Uses in daily life
Uses in daily life
Uses in daily life
There are several methods of defining acids and
bases. While these definitions don't contradict
each other, they do vary in how
inclusive they are. Antoine Lavoisier,
Humphry Davy, and Justus Liebig also made
observations regarding acids and bases,
but didn't formalize definitions.
Arrhenius definition : Any substance that, when dissolved in
water, increases the concentration of hydronium ion (H3O+)
Bronsted-Lowry : A proton donor
Gilbert Newton Lewis : An electron acceptor
Properties of acids
taste sour (don't taste them!)... the word 'acid' comes
from the Latin acere, which means 'sour'
acids change litmus (a blue vegetable dye) from blue to
their aqueous (water) solutions conduct electric
current (are electrolytes)
react with bases to form salts and water
evolve hydrogen gas (H2) upon reaction with an active
metal (such as alkali metals, alkaline earth metals,
Classification of acids:
(break down completely to give off many H+ ions)
(only partially breaks down, gives less H+)
All others considered Weak (examples)
Acetic acid (vinegar)
Preparation of Acids
There are several methods of preparation of acids. These include the following:
By the reaction between an acidic oxide of a non-metal (acid anhydride)
SO2(g) + H2O(l) → H2SO3(aq) Trioxosulphate(IV)
P4O10(s) + 2H2O(l) → 4HPO3(aq) Trioxophosphate(V)
Displacement of a weaker of more volatile acid from its salt by a stronger
or less volatile acid.
NaCl(s) + H2SO4(aq) → NaHSO4(aq) + HCl(aq)
Na2B4O7(s) (Borax) + H2SO4(aq) + 5H2O(l) →
Na2SO4(aq) + 4H3BO3(aq) (trioxoborate(III) acid)
Displacement of insoluble sulphide from a metallic salt by hydrogen
Pb(C2H3O2)2(aq) + H2S(g) → PbS(s) + 2CH3COOH(aq) (Ethanoic acid)
Uses of Acids
Acids have numerous uses, some of which include:
HCl in stomach
H2SO4 in car batteries, as drying agent’
HNO3 in manufacturing of fertilizers
Ethanoic acid in food industry
Fatty acids in soap making
Ascorbic acid in medicine
bases produce OH- ions in aqueous solutions.
water required, so only allows for aqueous solutions
only hydroxide bases are allowed; required to produce hydrogen
Brønsted – Lowry:
bases are proton acceptors
bases besides hydroxides are permissible
Gilbert Newton Lewis:
bases are electron pair donors
least restrictive of acid-base definitions
Properties of Bases
taste bitter (don't taste them!)
feel slippery or soapy (don't arbitrarily touch them!)
bases don't change the color of litmus; they can turn
red (acidified) litmus back to blue
their aqueous (water) solutions conduct and electric
current (are electrolytes)
react with acids to form salts and water
Classification of Basis:
Strong bases :
A strong base is a basic chemical compound that deprotonates very weak
acids in an acid-base reaction. Common examples of strong bases include
hydroxides of alkali metals and alkaline earth metals like NaOH and Ca(OH)
Very strong bases can even deprotonate very weakly acidic C–H groups in
the absence of water. Here is a list of several strong bases:
By analogy with weak acids, weak bases are not strong enough
proton acceptors to react completely with water. A typical
example is ammonia, which reacts only to a limited extent:
NH3 + H2O NH4+ + OH–
Preparation of Bases:
There are various methods for the preparation of bases.
Reaction of oxygen with metals to form metal oxide:
Many metals react with oxygen gas to form the metal oxide. For example,
calcium reacts in the following manner.
2Ca(s) + O2(g) 2 CaO(s)
Thermal decomposition of carbonates:
Metal carbonates such as calcium carbonate break down when heated
strongly. This is called thermal decomposition. Here are the equations for
the thermal decomposition of calcium carbonate:
CaCO3 ―> CaO + CO2
By double decomposition reaction:
A chemical reaction between two compounds in which parts of each are
interchanged to form two new compounds
By dissolving basic oxides in water:
The oxides of feebly acidic cations react exothermically with water
producing the hydroxide.
CaO + H2O ‹―› Ca(OH)2
Uses of Bases:
Sodium hydroxide (caustic soda) is used in the manufacture of soap. It is
used in petroleum-refining; in making medicines, paper, pulp, etc. It is
used in making rayon.
Calcium hydroxide is also known as slaked lime. It is used to neutralize
acid in water supplies; in the manufacture of bleaching powder; as a
dressing material for acid burns; as an antidote for food poisoning; in the
preparation of fungicides and in the mixture of whitewash. It is mixed with
sand and water to make mortar which is used in the construction of
buildings. It is also used by farmers on the fields to neutralize the harmful
effects of acid rain.
Ammonium hydroxide is used to remove ink spots from clothes and to
remove grease from window-panes. It is used in the cosmetic industry.
Alkalis are used in alkaline batteries. Generally, potassium hydroxide is
used in such batteries.
When H+ ion of an acid is replaced by a metal ion, a salt is
H2SO4(aq) + 2NaOH(aq) ==== Na2SO4(aq) + 2H2O(l)
Here sodium sulphate (Na2SO4) is the salt formed. Salts are ionic
The chemical symbol for table salt is NaCl
Properties of salts
Most of the salts are crystalline solid.
Salts may be transparent or opaque.
Most of the salts are soluble in water.
Solution of salts conducts electricity. Salts conduct electricity in their
molten state also.
The salt may be salty, sour, sweet, bitter and umami (savoury).
Neutral salts are odourless.
Salts can be colourless or of coloured.
Classification of Salts
There are different kinds of salts. These include:
1. Normal salt
The hydrogen ions of the acid are completely replaced by metallic ions .
Examples are NaCl, CuSO4, KNO3, and CaCO3. Normal salts are
2. Acid salt
The salt still has hydrogen atom(s) from an acid which can further be
replaced by metallic ions. Examples include: NaHSO4, NaHCO3 and
3. Basic salt
The salt contains hydroxides together with metallic ions and negative ions
from an acid. Examples are basic zinc chloride, ZnOHCl, basic
4. Double salt
Salt that ionizes to produce three different types of ions in
solution, two of these are usually positively charged and the
other negatively charged. Examples are ammonium iron(II)
tetraoxosulphate(VI) hexahydrate, (NH4)2 Fe(SO4)2.6H2O;
potash alum or aluminium potassium tetraoxosulphate(VI)
dodecahydrate, KAl(SO4)2. 12H2O; and chrome alum or
chromium(III) potassium tetraoxosulphate(VI) dodecahydrate,
5. Complex salt
The salt contains complex ions, i.e. ions consisting of a charged
group of atoms. Examples are sodium tetrahydroxozincate(II)
Preparation of salts
Hydrolysis of Salts
When salts dissolve in water they are hydrolyzed. The reaction between a salt
and water to give either acidic or basic solution is known as hydrolysis.
Hydrolysis involves the split of water molecules into its ions, H+ and OH-.
These ions then get attracted to the opposite ions of the salt. The degree of
attraction determines which ion, i.e. H+ or OH- will be more in solution,
thereby resulting in the solution being acidic (more H+ in solution) or basic
(more OH- in solution) or neutral (equal conc. of H+ and OH- in solution).
The nature of the resultant solutions depends on the nature of the salts:
Salts formed from strong acids and strong bases (example, NaCl – HCl +
These salts give neutral solutions (the H+ and OH- an attracted to the opposite
ions of the salt in the same degree). Example, for the hydrolysis of NaCl,
H+ and OH- ions are attracted at equal ease to Cl- and Na+ respectively to
from HCl and NaOH.
Therefore, the solution contains equal concentration of H+ and OH- ions.
Salts formed from strong acids and weak bases (example, NH4Cl –
HCl + NH3)
Solutions of these salts are acidic (i.e. conc. of H+ is more than that of
OH-). The OH- ions are attracted more to the positive ions of the salts
than the H+ ions are attracted to the negative ions.
Example, for the hydrolysis of NH4Cl, OH- ions are attracted more to
NH4+ than H+ ions attracted to Cl- ions. Hence, there is more
concentration of H+ ions in solution, which results in the solution
Salts formed from weak acids and strong bases (e.g. NaHCO3 –
NaOH + H2CO3 ; Na2CO3 – NaOH + H2CO3)
The solutions are basic (i.e. the concentration of OH- ions is more than
that of H+ ions). This is because H+ ions are more attracted to the
negative ions of the salt than OH- ions attracted to the positive ions of
lt will be acidic if the acid salt is formed from a strong
acid, example, NaHSO4 (the hydrogen atom will be furnished in
solution as the only positive ion).
Salts formed from weak acids and weak bases (e.g. (NH4)2CO3)
The solutions of these salts are neutral (equal attraction between the
positive ions of the salt and OH- ions of water; and the negative ions of
salt and H+ ions of water. Hence equal concentration of H+ and OH- are
Example, when NaCl is hydrolysed, it produces HCl and NaOH - from
which it was initially produced with the elimination of water
Uses of Salts
In torch batteries
As drying agent
In Iron tablets
In gunpowder etc.
In making soap.
The negative logarithm of the hydronium ion concentration of an aqueous
solution; used to express acidity.
• pH is the measure of the acidity
or basicity of a solution.
• The pH scale ranges from 1 to 14
• 1 through 6 being acidic
• 7 is considered neutral
• 8 through 14 being basic
pH is a way to measure how acidic or basic a solution is
Low pH values = acids
High pH values = bases
pH measures the concentration of hydrogen ions = H+
If a hydrogen atoms (1 proton, 1 electron), loses its electron,
what is left?
So, H+ is also referred to as a proton
The pH scale ranges from 1 to 10-14 mol/L or from 1 to 14.
pH = - log [H3O+]
1 2 3 4 5 6 7 8 9 10 11 12 13 14
Algebraic manipulation of:
pH = - log [H3O+]
[H3O+] = 10-pH
If pH is a measure of the hydronium ion concentration
then the same equations could be used to describe the
hydroxide (base) concentration.
[OH-] = 10-pOH
pOH = - log [OH-]
pH + pOH = 14 ; the entire pH range!
• ACID - A class of compounds whose water solutions taste
sour, turn blue litmus to red, and react with bases to form
• BASE - A class of compounds that taste bitter, feel slippery
in water solution, turn red litmus to blue, and react with
acids to form salts.
• Salt - These are items that are neither acids or bases.