This document provides information about acid-base chemistry including: 1. Acids and bases are defined, and indicators like litmus paper are described for testing acidity and basicity. 2. The pH scale is introduced to measure acidity and alkalinity, and examples of strong and weak acids and bases are given. 3. Common acids, bases, and salts are described including their properties and reactions. Processes like neutralization, ionization, and the formation of soap as a salt are explained.

1. Standard/ Class/ Grade - X SSC, CBSE; - VIII ICSE
Acid-Base Chemistry
Gurudatta K Wagh

2. Contents
Acids and Bases
Indicators
Strengths of acids and bases
Importance of pH
Acids, bases and their reactivity
Ionization of acids and bases
Various salts
Water of crystallization
Soap as a salt

6. Standard 10 Chapter 3 Acid-Base Chemistry
Acids and Bases
‘Acidus’ in Latin means sour. Bases are bitter.
Indicators
Indicators indicate the acidic and basic nature of
compounds
Litmus paper or solution is obtained from lichens. Blue
litmus turns red in acids. Red litmus turns blue in
bases.
Universal indicator is a mixture of several indicators.

7. Types of indicators
Natural Synthetic
rose petals,
turmeric, beet root
phenolphthalein,
methyl orange, eosin
Turmeric paper
Methyl orange
Phenolphthalein
Litmus paper

8. Strengths of acids and bases
A universal indicator shows different colours in
different concentrations of hydrogen in a solution
pH helps in measuring hydrogen ion concentration in
solutions.
p - Potenz - means strength in German
pH scale 0-14
0 = most acidic; 7 = neutral; 14 = most alkaline/basic
pOH represents strength of base
Acids H+ Bases OH-
hydrogen ions hydroxyl ions

9. Like dissolves like
Based on the principle of solubility acidity can be
controlled by acidic substance mixed with basic
substance.
E.g. Lime water with butter having butyric acid can
cure acidity. Jaggery with tamarind in cooking helps
maintain body pH.
Lime water means a saturated solution of calcium
hydroxide Ca(OH)2. [Here, lime water is not lemon
water.] It is basic in nature. Hence, it cures acidity,
aids digestion.

10. We mix butter containing butyric acid for two reasons:
1. Lime water being strong, is difficult to eat. Butter
makes it mild and easy to eat, 2. It also starts
neutralization reaction.
Lime called Choona is used in India in paan, a mixture
of areca nuts, calcium hydroxide and a variety of
seeds wrapped in betel leaves, and as a substitute
for baking soda in making papadam

11. Importance of pH
Rain pH of rain water is < 7 (acidic). It lowers the pH of
river water. Aquatic life gets affected. Human body
works within the pH range 7.35-7.45.

12. Human body Tooth enamel is made up of hard matter
calcium phosphate. Food particles are degraded by
bacteria in the mouth to produce acid with pH < 6 and
corrode phosphates to cause tooth decay.
Hydrochloric acid HCl produced in the stomach helps
in digestion of food. The acidity/ indigestion problems
can be controlled by adding basic substances called
antacids.

13. Supplementary information
Calcium phosphate is the name given to a family of
minerals containing calcium ions (Ca2+) together with
orthophosphates (PO4
3−), metaphosphates or
pyrophosphates (P2O7
4−) and occasionally hydrogen
or hydroxide ions. Monocalcium phosphate,
Ca(H2PO4)2, Dicalcium phosphate, CaHPO4,
Tricalcium phosphate, Ca3(PO4)2

14. Acids, bases and their reactivity
• Reactivity with metals
Acid + metal → salt + hydrogen
Mg(s) + 2HCl(aq) → MgCl2(aq) + H2(g)
Hydrogen is displaced by the active metal from the
acid.
Metal combines with remaining part of the acid and
forms compound called salt
Base + metal → salt + hydrogen
2Al + 2NaOH + 2H2O → 2NaAlO2 + 3H2

15. • Reactivity of acids towards carbonates and
bicarbonates of metals
Acid + metal carbonate → metal salt + water + carbon
dioxide
When CO2 is passed through lime water [saturated
solution of calcium hydroxide Ca(OH)2], it turns lime
water milky. Here chalk powder (calcium carbonate
CaCO3) in water can be used in place of lime water.
Na2CO3(s) + 2HCl(aq) → 2NaCl(aq) + H2O(l) + CO2(g)

16. • Reactivity of acids with metallic oxides
metal oxide + acid → salt + water
CuO + 2HCl → CuCl2 + H2O
Blue coloured copper chloride solution is formed
• Reactivity of base with non-metallic oxides
(Neutralization)
calcium hydroxide + carbon dioxide → calcium
carbonate + water
Ca(OH)2(aq) + CO2(g) → CaCO3(s) + H2O(l)

17. • Reactivity of acid and base with each other
(Neutralization)
acid + base → salt + water
2-3 ml dil HCl in test tube + 1-2 drops
phenolphthalein indicator.
Add NaOH solution dropwise to the test tube.
End point is colourless to pink.
HCl(aq) + NaOH(aq) → NaCl(aq) + H2O

18. Difference between alkali and base
• Alkali is a base that dissolves in water.
• All alkalis are bases but all bases are not alkalis.
• Alkalis are soapy to touch, bitter to taste and
corrosive.
• Tasting or touching an alkali is harmful.

20. Ionization of acids and bases
25 ml sugar solution in 100 ml beaker. Dip two carbon
electrodes. Connect the electrodes to two terminals of
a 6 volt battery through a bulb and switch.
If glucose and methyl alcohol is used bulb will not
glow because ions are not formed in these solutions.

22. • Behaviour of acid and base in an aqueous
medium
Separation of HCl into H+ and Cl- ions will be possible
in presence of water. The process is termed as
ionization.
Hydrogen ions cannot exist alone. They will always
combine with water and form hydronium ion H3O+
H+ + H2O → H3O+
Bases like NaOH when dissolved in H2O (aq) undergo
reactions as follows:
NaOH(S) + H2O → Na+
(aq) + OH-
(aq)

23. In aqueous medium acids generate H+ (Hydrogen
ions) and bases generate OH- (Hydroxyl ions).
The perfect reaction for neutralization can be viewed
as: acid + base → salt + water
HA + BOH → BA + H20
A = anion e.g. Cl-, Br-, I-, NO3
-, etc.
B = cation e.g. Na+, K+, Ca++,etc.)
The H+ ions of acid and OH- ions of alkali react with
each other to form unionized water.
H+
(aq) + OH- (aq) → H20(l)

24. Various salts
It is possible to identify the acids and bases from
which salts are obtained.
pH = 7 strong acid X strong base
pH < 7 strong acid X weak base
pH > 7 weak acid X strong base

25. • Common salt NaCl
Strong acid HCl and strong base NaOH react
together to form salt sodium chloride NaCl
NaCl(s) + aqs → Na+
(aq) + Cl-
(aq)
Impure sodium chloride NaCl is brown in colour and
is known as rock salt. Purified sodium chloride is
colourless, crystalline ionic compound. It is
fundamental ionic compound used in preparation of
other salts as Na2CO3, NaHCO3 etc.

26. Electrolysis of NaCl in solution and in fused state yield
different products
1.When electricity is passed through solution of
sodium chloride, which is termed as brine (10%
NaCl), it decomposes to form sodium hydroxide, an
important basic compound.
2NaCl(aq) + 2H2O(l) → 2NaOH(aq) + Cl2(g) + H2(g)
Cl2(g) is liberated at anode and H2(g) at cathode,
respectively

27. 2. When salt is heated at high temperature
the molten state is termed as fused state.
NaCl is able to conduct electricity even in fused state.
During electrolysis Cl2(g) is liberated at anode and
sodium is deposited at cathode.

28. • Sodium bicarbonate NaHC03 (Baking soda)
What is added to the cake to make it spongy?
The white amorphous powdered soda is termed as
baking soda. Its chemical name is sodium hydrogen
carbonate or sodium bicarbonate and its formula is
NaHC03.
When tested with litmus, NaHC03 turns red litmus
blue, which indicates that it is alkaline in nature.
When heated strongly it
decomposes as follows:
2NaHCO3 + H2O + CO2

29. Sodium bicarbonate is extensively used in day-to-day
life.
It is used to prepare light and spongy bread, cakes
and dhokala.
Being alkaline it also helps to reduce acidity in
stomach.
It is very useful in preparing C02 gas and is one of the
contents of fire extinguishers.

30. Supplementary information
Baking soda and baking powder
Baking soda and baking powder are both leaveners,
however they are chemically different.
What is Baking Soda?
Bicarbonate of soda or sodium bicarbonate.
What is Baking Powder?
Baking powder contains baking soda. It is a mixture of
baking soda, cream of tartar (Potassium bitartrate,
also known as potassium hydrogen tartrate, with
formula KC4H5O6, is a byproduct of winemaking. In
cooking it is known as cream of tartar) and sometimes
cornstarch.

31. • Bleaching powder CaOCl2
The white powder which is generally sprinkled to
disinfect any place which is not clean is also used to
disinfect water. You must have experienced the typical
strong odour from well water during the rainy season.
The white powder is called bleaching powder and the
strong odour is due to chlorine gas which is released
when bleaching powder is added to water.

32. When dry slaked lime reacts with chlorine gas, it
forms bleaching powder
Ca(OH)2(s) + Cl2(g) → CaOCl2(s) +H2O(l)
When bleaching powder comes in contact with
atmospheric C02 gas, it forms CaC03(S) and Cl2(g).
This Cl2(g) helps in the bleaching action on cotton in
the textile industry, wood pulp in paper factories and
washed clothes in laundry.

33. Bleaching powder acts as an oxidizing agent in many
chemical reactions and is useful in preparation of
organic solvent chloroform which is also used as an
anesthetic.
Bleaching powder is also known as chloride of lime
and the chlorine generated is known as ‘available
chlorine’. The bleaching powder brands available in
the market are classified on the basis of percentage of
available chlorine present in them.

34. • Sodium carbonate Na2CO3 (Washing soda)
Sodium bicarbonate NaHC03 is a white crystalline
solid readily soluble in H20. NaHC03 on decomposition
forms sodium carbonate whose formula is
Na2C03.10H20.
When tested with litmus paper, it turns red litmus blue,
indicating its basic nature.
When sodium carbonate reacts with HCl, C02 is
evolved.
Na2C03 + 2HCl → 2NaCl + H20 + C02
Na2C03.10H20 has wide applications.

35. Supplementary
information

36. Washing soda is used in washing clothes as a
cleansing agent. It is very useful in manufacturing
detergent powder, paper and glass. It is also used to
refine petroleum.
What makes water hard?
Presence of chlorides and sulphates of Ca and Mg
make water hard. Na2C03 plays a very important role
to make it soft and potable.

37. Water of crystallization
Take few crystals of copper sulphate CuSO4
in a boiling test tube. Heat the test tube.
Does the colour of copper sulphate
change?
What is seen on the inner side of the test
tube?
The droplets of water on sides of the test tube are
known as 'water of crystallization'. They are the fixed
number of water molecules present in the crystal
structure. 0n heating or on exposure to air, salts lose
water of crystallization and turn into substance which
is termed as anhydrous substance.

38. Soap as a salt
When oil or fats are boiled with aqueous solution of
sodium hydroxide (NaOH) or potassium hydroxide
(KOH), then sodium or potassium salt of carboxylic
acids [carboxyl group -COOH] are obtained. These
salts are known as soap. The process of alkaline
hydrolysis of oils or fats is known as saponification.

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