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Acid-base theory

Arrhenius theory of acid-base
Arrenius is a Swedish scientist. The acid-base theory was established. In

1887, Arrhenius studied aqueous solution and the conductivity of that solution. He
found that the electrolytes are ionized. When dissolved in water and the acid is
defined as

“Acids are substances that, when dissolved in water, break down to form
hydrogen ions.”

“Bases are substances that, when dissolved in water, break down to form
hydroxide ions.”

Quiz

The 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-

Béin State-Lavri's Acid-Base Theory
Johans Nicholas Brinstate, Danish chemist and British chemist Thomas

Martin Lavri. Have studied the giving and receiving of protons of substances For
a broader way to describe and classify acids-bases And established the acid-
base theory in 1923 (1923)

An acid is a substance that can provide protons with other substances
(Proton donor).

Bases are substances that can accept protons from other substances
(proton acceptors).

นางสาวณิชาฎา แสนกลา เลขท่ี 17

Example

Quiz

Based on the theory of Arrhenius and Berinstead Laure, what group of
substances are classified as bases?

A.CO32- HPO32- Cl - NH4 +
B.Na + Ca (OH) 2 NO3- NH3
C.OH32- HCO3- SO 42- NH3
D.KOH H2PO4- H3O + SO 32-
Substances that are both acids and bases (Amphoteric)

Some substances act as acids. When reacting with one substance And acts as a
base When reacting with another substance That is, it can be both an acid and a base.
Substances that look like this are called Emoteric substances (Amphoteric) such as
H2O, HCO3 - etc.
The case of H2O

In this case, H2O is acidic when reacted with NH3 and base when reacted with NH4 +.
Emporic substances If it reacts better with proton-producing substances It itself
accepts protons (acting as bases), but if they react poorly with protons-producing
substances, It itself is responsible for the proton and the substance (acting as an
acid).

นางสาวณิชาฎา แสนกลา เลขท่ี 17

Lewis's acid-base theory
In 1923, Lewisdi proposed the following definition of an acid and a base:

An acid is a substance that accepts an electron pair from a base and
forms a covalent bond.

Bases are substances capable of giving electron pairs in the formation of
covalent bonds.

This theoretical acid-base reaction is described in terms where electron pairs
are shared Acids accept electrons are called electrophiles, and bases give
electrons a nucleophile, and according to this theory, the base substance must
have free electron pairs, for example:

In this case, NH3 is a base with a pair of electrons, it gives an electron
pair with an acid to form a covalent bond, and BF3 receives an electron from
NH3BF3 is acidic.

Quiz

1. When mixing HI acid solutions, base Ca (OH) 2 solutions, at different concentrations and
volumes Calculate the concentration of the remaining substance.

1.1 HI 0.1 M, 500 cm3 and Ca (OH) 2 0.5 M, 100 cm3.
1.2 HI 0.1 M, 1000 cm3และ Ca(OH)2 0.5 M, 100 cm3
1.3 HI 0.1 M, 400 com3Ca(OH)2 0.1 M, 100 cm3
.
2. Concentrated HCl acid 0.02 mol / dm3 mixed with NaOH of 0.01 mol / dm3 content
50 cm3.
3. When mixing the solution Ca (OH) 1.0 M concentration 30.00 mL with a 2 M HBr
solution of 10.00 mL, how many molar concentrations of H2O + were obtained?
And what's the pH of this solution?

นางสาวณิชาฎา แสนกลา เลขที่ 17

answer 2.

1.1

1.2 Not left 3.

= [HI], [Ca (OH) 2] both.

1.3

นางสาวณชิ าฎา แสนกลา เลขท่ี 17

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 from the 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 - there are 3 types of bases in
the base:

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

1.Which statement is most accurate?

A. series 1, 3 will change litmus paper from blue to red.
B. series 1, 2 will change litmus paper from red to blue.
C. 3, 4 solution will change litmus paper from blue to red.
D. The solution set 1, 4 will change litmus paper from red to blue.
Answer
A. series 1,3 will change litmus paper from blue to red.

2. In what is the descending order of acid strength?

A. H2O> HClO4> HCl> HCN
B. HCl> HCN> HClO4> H2O
C. HClO4> HCl> HCN> H2O
D. HCl> HClO4> HCN> H2Or
Answer
C. HClO4> HCl> HCN> H2O

3. In the reaction Pb 2 + (aq) + H2S (aq) PbS (s) + 2H + (aq) if desired
PbS settles more and more, what should I do?
A. Catalyst
B. increases the acidity of the solubility.
C. Add water to the solution.
D. to add the base to the solubility
Answer
D. to add the base to the solubility

MS.ARRAYA SAPTHWIPON NO.8 M.5/5

Acid-base definition

Arrhenius 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 s trength 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

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

Strength of acids and bases

Strong acids are acids that are 100% dissociable in water, such as HCl, H2SO4, HN03, HBr, HClO4, and HI.

The strong base (weak base) is an acid that is 100% dissociable in water, such as Hydroxide of the
elements group 1 and 2 (NaOH LiOH CsOH Ba (OH) 2 Ca (OH) 2).

Weak acid is an acid that can be partially ionized, such as the acetic acid in vinegar, aspirin
(acetylsalicylic acid), used to relieve headaches, saccharin is a sweetener, niacin (nicotinic acid). ) Or

vitamin B, etc. An example reaction of CH 3COOH acid solution in a vinegar mixture is as follows:

CH 3COOH (aq) + H2O (1) H3O + (aq) + CH3COO - (aq) has K a.

A weak base is a base that can only partially disintegrate, for example, NH 3 urea aniline, etc. An

example of ammonia reaction is as follows.

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

Question

1.Eating acids must not discolor gentian violet.
1) Yes, because it will turn red.
2) Yes, as it must turn yellow.
3) No, because it has to be changed to green.
4) No, as there will be no color changes.
Answer 4) No, as the color will not change.

2.What is the most naturally occurring acid?
1) hydrochloric acid
2) carbonic acid
3) sulfuric acid
4) acitric acid
Answer 1) Hydrochloric acid
3. If you want to test the acidity of the substance, what kind of flower should be used
1) rose
2) hibiscus
3) bougainvillea
4) Anchan
Answer 4) Anchan

Acid-Base

The breakdown of strong acids and strong bases

Strong acids and strong bases are mature electrolytes, when dissolved in
water, ionizes well. Can almost completely break down100%, which is
considered completely ruptured, therefore only forward reaction occurs.
Therefore, if the concentration of strong acids orThe old bases can be
calculated to find the concentrations of H3O + and OH- in solution, for
example:

Strong acid Old bass Percentage dissolution That happened
of weak acid
acid begin

Weak acid-base breakdown

Weak acids and weak bases are classified as weak electrolytes. when
dissolved in water, it cannot be completely dissolved.Only partially and is
very small compared to the initial concentrations of weak acids or weak
bases weak acid break downand a weak base is a reversible change.
at equilibrium there are both weak acid molecules or weak bases and
ions.Caused by the breakdown of weak acids and weak bases
Determining the concentration of H3O + and OH- caused by disintegration
of weak acid and weak base Popular say in a percentage called Percentage
disintegration (percent ionization: α) i.e. weak acid haconcentrate 1 mol /
dm3 is 5% dissolved, meaning that in 1 dm3 of solution there is 1 mol of
HA acid dissolved.and when we reach equilibrium, ha acid only dissolves
0.05 mol and remains 0.95 mol.

Weak acid dissolution amount In addition to telling a percentage Can also
be told using the equilibrium constantThe reaction is called the acid
equilibrium constant or the acid ionization constant.constant: Ka)

Practice model

1.Next, identify the base pair for each type of acid.

NH4 คBูเ บesสtคpือair NH3
HClO คBเู บesสtคpอื air ClOH2
P2O4
Bคeูเ บstสpคaอื ir HPO4

HIO4 คBูเบesสtคpือair IO4
CH3COOH คBูเ บesสtคpอื air CH3COO

Answers คBูเeบsสt คpอืair NH3
Bคูเeบstสpคaือir ClOH2
NH4 Bคูเeบstสpคaือir HPO42
HClO คBูเeบstสคpaือir IO4
P2O4 Bคเูeบstสpคaือir CH3COO
HIO4
CH3COOH

2.The buffer solution was formed by mixing NH4OH soft base solution
and NH4Cl salt with the same 0.1 mol / L concentration and the same
volume of 100cm Equal to 1.8 x 10-5. What pH is this buffer solution?

Answers = - log 1.8 x 10-5 + log (0.1 / 0.1 )
= 5 – log 1.8 +log 1
= 5 – 0.26
= 4.74
pH = 14 – pOH
= 14 – 4.74
= 9.26

3.Concentrated HCl acid 0.02 mol / dm3 mixed with NaOH 0.01 mol /
dm3 50 cm3. Find the pH of this mixture.

Answers

Kanyapat Wongpranut No20 Class

Acid-Base

Acid–base reaction

"Acid-base" redirects here. For chemicals that can behave as acids or bases, see Amphoterism.
An acid–base reaction is a chemical reaction that occurs between an acid and a base. It can be used to
determine pH. Several theoretical frameworks provide alternative conceptions of the reaction mechanisms
and their application in solving related problems; these are called the acid–base theories, for example,
Brønsted–Lowry acid–base theory.

Their importance becomes apparent in analyzing acid–base reactions for gaseous or liquid species, or when
acid or base character may be somewhat less apparent. The first of these concepts was provided by the
French chemist Antoine Lavoisier, around 1776.

It is important to think of the acid-base reaction models as theories that complement each other.[2] For
example, the current Lewis model has the broadest definition of what an acid and base are, with the
Brønsted-Lowry theory being a subset of what acids and bases are, and the Arrhenius theory being the most
restrictive.

Practice model

1. For each of the species below, identify the most acidic proton and provide the structure of the
corresponding conjugate base. You might want to draw detailed Lewis formulas in some cases.

Answers

2. Rank the following in order of increasing basicity: CH3 O-, H2 N-, H2 O, and NH3 .
Answers H2 O < NH3 < CH3 O- < H2 N-

Negatively charged ions are stronger bases than neutral counterparts. A table of pKa values will further
aid in deciding the final order of basicity.

3. Consider the species CH3O-, NH2 -, and CH3COO-. Rank these ions in order of increasing basicity,
and explain your rationale.

CH3COO- < CH3O- < NH2 –
first factor to consider is the nature of the atom which bears the negative charge. The more
electronegative the atom that bears the negative charge, the more stable the anion. Stable anions are
less reactive and are hence weaker bases. Since O is more electronegative than N, the NH2 - is the
strongest base in the set. In the remaining two species, the negative charge is on the O, but in the case
of CH3COO-, the negative charge is also delocalized by resonance.

References : https://personal.utdallas.edu/~scortes/ochem/OChem1_Lecture/exercises/bronst_acid_base_qs.pdf

Phornnapa Ngamloet. M5/5 No.21

นายณฐั กิจ โตดประโคน ม.5/5 เลขท่ี 23
Acid-base pair
From the reaction of acids and bases already mentioned According to Brinstate-Laurie theory, one reaction Two acid-base
pairs can be paired together, for example:

This example reaction The forward reaction NH 4 + acts as an acid because H + and H 2 O are given as NH 3 and H 2 O get
H + acting as a base. The reverse reaction H 3 O + is acidic because it gives H + and NH 3 which is the base, H 2 O and
NH 4 + respectively.
NH 4 + is called the acid pair of NH 3 (base).
H 2 O that the base pair of H 3 O + (acid)
NH 3 that the bass pair of NH 4 +
H 3 O + that the acid pair of H 2 O
It can be seen that the acid-base pair has one different number of protons (H). The number of protons of the acid pair Always
going to be one more base pair proton
Other examples Of acid-base pair reactions

Strength of acids and bases
Comparison of the strength of acids and bases May be considered as follows

1.View from the breakdown of the acid.
Very dissolved acids Very acidic 100% dissociable acids and bases are called strong acids and strong bases,

respectively, which conduct good electricity. But if the acid and the base are partially broken down, they are called weak acids
or weak bases, respectively, where the conductivity is bad.

For determining the dissolution of acids and bases, In addition to being calculated from the percentage of
dissolution Or it can be viewed from the acidic or base dissolution equilibrium constant (K a or K b ), for example

Bass strength Considered by the value of K b, that is, if there is a large K b , there is less base than K b, for example

NH 3 K b = 1.76 x 10 -5

N 2 H 4 K b = 9.5 x 10 -7

C 6 H 5 NH 2 K b = 4.3 x 10 -10

Bassity NH 3 > N 2 H 4 > C 6 H 5 NH 2

แบบฝึ กหดั

จงระบุคูก่ รด-เบสในปฏิกิริยาต่อไปน้ี

Acid-Base

Acid–base reaction

"Acid-base" redirects here. For chemicals that can behave as acids or bases, see Amphoterism.
An acid–base reaction is a chemical reaction that occurs between an acid and a base. It can be
used to determine pH. Several theoretical frameworks provide alternative conceptions of the
reaction mechanisms and their application in solving related problems; these are called the
acid–base theories, for example, Brønsted–Lowry acid–base theory.

Their importance becomes apparent in analyzing acid–base reactions for gaseous or liquid
species, or when acid or base character may be somewhat less apparent. The first of these
concepts was provided by the French chemist Antoine Lavoisier, around 1776.

It is important to think of the acid-base reaction models as theories that complement each
other.[2] For example, the current Lewis model has the broadest definition of what an acid and
base are, with the Brønsted-Lowry theory being a subset of what acids and bases are, and the
Arrhenius theory being the most restrictive.

+

Practice model

What is the descending order of acid strength?
Answers HClO4 > HCl > HCN > H2O
A weak acid, concentrated 1.0 mol / l, dissolves 10%. The same acid as 0.10 mol / l thickening
How many percent will it break down?
Answers Equal to 100%
Which of the following solutions is a mature electrolyte solution with base properties?
Answers Solution A changes the color of litmus paper from red to blue. The lamp is very bright.

https://sribura1617.files.wordpress.com/2014/04/e0b981e0b89ae0b89ae0b897e0b894e0b8
aae0b8ade0b89ae0b881e0b8a3e0b894-e0b980e0b89ae0b8aa12.pdf

Teerachat Priabaphichai M5/5 No. 24

Acid-base

Strength of acids and bases
Strong acids are acids that are 100% dissociable in water,
such as HCl, H2SO4, HN03, HBr, HClO4, and HI.
The strong base (weak base) is an acid that is 100%
dissociable in water, such as Hydroxide of the elements
group 1 and 2 (NaOH LiOH CsOH Ba (OH) 2 Ca (OH) 2).
Weak acid is an acid that can be partially ionized, such as the
acetic acid in vinegar, aspirin (acetylsalicylic acid), used to
relieve headaches, saccharin is a sweetener, niacin (nicotinic
acid). ) Or vitamin B, etc. An example reaction of CH 3COOH
acid solution in a vinegar mixture is as follows:
CH 3COOH (aq) + H2O (1) H3O + (aq) + CH3COO - (aq) has K a.
A weak base is a base that can only partially disintegrate, for
example, NH 3 urea aniline, etc. An example of ammonia
reaction is as follows.
NH3 (aq) + H2O (aq) NH4 + (aq) + OH - (aq)

Question

1. From the following reaction at 25 ° c CH3COO- + H3O +
CH3COOH + H2O.When adding a hydrochloric acid solution to
a 0.10 mol / l 25 ° c solution of concentrated acetic acid,
which statement is most correct?

A.The dissolution of acetic acid does not change.
B.The dissociation constant (Ka) of acetic acid does not

change.
C.Concentration of CH3COO add more
D.The concentration of CH3COO-decreases.

Answer

B.The dissociation constant (Ka) of acetic acid does not
change.

2. The chemical oxide chemical properties test of which
element showed the most basal?

A MgO

B. Al2O3
C. SO2
D. SiO2

Answer

A. MgO

3. Calculate the concentration of OH-ions in mol / L in
concentrated hydrochloric acid solution. 0.1 mol per liter

A.W 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

MS.JARUPHAT THANARIYAKUL NO.26 M.5/5

Busayarin Suadthamakit M.5/5 No.27

Buffer solution

A buffer solution (more precisely, pH buffer or hydrogen ion buffer) is an aqueous solution
consisting of a mixture of a weak acid and its conjugate base, or vice versa. Its pH changes very
little when a small amount of strong acid or base is added to it. Buffer solutions are used as a
means of keeping pH at a nearly constant value in a wide variety of chemical applications. In
nature, there are many systems that use buffering for pH regulation. For example, the bicarbonate
buffering system is used to regulate the pH of blood, and bicarbonate also acts as a buffer in the
ocean.

Principles of buffering

Buffer solutions achieve their resistance to pH change because of the presence of an
equilibrium between the weak acid HA and its conjugate base A−

HA ⇌ H+ + A

When some strong acid is added to an equilibrium mixture of the weak acid and its
conjugate base, hydrogen ions (H+) are added, and the equilibrium is shifted to the left, in
accordance with Le Châtelier's principle. Because of this, the hydrogen ion concentration increases
by less than the amount expected for the quantity of strong acid added. Similarly, if strong alkali
is added to the mixture, the hydrogen ion concentration decreases by less than the amount
expected for the quantity of alkali added. The effect is illustrated by the simulated titration of a
weak acid with pKa = 4.7. The relative concentration of undissociated acid is shown in blue, and
of its conjugate base in red. The pH changes relatively slowly in the buffer region, pH = pKa ± 1,
centered at pH = 4.7, where [HA] = [A−]. The hydrogen ion concentration decreases by less than
the amount expected because most of the added hydroxide ion is consumed in the reaction

OH− + HA → H2O + A−

Busayarin Suadthamakit M.5/5 No.27

and only a little is consumed in the neutralization reaction (which is the reaction that results in
an increase in pH)

OH− + H+ → H2O.

Once the acid is more than 95% deprotonated, the pH rises rapidly because most of the added
alkali is consumed in the neutralization reaction.

Simple buffering agents

"Universal" buffer mixtures

By combining substances with pKa values differing by only two or less and adjusting the
pH, a wide range of buffers can be obtained. Citric acid is a useful component of a buffer mixture
because it has three pKa values, separated by less than two. The buffer range can be extended
by adding other buffering agents. The following mixtures (McIlvaine's buffer solutions) have a
buffer range of pH 3 to 8.

Busayarin Suadthamakit M.5/5 No.27

Exercise

1.Given that Ka = 1.8 x 10–5 for acetic acid, calculate the pH of each of the following
solutions:

(a) A solution containing 0.10 M acetic acid (CH3COOH) and 0.10 M sodium acetate (NaCH3CO2).

(b) A solution containing 0.10 M CH3CO2H and 0.050 M NaCH3CO2.

(c) A solution containing 0.050 M CH3CO2H and 0.10 M NaCH3CO2.

Answer: (a) pH = 4.74; (b) pH = 4.44; (c) pH = 5.04)

2. (a) Calculate [H3O + ] and the pH of a solution that contains 0.10 M NH3 and 0.10 M
NH4Cl. (Ka(NH4 + ) = 5.6 x 10–10)

Answer: (a) [H3O + ] = 5.6 x 10–10 M, pH = 9.25)

(b) Calculate [H3O+] and the pH a solution that contains 0.20 M NH3 and 0.10 M NH4Cl.
Answers: [H3O+] = 2.8 x 10–10 M, pH = 9.55)
3. A phosphate buffer solution is prepared by dissolving 25.0 g of potassium hydrogen
phosphate(K2HPO4; FM = 174.18) and 12.0 g of potassium dihydrogen phosphate (KH2PO4;
FM = 136.09) in250. mL of the buffer solution.
(a) Calculate the molar concentrations of HPO42-and H2PO–, respectively, and the pH of the
buffersolution using the following equilibrium:

H2PO4–(aq) + H2O ⇌ H3O+(aq) + HPO42–(aq); (Ka = 6.2 x 10–8)
(b) Write an equation for the buffering reaction: (i) when a strong acid is added; (ii) when a
strong baseis added to the phosphate buffer solution.
(c) Calculate the final pH of the solution: (i) when 2.0 mL of 6.0 M HCl(aq) is added to thebuffer;
(ii)when 2.0 mL of 6.0 M NaOH(aq) is added to the buffer. (In each case, assume the final volume
of thesolution is 250. mL)
Answer: (a) [HPO42–] = 0.574 M; [H2PO–] = 0.353 M, and pH = 7.42;(c) (i) pH = 7.33; (ii) pH = 7.52)

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 appearance
Acid-base definition
Arrhenius Concept
An acid is a compound with H and dissolves in water to H + or H 3O +.
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 NH 3 bases?

The acid-base question

1.Based on Berinstead Lavre's theory of acid-base, what group of
substances are classified as all bases?
A.CO32-, HPO32-, Cl -, NH4 +
B.Na +, Ca (OH) 2, HNO3, NH3
C.OH-, HCO3-, SO42-, NH3
D.KOH, H2PO4-, H3O +, SO32-

ANSWER

C.OH-, HCO3-, SO42-, NH3

2.Acid pair of base PO43 - what is it?

A.H3PO4
B.H2PO4-
C.HPO42-
D.PO42-
ANSWER
C.HPO42-

3.Which of the following pairs of substances Which of these is not an

acid-base pair?
A.H2O - OH-
B.NH4 + - NH3
C.H2PO4- - HPO42-
D.H2CO3 - CO32-

ANSWER

D.H2CO3 - CO32-

MS.KHEMWIKA SAIYUEN NO.28 M.5/5

ศกั ดพิ งศ์ 29

Acid-Base Titrations

Strong Acid-Strong Base Titrations

A strong acid will react with a strong base to form a neutral (pH = 7) solution.

LEARNING OBJECTIVES

Calculate the concentration of an unknown strong acid given the amount of base necessary to titrate it.

KEY TAKEAWAYS

Key Points

• An acid – base titration is used to determine the unknown concentration of an acid or base by neutralizing it with an acid or base of
known concentration.

• Neutralization is the reaction between an acid and a base, producing a salt and a neutralized base.
• A strong acid yields a weak conjugate base (A–), so a strong acid is also described as an acid whose conjugate base is a much weaker base

than water.

Key Terms

• strong acid: A strong acid is one that completely ionizes (dissociates) in water; in other words, one mole of a strong acid (HA) dissolves
in water yielding one mole of H+ and one mole of the conjugate base, A−.

• titration: The determination of the concentration of some substance in a solution by slowly adding measured amounts of some other
substance (normally using a burette) until a reaction is shown to be complete—for instance, by the color change of an indicator.

• stoichiometry: The calculation of relative quantities or reactants and products in chemical reactions.
• strong base: A strong base is a basic chemical compound that is able to deprotonate very weak acids in an acid-base reaction. Common

examples of strong bases are the hydroxides of alkali metals and alkaline earth metals, such as NaOH and Ca(OH)2. Very strong bases
are even able to deprotonate very weakly acidic C–H groups in the absence of water.

An acid-base titration is used to determine the unknown concentration of an acid or base by neutralizing it with an acid or base of known
concentration. Using the stoichiometry of the reaction, the unknown concentration can be determined. It makes use of the neutralization reaction
that occurs between acids and bases and the knowledge of how acids and bases will react if their formulas are known.

Stages of a Strong Acid-Strong Base Titration

ศกั ดพิ งศ์ 29
A strong acid- strong base titration is performed using a phenolphthalein indicator. Phenolphtalein is chosen because it changes color in a pH range
between 8.3 – 10. It will appear pink in basic solutions and clear in acidic solutions. In the case of a strong acid-strong base titration, this pH
transition would take place within a fraction of a drop of actual neutralization, since the strength of the base is high.
The addition of reactants is done from a burette. The reactant of unknown concentration is deposited into an Erlenmeyer flask and is called the
analyte. The other reactant of known concentration remains in a burette to be delivered during the reaction. It is known as the titrant. The
indicator—phenolphthalein, in this case—has been added to the analyte in the Erlenmeyer flask.

Titration: Titration of an acid-base system using phenolphthalein as an indicator.

Neutralization is the reaction between an acid and a base, producing a salt and neutralized base. For example, hydrochloric acid and sodium
hydroxide form sodium chloride and water:
HCl(aq)+NaOH(aq)→H2O(l)+NaCl(aq)HCl(aq)+NaOH(aq)→H2O(l)+NaCl(aq)
Neutralization is the basis of titration. A pH indicator shows the equivalence point —the point at which the equivalent number of moles of a base
have been added to an acid. It is often wrongly assumed that neutralization should result in a solution with pH 7.0; this is only the case in a strong
acid and strong base titration.

ศกั ดิพงศ์ 29

EXAMPLE:

What is the unknown concentration of a 25.00 mL HCl sample that requires 40.00 mL of 0.450 M NaOH to reach the equivalence point in a titration?

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

Step 1: First calculate the number of moles of NaOH added during the titration.

0.450molesLNaOH×0.0400L=0.018 moles NaOH0.450molesLNaOH×0.0400L=0.018 moles NaOH

Step 2: Use stoichiometry to figure out the moles of HCl in the analyte.
The mole ratio between HCl and NaOH in the balanced equation is 1:1.

0.018 moles NaOH×1 mole HCl1 mole NaOH=0.018 moles HCl0.018 moles NaOH×1 mole HCl1 mole NaOH=0.018 moles HCl

Step 3: Calculate the molar concentration of HCL in the 25.00 mL sample.

Molarity of HCl = 0.018 moles HCl0.025 L HCl=0.72 Molar HCl0.018 moles HCl0.025 L HCl=0.72 Molar HCl

Weak Acid-Strong Base Titrations

A weak acid will react with a strong base to form a basic (pH > 7) solution.

EXAMPLE:

The titration of acetic acid (HC2H3O2) with NaOH.

HC2H3O2+OH−→H2O+C2H3O−2HC2H3O2+OH−→H2O+C2H3O2−

During this titration, as the OH– reacts with the H+ from acetic acid, the acetate ion (C2H3O2–) is formed. This conjugate base reacts
with water to form a slightly basic solution.

C2H3O−2+H2O→HC2H3O2+OH−C2H3O2−+H2O→HC2H3O2+OH−

Strong Acid-Weak Base Titrations

A strong acid will react with a weak base to form an acidic (pH < 7) solution.

EXAMPLE:

In the titration of a weak acid with a strong base, which indicator would be the best choice?

A. Methyl Orange

B. Bromocresol Green

C. Phenolphtalein The correct answer is C. In the titration of a weak acid with a strong base, the conjugate base of the weak acid will make
the pH at the equivalence point greater than 7. Therefore, you would want an indicator to change in that pH range. Both methyl orange and
bromocresol green change color in an acidic pH range, while phenolphtalein changes in a basic pH.

ศกั ดิพงศ์ 29

Acid-base

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 the H + unequal difference, the first 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 H + as the 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 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 base. There are three
types of bases:

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

Question

1. From the Ge Yi theory Arrhenius and Brinstead Lautre bases Which substances
are classified as bases?Every day

A. CO32-HPO32- Cl - NH4 +
B.Na + Ca (OH) NO- NH3
C.OH32- HCO3 SO 42- NH3
D.KOH H2PO- H3O + SO 32-

Answer

C.OH32- HCO3 SO 42- NH3

2.Which of the following tests would you consider supporting the HCl ionization
theory?Dissolved

A The HCl solution can change the color of litmus paper from blue to red.
B.The fact that HCl acts as a metal to sift
C. The reaction of HCl with AgNO3Get white sediment
D. Where the electrolysis HCl (aq) has H2Occurs at negative point and Cl2

Born in the past

Answer

D. Where the electrolysis HCl (aq) has H2Occurs at negative point and Cl2
Born in the past

3. A weak acid, concentrated 1.0 mol / l, dissolves 10% of the same acid
when thickening 0.10 mol / l.How many percent is it going to be broken?
A. More than 10%
B. Less than 10%
C is equal to 10%
D equal to 100%

Answer

D equal to 100%

MS.NATTHAPORN YODCHALOOD NO.30 M.5/5

Acid–base definitions

Historic development
The concept of an acid-base reaction was first proposed in 1754 by Guillaume-

François Rouelle, who introduced the word "base" into chemistry to mean a substance which
reacts with an acid to give it solid form (as a salt).
Lavoisier's oxygen theory of acids

The first scientific concept of acids and bases was provided by Lavoisier in around
1776. Since Lavoisier's knowledge of strong acids was mainly restricted to oxoacids, such
as HNO3 (nitric acid) and H2SO4 (sulfuric acid), which tend to contain central atoms in
high oxidation states surrounded by oxygen, and since he was not aware of the true
composition of the hydrohalic acids (HF, HCl, HBr, and HI), he defined acids in terms of their
containing oxygen, which in fact he named from Greek words meaning "acid-former" (from
the Greek οξυς (oxys) meaning "acid" or "sharp" and γεινομαι (geinomai) meaning
"engender"). The Lavoisier definition held for over 30 years, until the 1810 article and
subsequent lectures by Sir Humphry Davy in which he proved the lack of oxygen
in H2S, H2Te, and the hydrohalic acids. However, Davy failed to develop a new theory,
concluding that "acidity does not depend upon any particular elementary substance, but upon
peculiar arrangement of various substances".[4] One notable modification of oxygen theory
was provided by Jöns Jacob Berzelius, who stated that acids are oxides of nonmetals while
bases are oxides of metals.

Chanthapha Thumphut M.5/5 No. 31

Liebig's hydrogen theory of acids
In 1838, Justus von Liebig proposed that an acid is a hydrogen-containing compound

whose hydrogen can be replaced by a metal.[5][6][7] This redefinition was based on his extensive
work on the chemical composition of organic acids, finishing the doctrinal shift from oxygen-
based acids to hydrogen-based acids started by Davy. Liebig's definition, while completely
empirical, remained in use for almost 50 years until the adoption of the Arrhenius definition.

Chanthapha Thumphut M.5/5 No. 31

Practice model

Fill in the missing message

A diagram of the apparatus at the end of the experiment.

Once the apparatus had cooled down, Lavoisier took the new measurements.
He discovered that 8 cubic inches of gas weighing exactly 3.5 grains (0.23 grammes) had
"disappeared" from the bell jar.
The mercury + calx in the retort flask has gained exactly 3.5 grains.
When he tested the gas left in the bell jar he found that it had lost its "active" ingredient. It no
longer supported combustion or respiration.
Lavoisier concluded that the Mercury had taken this "active gas" from the air.
Experiment 2: It was Joseph Priestley's observations on heating mercury calx that gave
Lavoisier the information he needed to move on. According to Priestley

Chanthapha Thumphut M.5/5 No. 31

The dissolution of strong acids and strong

bases is 100% disintegrated, meaning the disintegration of strong acids and bases. The ions
are depleted in solvents, mostly water, such as HCl acid dissociation, H + or H 3 O + and Cl - no
HCl residues or base dissociation, such as NaOH, Na + and OH -. There is no NaOH left.

Disintegration of strong acids

Strong acid refers to an acid that, when dissolved in water, is 100% ionized.

Examples of common strong acids are: Acid name

chemical formula

Hydrochloric acid (hydrochloric
HCl acid)

HBr Hydrobromic acid

HI Hydroiodic acid (hydroiodic acid)

HNO 3 Nitric acid
HClO 4 Perchloric acid (perchloric acid)
H 2 SO 4
Sulfuric acid

Ms. Chanita Kaewphiwart No.33 Class 5/5

Acid, HCl, HBr, the HI HNO 3 HClO 4 acid-1 molecules can break apart the one the H +, the
acid-1 molecules are broken down to 1 the H +, this acid Monmouth's pro Athletic (monoprotic)
the disintegration of strong acids Monte de pro. Stick It is similar in that it dissociates to
H + (which combines with water to form hydronium ions (H 3 O + )

and negative ions with the same concentration and acidityas equation
HA (aq) + H 2 O (l) ---- > A - (aq) + H 3 O + (aq)

Disintegration of the old bass

Old base refers to a base that, when dissolved in water, is 100% ionized.

Examples of old bases are: Lithium hydroxide
Sodium hydroxide (sodium hydroxide)
LiOH
NaOH Potassium hydroxide
KOH Rubidium hydroxide (rubidium hydroxide)
RbOH
CsOH Cesium hydroxide (cesium hydroxide)
Ca (OH) 2 Calcium hydroxide
Ba (OH) 2
Sr (OH) 2 Barium hydroxide (balium hydroxide)
Strontrium hydroxide

Hydroxide compounds of group 1, which have the general formula XOH, dissolve in water to

cation and hydroxide ions. By mole or cation concentration Hydroxide ions and bases are equal
XOH (aq) ----> X + (aq) + OH - (aq)
in equation.

Ms. Chanita Kaewphiwart No.33 Class 5/5

examination

1. Calculate [H 3 O + ], [NO 3 - ] in solution of 0.015 M HNO 3.
How to do HNO 3 + H 2 O → H 3 O + + NO 3 -

0.015
Therefore [H 3 O + ] = [NO 3 - ] = 0.015 mol / l.

2. If KOH 0.1 mol is soluble and solution has a volume of 2 liters in solution.
What ions are there, and how many moles per liter?
How to do KOH, (s,) → the K +, (AQ) +, OH More - (AQ).

0.1 mol / 2 l
2 liters of KOH solution contains 0.1 mol KOH.
1 liter of KOH solution has KOH = 0.05 mol / l.
Therefore, KOH will dissolve to K + and OH - each 0.05 mol / l.

3. A 250 cubic centimeter of strong acid (HA) solution has an amount of H 3 O + ions 0.05 mol.
What is the concentration of this solution? If more 0.2 moles of this acid were added, with the
solution having the same volume. What is the concentration of the resulting solution?
How to do HA → H 3 O + (aq) + A - (aq)

0.05 mol / 250 cm 3
HA 250 cm 3 solution contains HA 0.05 mol.
HA1000cm 3 solution has HA = 0.20 mol.
Therefore the solution has a concentration of 0.20 mol / l.
If we add 0.2 moles of acid.
The solution has a total of HA = 0.05 + 0.2 = 0.25 mol.
HA 250 cm 3 solution contains HA 0.25 mol.
HA1000cm 3 solution has HA = 1.00 mol.
Therefore the solution that has a concentration of 1.00 mol / L

According to:https://reanooanirut.wordpress.com

Ms. Chanita Kaewphiwart No.33 Class 5/5

Acid-Base

"Acid-base" redirects here. For chemicals that can behave as acids or bases, see Amphoterism.
An acid–base reaction is a chemical reaction that occurs between an acid and a base. It can be
used to determine pH. Several theoretical frameworks provide alternative conceptions of the reaction
mechanisms and their application in solving related problems; these are called the acid–base
theories, for example, Brønsted–Lowry acid–base theory.
Their importance becomes apparent in analyzing acid–base reactions for gaseous or liquid species,
or when acid or base character may be somewhat less apparent. The first of these concepts was
provided by the French chemist Antoine Lavoisier, around 1776.[1]

Acid Base Reaction Theories as superset and subset models.

It is important to think of the acid-base reaction models as theories that complement each
other.[2] For example, the current Lewis model has the broadest definition of what an acid and base
are, with the Brønsted-Lowry theory being a subset of what acids and bases are, and the Arrhenius
theory being the most restrictive.

Acid–base definitions[edit]

Historic development[edit]

The concept of an acid-base reaction was first proposed in 1754 by Guillaume-François Rouelle,
who introduced the word "base" into chemistry to mean a substance which reacts with an acid to
give it solid form (as a salt).[3]

Lavoisier's oxygen theory of acids[edit]

The first scientific concept of acids and bases was provided by Lavoisier in around 1776. Since
Lavoisier's knowledge of strong acids was mainly restricted to oxoacids, such as HNO
3 (nitric acid) and H
2SO
4 (sulfuric acid), which tend to contain central atoms in high oxidation states surrounded by oxygen,
and since he was not aware of the true composition of the hydrohalic acids (HF, HCl, HBr, and HI),
he defined acids in terms of their containing oxygen, which in fact he named from Greek words
meaning "acid-former" (from the Greek οξυς (oxys) meaning "acid" or "sharp" and γεινομαι
(geinomai) meaning "engender"). The Lavoisier definition held for over 30 years, until the 1810
article and subsequent lectures by Sir Humphry Davy in which he proved the lack of oxygen in H
2S, H2Te, and the hydrohalic acids. However, Davy failed to develop a new theory, concluding that
"acidity does not depend upon any particular elementary substance, but upon peculiar arrangement
of various substances".[4] One notable modification of oxygen theory was provided by Jöns Jacob
Berzelius, who stated that acids are oxides of nonmetals while bases are oxides of metals.

Liebig's hydrogen theory of acids[edit]

In 1838, Justus von Liebig proposed that an acid is a hydrogen-containing compound whose
hydrogen can be replaced by a metal.[5][6][7] This redefinition was based on his extensive work on the
chemical composition of organic acids, finishing the doctrinal shift from oxygen-based acids to
hydrogen-based acids started by Davy. Liebig's definition, while completely empirical, remained in
use for almost 50 years until the adoption of the Arrhenius definition.[8]

Arrhenius definition[edit]

Svante Arrhenius

The first modern definition of acids and bases in molecular terms was devised by Svante
Arrhenius.[9][10] A hydrogen theory of acids, it followed from his 1884 work with Friedrich Wilhelm
Ostwald in establishing the presence of ions in aqueous solution and led to Arrhenius receiving
the Nobel Prize in Chemistry in 1903.

As defined by Arrhenius:

• an Arrhenius acid is a substance that dissociates in water to form hydrogen ions
(H+);[11] that is, an acid increases the concentration of H+ ions in an aqueous solution.

This causes the protonation of water, or the creation of the hydronium (H3O+) ion.[note 1] Thus, in
modern times, the symbol H+ is interpreted as a shorthand for H3O+, because it is now known that a
bare proton does not exist as a free species in aqueous solution.[14]

• an Arrhenius base is a substance that dissociates in water to form hydroxide (OH−) ions;
that is, a base increases the concentration of OH− ions in an aqueous solution."

The Arrhenius definitions of acidity and alkalinity are restricted to aqueous solutions, and refer to the
concentration of the solvent ions. Under this definition, pure H2SO4 and HCl dissolved in toluene are
not acidic, and molten NaOH and solutions of calcium amide in liquid ammonia are not alkaline. This

led to the development of the Brønsted-Lowry theory and subsequent Lewis theory to account for
these non-aqueous exceptions.[15]

Overall, to qualify as an Arrhenius acid, upon the introduction to water, the chemical must either
cause, directly or otherwise:

• an increase in the aqueous hydronium concentration, or
• a decrease in the aqueous hydroxide concentration.

Conversely, to qualify as an Arrhenius base, upon the introduction to water, the chemical must either
cause, directly or otherwise:

• a decrease in the aqueous hydronium concentration, or
• an increase in the aqueous hydroxide concentration.

The reaction of an acid with a base is called a neutralization reaction. The products of this reaction
are a salt and water.

acid + base → salt + water

In this traditional representation an acid–base neutralization reaction is formulated as a double-
replacement reaction. For example, the reaction of hydrochloric acid, HCl, with sodium
hydroxide, NaOH, solutions produces a solution of sodium chloride, NaCl, and some additional
water molecules.

HCl(aq) + NaOH(aq) → NaCl(aq) + H2O

The modifier (aq) in this equation was implied by Arrhenius, rather than included explicitly. It
indicates that the substances are dissolved in water. Though all three substances, HCl,
NaOH and NaCl are capable of existing as pure compounds, in aqueous solutions they are
fully dissociated into the aquated ions H+, Cl−, Na+ and OH−.

The Brønsted–Lowry definition, formulated in 1923, independently by Johannes Nicolaus
Brønsted in Denmark and Martin Lowry in England,[16][17] is based upon the idea
of protonation of bases through the deprotonation of acids – that is, the ability of acids to
"donate" hydrogen ions (H+)—otherwise known as protons—to bases, which "accept"
them.[18][note 2]

An acid–base reaction is, thus, the removal of a hydrogen ion from the acid and its addition
to the base.[19] The removal of a hydrogen ion from an acid produces its conjugate base,
which is the acid with a hydrogen ion removed. The reception of a proton by a base
produces its conjugate acid, which is the base with a hydrogen ion added.

Unlike the previous definitions, the Brønsted–Lowry definition does not refer to the formation
of salt and solvent, but instead to the formation of conjugate acids and conjugate bases,
produced by the transfer of a proton from the acid to the base.[11][18] In this approach, acids
and bases are fundamentally different in behavior from salts, which are seen as electrolytes,
subject to the theories of Debye, Onsager, and others. An acid and a base react not to
produce a salt and a solvent, but to form a new acid and a new base. The concept of
neutralization is thus absent.[4] Brønsted–Lowry acid–base behavior is formally independent
of any solvent, making it more all-encompassing than the Arrhenius model. The calculation
of pH under the Arrhenius model depended on alkalis (bases) dissolving in water (aqueous
solution). The Brønsted–Lowry model expanded what could be pH tested using insoluble
and soluble solutions (gas, liquid, solid).

The general formula for acid–base reactions according to the Brønsted–Lowry definition is:

HA + B → BH+ + A−

where HA represents the acid, B represents the base, BH+ represents the conjugate
acid of B, and A− represents the conjugate base of HA.

For example, a Brønsted-Lowry model for the dissociation of hydrochloric acid (HCl)
in aqueous solution would be the following:
HCl + H2O ⇌ H3O+ + Cl−

The removal of H+ from the HCl produces the chloride ion, Cl−, the conjugate base of
the acid. The addition of H+ to the H2O (acting as a base) forms the hydronium ion,
H3O+, the conjugate acid of the base.

Water is amphoteric—that is, it can act as both an acid and a base. The Brønsted-
Lowry model explains this, showing the dissociation of water into low concentrations
of hydronium and hydroxide ions:
H2O + H2O ⇌ H3O+ + OH−

This equation is demonstrated in the image below:

Here, one molecule of water acts as an acid, donating an H+ and forming the
conjugate base, OH−, and a second molecule of water acts as a base, accepting
the H+ ion and forming the conjugate acid, H3O+.

As an example of water acting as an acid, consider an aqueous solution
of pyridine, C5H5N.
C5H5N + H2O ⇌ [C5H5NH]+ + OH−

In this example, a water molecule is split into a hydrogen ion, which is
donated to a pyridine molecule, and a hydroxide ion.

In the Brønsted-Lowry model, the solvent does not necessarily have to be
water, as is required by the Arrhenius Acid-Base model. For example,
consider what happens when acetic acid, CH3COOH, dissolves in liquid
ammonia.

The acid-base question

1.Calculate the concentration of the OH-ions in moles per liter in a 0.1 mol / liter 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
1.0* 10-13

2. If A and B are mixed together, A will act as an acid, B will act as a base, and which is B 8?

A. CH3COOH, HCl
B. Ba (OH) 2, NaHCO3
C. KCl CH3COONa
D. NaHCO3, NH3
Answer
NaHCO3, NH3

3. Which of the following substances or ions can be both an acid and a base?
1. H2O
2.HC2O4-
3.HS-
4.NO3-

Answer
NO3-

Ms.Piyada Sienprakhon Class m.5/5 No.34

Acid-Base Reactions

Acid–base reactions are essential in both biochemistry and industrial chemistry. Moreover,
many of the substances we encounter in our homes, the supermarket, and the pharmacy are
acids or bases. For example, aspirin is an acid (acetylsalicylic acid), and antacids are bases. In
fact, every amateur chef who has prepared mayonnaise or squeezed a wedge of lemon to
marinate a piece of fish has carried out an acid–base reaction. Before we discuss the
characteristics of such reactions, let’s first describe some of the properties of acids and bases.

Definitions of Acids and Bases

We can define acids as substances that dissolve in water to produce H+ ions, whereas bases
are defined as substances that dissolve in water to produce OH− ions. In fact, this is only one
possible set of definitions. Although the general properties of acids and bases have been
known for more than a thousand years, the definitions of acid and base have changed
dramatically as scientists have learned more about them. In ancient times, an acid was any
substance that had a sour taste (e.g., vinegar or lemon juice), caused consistent color changes
in dyes derived from plants (e.g., turning blue litmus paper red), reacted with certain metals to
produce hydrogen gas and a solution of a salt containing a metal cation, and dissolved
carbonate salts such as limestone (CaCO3) with the evolution of carbon dioxide. In contrast, a
base was any substance that had a bitter taste, felt slippery to the touch, and caused color
changes in plant dyes that differed diametrically from the changes caused by acids (e.g.,
turning red litmus paper blue). Although these definitions were useful, they were entirely
descriptive.

The Arrhenius Definition of Acids and Bases
The first person to define acids and bases in detail was the Swedish chemist Svante Arrhenius
(1859–1927; Nobel Prize in Chemistry, 1903). According to the Arrhenius definition, an acid is a
substance like hydrochloric acid that dissolves in water to produce H+ ions (protons; Equation
4.3.1 ), and a base is a substance like sodium hydroxide that dissolves in water to produce
hydroxide (OH−) ions (Equation 4.3.2 ):

→HCl(g)anArrheniusacid− −−H2O(l)H+(aq)+Cl−(aq)(4.3.1)
→NaOH(s)anArrheniusbase− −−H2O(l)Na+(aq)+OH−(aq)(4.3.2)

First, because acids and bases were defined in terms of ions obtained from water, the
Arrhenius concept applied only to substances in aqueous solution.
Second, and more important, the Arrhenius definition predicted that only substances that
dissolve in water to produce H+ and OH− ions should exhibit the properties of acids and
bases, respectively. For example, according to the Arrhenius definition, the reaction of
ammonia (a base) with gaseous HCl (an acid) to give ammonium chloride (Equation 4.3.3 )

→is not an acid–base reaction because it does not involve H+ and OH− :

NH3(g)+HCl(g) NH4Cl(s)(4.3.3)

The Brønsted–Lowry Definition of Acids and Bases
Because of the limitations of the Arrhenius definition, a more general definition of acids and
bases was needed. One was proposed independently in 1923 by the Danish chemist J. N.
Brønsted (1879–1947) and the British chemist T. M. Lowry (1874–1936), who defined acid–base
reactions in terms of the transfer of a proton (H+ ion) from one substance to another.
According to Brønsted and Lowry, an acid t can dissociate to form an anion and an H+ ion is
any substance that can donate a proton, and a base (a substance that produces one or more
hydroxide ions ( OH− and a cation when dissolved in aqueous solution, thereby forming a
basic solution) is any substance that can accept a proton. The Brønsted–Lowry definition of an
acid is essentially the same as the Arrhenius definition, except that it is not restricted to
aqueous solutions. The Brønsted–Lowry definition of a base, however, is far more general
because the hydroxide ion is just one of many substances that can accept a proton. Ammonia,
for example, reacts with a proton to form NH+4 , so in Equation 4.3.3 , NH3 is a Brønsted–
Lowry base and HCl is a Brønsted–Lowry acid. Because of its more general nature, the
Brønsted–Lowry definition is used throughout this text unless otherwise specified.