Modern Graded Science 10

Zinc + Sulphuric acid Zinc sulphate + Hydrogen [word equation]

Zn + dil. H2SO4 ZnSO4 + H2↑ [formula equation]

Reactants Products

This equation consists of two parts. They are reactants and products, which are
separated by an arrow (→). The direction of the arrow indicates chemical changes in
reactants into products. The reactants are those substances that undergo a chemical
change during a chemical reaction. They are always written on the left-hand side of the
chemical equation before the arrow.

Likewise, products are those substances which are formed as a result of the chemical
change in the reactants. They are always written on the right-hand side of the chemical
equation, after the arrow. In the above equation, zinc and sulphuric acid are the reactants
while zinc sulphate and hydrogen are the products.

The chemical equation may be unbalanced or balanced. The chemical equation in
which the number of atoms of different elements in reactions in not equal to the products
is called unbalanced equation. For example,

Nrea2c+tanHts2 prNodHuct3 [unbalanced chemical equation]

In this chemical equation, the number of nitrogen and hydrogen atoms in the reactants
is not equal to the number of them in the product. So, the equation is called an unbalanced
equation.

According to law of conservation of mass, mass can neither be created nor destroyed
during a chemical reaction. So, total mass of reactants must be equal to the total mass of
the product(s). Therefore, we should always express the chemical reaction as balanced a
chemical equation. For example,

Nrea2c+tan3tHs 2 pro2duNctH3 [balanced chemical equation]

The chemical equation is which the number of atoms of different reacting elements is
equal to the number of their atoms in the product(s) is called a balanced chemical equation.

Types of chemical reactions

There are many types of chemical reactions taking place in the nature. To make
systematic study and their sequential forms, all the chemical reactions are grouped into
common classes. The following are the principal classes or types of chemical re actions.

1. Addition or synthesis or combination reaction

2. Decomposition or dissociation or analysis reaction

3. Displacement or replacement reaction

4. Acid-base or neutralization reaction

1. Combination reaction
When a single compound is formed by the direct combination of two or more reactants

during a chemical reaction, the process is called combination reaction. This is also called
synthesis reaction. The reactions may occur by the application of heat, light, electricity or
pressure.

CHEMICAL REACTION CLASS - 10 MODERN GRADED SCIENCE 147

Examples:

a. When sodium combines directly with chlorine to form sodium chloride:

2Na + Cl2 2NaCl

b. When iron fillings are heated with sulphur, ferrous sulphide is produced:

Fe + S ∆ FeS

c. When nitrogen and hydrogen gases are heated together in the presence of catalyst Fe/
Mo at 200 - 900 atmosphere, ammonia is obtained:
N2 + 3H2 500°C/900atm/ Fe/Mo 2NH3

d. When potassium combines with chlorine to form potassium chloride:

2K + Cl2 2 KCl

e. When sodium combines with oxygen to form sodium oxide:

4Na + O2 2Na2O

f. When aluminium combines with nitrogen to form aluminium nitride:

2Al + N2 2AlN

g. When iron combines with oxygen to form iron oxide:

4Fe + 3O2 2Fe2O3

2. Decomposition reaction

When a single compound or The photographic film used in a camera is coated
substance is decomposed into two or with silver bromide. When the light of the object
more simple molecules in the form of falls on the coated film while taking a snap,
products during a chemical reaction, it is a chemical reaction occurs. The film is taken
called decomposition reaction. This is also in the developer where the reaction takes place
called analysis reaction. The reaction can changing the silver bromide into silver. The film
also be brought about by the application is then called a negative.
of light, heat, electricity, etc.

Examples:

a. When lead oxide is heated, it decomposes into lead and oxygen.
2PbO ∆ 2Pb + O2

b. When potassium chlorate is heated in the presence of catalyst MnO2, it forms
potassium chloride and oxygen.

2KClO3 ∆/MnO2 2KCl + 3O2

c. When calcium carbonate is heated, it decomposes into calcium oxide and carbon dioxide:
CaCO3 ∆ CaO + O2

d. When water is electrolysed, it gives hydrogen and oxygen:
2H2O electrolysis 2H2 + O2

e. When silver bromide undergoes decomposition in the presence of light, it changes
into silver and bromine:
2AgBr light 2Ag + Br2

148 MODERN GRADED SCIENCE CLASS - 10 CHEMICAL REACTION

f. When ultraviolet rays of the sunlight affect the oxygen at the stratosphere of
atmosphere, it changes into ozone.
3O2 ultraviolet rays O2Ozo3ne

g. When hydrogen peroxide is treated with a catalyst manganese dioxide, it gives
oxygen gas and water.
2H2O2 MnO2 2H2O + O2↑

3. Displacement reaction

The chemical reaction in which an atom or a group of atoms in the molecule is replaced
by another atom or a group of atoms, it is called displacement reaction. It is also called
substitution or replacement reaction. There are two types of displacement reactions:

I. Single displacement reaction II. Double displacement reaction

I. Single displacement reaction: In this chemical reaction, an atom in a molecule is
replaced by another atom forming the end products.

Examples:

a. When zinc reacts with dilute sulphuric acid, hydrogen gas is liberated and zinc
sulphate is formed.

Zn + H2SO4 ZnSO4 + H2

b. When zinc reacts with copper sulphate solution, copper is obtained along with the

solution of zinc sulphate.

Zn + CuSO4 ZnSO4 + Cu

c. When potassium reacts with hydrochloric acid, hydrogen displaces the potassium,

hydrogen is evolved and potassium chloride is obtained.

2K + 2HCl 2KCl + H2

d. When calcium reacts with sulphuric acid, hydrogen gas is produced and calcium

sulphate is obtained.

Ca + H2SO4 CaSO4 + H2

II. Double displacement reaction: The reaction in which two compounds react together

to form two other compounds by mutual exchange of their ions is called double

decomposition reaction.

Examples:

a. When a solution of silver nitrate is treated with a solution of sodium chloride, a white
precipitate of silver chloride is formed.

AgNO3 + NaCl AgCl + NaNO3

b. When a solution of mercuric chloride is treated with a solution of potassium iodide,

a precipitate of mercuric iodide is formed.

HgCl2 + 2Kl 2KCl + HgI2.

c. When a solution of calcium chloride is treated with a solution of silver nitrate, calcium

nitrate and silver chloride are formed.

CaCl2 + 2AgNO3 Ca(NO3)2 + 2AgCl

CHEMICAL REACTION CLASS - 10 MODERN GRADED SCIENCE 149

4. Acid-base reaction

Acid base reaction is double displacement reaction of acid and base. In it an acid
reacts with a base, in which the characteristic properties of both of them are destroyed
or neutralized to give salt and water. Such reaction is called acid-base reaction or
neutralization reaction. This reaction is simply expressed as,

acid + base salt + water

Examples:

a. When sodium hydroxide is treated with hydrochloric acid, sodium chloride and
water are formed.

NaOH + HCl NaCl + H2O

b. When sulphuric acid reacts with calcium oxide, the reaction gives calcium sulphate

and water.

H2SO4 + CaO CaSO4 + H2O

c. When potassium hydroxide reacts with nitric acid, potassium nitrate and water are

formed.

KOH + HNO3 KNO3 + H2O

d. When calcium oxide is treated with hydrochloric acid to form calcium chloride and

water:

CaO + 2HCl CaCl2 + H2O

Memorize the following: :

Combination reaction : A+B AB

Decomposition reaction : AB A+B

Single displacement reaction : AB + C CB + A

Double displacement reaction : AB + CD CB + AD

Acid base reaction : A+B S+W

Rate of chemical reaction

Chemical reactions take place in varying rates. Some chemical reactions are so rapid
that they occur as soon as the reactants change into products. For example, when sodium
reacts with water, it gives hydrogen and sodium hydroxide very fast. On the other hand,
there are certain chemical reactions which take place at an extremely slow rate. For
example, rusting in iron occurs so slowly that we feel no reaction is taking place at all.

The knowledge about the rate of a chemical reaction is essential from industrial point of
view. From industrial point of view, it might be necessary to accelerate most of the reactions
and some others to slow down for careful control of some violently explosive reactions.

The rate of chemical reaction is defined as the change in the concentration of any one
of the reactants or products per unit time to complete the reaction.

Rate of chemical = change in concentration of a reactant or a product
time take for the change

The rate of chemical reaction depends upon different conditions such as concentration
of reactants, temperature, catalyst, nature of reactants, etc.

150 MODERN GRADED SCIENCE CLASS - 10 CHEMICAL REACTION

Factors or conditions required in a chemical reactions

Some factors play an important role during chemical reaction. Some of them are as
follows:

1. Surface area: If the surface area of two or more reactants is small, the rate of chemical
reaction is slow. This is because there is a less chance of contact between them. But, if
their surface area is large, there is a great chance of collision course together and the
reaction rate is increased. Thus, to increase the reaction rate, the reactants are taken
with larger surface areas.

When, large-sized granulated zinc is treated with dilute hydrochloric acid, they react
together rapidly and form hydrogen gas and zinc chloride.

Zn + dil. 2HCl ZnCl2 + H2↑
Activity 8.1

To demonstrate that the rate of chemical reaction increases with the increase of surface
area.

Materials required:

Apparatus: Watch glasses, glass rod, beakers, grinders.

Chemicals: Marble pieces, powder of marble or calcium carbonate, dilute hydrochloric
acid.

Method:

1. Take two beakers and pour 50 ml of dilute hydrochloric acid in each.

2. Weigh 10 gm marble pieces and 10 gm marble powder take them in separate watch
glasses.

3. Add marble pieces in the beaker marked as A and marble powder in the beaker
marked as B.

4. Observe each beaker. In which beaker do air bubbles release out rapidly or effervesce
more.

Observation:

The air bubbles release out more rapidly from mixture B which contains marble powder
and dilute hydrochloric acid than from the beaker A that contains marble pieces.

Result:

The marble powder has more surface area than that of the marble pieces of same mass
and the rate of chemical reaction between marble powder and dilute hydrochloric acid
takes place faster. Therefore, the rate of chemical reaction increases with the increase of
the surface area or physical state of the reactants.

2. Catalyst: In some reactions, a catalyst changes the speed of a chemical reaction without
undergoing any chemical change. For example, manganese dioxide (MnO2) acts as a
catalyst in the decomposition of potassium chlorate on heating at low temperature.
At the end of the chemical reaction, the amount of catalyst remains similar to that of
the beginning.

2KClO3 MnO2 /240°C 2KCl + 3O2↑

CHEMICAL REACTION CLASS - 10 MODERN GRADED SCIENCE 151

3. Pressure: Pressure is also one of the most important conditions for a chemical reaction.
Some chemical reactions take place by the application of pressure. For example, when
sulphur and potassium chlorate are mixed together and placed under high pressure,
they explode loudly. Similarly, nitrogen reacts with hydrogen under high pressure to
give ammonia gas.

200 - 900 atm 2NH3
N2 + 3H2 500°C, Fe & Mo
(2 vols)
(1 vol) (3 vol)

4. Heat: Most of the reactions take place only

when the reactants are heated with high In chemical reactions, if the volume of

temperature. Heat also increases the rate of reactants is more than that of products,

chemical reaction. For example, there is fast the reaction needs high pressure whereas if

reaction between copper and sulphuric acid the volume of reactants is less than that of

on heating and SO2 gas is produced. products, the reaction needs low pressure.

Cu + Conc. 2H2SO4 ∆ CuSO4 + SO2 + 2H2O

Activity 8.2

To demonstrate that the rate of chemical reaction increases with the increase of
temperature.

Materials required:

Apparatus: beakers, tripod, wire gauze, spirit lamp or Bunsen's burner, glass rod, match
stick.

Chemicals: Potassium thiosulfate (K2S2O3), dilute sulphuric acid (H2SO4), potassium
permanganate (KMnO4), water, oxalic acid [C2H2O4 or (COOH)2]

Method:

1. Take 5 gm of oxalic acid crystals in two beakers each and mark A and B.

2. Pour 15 ml dilute sulphuric acid and then 10 ml of potassium permanganate
solution one by one in each beaker.

3. Stir the mixture of each beaker with a glass rod and the mixture of solution in both
the beakers appears pink.

4. Heat the solution of beaker A with a spirit lamp or Bunsen's burner for about 50°C
to 70°C and leave the solution of beaker B for about one hour without disturbance.

5. Observe the change of colour of the solution in each beaker. Does the pink colour of
the solution of both beakers disappear at the same period of time?

Observation:

The pink colour of the solution of beaker A is decolorized while heating but the solution
of beaker B takes long time to decolourize at ordinary temperature.

Result:

The rate of chemical reaction between oxalic acid, dilute sulphuric acid and potassium
permanganate solution is faster due to increase in temperature on heating.

5. Light: Some reactions require light. Light stimulates the reactants for chemical
reaction. For example, hydrogen reacts violently with chlorine in the presence of
diffused sunlight to produce hydrogen chloride.

H2 + Cl2 sunlight 2HCl

152 MODERN GRADED SCIENCE CLASS - 10 CHEMICAL REACTION

In the presence of sunlight, green plants manufacture food in the form of glucose
using carbon dioxide and water as raw materials.
Sunlight

6H2O + 6CO2 Chlorophyll C6H12O6 + 6O2

Catalyst

A catalyst is defined as a chemical substance that changes the rate of chemical reaction
itself without undergoing any permanent chemical change during the course of a chemical
reaction. The process of changing the rate of a chemical reaction by the use of a catalyst is
called catalysis. Catalysts are of two types: positive catalysts and negative catalysts.

The catalyst which increases the rate of chemical reactions is called a positive catalyst.
For example, manganese dioxide (MnO2) acts as a positive catalyst in the decomposition
of hydrogen peroxide without heating. This is because it increases the decomposition rate
of hydrogen peroxide.
2H2O2 MnO2 2H2O + O2↑

The catalyst which decreases the rate of chemical reactions is called a negative
catalyst. For example, glycerine [C3H5(OH)3] acts as a negative catalyst. It decreases the
rate of reaction during the decomposition of hydrogen peroxide into water and oxygen.
2H2O2 glycerine 2H2O + O2

Properties of catalyst
1. A catalyst remains unchanged in its mass and chemical composition in the chemical

reaction.
2. A small quantity of a catalyst is required.
3. A catalyst does not initiate the chemical reaction but it alters the rate of the undergoing

chemical reaction.

Endothermic reaction and exothermic reaction

There are two types of chemical reactions on the basis of heat energy released or absorbed
during chemical reaction. They are endothermic reaction and exothermic reaction.

The reactions in which heat is absorbed from the surroundings are called endothermic
reactions. The compounds formed by absorption of heat are called endothermic
compounds. Some examples of endothermic reactions are as follows:

CaCO3 + heat CaO + CO2 ↑
2KClO3 + heat 2KCl + 3O2 ↑
N2 + O2 + heat 2NO

Nitric oxide

The reactions in which heat energy is released to the surroundings are called
exothermic reactions. The compounds formed by exothermic reactions are called
exothermic compounds. Some examples of the exothermic compounds are carbon
dioxide, water, slaked lime, zinc chloride, etc.

C(s) + O2(g) CO2(g) + heat

2H2(g) + O2(g) 2H2O(l) + heat

CaO(s) + H2O(l) Ca (OH)2 (aq slaked lime) + large amount of heat

Zn(s) + 2HCl(aq) ZnCl2(aq) + H2(g) + heat

CHEMICAL REACTION CLASS - 10 MODERN GRADED SCIENCE 153

S me Reasonable Facts

1. Glycerine [C3H5(OH)3] is known as a negative catalyst because it decreases the rate of
chemical reaction.

2. The conversion of wood into ash on burning is a chemical change because the chemical
composition and properties get changed permanently and a new substance is formed.

Things To Know

1. A chemical change is a permanent change in which a new substance with different

properties is formed.

2. A chemical equation is the symbolic presentation of a chemical reaction in terms of

symbols and formulae.

3. During the reactions, heat energy is released to the surroundings; such reactions are

called exothermic reactions.

4. During the reactions, heat is absorbed from the surroundings; such reactions are

called endothermic reactions.

5. The main conditions required for a chemical reaction are surface area of reactants,

pressure, heat, light and catalyst.

6. A chemical reaction is a process of converting one or more substances into other new

substances.

7. The main four types of reactions:

a. combination reaction b. decomposition reaction

c. displacement reaction and d. acid-base reaction

8. The chemical substance that alters the rate of a chemical reaction is called a catalyst.

9. The catalyst that increases the rate of a chemical reaction is called a positive catalyst.

10. The catalyst that decreases the rate of a chemical reaction is called a negative catalyst.

Things To Do

Take two test tubes and put a small piece of magnesium in each. Add little dilute
hydrochloric acid in one test tube and little acetic acid in another one. Observe the rate of
reactions taking place in both the test tubes. In which test tube is the reaction faster and
why? Write in your notebook.
Repeat this activity taking calcium carbonate instead of magnesium and observe the
reactions. Note in which test tube the reaction is faster and why?

Test Yourself

1. Multiple choice questions (MCQs).

a. The exchange of ions or groups between two substances takes place in ………

reaction.

A. combination B. double displacement

C. addition D. neutralization
b. CaCo3 ∆ ZnSO4 + H2↑ represents. B. single displacement reaction

A. combination reaction

C. exothermic reaction D. endothermic reaction

154 MODERN GRADED SCIENCE CLASS - 10 CHEMICAL REACTION

c. Which necessary condition is required by green plants to make glucose as food

using carbon dioxide and water?

A. sun light B. heat

C. catalyst D. pressure

d. The reaction between hydrogen and sulphur to produce hydrogen sulphide is

…… reaction.

A. decomposition B. synthetic

C. neutralization D. displacement

e. Zn + dil. H2SO4 ZnSO4 + H2↑ represents:

A. neutralization B. addition

C. single displacement D. double displacement

f. Which one of the following undergoing reactions is a neutralization reaction?

A. Zinc reacts with dilute hydrochloric acid.

B. Sodium reacts with chlorine.

C. Calcium carbonate reacts with sulphuric acid.

D. Sodium hydroxide reacts with hydrochloric acid.

g. Nitrogen reacts with hydrogen to form ammonia gas. Out of the given necessary

conditions, which one is not required?

A. UV light B. high pressure

C. Iron catalyst D. high temperature

h. Heat is absorbed in …… reaction.

A. endothermic B. exothermic

C. reversible D. neutralization

2. Answer the following questions.

a. Define exothermic reaction? Give an example.

b. What are the conditions required for a chemical reaction? Explain any three with

an example.

c. Name the chemical reaction in which two substances exchange ions?

d. Explain the following types of chemical reactions with an example.

i. addition reaction ii. single displacement reaction

iii. decomposition reaction iv. double displacement reaction

e. What is acid-base reaction with an example.

f. How do combination and decomposition reactions differ from each other?

g. Write the characteristics of a catalyst.

h. Define the following terms.

i. endothermic reaction ii. chemical reaction

i. Describe a n experiment to demonstrate that the rate of chemical reaction

increases with the increase of the surface area of the reactants.

j. Describe an experiment to demonstrate that the rate of chemical reaction increases

with the increase of temperature.

k. Write the balanced chemical equation of the reaction between nitrogen and

hydrogen to ammonia which is carried out by different necessary conditions.

Which type of chemical reaction is it? Define it.

CHEMICAL REACTION CLASS - 10 MODERN GRADED SCIENCE 155

3. Differentiate between:
a. Physical change and chemical change
b. Exothermic reaction and endothermic reaction
c. Positive catalyst and negative catalyst

4. Give reasons.
a. Glycerine is known as a negative catalyst.
b. Paper burns to ash is a chemical change.
c. Acid base reaction is also called a neutralization reaction.
d. Physical change is a temporary change.

5. Change the following word equations into balanced equations.

a. Hydrogen + Chlorine Hydrogen chloride

b. Lead oxide + Carbon Carbon monoxide + Lead

c. Hydrogen + Nitrogen Ammonia

d. Potassium chlorate Potassium chloride + Oxygen

e. Aluminium + Chlorine Aluminium chloride

f. Zinc + Hydrochloric acid Zinc chloride + Hydrogen

g. Magnesium + Sulphuric acid Magnesium sulphate + Hydrogen

h. Ammonium chloride + Sodium nitrite Sodium chloride + Water + Nitrogen

i. Aluminium + Sulphuric acid Aluminium sulphate + Hydrogen

j. Lime water + Carbon dioxide Calcium carbonate + Water

k. Sodium carbonate + Silica Sodium silicate + Carbon dioxide

l. Ammonia + Sulphuric acid Ammonium sulphate

m. Iron + Oxygen Iron oxide

n. Aluminium + oxygen Aluminium oxide

o. Phosphorus + oxygen Phosphorus pentoxide

6. Fill in the gaps and balance the following equations.

a. CuCO3 ∆ .................. + ..................

b. CH4 + O2 .................. + H2O

c. 6HCl + .................. AlCl3 + ..................

d. Mg(HCO3)2 .................. + .................. + CO2

e. 2Al + 3H2SO4 .................. + H2↑

f. HNO3 + .................. NH4NO3 + ..................

g. Ca(OH)2 + .................. CaCO3 + ..................

h. .................. KCl + O2

i. H2O2 H2O + ..................

Radiation : rays and atomic particles from radioactive substances
Explosive : likely or able to explode easily
Collision : the act of striking to each other

156 MODERN GRADED SCIENCE CLASS - 10 CHEMICAL REACTION

Chapter ACID, BASE AND SALT

9 Total estimated periods: 9 (T 7 + P 2)

define acid, base and salt.
explain the general characteristics of acid, base and salt.
differentiate between acid and base.
describe the use of acid, base and salt in our daily life.

We have already learnt that a large number of compounds are used in our daily life.
So, it is essential to study the composition and properties of these compounds. But it is
practically impossible to study all the compounds at a time. Therefore, they are classified
as acid, base and salt. Acids like citric acid, tartaric acid, ascorbic acid, etc. are present in
different fruits and vegetables which we use as foodstuffs. Bases like caustic soda used
for making soap and lime are used for white washing. They are also used for neutralizing
acidic soils. In the same way, different kinds of salts are used as medicines while we
eat common salt or kitchen salt daily. However, acids, bases and salts are essentially
important for human beings.

In this unit, we are going to study about acids, bases and salts and their preparation,
properties and uses.

Acids

The word acid is derived from the Latin word 'acidus' meaning sour, since sour taste
is one of the characteristics of this category of substances. The first acid known to human
was acetic acid in the form of vinegar.

In 1884 AD, S. Arrhenus, a Swedish chemist put forward the ionic theory of ionisation.
According to this theory, when acids, bases and salts are dissolved in water, they ionise
into ions or charged particles.

These ions can conduct electricity in the aqueous solution. According to the ionic
theory– "an acid is defined as the substance which gives hydrogen ions or protons (H+)
when dissolved in an aqueous solution and that tastes sour." Hydrochloric acid (HCl),
sulphuric acid (H2SO4), nitric acid (HNO3), hydrobromic acid (HBr), chloric acid (HClO3)

ACID, BASE AND SALT CLASS - 10 MODERN GRADED SCIENCE 157

acetic acid (CH3COOH) and carbonic acid (H2CO3) are some examples of acid. All acids
dissociate in water to form H+ ions. For example,

HCl H+ + Cl–

H2SO4 2H+ + SO4– –
HNO3 H+ + NO3–
HBr H+ + Br–

H2CO3 H+ + HCO3–

CH3COOH H+ + CH3COO–

H3PO4 3H+ + PO4– – –

According to the modern concept, acids dissociate and give hydrogen ions in

the aqueous solution. Such hydrogen ions cannot exist as such in the solution. They

immediately combine with water molecule to produce hydrated hydrogen ions or

hydronium ions.

HCl H+ + Cl–

H+ + H2O H3O+
HCl + H2O H3O+ + Cl–

These hydrogen ions or hydronium ions are responsible for the properties of acids.

For example, acids are sour in taste and they turn blue litmus paper into red.

Classification of acid

On the basis of strength, acids are classified into two types. They are strong acids and
weak acids.

A. Strong acids: Those acids which dissociate almost completely into their ions in an
aqueous solution to produce more hydrogen ions (H+) are called strong acids. The
production of hydrogen ions and also the reaction arrow, that only points to the right
(irreversible) all of the strong acid (reactant) is ionised into ions (product).

For example:

HNO3 H+ + NO3 –
HCL H+ + Cl –

Hydrochloric acid, sulphuric acid, nitric acid, chloric acid, etc. are strong acids. They
are also called mineral acids and are used in laboratory. Strong acids have high degree
of ionization and they can conduct electricity very easily. They react more vigorously
with metals to produce hydrogen gas. They have a low pH value.

B. Weak acids: Weak acids are those which do not completely ionise into their ions in
an aqueous solution. They produce less hydrogen ions (H+) due to partial ionisation.
The other molecules remain unchanged in acids.

For example, hydrofluoric acid (HF) ionises into H+ and F– ions in an aqueous
solution, but some hydrofluoric acids (HF) remain in the solution. Most of the organic
acids like oxalic acid (C2H2O4), acetic acid (CH3COOH), formic acid or methanoic acid
(HCOOH), citric acid (C6H8O7) and other acids like carbonic acid (H2CO3), phosphonic
acid (H3PO4) sulphurous acid (H2SO3), etc. are weak acids.

158 MODERN GRADED SCIENCE CLASS - 10 ACID, BASE AND SALT

For example:

CH3COOH H+ + CH3COO –

(ethanoic acid) (acetate or ethanoate ion)

At any one time, only about 1% of acetic acid converts into ions, the other remains as
simple acetic acid in solution. The reaction proceeds in both directions.

Weak acids are poor conductors of electricity. They have high pH value. They react
slightly with metals to produce hydrogen gas steadily. The reaction arrow in the chemical
equation points to both directions (reversible). They are less corrosive acids.

Note

Hydrofluoric acid (HF) is an extremely corrosive but weak acid. It is not a strong acid like HCL
because it does not dissociate completely into ions in water. Also hydrogen ion (H+) and fluoride
ion (F–) are strongly attracted to each other.

Difference between strong and weak acids

Strong Acid Weak Acid

1. It undergoes almost complete 1. It undergoes very less ionisation to

ionization to give more concentration give less concentration of hydrogen

of hydrogen. ions.

2. Most of the mineral acids are strong 2. All the organic acids and a few mineral

acids. acids are weak acids.

3. It is more corrosive in nature. 3. It is less corrosive in nature usually.

Example: Sulphuric acid. Example: Acetic acid.

On the basis of sources of origin, acids are classified into two types: organic acid and
inorganic acid.

A. Organic acids: The acids which are obtained from living organisms and contain
carbon in their molecular structures, are called organic acids. They do not completely
dissociate in water. These acids contain functional group, the carboxyl (–COOH).
Tartaric acid, citric acid and acetic acid are some examples of organic acids. Formic
acid or methanoic acid (HCCOH) is found in ant bites ad nettle sting.

B. Inorganic acids: The acids which are
obtained from minerals found on
the earth's crust and do not contain
carbon atoms in their molecular Carbonic acid (H2CO3) contains carbon atom but
structures are called inorganic acids. it is obtained from minerals and has electrovalent
(Carbonic acid is exceptional). They bonding. Thus, this acid is called inorganic.
can also be prepared in laboratories Litmus, methyl orange and phenolphthalein are
and industries. They are also called indicators. They are indicated by the range of
mineral acids. They may be strong or colour whether a solution is acidic or alkaline.
weak. Hydrochloric acid, sulphuric They also show the end of a chemical reaction by
acid, carbonic acid, phosphoric acid, changing colour.
boric acid (H3BO3) and nitric acid, etc.
are inorganic acids. Hydrochloric acid is also produced inside the stomach though
it is taken as an inorganic acid because it has no carbon atom. Most of the inorganic

ACID, BASE AND SALT CLASS - 10 MODERN GRADED SCIENCE 159

acids are widely used in laboratories. Sulphuric acid is called king of acid because of
its high application in industries and laboratories.

Difference between organic acids and mineral acids

Organic acids Mineral acids

1. They are organic compounds with 1. They are inorganic compounds with

acidic properties. acidic properties.

2. They are obtained from living 2. They are obtained from minerals

organisms, i. e. plants and animals. present on the earth's crust.

3. Generally, they are weak acids. 3. Generally, they are strong acids.

4. They contain carbon. 4. Usually, they do not contain carbon.

5. Generally they are insoluble in water 5. Generally they are soluble in water

but soluble in organic solvents. but insoluble in organic solvents.

6. They are poor conductors of electricity. 6. They are poor as well as good

Example: Citric acid conductors of electricity. Example:

Nitric acid

Characteristics of acids

1. Acids have a sour taste. But acids like stearic acid, boric acid, salicylic acid do not have
a sour taste. Fruits like lemon, grapes, vinegar, milk, tomatoes, coca-cola, etc. contain
citric acid, tartaric acid, acetic acid, lactic acid, oxalic acid, carbonic acid respectively.
These are edible acids. It is dangerous to taste all the mineral acids.

2. Strong acids are corrosive in nature i. e. they eat away skin, metal, wood, etc.

3. Acids turn blue litmus paper to red, light yellow colour of methyl orange to red,
phenolphthalein to colourless and purple cabbage juice into red.

4. They react with metals like zinc, magnesium, iron, etc. to form salt and hydrogen.

Mg + H2 SO4 Mg SO4 + H2↑

Zn + H2 SO4 Zn SO4 + H2↑

Zn + 2HCl Zn Cl2 + H2↑

2Al + 6HNO3 2Al(NO3)2 + 3H2↑

5. Acids react with carbonates and bicarbonates to give carbon dioxide, salt and water.

2HCl + Na2CO3 2NaCl + H2O + CO2↑

H2SO4 + Mg CO3 Mg SO4 + H2O + CO2↑

2HCl + Ca (HCO3)2 CaCl2 + 2H2O + CO2↑

HNO3 + NaHCO3 NaNO3 + H2O + CO2↑

H2SO4 + Mg(HCO3)2 MgSO4 + 2H2O + 2CO2↑

6. Acids react with base to give salt and water.

2HCl + CaO CaCl2 + H2O
HCl + NaOH NaCl + H2O
Ca(OH)2 + 2HCl
KOH + HNO3 CaCl2 + H2O
KNO3 + H2O

160 MODERN GRADED SCIENCE CLASS - 10 ACID, BASE AND SALT

7. They give off hydrogen ion (H+) when dissolved in water. They conduct electricity.

HCl H+ + Cl–

H2SO4 2H+ + SO4– –

Uses of acids

1. Sulphuric acid is used for making chemical fertilizers like (NH4)2 SO4, NH4NO3, etc.;
drugs and detergents.

2. Nitric acid is used in manufacturing chemical fertilizers like NH4NO3, explosive and
plastics.

3. Hydrochloric acid is used for bleaching purpose in textile industries, for making
glue, etc.

4. Carbonic acid is used in soft drinks like soda water, coca cola, etc.
5. Acetic acid is found in vinegar which is used for flavour.
6. Tartaric acid is used in baking powder.
7. Many acids are used for medicines e.g. ascorbic acid is used in the treatment of scurvy.
8. Citric acid functions as a source of vitamin C. It is found in citrus fruit.
9. Boric acid is used for washing eyes and wounds.
10. Carbolic acid (C6H5OH), also known as phenol is used as an antiseptic and germ

killer.
11. Phosphoric acid helps to form nucleic acids (DNA and RNA).

Base

Metallic oxides and hydroxides which are bitter in taste and give hydroxyl ions (OH¯)
if they dissolve in water are called bases. Sodium oxide (Na2O), potassium oxide (K2O),
magnesium oxide (MgO), calcium oxide (CaO), zinc oxide (ZnO), ferric oxide (Fe2O3),
aluminium oxide (Al2O3), sodium hydroxide (NaOH), calcium hydroxide [Ca(OH)2 etc.
are some examples of bases.

In other words, bases are metal oxides and hydroxides that react to give salt and
water.

NaOH + HCl NaCl + H2O

The hydroxyl ions (OH–) are responsible for the properties of bases. Bases are bitter in

taste. They turn red colour litmus into blue, etc.

Ammonium hydroxide (NH4OH) is a common alkali but generally differs from other
alkalis because it does not contain a metal. Here, ammonium ion (NH4+) acts like a positive
radical. Some other alkalis are NaOH, KOH, Ca(OH)2.

Mercuric oxide, cupric oxide, ferric oxide, etc. are some other types of bases. Since
they are oxides of metals and insoluble in water, they are not alkalis. Therefore, all alkalis
are bases but all bases are not alkalis.

Classification of bases

On the basis of strength, or amount of hydroxyl ions (OH–) produced when dissolved in
water, bases are classified into two types: strong bases and weak bases.

ACID, BASE AND SALT CLASS - 10 MODERN GRADED SCIENCE 161

A. Strong bases

If almost all the molecules of bases undergo ionization to produce high concentration
of hydroxyl (OH–) in an aqueous solution, they are called strong bases. Sodium hydroxide,
calcium hydroxide, potassium hydroxide, etc. are some examples of strong bases. Their
dissociation reaction is irreversible.

For example: KOH K + OH–

B. Weak bases

Those bases which do not undergo almost complete ionization in an aqueous solution
and produce low concentration of hydroxyl ions (OH–) are weak bases. Ferric hydroxide
[Fe(OH)3], copper hydroxide [Cu(OH)2], ammonium hydroxide [NH4OH], etc. are some
examples of weak bases. Their dissociation reaction is reversible.

For example: NH4OH NH4+ + OH–

Difference between bases and alkalis

Bases Alkalis

1. All metallic oxides are called bases. 1. Water soluble metallic oxides and
hydroxides are called alkalis.

2. They may or may not be soluble in 2. They are soluble in water. Example,

water. Example, CaO, K2O, CuO, etc. NaOH, NH4OH, KOH, etc.

Characteristics of bases

1. Bases are bitter in taste and feel soapy when touched.

2. They turn red litmus paper to blue, colourless phenolphthalein to pink, methyl

orange to yellow and purple cabbage juice into green.

3. Bases react with acids to form salt and water.

NaOH + HCl NaCl + H2O

Ca(OH)2 + 2HCl CaCl2 + 2H2O

NaOH + CH3COOH CH3 COONa + H2O

NH4OH + HNO3 NH4 NO3 + H2O

4. Alkalis react with carbon dioxide to produce carbonate salt and water e.g.

2NaOH + CO2 Na2CO3 + H2O

Ca (OH)2 + CO2 CaCO3 + H2O

5. Alkalis react with ammonium salts on heating to produce ammonia gas.

(NH4)2 CO3 + Ca (OH)2 ∆ 2NH3↑ + CaCO3 + 2H2O
NH4Cl + NaOH ∆ NH3↑ + NaCl + H2O

6. When alkalis like sodium hydroxide and ammonium hydroxide mix with copper

sulphate and ferric chloride salts separately, they react together and give insoluble

precipitates of copper hydroxide and ferric oxide respectively.

CuSO4 + 2NaOH Cu (OH)2 ↓ + Na2 SO4

Insoluble

FeCl 3 + 3NH4OH FInes(oOluHbl)e3 ↓ + 3NH4Cl

162 MODERN GRADED SCIENCE CLASS - 10 ACID, BASE AND SALT

7. Water soluble bases (alkalis) from OH¯ ions by dissolving in water:

NaOH Na+ + OH¯

Ca(OH)2 Ca++ + 2OH¯

Uses of bases

1. Caustic soda (NaOH) is used for the manufacture of soap, paper and rayon. It is also
used in refining petroleum products.

2. Ammonium hydroxide [NH4OH] is used for making chemical fertilizers, dyes and
different types of plastics. It is also used as a laboratory reagent.

3. Slaked lime [(Ca(OH)2] is used for whitewashing of buildings. Its solution is used as
a laboratory reagent. Its solid form is used to make bleaching powder. It can be used
as an antidote for acid poisoning.

4. Caustic potash (KOH) is used for the preparation of soft soaps.
5. Quick lime (CaO) is used for softening hard water. It is also used for manufacturing

cement.
6. Milk of magnesia [Mg(OH)2] and aluminium hydroxide [Al(OH)3] are used as antacid

for reducing hyperacidity of the stomach.
Difference between acid and base

Acid Base

1. Acid gives off hydrogen ions when 1. Base gives off hydroxyl ion when

dissolved in water. dissolved in water.

2. It turns blue litmus paper into red. 2. It turns red litmus paper into blue.

3. It has a sour taste. 3. It has a bitter taste.

4. It is usually sticky. 4. It is slippery or soapy.

5. Its pH value is below 7. 5. Its pH value is above 7.

Example: HCl, H2SO4, etc. Example: NaOH, KOH, etc.
6. Acids are proton donors. 6. Bases are proton acceptors.

Salts

Salts are formed by the neutralization of acid with

base. Salt is defined as a compound which is formed

of the partial or complete replacement of one or more The acidic property of an acid is due
hydrogen atoms of an acid by one or more metal to the presence of hydrogen ions
atom(s) or positive radical(s). Examples: NaCl, KCl, (H+) while that of a base or alkali
Na2SO4, MgSO4, etc is due to the presence of hydroxyl
(OH–) ions in them.
For example, sodium chloride (NaCl) is a salt
which is formed by the replacement of one atom of

hydrogen by one sodium atom. Similarly, sodium

hydrogen sulphate and sodium sulphate are the salts which are formed by partial and

complete replacement of one atom of hydrogen by one sodium atom.

NaOH + HCl NaCl + H2O

NaOH + H2SO4 NaHSO4 + H2O (partial displacement)

2NaOH + H2SO4 Na2SO4+ 2H2O (complete displacement)

ACID, BASE AND SALT CLASS - 10 MODERN GRADED SCIENCE 163

Each salt molecule contains two radicals. One is acid radical and the other is basic

radical. The radicals that come from acids and bases are acid radicals and basic radicals

respectively. In the molecule of CuSO4, Cu is a basic radical whereas SO4 is an acid
radical. The basic radical forms positive ion and the acid radical forms negative ion when

dissolved in water.

CuO + H2SO4 CuSO4 + H2O
CuSO4
Cu+ + + SO4 – –
cation anion

Kinds of salt

Depending upon pH value, there are five kinds of salts. They are normal salt, acidic
salt, basic salt, hydrated salt and anhydrous salt.

1. Normal or neutral salt: Neutral salts are those salts which are prepared by the
reaction of strong acids and strong bases or weak acids and weak bases. e.g. NaCl,
K2SO4, KNO3, (NH4)2CO3, KCl, etc. are some neutral salts. Normal salts are neutral
to litmus paper. When HCl, a strong acid reacts with NaOH, a strong base, then the
resulting salt is neutral. Normal salts are formed when all the replaceable hydrogen
ions in the acid have been completely replaced by metallic ions of bases. For example,

HCl + NaOH NaCl + H2O

(aq) (aq) (s) (l)

sodium chloride

2. Acidic salt: Those salts which are produced by

the reaction of strong acids and weak bases are

called acidic acids. Acidic salt is also produced When a weak acid and a weak base react
by the partial displacement of hydrogen atom with each other, complete neutralization
of an acid molecule by a metal or electro- does not occur due to incomplete
positive radical. It is acidic in nature, ionization of the acid and base.

For example,

H2SO4 + KOH KHSO4 + H2O
NaH2PO4 + H2O
H3PO4 + NaOH Na2HPO4 + 2H2O

H3PO4 + 2NaOH (aq) (l)
(aq) (aq)

Acid salts are produced only by acids containing more than one replaceable hydrogen
ion. Therefore, an acid with the replaceable ions e.g. Acid salt turns blue litmus to
red. In the presence of excess metallic ions, an acid salt is converted into normal salt
as its replaceable hydrogen ions become replaced.

For example,

KHSO4 + KOH K2SO4 + H2O

Sodium bisulphate (NaHSO4), copper sulphate (CuSO4), ammonium nitrate
(NH4NO3), etc. are some of the examples of acidic salts.

3. Basic salt: Basic salt is produced by partial replacement of hydroxyl ions of the base by

the acid radical. Thus, those salts which are produced by the reaction of weak acids and

strong bases are called basic salts. It is alkaline in nature. Sodium acetate (CH3COONa),

164 MODERN GRADED SCIENCE CLASS - 10 ACID, BASE AND SALT

sodium carbonate, zinc hypochloride, lead hypochloride, sodium carbonate, calcium
bicarbonate etc. are some basic salts. Basic salts contain hydroxyl ions (OH–). They are
produced when insufficient acid is allowed for the complete neutralization of the base.
They turn red litmus to blue. They react with excess acid to form normal salt.

For example:

NaOH + H2CO3 Na2CO + H2O
KOH + CH3COOH CH3COOK + H2O

4. Hydrated salts: Those salt which contain certain amount of water, are called hydrated
salts. In other words, the salts which contain water of crystallization or water of
hydration are called hydrated salts.

Examples:

Sodium carbonate decahydrate Na2CO3.10H2O
Sodium sulphate decahydrate Na2SO4.10H2O
Magnesium sulphate heptahydrate (Epsom salt) MgSO4.7H2O
Copper II sulphate pentahydrate (Blue vitrol) CuSO4.7H2O
Zinc sulphate heptahydrate (White vitrol) ZnSO4.7H2O
Calcium sulphate heptahydrate (Gypsum salt) CaSO4.7H2O

5. Anhydrous salt: Salt without water of crystallization is called anhydrous salt. Copper

sulphate (CuSO4), sodium carbonate (Na2SO3), sodium sulphate (Sa2SO4), etc. are
some anhydrous salts.

Properties of salts Preparation of salts

1. Common salt (NaCl) is an The general methods of preparation of salts are
essential constituent of our mentioned below:

diet. It is salty in taste. Some 1. By direct combination of elements (metals

other salts have a bitter taste or and non-metals)

sometimes they are tasteless. 2Na + Cl2 2NaCl (sodium chloride)

2. The salts of K, Na, Al, Ca, Mg 2. By action of acids on metal
and Ba are white in colour or
colourless while salts of Cu, Fe, Zn + H2SO4 ZnSO4 + H2↑
Co, Mn, Cr are coloured.
3. By reaction of acid on metallic oxides
3. Generally, normal salts (e.g.
NaCl, KNO3, etc.), are neutral MgO + H2SO4 MgSO4 + H2O
to indicators. But acidic salt like
4. By neutralization of acid and hydroxide

(base)

CuSO4 show acidic property and NaOH + HCl NaCl + H2O
basic salt like Na2CO3 show basic
properties. 5. By action of acid on metallic carbonates
4. Most salts are soluble in water
CaCO3 + 2HCl CaCl2 + H2O + CO2↑

but few of them are insoluble. The solution of salt can conduct electricity.

5. All of the salts of Na, K and NH4 are soluble in water but carbonates of metals except
of Na, K and NH4 are water insoluble. Chlorides of metals except of Ag, plumbous
and mercurous are water soluble and sulphates of metal except of lead and Ba are
water soluble. All the common acetates and nitrates of metal are water soluble.

ACID, BASE AND SALT CLASS - 10 MODERN GRADED SCIENCE 165

6. Salts formed by strong acid and strong base and weak acid and weak base are usually
neutral to the indicators e.g. NaCl, CH3COONH4 (ammonium acetate), etc. But the
salt formed by the neutralization reaction between strong acid and weak base is
acidic while that of strong base and weak acid is basic.

Uses of salts

1. Sodium chloride (NaCl) is used as preservative. It is used as a raw material for the
manufacture of washing soda, hydrochloric acid, sodium hydroxide, etc. It is used in
our diet.

2. Sodium carbonate (Na2CO3.10H2O) is used for the manufacture of soap, detergents
and glasses. It is also used for softening hardness of water.

3. Sodium bicarbonate (NaHCO3) is used in the preparation of baking powder. It is also
used to reduce hyper-acidity of the stomach.

4. Copper sulphate (CuSO4.5H2O) is used in electroplating. It is also used as fungicide
to kill fungi of plants.

5. Ferrous sulphate (FeSO4.7H2O) is used in medicine to iron deficiency anaemia.
6. Ammonium sulphate [(NH4)2SO4] and potassium nitrate (KNO3) are used as chemical

fertilizers and also used to make gun powder.

7. Ammonium chloride (NH4Cl) is used as a good electrolyte in dry cells.
8. Calcium sulphate or plaster of paris or gypsum (CaSO4.7H2O) is used for plastering

fractured bones of the body and for making ceramics and cement.

9. Silver nitrate (AgNO3) is used as a laboratory reagent and zinc salts are used in
medicines.

10. Silver bromide (AgBr) is used in photography.

11. Zinc sulphate (ZnSO4.7H2O) is used in medicine related to eye and prepare white
pigments.

Neutralization reaction

An acid reacts with base, in which the properties

of both of them are destroyed or neutralized to form Neutralization reactions are always
salt and water. Such reaction is called neutralization exothermic in nature which means
reaction. Chemically, neutralization reaction is written they liberate heat.
as:

HX + BOH BX + H2O (double replacement)
Acid + Base
Salt + Water

In this reaction, H+ ion of the acid combines with the OH− ion of the base to give water.

Some examples of neutralization reaction:

HCl + NaOH NaCl + H2O
NaOH + HNO3 NaNO3 + H2O
Ca(OH)2 + 2HCl CaCl2 + 2H2O

166 MODERN GRADED SCIENCE CLASS - 10 ACID, BASE AND SALT

Application of neutralization reaction
Some applications of neutralization reaction are given below.

1. Neutralization reaction is used to control the pH of soil. Farmers use quick lime or
calcium oxide (CaO) to remove the acidity of the soil.

2. Neutralization is used in the manufacturing of antacid. An acidic stomach can be
relieved by taking an antacid in the form of magnesium hydroxide. The antacid is
alkaline/basic and helps neutralize the stomach's acidic environment.

3. Bee or ant stings are acidic in nature as they spew formic acid in the skin, in which
a household remedy for such sting is sodium bicarbonate or baking soda and soap.
Baking soda and soap are basic substances that neutralize the formic acid of the skin
after sting.

4. A wasp sting is mild basic, so a household remedy for this will be vinegar or acetic
acid. This treatment minimizes painful stings by a neutralization process.

S me Reasonable Facts

1. Copper sulphate solution shows acidic nature. Copper sulphate is a salt that is formed
from a weak base Cu(OH)2 and strong acid H2SO4. Thus, it is acidic salt and it shows
the properties of acid.

2. All the alkalis are base but all the bases are not alkali. Some bases are soluble in
water and others are insoluble in water. Water-soluble bases are called alkali while
the bases, which are not soluble in water, are not alkali. Therefore, all alkalis are base
but all bases are not alkali.

3. Lemon juice has a sour taste because it has H+ ions that give a sour taste.

4. Hydrochloric acid turns blue litmus into red. It is because HCl can give hydrogen
ions (H+ ion) by dissolving in water; that turns blue litmus into red.

5. Agricultural lime is used in acidic fields. It is because lime is basic in nature that
reacts with acidic soil and the acidity of the soil is reduced.

6. Magnesium hydroxide and aluminium hydroxide are antacids. It is because Mg(OH)2
and Al(OH)3 are weak alkalis and are used to neutralize hyper-acidity in our stomach.

7. Acids are also called proton donors as they give H+ ion or proton by dissolving in
water.

8. H2SO4 is called King of acid as it is widely used in industries and laboratories.
9. NaHSO4 is an acid salt because it is formed by the partial displacement of hydrogen

in sulphuric acid by sodium and contains hydrogen.

Things To Know

1. An acid is defined as the compound which gives off a hydrogen ion or proton (H+)
when dissolved in water.

2. The acids which produce more hydrogen ions (H+) after complete dissociation in an
aqueous solution are called strong acids.

3. The acids, which produce fewer hydrogen ions (H+) due to partial ionization in an
aqueous solution, are called weak acids.

ACID, BASE AND SALT CLASS - 10 MODERN GRADED SCIENCE 167

4. The acids which are obtained from living organisms are called organic acids.
5. The acids which are prepared in the laboratory are called inorganic acids.
6. Bases are metallic oxides. Some metallic oxides are soluble in water to give metallic

hydroxides.
7. Water-soluble bases or hydroxides are called alkalis which gives hydroxyl ions in an

aqueous solution.
8. An indicator is a chemical substance used for detecting acidity or alkalinity of

substances. Examples: litmus paper, methyl orange and phenolphthalein.
9. Salt is a compound formed by partial or complete replacement of hydrogen of an acid

by a metal or electro-positive or basic radical.
10. There are three kinds of salts. They are acidic salts, normal salts and basic salts.

Things To Do

Take a small magnesium ribbon and burn it in air. It burns brightly and produces white
ash of magnesium oxide (MgO). Take little amount of this metal oxide in a test tube
and water in it. The magnesium oxide reacts with water to give magnesium hydroxide
[Mg(OH)2] which is an alkali.

2Mg + O2 2 MgO

2MgO + H2O Mg (OH)2

To test whether Mg(OH)2 is alkali or acidic, when a red litmus paper is dipped into
magnesium hydroxide solution, it changes into blue.

Test Yourself

1. Multiple choice questions (MCQs).

a. CuSO4 solution is …………. B. basic
A. acidic

C. neutral D. alkaline

b. In an ant bite, we feel burning due to…………..

A. citric acid B. formic acid C. acetic acid D. lactic acid
D. both A and B
c. Generally, metal oxides are ………….
D. potassium
A. basic B. acidic C. neutral D. moderate acid

d. Blue vitrol is………….

A. FeSO4.7H2O B. Na2SO4.7H2O

C. MgSO4.10H2O D. CuSO4.5H2O

e. Plaster of paris is a salt of ……………

A. calcium B. copper C. sodium

f. Sulphuric acid is a………….

A. strong acid B. weak acid C. strong base

168 MODERN GRADED SCIENCE CLASS - 10 ACID, BASE AND SALT

g. Acidic stomach can be relieved by taking antacid in the form of

A. calcium hydroxide B. sodium hydroxide

C. potassium hydroxide D. magnesium hydroxide

h. The colour of phenolphthalein in an alkali solution is

A. colourless B. pink C. red D. yellow

2. Differentiate between: B. Strong acid and weak acid
A. Acid and base D. Organic acid and inorganic acid
C. Base and alkali

3. Give reason.

a. Pickle is not stored in a metal vessel for a long time.

b. The taste of acid is sour.

c. Acetic acid is a weak acid.

d. Hydrochloric acid is known as a strong acid.

e. Sodium bicarbonate is called an acidic salt.

f. Water is known as an acid as well as a base.

g. Ammonium hydroxide is called a weak alkali.

h. H2SO4 is called the king of chemicals.
i. Acid is also called a proton donor.

j. Antacids relieve hyper-acidity.

4. Answer the following questions.

a. Define acid. What are the properties of an acid?

b. Write down the name and molecular formula of a compound which gives
hydrogen ion and chloride ion in the solution state. In which colour is the methyl
orange changed after treating it with this compound? Why? Write the name of
salt when the compound is treated with lime water. Write down the chemical
equation.

c. Define organic and mineral acids.

d. What is a base? Mention any three ways of making bases.

e. What are salts? What are the characteristics of salts?

f. What is an alkali? Name any three alkalis.

g. What do you mean by neutralization reaction? Write the importance of this
reaction.

h. "Acids can be said to be proton donors". Justify.

i. Which alkali has no metal?

j. What is litmus paper? Where is it used? How is it used for identifying acid and
base?

k. How normal acidic and basic salts formed? Explain with the chemical reaction.

ACID, BASE AND SALT CLASS - 10 MODERN GRADED SCIENCE 169

l. What change of colour would you observe when the following indicators are
added to the substances listed below.

Substance Methyl orange Phenolphthalein Blue litmus Red litmus

paper paper

Suphuric acid

Ammonia
solution

Salt solution

Water

m. Write any three uses of the following.

i. Acid ii. Base iii. Salt

n. What is hydrated salt? Write its two examples.

o. Complete the following chemical equations in the form of balanced equations by
placing the related compounds/elements.

i. Acid + Metal

ii. Acid + Metal oxide

iii. Acid + Metal carbonate

p. Write the application of neutralization reaction.

q. What happens when ( write with balanced chemical equation)?

i. magnesium reacts with sulphuric acid.

ii. hydrochloric acid reacts with sodium carbonate.

iii. hydrochloric acid reacts with sodium hydroxide.

iv. copper oxide reacts with sulphuric acid.

v. magnesium burns in oxygen.

vi. sulphuric acid dissolves in water.

r. Write the molecular formula and uses of each of the following:

i. sulphuric acid ii. carbonic acid iii. acetic acid

iv. calcium hydroxide v. sodium carbonate vi. carbolic acid

Spew : eject forcibly and in a stream
Litmus
: an indicator made by dissolving plant pigments into ethanol and
Reagent soaked in paper

Antidote : a substance used to cause a chemical reaction, especially to detect
another substance

: a remedy to counteract the effects of poison

170 MODERN GRADED SCIENCE CLASS - 10 ACID, BASE AND SALT