined. And it was not possible to determine the non-hydrogen acidity
such as AlCl3 or a base without hydroxide ions such as NH3 or N (CH3) 3, so it was redefined by a
later generation of chemists.
Arrhenius acid-base neutralization reaction

Neutral reaction (Neutralization) Arrhenius acid-base is a reaction between hydrogen ion (H
+) and hydroxide ion (OH−) to form water, as equation : H + (aq) + OH− (aq) → H2O (l)

Brinstead-Laowry definition

Johannes Nicolaus Brønsted and Thomas Martin Lowry, two chemists, defined a new
acid-base in 2009. It is a theory that covers and explains the properties of acid-base better
than Arrhenius' theory, saying that "acid (AH) means a substance that gives Proton Donor to
base "and" base (B) means proton acceptor from acid "as equation: AH + B ⇌ A− + BH +.

Consider the hydrolysis of acetic acid (CH3COOH) as the equation:
CH3COOH (aq)) + H2O (l) ⇌ CH3COO− (aq)) + H3O + (aq)

Water acts as a Brønsted Base because it accepts protons (H +) from acetic acid. And
acetic acid acts as Brønsted Acid, and when considering the reversing equation, the acetate
ion (CH3COO−) acts as the brinsted base. Because it receives a proton (H +) from the
hydronium ion (H3O +) that is the brinacetate (because it gives the proton to the acetate
ion).

In the above example, a conjugate acid – base pair is formed, where acetic acid
(CH3COOH) is the conjugate acid pair of the acetate ion (CH3COO−) and the acetate. The ion
(CH3COO−) is the conjugate base pair of acetic acid. And similarly, water (H2O) is a base pair
of hydronium ions (H3O +).

Examples of the Brinstead acid-base reaction

 H3O + + NH3 ⇌ H2O + NH4 +
 [Fe (H2O) 6] 3+ + H2O ⇌ [Fe (H2O) 5OH] 2+ + H3O +
 H2SO4 + H2O ⇌ HSO4− + H3O +
 CH3COOH + NH3 → NH4 + + CH3COO−
 NH4 + + H2O ⇌ H3O + + NH3

As above Acid-base definition according to Brinstead's theory The acid-base reaction
that cannot be explained by Arrhenius theory can also be explained, such as:

 H3O + (aq) + Cl− (aq) + NH3 (g) → Cl− (aq) + NH4 + (aq)
 HCl (benzene) + NH3 (benzene) → NH4Cl (s).
 HCl (g) + NH3 (g) → NH4Cl (s).

Amphoteric

Compounds that act on both brinstead and brinstead bases are called amphoteric,
with water being an example of amphoteric as the equation:

 AH + B ⇌ A− + BH +
 HNO3 + H2O ⇌ NO3− + H3O + (Water acts as a base)
 H2O + NH = C (NH2) 2 ⇌ OH− + H2N = C (NH2) 2+ (Water acts as acid)

Belinstead acid-base neutralization reaction

Brinstead acid-base neutralization refers to the reaction between an acid-base pair
and a base pair of a molecule, for example:

 H + + OH− ⇌ H2O
 NH4 + + NH2− ⇌ 2NH3
 H3SO4 ++ HSO4 − ⇌ H2SO4

Self-ionization process

Self-ionization process (Autoionization Process) that is normally found in protic solvent
(protic solvent) is the reverse reaction of the neutralization reaction itself.

 H2O ⇌ H + + OH−
 2NH3 / NH4 + + NH2−
 H2SO4 ⇌ H3SO4 ++ HSO4−

Furthermore, the self-ionizing equilibrium constant is called the self-proton
dissociation constant. (Autoprotolysis Constant: KAP) or ion product (Ionic Product) in the
case of water, the KAP value uses a unique symbol as KW, which is equal to 1.0 × 10−14 at
25 ° C: KAP = KW = [H +] [OH−]. = 1.0 × 10−14 at 25 ° C

H2SO4's pKAP was 2.9 at 25 ° C and NH3's pKAP was 27.7 at −50 ° C. The pKAP value
typically changed with temperature.

Relative strength of brinstead acid

The strength of Brinstead acid can be compared by using Acid Dissociation Constant
(Ka)

The acid dissociation constant is a constant that is unique at a given temperature.
And the value changes with the temperature Including depending on the type of solvent as
well The table is an example of the pKa value of some acids in different solvents at 25 ° C.

Lewis definition

Gilbert Newton Lewis (American chemist) In 1923 the definition of an acid-base was
proposed by considering the electron pair giving and receiving, which states that "acid refers

to a substance that accepts an electron pair (Electron Pair Acceptor)" and "base" refers to an
electron pair. Electron pair donor, such as: Me3N: + BF3 → Me3N: + BF3

Me3N: is Lewis Base because it gives electron pairs to BF3 and BF3 is Lewis Acid
because it receives the electron pair from Me3N: The product of Lewis's acid-base reaction is
called the Adduct. ) Or complex

Example of Lewis's acid-base reaction

 BF3 + F− → BF4−
 BF3 + OMe2 → BF3OMe2
 I2 + I− → I3−
 SiF4 + 2 F− → SiF62−

IUPAC definition

The International Union of Pure and Applied Chemistry (IUPAC) defines the meaning
of an acid-base, combining the Brinstead definition and the Lewis definition as follows:

"An acid refers to any molecular unit or species chemically capable of providing
Hydron (protons) (by definition, brinstead) or has the ability to form covalent bonds by
receiving electron pairs. (By Lewis acid definition) "

Base refers to any unit at the molecular level or species chemically capable of
forming covalent bonds with hydrons (Hydron) (protons) (as defined by basebensted) or with
orr. The available bitals of other species (by definition base Lewis) "

Question

1.Following reaction Which reactants act as acids? Which substance acts as a base according
to Arrhenius theory?
A. HSO4- (aq) + H2O (l) SO4 2- + H3O + H2O
B. LiOH (s) Li2 + + OH-
C. H2O + H2O H3O + + OH-
Answer C. H2O is both an acid and a base. One molecule causes H3O + (acid), the other
molecules break down to OH- (base).
2.In what reaction does the HCO3-ion act as an acid?
A. HCO3- (aq) + H2O (l) H2CO3 (aq) + OH- (aq)
B. HCO3- (aq) + OH- (aq) H2O (l) + CO3 2- (aq)
C. HCO3- (aq) + HSO4 - (aq) H2CO3 (aq) + SO 4 2- (aq)
D. HCO3- (aq) + CH3COOH (aq) H2O (l) + CO2 (g) + CH3COO- (aq)
Answer B. HCO3- (aq) is acidic because it gives H + and OH-.

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chemical

ACID AND BASE

ACID-BASE DEFINITION In the forward reaction, NH3 receives a
proton from H2O, so NH3 is a base and H2O
Arrhenius Concept is an acid, but in the reverse reaction, NH4 +
An acid is a compound with H and gives a proton to OH-, so NH4 + is an acid
dissolves in water to H + or H3O +. and OH- is a base. The direction of the
Bases are OH-containing compounds and, reaction depends on the strength of the
when dissolved in water, breaks down to base.
OH-
The limitation of this theory is The LEWIS CONCEPT
compound must be soluble in water. And
cannot explain that Why are some An acid is a substance that can receive an
compounds such as NH3 bases? electron pair acceptor from another
Bronsted-Lowry Concept substance.
An acid is a substance that can give a Bases are substances that can give electron
proton (proton donor) to another pair donors to other substances.
substance. The theory is used to describe the acid-
A base is a substance that can accept a base concept of Arrhenius and the
proton (proton acceptor) from another Bronsted-Lowry, and has the advantage
substance. that it can explain acid-bases in the event
The reaction between acids and bases is of interactions. And a compound with a
the transfer of protons from the acid to the covalent bond, for example
base, such as ammonia, dissolved in water.
NH3 (aq) + H2O (1) = NH4 + (aq) + OH- (aq) OH - (aq) + CO2 (aq) HCO3- (aq)
base 2 ........ acid 1 ........ acid 2 ........ base 1
BF3 + NH3 BF3-NH3

Types of acids and bases Strength of acids and bases
Type of acid
1. Monoprotic acid breakdown 1 is Strong acids are acids that are 100%
HNO3, HClO3, HClO4, HCN. dissociable in water, such as HCl,
2. Diprotic acid breaks down 2, namely H2SO4, HN03, HBr, HClO4, and HI.
H2SO4, H2CO3.
3. Polyprotic acid breaks down 3 ie The strong base (weak base) is an
H3PO4. acid that is 100% dissociable in water,
Each polyprotic acid dissociation gives such as Hydroxide of the elements
H + not the same, the first will break group 1 and 2 (NaOH LiOH CsOH Ba
very well, the Ka value is very high, but (OH) 2 Ca (OH) 2).
the subsequent rupture will have a very
low Ka value because the negative ions Weak acid is an acid that can be
in the ions attract H + as equation partially ionized, such as the acetic acid
H2SO4 H + + HSO4- Ka1 = 1011 in vinegar, aspirin (acetylsalicylic acid),
HSO4- H + + SO42- Ka2 = 1.2 x 10-2 used to relieve headaches, saccharin is
Since polyprotic acids are usually K1 a sweetener, niacin (nicotinic acid). )
>> K2 >> K3 H +, most of the solutions Or vitamin B, etc. An example reaction
are obtained from the first dissolution. of CH 3COOH acid solution in a
If the K1 value is greater than K2 = 103 vinegar mixture is as follows:
times, the pH of the polyprotic acid
solution can be determined from the K1 CH 3COOH (aq) + H2O (1) H3O +
value only, but if the K2 value is not (aq) + CH3COO - (aq) has K a.
very low, the K2 value must be taken
into account. A weak base is a base that can only
Bass type partially disintegrate, for example, NH 3
Bases are classified according to the urea aniline, etc. An example of
number of OH- in the base. There are ammonia reaction is as follows.
three types of bases:
1.Basses that have a single OH-, such NH3 (aq) + H2O (aq) NH4 + (aq) +
as LiOH NaOH KOH RbOH CsOH. OH - (aq)
2. Bases with OH-2 such as Ca (OH)
2 Sr (OH) 2 Ba (OH) 2
3. Bases with OH- 3 such as Al (OH)
3 Fe (OH) 3

Types of acids and bases
Acids can be divided into 3 types of dissociation.
1. Monoprotic acid breakdown 1 is HNO 3, HClO 3, HClO 4, HCN.
2. Diprotic acid breaks down 2, namely H 2SO 4, H 2CO 3.
3.Polyprotic acid breaks down 3, namely H 3PO 4.
Each polyprotic acid dissociation yields an unequal H +. The first break is very good, the
Ka value is very high, but the subsequent rupture will have a very low Ka value because
the negative ions in the ions attract the same H +. The
H 2SO 4 H + + HSO 4 - Ka 1 = 10 11
HSO 4 - H + + SO 4 2- Ka 2 = 1.2 x 10 -2
Since polyprotic acids are usually K 1 >> K 2 >> K 3 H +, most of the solutions are
obtained by first dissolution.
If the K 1 value is 3 times greater than K 2 = 10, the pH of the polyprotic acid solution can
be determined from the K 1 value only, but if the K 2 value is not very low then the K 2
value must be taken into account.
Bases are classified by the number of OH - in the base there are 3 types:
1.Bass with OH - single, such as LiOH NaOH KOH RbOH CsOH.
2. Bases with OH - 2 such as Ca (OH) 2 Sr (OH) 2 Ba (OH) 2
3. Bases with OH - 3 such as Al (OH) 3 Fe (OH) 3

Acid and base titrations
Acid-base titration It is a titration between an acid and base solution. It is used to
determine the exact amount or concentration of an acid or base. This is done by titrating
the sample to an acid or base of known concentration. Then observe the color of the
indicator changing when the reaction reaches the equivalence point during titration pH. If
the appropriate indicator is selected, the endpoint closest to the equivalence point can be
used. Acid-base titration It can be divided into 4 types, each titration has different results
as follows.
1. Titration between strong acids and strong bases.
2. Titration between weak and strong acids.
3. Titration between weak acid and strong base
4. Titration between weak acid and

Buffer solution
Refers to a solution obtained by mixing a weak acid with a base pair of that acid. Or a
weak base and an acid pair of that base. Is going to have a solution with a common ion.
The key functions of the buffer solution Is a solution used to control the acidity and base
of the solution So as not to change much When adding a little acid or base That is, the
pH level of the solution can be kept almost constant. Even with a little water or a little acid
or base added, it will not change the pH of the solution much. We call this pH variable
resistance buffer capacity.

Questions 3. Find the pH of a solution with H3 O +
equal to 1 x 10 -11 and 6 x 10 -14 mol / l.
1. The following substances Which of
these works for both acids and bases? Answer
1) HC2O4 2- How to do
2) CO3 2-
3) CN - [H3 O +] = 1 x 10-11
4) HSO4 - pH = -log [H3 O +]

Answer = -log [1 x 10-11]
Clause 1) and 4) can be both an acid and a = 11
base. Because they can give and receive H [H3 O +] = 6 x 10-4
+ pH = -log [H3 O +]
Verses 2) and 3) can only be a base. = -log [6 x 10-4]
Because protons cannot be given because = 4 - log6
they do not have H, but can receive protons, = 4 - 0.78
becoming HCO3- and HCN respectively = 3.22

2. Find the pH of a solution with a
concentration of H3 O + = 4.8 x 10-13 mol / l.

Answer pH = -log [H3 O +]
How to do = -log [4.8 x 10-13]
= 13 - log 4.8
= 12.32

Mrs. Narissara Kangngon M.5/5 No. 11

Acid-Base Properties of Salts

Salts that consist of the cations of strong bases and the anions of strong acids have
no effect on H+ when dissolved in water. In other words, aqueous solutions like NaCl, KCl,
and NaNO3 are neutral, or have a pH = 7.

When cations of weak bases or anions of weak acids are dissolved water, though, pH
is affected. An example is NaC2H3O2. Since C2H3O2- is the conjugate base of a weak acid, it
has an affinity for protons.In water, it acts as a base to form OH- ions. For reactions such as
this, the equilibrium expression is the same as for any acid or base, but sometimes,

the Kb or Ka value is unknown. To find these values, we use the equation (Kb)(Ka) =
Kw and Kw is equal to 1.0X10-14. So, to solve for the Kb of a conjugate base,you divide
Kw by the Ka of the weak acid, or for a conjugate acid, you divide Kw by the Kb of the weak
base. Ex. Find the Kb of C2H3O2-, the Ka of C2H3O2- is 1.8X10-5 (1.0X10-14) / (1.8X10-
5) = 5.6X10-10

Remember that acids and bases are competing for H+ and OH- ions with water, so
while the Ka of an acid,such as HCN is very small (6.2X10-10) and it would be expected to
be a strong base, (1X10-14) / (6.2X10-10)= 1.6X10-5, which is still a weak base relative to
other strong bases. Base strength goes OH- > Weak Bases > H2O

Other salts produce acids in solution, such as NH4Cl. It dissociates to Cl- and NH4+,
and NH4+ dissociates into H+ and NH3. Cl- has little to no affinity for protons in water, so it
does not affect pHwhile ammonium does. In general, salts in which the anion is not a base
and the cation isthe conjugate acid of a weak base produce acidic solutions.

Panjapohn Janyathai M.5/5 No.12

Another salt that produces an acidic solution is one with a highly charged metal
ion. An example is AlCl3, which produces a highly acidic solution in water. Al(H2O)63+ also
functions as a weak acid, even though it is not a Bronsted-Lowry acid. Al(H2O)63+(aq) <=>
Al(OH)(H2O)52+(aq) + H+(aq)

This is because the highly charged metal ions polarize the OH bonds in the water
molecules, making the hydrogen in the water molecules more acidic than normal hydrogen
in free water ions. Generally, the higher the metal ion charge, that stronger the acidity of the
hydrated ion.

In a salt where both the anion and the cation affect pH, equilibrium expressions can
become very complicated. To predict acidity of these solutions, the Ka and Kb values are
compared. If the Ka value of the acidic ion is greater than the Kb value of the basic ion, the
solution will be acidic while if the Kb value of the basic ion is greater than the Ka value of
the acidic ion, the solution will be basic.

When is a salt solution basic or acidic?
There are several guiding principles that summarize the outcome:

1. Salts that are from strong bases and strong acids do not hydrolyze. The pH
will remain neutral at 7. Halides and alkaline metals dissociate and do not affect the H+ as
the cation does not alter the H+ and the anion does not attract the H+ from water. This is
why NaCl is a neutral salt. In General: Salts containing halides (except F-) and an alkaline
metal (except Be2+) will dissociate into spectator ions.

2. Salts that are from strong bases and weak acids do hydrolyze, which gives it
a pH greater than 7. The anion in the salt is derived from a weak acid, most likely organic,
and will accept the proton from the water in the reaction. This will have the water act

Panjapohn Janyathai M.5/5 No.12

as an acid that will, in this case, leaving a hydroxide ion (OH-). The cation will be from a

strong base, meaning from either the alkaline or alkaline earth metals and, like before, it will

dissociate into an ion and not affect the H+.

3. Salts of weak bases and strong acids do hydrolyze, which gives it a pH less

than 7. This is due to the fact that the anion will become a spectator ion and fail to attract

the H+, while the cation from the weak base will donate a proton to the water forming a

hydronium ion.

4. Salts from a weak base and weak acid also hydrolyze as the others, but a

bit more complex and will require the Ka and Kb to be taken into account.Whichever is
the stronger acid or weak will be the dominate factor in determining whether it is acidic or

basic. The cation will be the acid, and the anion will be the base and will form either form a

hydronium ion or a hydroxide ion depending on which ion reacts more readily with the

water.

Questions 1

a. Predict whether the pH of each of the following salts placed into water is acidic,

basic, or neutral

b. NaOCl(s)
c. KCN(s)
d. NH4NO3(s)
The ions present are Na+ and OCl- as shown by the following reaction

NaOCl(s)→Na+(aq)+OCl−(aq)NaOCl(s)→Na(aq)++OCl(aq) While Na+ will not hydrolyze, OCl- will

(remember that it is the conjugate base of HOCl). It acts as a base, accepting a proton from water.

OCl−(aq)+H2O(l)⇌HOCl(aq)+OH−(aq)OCl(aq)−+H2O(l)⇌HOCl(aq)+OH(aq)−Na+
is excluded from this reaction since it is a spectator ion. Therefore, with the production of OH-, it will

cause a basic solution and raise the pH above 7.

pH>7

The KCN(s) will dissociate into K+ and CN_(aq) by the following reaction:
(aq)

KCN(s)→K+(aq)+CN−(aq)(7.8.3)(7.8.3)KCN(s)→K(aq)++CN(aq)−

K+ will not hydrolyze, but the CN- anion will attract an H+away from the water:

CN−(aq)+H2O(l)⇌HCN(aq)+OH−(aq)(7.8.4)(7.8.4)CN(aq)−+H2O(l)⇌HCN(aq)+OH(aq)−
Because this reaction produces OH-, the resulting solution will be basic and cause a pH>7.

pH>7
e. The NH4NO3 (s) will dissociate into NH4+ and NO3- by the following reaction:
NH4NO3(s)→NH+4(aq)+NO−3(aq)(7.8.5)(7.8.5)NH4NO3(s)→NH4(aq)++NO3(aq)−
Now, NO3-won't attract an H+ because it is usually from a strong acid. This means the Kb will be
very small. However, NH4+ will lose an electron and act as an acid (NH4+ is the conjugate acid of NH3) by
the following reaction:
NH+4(aq)+H2O(l)⇌NH3(aq)+H3O+(aq)(7.8.6)(7.8.6)NH4(aq)++H2O(l)⇌NH3(aq)+H3O+ (aq)
This reaction produces a hydronium ion, making the solution acidic, lowering the pH below 7.

pH<7

Questions 2
2. Find the pH of a solution of .200 M NH4NO3 where (Ka = 1.8 * 10-5)

NH+4(aq)+H2O(l)⇌NH3(aq)+H3O(aq)NH4(aq)++H2O(l)⇌NH3(aq)+H3O(aq)
x20.2−x=1∗10−141.8×10−5x20.2−x=1∗10−141.8×10−5
x=1.05∗10−5M=[H3O+]x=1.05∗10−5M=[H3O+] pH=4.98

Questions 3
3. Find the pH of a solution of .200 M Na3PO4 where (Ka1 = 7.25 * 10-5, Ka2 = 6.31

* 10-8, Ka3 = 3.98 * 10-3)
PO3−4(aq)+H2O(l)⇌HPO2−4(aq)+OH−(aq)PO3−4(aq)+H2O(l)⇌HPO4(aq)2−+OH(aq)−

The majority of the hydroxide ion will come from this first step. So only the first step
will be completed here. To complete the other steps, follow the same manner of this
calculation.

x20.2−x=1∗10−143.98×10−13(7.8.7)(7.8.7)x20.2−x=1∗10−143.98×10−13
x=0.0594=[OH−](7.8.8)(7.8.8)x=0.0594=[OH−]
pH=12.77

Panjapohn Janyathai M.5/5 No.12





Exercise

1.If A and B are mixed together, A acts as an acid, B acts as a base, A and B 8.
1. CH3COOH , HCl
2. Ba(OH)2 , NaHCO3
3. KCl , CH3COONa
4. NaHCO3 , NH3

Answer: 4. NaHCO3 , NH3

2. In the reaction that is in equilibrium
HF (aq) + H2O (l) H3O + (aq) + F- (aq)
If the direction of balance is from right to left How can it be concluded?

1. HF is a strong acid.
2. F- is a base that is older than water.
3. More than 1 equilibrium constant
4. The equilibrium constant is approximately 1
Answer: 2. F- is a base that is older than water.

3. A solution of 0.10 mol / l. HF breaks down by 8%. Calculate the Ka of this acid.
1. 5.0 * 10-2
2. 4.5 * 10-4
3. 6.9 * 10-4
4. 4.2 * 10-3

Answer: 3. 6.9 * 10-4

Phatthiya Promlee No.13 Class M.5/5

Acid-base
Acid-base theory of Arrhenthiuesory

Arrhenius theory defines an acid as a substance that dissolves water and dissolves to
hydrogen ions while the base is a substance that dissolves water and dissolves to form
hydroxide ions. Which can express the general equation as follows

In this equation, HA is the general formula for acids such as HNO3, HClO4, BOH is the general
formula for bases such as NaOH, KOH.

The definition of arrhenius is that an acidic or base substance must be dissolved in
water or another solvent. If it is insoluble in a solvent, it is not classified as an acid or a base.
In addition, it cannot be used to describe the acidity or base of a substance that does not
contain H + or OH- in molecules such as NH4Cl or CH3COONa, but their acidic and base
properties respectively

Acid-base theory of Berinstead-Laowry
Brinstead-Laowry acid-base theory defines an acid as a proton-producing agent, and

a base is a proton-receptor
The Brinstead-Laowry acid-base definition explains the acidity of NH4Cl and the

base's CH3COONa, in which the molecule does not contain H + or OH-, but when dissolved
in water, a solution with acidic and base properties is obtained.

NH4Cl is an ionic compound. When dissolved, water is ionized and changes as
follows.

NH4 + gives H + to H2O, so NH4 + acts as acid while H2O takes H + from NH4 +, so
H2O acts as base. And in the solution, H3O + is formed. NH4Cl solution has acidic properties.

Lewis theory of acid-base
Lewis' acid-base theory defines an acid as a substance capable of accepting

electron pairs and a base, a substance that can give an electron pair, such as the reaction
between boron trifluoride (BF3) and ammonia.

NH3 has one lone electron pair, which gives an electron pair, BF3 is an electron
pair, NH3 is a base and BF3 is an acid.

Lewis's acid-base theory can also be used to explain the acid-base acidity of
protons-containing substances, as in Brinstead-Lavri's theory.

In this reaction, OH- gives an electron pair with H +, therefore a base, and H + is
an acid because it receives an electron pair from OH- and an O-H bond is formed.

Question

1. In what reaction does the HCO3-ion act as an acid?
A. HCO3- (aq) + H2O (l) H2CO3 (aq) + OH- (aq)
B. HCO3- (aq) + OH- (aq) H2O (l) + CO3 2- (aq)
C. HCO3- (aq) + HSO4 - (aq) H2CO3 (aq) + SO 4 2- (aq)
D. HCO3- (aq) + CH3COOH (aq) H2O (l) + CO2 (g) + CH3COO- (aq)

Answer B. HCO3- (aq) is acidic because it gives H + and OH-.
2. Following reaction Which reactants act as acids? Which substance acts as a base
according to Arrhenius theory?

A. HSO4- (aq) + H2O (l) SO4 2- + H3O + H2O
B. LiOH (s) Li2 + + OH
C. H2O + H2O H3O + + OH
Answer C. H2O is both an acid and a base. One molecule causes H3O + (acid), the
other molecules break down to OH- (base).
อา้ งอิง
http://www.ed.in.th/sub/sci/161010301/C3.htm

นางสาวสุนติ า เดชแกว้ เลขที่14 ม.5/5

Miss Irada Wanna M.5/5 No. 15

Acid-Base

Arrhenius Concept

An acid is an H compound and when dissolved in water breaks down to H
+ or H3O +.

Bases are OH-containing compounds and, when dissolved in water, breaks
down to OH-

The limitation of this theory is The compound must be soluble in water.
And cannot explain that Why are some compounds such as NH3 bases

Bronsted-Lowry Concept

An acid is a substance that can give a proton (proton donor) to another
substance.

A base is a substance that can accept a proton (proton acceptor) from
another substance.

The reaction between acids and bases is the transfer of protons from the acid
to the base, such as ammonia, dissolved in water.

NH3 (aq) + H2O (1) = NH4 + (aq) + OH- (aq)

base 2 ........ acid 1 ........ acid 2 ........ base 1

In the forward reaction, NH3 receives a proton from H2O, so NH3 is a base
and H2O is an acid, but in the reverse reaction, NH4 + gives a proton to OH-
, so NH4 + is an acid and OH- is a base. The direction of the reaction
depends on the strength of the base.

Lewis Concept

An acid is a substance that can receive an electron pair acceptor from
another substance.

Bases are substances that can give electron pair donors to other substances.

The theory is used to describe the acid-base concept of Arrhenius and the
Bronsted-Lowry, and has the advantage that it can explain acid-bases in the
event of interactions. And a compound with a covalent bond, for example

OH - (aq) + CO2 (aq) HCO3- (aq)

BF3 + NH3 BF3-NH3

Types of acids and bases

Type of acid
1. Monoprotic acid breakdown 1 is HNO3, HClO3, HClO4, HCN.

2. Diprotic acid breaks down 2, namely H2SO4, H2CO3.

3. Polyprotic acid breaks down 3 ie H3PO4.
Each polyprotic acid dissociation gives H + not the same, the first will break
very well, the Ka value is very high, but the subsequent rupture will have a
very low Ka value because the negative ions in the ions attract H + as
equation

H2SO4 H + + HSO4- Ka1 = 1011

HSO4- H + + SO42- Ka2 = 1.2 x 10-2

Since polyprotic acids are usually K1 >> K2 >> K3 H +, most of the
solutions are obtained from the first dissolution.

If the K1 value is greater than K2 = 103 times, the pH of the polyprotic acid
solution can be determined from the K1 value only, but if the K2 value is
not very low, the K2 value must be taken into account.

Bass type
Bases are classified according to the number of OH- in the bass.

1.Basses that have a single OH-, such as LiOH NaOH KOH RbOH CsOH.

2. Bases with OH-2 such as Ca (OH) 2 Sr (OH) 2 Ba (OH) 2

3. Bases with OH- 3 such as Al (OH) 3 Fe (OH) 3

Exercise

1.Calculate the concentration of OH-ions in moles per liter in a
0.1mol/liter of concentrated hydrochloric acid solution.

a. 1.0 * 10-1
b. 1.0 * 10-8
c. 1.0 * 10-13
d. 1.0 * 10-14

Answer. c. 1.0 * 10-13

2.Which of the following substances or ions can be both an acid and a
base?

a. H2O
b. HC2O4-
c. HS-
d. NO3-

Answer. d. NO3-

3. A 0.04 M concentrated monoprotic acid solution has 14%
disintegration. Calculate the fracture constant.
Acid
Answer. Break 14% = (14/100)x 0.04 M = 0.0056 M

HA H+ + A-

initail 0.04 M 0M 0M

balance (0.04-0.0056 M) 0.0056 M 0.0056 M
Ka =
[H+ ][A- ]
[HA]

Ka = (0.0056 M)(0.0056 M)
(0.0344 M)

= 9.1x10-4







Exercise

1. Based on Brønsted-Lowry theory, which of the following are acid-

base reactions?

A.

B.
C.
D.

Answer : C.

2.

A.
B.
C.
D.

Answer : B.

3.

A.6.00
B.7.45
C.7.90
D.7.00

Answer: B. 7.45