The three main categories of chemical compounds are acids, bases and salts. These compounds are always part of our daily lives in terms of what we eat and use. The human body contains some very common acids like dilute hydrochloric acid in the stomach, which aids in digestion of food. If the contents of our stomach become too acidic, it results to a burning sensation in the stomach. Acids and bases also regulate metabolic activities in the human body through equilibrium processes. Acids contain hydrogen ions (H+). A base is a substance, which on dissolving in water yields hydroxyl ions (OH-) as the only negative ions. Salts are formed by the combination of an acid and base.

1. ACIDS, BASES AND
SALTS
By Prof. Liwayway Memije-Cruz

2. Acids, Bases and Salts
 Acids, bases and salts are three main
categories of chemical compounds. They have
certain definite properties which distinguish
one class from the other.

3. ACIDS

4. Acids
 contain hydrogen ions (H+
)
 The word 'acid' is derived from a Latin
word, which means "sour".

5. Examples of acids

6. Properties of Acids
 Acid is a compound which yields
hydrogen ion (H+
), when dissolved in
water.
 Acid is sour to the taste and corrosive in
nature. The pH value for acids is less
than 7.
 Generally, all acids readily react with
metal to release hydrogen gas. For
example, metal zinc reacts with
hydrochloric acid to form zinc chloride

7.  Acids react with limestone (CaCO3) to produce
carbon dioxide. For example, hydrochloric acid
reacts with limestone to produce carbonic acid
and calcium chloride.
 Acids can be classified into organic and
inorganic acids. Acetic acid (CH3COOH) is the
best example of organic acid, and acids
produced from minerals are termed as
inorganic acids like sulfuric acid (H2SO4),
hydrochloric acid (HCl), etc.
 Acid turns blue litmus paper to red in color.

8.  Acids have a tendency to corrode
metal surfaces quickly.
 Phenolphthalein solution is colorless
in an acidic solution and turns methyl
orange solution to red. Red cabbage
juice which is purple in color changes
to red in an acidic medium.

9. On the basis of number of hydrogen
ion, acids can be classified as:
 Monoprotic acid – Such type of acids
produce one mole of H+
ions per mole of
acid, e.g., HCl, HNO3, etc.
 Diprotic acid – They can produce two
moles of H+
ions per mole of acid, e.g.,
H2SO4.
 Triprotic acid – They produce three moles
of H+
ions per mole of acid, e.g., H3PO4.

10. On the basis of strengths or capacity to
donate hydrogen ions, acids can be
described as:
 Strong acids: Which are completely (100%)
ionized in aqueous solutions. Hence at
equilibrium, the concentration of acid
molecules is very less and concentration of
hydrogen ion reaches to maximum, e.g., HCl,
HNO3, HClO4.
 Weak acids: They are only partially ionized in
solution at equilibrium state. At equilibrium
state, acid molecules are present and the
concentration of hydrogen ion is less, e.g., HF,
CH3COOH.

11. Strong Acids
 HCl - hydrochloric acid
 HNO3 - nitric acid
 H2SO4 - sulfuric acid
 HBr - hydrobromic acid
 HI - hydroiodic acid (also known as hydriodic
acid)
 HClO4 - perchloric acid
 HClO3 - chloric acid

12. BASES

13. Bases
 a substance, which on
dissolving in water
yields hydroxyl ions
(OH-
) as the only
negative ions. A base
may be an oxide or a
hydroxide of a metal. If
a base is soluble in
water, it dissociates to
form a metal ion and it
is the only negative
hydroxyl ion (OH-
).

14. Properties of Bases
 Bases are compounds which yield
hydroxide ion (OH-
), when dissolved
in water.
 Bases are bitter to taste and
corrosive in nature. They feel slippery
and soapy.
 Bases are good conductor of
electricity and show a pH value of
more than 7.

15.  Bases react with oils and grease to
form soap molecules.
 Bases convert red litmus paper to
blue in color.
 Bases also have the tendency to
corrode metal surfaces.

16.  A reaction between a base and a metal is
similar as for acid to form salt and release
hydrogen gas. But this reaction can only occur
when a metal is strong enough to displace
another metal from its parent constituent.
2NaOH+ Zn → Na2ZnO2 + H2
 Phenolphthalein solution turns pink in color in a
basic solution. Bases turn methyl orange to
yellow. Red cabbage juice which is purple in
color changes to yellow in a basic medium.

17. Strength of bases
 Strong bases: They are completely
ionized in water to produce hydroxide
ions, e.g, sodium hydroxide: NaOH(s) Na⇌ +
(aq) + OH-
(aq)
 Weakbases: Partially ionize and
equilibrium lies mostly towards reactants
side, e.g., ammonia in water: NH3(aq) + H2O(l)
NH⇌ 4
+
(aq) + OH-
(aq)

18. Arrhenius concept of Acid
 Arrhenius concept is the oldest concept to
explain acids and bases. According to this
concept.
An acid is a hydrogen containing compound
which can give hydrogen ion (H+
) in aqueous
solution.
For example, Hydrochloric acid (HCl) gives H+
ion in its aqueous solution.
HCl(g) → H2O
H+
(aq) + Cl-1
(aq)
Such types of acids are called Arrhenius acids,
like nitric acid (HNO ), acetic acid (CH COOH),

19. Arrhenius concept of Bases
 Base is also a hydrogen containing
compound, which can give hydroxide ion (OH-
)
in an aqueous solution. For example, Sodium
hydroxide in water form s sodium ion (Na+
)
and hydroxide ion (OH-
). Such type of bases
are known as Arrhenius bases. Other example
of Arrhenius base are ammonium hydroxide
(NH4OH), aluminium hydroxide (Al(OH)3) and
magnesium hydroxide(Mg(OH)2).
NaOH(s) → H2O
Na+
(aq) + Cl-1
(aq)

20. Salts

21. Properties of salts
 Salts form by the combination of acid and base
through neutralization reaction.
 The acidic and basic nature of salts depends on
the acid and base combined in neutralization
reaction.
 The most common salt is sodium chloride or
table salt which forms by the combination of
sodium hydroxide (base) and hydrochloric acid.
Other examples include Epsom salts(MgSO4)
used in bath salts, ammonium nitrate (NH4NO3)
used as fertilizer, and baking soda (NaHCO3)

22. Examples of Salts

23. The pH Concept
 The pH scale takes its name from the words
po te ntialo f hydro g e n. It is a scale used to
measure the acidity or alkalinity of a solution.
The pH scale uses a range from 0 to 14, with
7.0 indicating neutrality. Numbers beginning at
7.0 and moving toward 0 indicate acidity, while
the numbers beginning at 7.0 and moving
toward 14 indicate alkalinity, so the scale
divides acids from bases. We owe the concept
of pH to Danish chemist S. P. L. Sørensen, who
introduced it in 1909.

24. pH Scale

25. pH
 is the negative of the logarithm of the
H3O+
ion concentration.
pH = - log [H3O+
]

26. pOH
 is the negative of the logarithm of the
OH-
ion concentration.
pOH = - log [OH-
]
pH + pOH = 14

27. References:
 http://chemistry.tutorvista.com/inorganic-
chemistry/acids-bases-and-salts.html
 http://cbc-wb01x.chemistry.ohio-
state.edu/~woodward/ch121/ch4_acids.htm
 http://chemistry.about.com/od/acidsbase1/a/str
ong-acids-list.htm
 http://www.wisegeek.org/what-is-the-ph-
scale.htm
 http://chemed.chem.purdue.edu/genchem/topi
creview/bp/ch17/ph.php