science 9

Advantages of hard water
1. The salts dissolved in hard water make it tasty to drink.
2. The soluble salts of calcium present in hard water make bones and
eeth strong.
3. Hard water is used in breweries to manufacture beer.
4. Hard water is supposed to control heart diseases.

Disadvantages of hard water
1. The main disadvantage of hard water is that it destroys the washing
capacity of soap.
2. It reduces the brightness of white clothes if it used for washing clothes.
3. It corrodes the inner walls of steam boilers and geysers.

Main points to remember

1. Water is the most useful and most abundant substance on the earth.
Water is found in all three states, i.e. solid (ice), liquid (water) and gas
(vapour).

2. Only the 1% of fresh water is available on the earth's surface and in the
form of vapour in the atmosphere.

3. Pure water is colourless, odourless and tasteless liquid.
4. Water dissolves larger number of solutes than any other solvent. So,

water is regarded as a universal solvent.
5. The water which contains the dissolved salts of magnesium and calcium

is called hard water.
6. The water which does not contain the dissolved salts of magnesium and

calcium is called soft water.
7. The hardness of water due to the dissolution of calcium bicarbonate or

magnesium bicarbonate in it is called temporary hardness of water.
8. The temporary hardness of water can easily be removed by boiling or by

the use of lime water.
9. The hardness of water due to the dissolution of chlorides and sulphates

of calcium and magnesium is called permanent hardness.
10. The permanent hardness of water is removed by the use of washing

soda and Permutit process.
11. Permutit process is used to remove permanent hardness of water in

industrial scale.
12. If water contains both temporary and permanent hardness at the

same time, it is removed by treating with a mixture of washing soda
(Na2CO3) and caustic soda (NaOH).

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Exercise

1. Choose the best alternative in each case.

1. What is the percentage of fresh water in nature?

a. 1% b. 3% c. 97% d. 69%

2. The water of ocean and sea is unfit for domestic use because

it is

a. frozen b. polluted c. tasteless d. salty

3. When does water have maximum density and minimum

volume?

a. 4°C b. 0°C c. 1°C d. 100°C

4. The water which contains dissolved magnesium and calcium

bicarbonate is called…

a. Hard water b. Soft water

c. Temporary hard water d.Permanent hard water

5. The permanent hardness of water is removed by

a.Caustic soda b. Boiling c. Lime d. Permutit

2. Answer these questions in very short.
1. What are the taste, colour and odour of pure water?
2. What is meant by anomalous expansion of water?
3. What is the chemical composition of water?
4. What is hydrolysis reaction? Give an example.
5. What is meant by cohesive property of water?
6. What is the importance of cohesive and adhesive property
of water in plants?
7. Define soft water and hard water.
8. Write down one method each to remove temporary and
permanent hardness of water.

3. Give reasons:
1. It is difficult to wash clothes in hard water.
2. Sea and ocean water cannot be used as drinking water.
3. Water is regarded as universal solvent.
4. Washing soda removes the permanent hardness of water.
5. Hard water is not good for laundries.

4. Write down differences between:
a. Cohesion and adhesion
b. Hard water and soft water
c. Temporary hardness and permanent hardness of water

5. Answer these questions in short.

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a. Write short note on:
i. Occurrence of Water in Different Sources and

States
ii. Solvent Property of Water
b. Write down the physical properties of water.
c. What is capillary action? Describe the capillary action of

water with an experiment.
d. Describe an experiment to distinguish between hard and

soft water.
e. What is temporary hardness of water? Name the salts with

their molecular formula that cause the temporary hardness
of water.
f. Write down the name and molecular formula of salts that
cause the permanent hardness of water.
g. Describe the process of removal of temporary hardness.
h. How do you remove the permanent hardness of water by
Permutit process? Describe with principle and process.
i. Write down the chemical properties of water with chemical
reactions.
j. Write down the advantages and disadvantages of hard
water.

Project Work

Collect water from different sources and test to identify whether the water
is soft or hard.

Glossary
Surface water: Water that flows on the surface of the earth, i.e. in
streams, springs, rivers, lakes, oceans, etc
Fresh water: Water that does not contain dissolved salts in
significant amount
Cohesion: The sticking together of particles of the same substance
Adhesion: The force of attraction that causes two different
substances to join
Surface tension: The attractive force exerted upon the surface
molecules of a liquid by the molecules beneath that tends to draw
the surface molecules into the bulk of the liquid and makes the
liquid assume the shape having the least surface area
Permutit: An ion exchange resin

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Chapter

15 Chemical Fertilizers Friedrich Wohler
Used In Agriculture

He is the best known for his synthesis of urea,

but also the first to isolate several chemical

elements. Estimated Periods :3

Objectives

At the end of the lesson, students will be able to:
• define organic and inorganic fertilizers;
• write the advantages and disadvantages of organic as well as inorganic
fertilizers;
• explain the importance and effects of chemical fertilizers.

Introduction

The essential nutrients for the growth and productivity of plants
are available in soil. The plants get two types of nutrients from
soil. They are macro-nutrients and micro-nutrients. The nutrients
which are required by plants in large quantities are called macro-
nutrients. The compounds containing nitrogen, phosphorus and
potash are macro-nutrients. On the other hand, the nutrients
which are required by the plants in small quantity are called micro-
nutrients. The compounds containing boron, iron, magnesium, zinc,
sulphur, etc are micro-nutrients. If the soil contains both of such
compounds, the productivity of soil increases.

The use of land for cultivation of crops for a long time leads to the
loss of essential nutrients. It means that the fertility of the soil
decreases due to longterm cultivation of crops in the field. This
results in the decrease in yield of crops. We can restore the fertility
of the soil by adding fertilizers. The fertilizers are the substances
which are added to the soil to increase the crop production by
supplying essential nutrients.

There are two types of fertilizers:
1. Organic fertilizers (manures)
2. Inorganic fertilizers

1. Organic fertilizers
The fertilizers which are obtained from the decomposition of the

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dead plants and the animal wastes are called organic fertilizers.

The organic fertilizer can be prepared by the decomposition of dung

and urine of cattle, leaves and soft twigs of trees, herbs, hay, straw,

dry leaves of trees, etc.

However, the decay and decomposition of such organic matter can

produce much methane gas and foul

smell. The mixing of much amount of

methane in the atmosphere causes air

pollution. This also causes greenhouse

effect and increases the temperature

of the earth. To avoid such effects, the

organic matter should be cut into

pieces before turning them into

fertilizers. The decaying matter

should be turned regularly so that

each part gets oxygen and decomposes Compost fertilizer
completely. Thus, there is good

fertilizer and less effect in the environment. Such a method of making

organic fertilizer in the sufficient supply of oxygen is called aerobic

method. The organic fertilizer can also be manufactured in the

absence of oxygen. Such a method is called anaerobic method. The

organic fertilizer can also be prepared by mechanical method.

The organic fertilizer can be classified into two types. They are:

a. Green organic fertilizers b. Animal based organic

fertilizers

a. Green organic fertilizers: The fertilizer, which is prepared by
cutting green plants and decomposing them under wet soil is called
green fertilizer. It is also called green manure. The plants such as
Dhaincha, Asuro, Titepati, etc are used to make green manure. The
green manure mainly provides nitrogen to the plants in the form of
nitrate.

Asuro Dhaincha Titepati (Mugwort)

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b. Animal based organic fertilizers: The commonest method to
prepare organic fertilizer in Nepal is the composting of dung and
urine of cattle along with plant parts. In this method, dung, urine
and the remains of fodder of cow and buffalo are collected in a pit or
shallow area and are allowed to decompose. The decomposition of
these matters produces organic fertilizers. The animal based organic
fertilizer is also prepared by burying the dead body of animal in a
deep pit and allowing it to decay and decompose. However, such
fertilizers do not contain the inorganic nutrients such as nitrogen,
potash and phosphorus.

Advantages
1. They are biodegradable and hence they cause less pollution.
2. Such fertilizers increase the water holding capacity of soil as well

as increase its fertility.
3. They are cheap as they are produced from wastes.
4. They are useful for all varieties of plants.
5. They do not have side effects on human beings as those of

inorganic fertilizers.

Disadvantages
1. Organic fertilizer is required in large quantity. So, it is difficult

to collect and transport them.
2. The organic fertilizers are insoluble in water.
3. Organic fertilizers are poor in inorganic nutrients like nitrogen,

phosphorus and potassium.

2. Inorganic or chemical fertilizers

The water soluble chemical compounds,
which are added to the soil to increase
crop production by supplying essential
nutrients are called inorganic or chemical
fertilizers. These fertilizers supply
nitrogen, phosphorus, potassium etc to
the soil. Ammonium sulphate, ammonium
phosphate, urea, potassium nitrate, etc are
some examples of chemical fertilizers.

Some chemical fertilizers

1. Nitrogen containing fertilizers

Ammonium sulphate : (NH4)2SO4

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Ammonium nitrate : NH4NO3

Urea : NH2 CO NH2

Functions of nitrogen

1. It helps in rapid growth of plants.

2. It helps to increases the crop yield.

3. It helps chlorophyll of leaves to have faster rate of photosynthesis.

4. It increases the amount of protoplasm, protein and chlorophyll

in cells of plants.

Deficiency of nitrogen

The deficiency of nitrogen in plants causes following symptoms:
1. Reduction in crop yield
2. Reduced and yellow leaves in plants
3. Reduced size of flowers, fruits and seeds of the crops

2. Phosphorus containing fertilizers

Ammonium phosphate : (NH4)3 PO4
Calcium super phosphate : Ca(H2PO4)2. 2CaSO4
Triple super phosphate : 3Ca(H2PO4)2
Bone meal (Bone dust)

Functions of phosphorus
1. It is needed for the growth of leaves, buds and roots.
2. It helps in developing seeds in crops.
3. It helps in fast maturity of the fruits and seeds.
4. It is essential for protein synthesis and cell division.

Deficiency of phosphorus

The deficiency of phosphorus in plants results in the following effects:
1. Poor growth of the roots of plants
2. Slowed rate of cell division in the plant

3. Potassium containing fertilizers

Potassium chloride : KCl

Potassium nitrate : KNO3

Potassium sulphate : K2SO4

Functions of potassium

1. It helps in preparing food for plants.

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2. It helps in protein synthesis and cell division.
3. It increases disease resistant capacity of plants.
4. It promotes the flowering of plants.

Deficiency of potassium
1. Reduction in the amount of protein in the cell
2. Slow rate of cell division
3. Drying or the death of leaves of plants
4. Small plants may die due to the deficiency of potassium.

Groups of fertilizers

The fertilizers can be divided into three groups on the basis of
number of inorganic nutrient present. They are:

a. Single fertilizer: The fertilizer which supplies only one basic
nutrient is called single fertilizer. Such fertilizer supplies only one
among nitrogen, phosphorus and potassium. For example, calcium
nitrate, potassium chloride, potassium sulphate, etc.

b. Mixed fertilizers: The fertilizers which supply more than one
basic nutrient are called mixed fertilizers. Ammonium phosphate,
potassium nitrate, etc are some examples of mixed fertilizers.

c. Complete fertilizers: The fertilizer, which contains all three
primary nutrients, viz, nitrogen, phosphorus and potassium, is
known as complete fertilizer or NPK fertilizer. They are made by
mixing two or more single or mixed fertilizers.

Advantages of chemical fertilizers
1. Chemical fertilizers are required in relatively small quantity.
Hence, it is easy to collect and transport them from one place to
another.
2. They contain most of the nutrients essential for the growth and
development of the plants.
3. They are soluble in water and are easily absorbed by plants.
4. They cause significant increase the crop production.

Disadvantages of chemical fertilizers

Chemical fertilizers cause the pollution of soil and water. The
continuous use of chemical fertilizers reduces the natural fertility of
soil. They increase the acidity or alkalinity of soil. If the nitrogenous
fertilizer reaches the water body, it causes rapid growth of aquatic
plants. These plants use up the available oxygen and create
deficiency of oxygen in water. Hence, the aquatic animals die due

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to the lack of oxygen. If children drink such nitrogenous fertilizer
containing water, their growth is retarded and they become dwarf.

Precautions while using chemical fertilizers
1. The excess use of chemical fertilizers may damage the plants.
So, we should use them in proper amount.
2. Urea can be easily damaged by water and moisture. So, it
should be stored in cold and dry place.
3. Some nitrogenous fertilizers catch fire easily and they can
cause fire hazards. Such fertilizers should be kept away from
dry wooden dust, coal, dry leaves, etc.
4. Chemical fertilizers should be stored away from the reach of
children.
5. The chemical fertilizers should be used only after testing soil.

Difference between organic fertilizers and chemical
fertilizers

Organic fertilizers Chemical fertilizers

1.Theyareobtainedbythedecomposition1. They are man-made chemicals
of dead plants and animal wastes. which contain specific element (s).

2. They are not soluble in water. So,2. They are readily soluble in water
they are absorbed slowly by plants. and are quickly absorbed by plants.

3. They are rich in oprhgoasnpichonrouutrsieanntds T3p.hhoesyTphheodyrousarnaenotd ripcpohrtoavsiisndiuemniot(rNrgoPagKenni)c.,
but poor in nitrogen, nutrients.
potassium (NPK).

4. They are not nutrient specific. 4. They are nutrient specific. For
example, potassium containing
fertilizers provide only potassium.

5. They cause less environmental5. They pollute the environment to

pollution. greater extent.

Main points to remember

1. The essential nutrients for the growth and productivity of pants are
available in soil.

2. The nutrients which are required by plants in large quantities are called
macro-nutrients.

3. The nutrients which are required by the plants in small quantity are
called micronutrients.

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4. The fertilizers, which are obtained from the decomposition of the dead
plants and the animal wastes are called organic fertilizers.

5. The fertilizer, which is prepared by cutting green plants and decomposing
them under wet soil is called green fertilizer.

6. The water soluble chemical compounds, which are added to the soil to
increase crop production by supplying essential nutrients are called
inorganic or chemical fertilizers.

7. The fertilizer, which contains all three primary nutrients, viz, nitrogen,
phosphorus and potassium, is known as complete fertilizer or NPK
fertilizer.

Exercise

1. Choose the best alternative in each case.

i. Which of the following is the micronutrient?

a. Nitrogen b. Phosphorus c. Iron d. Potash

ii. What is meant by organic fertilizer?

a. Fertilizers from decomposed matter of plants and animals

b. NPK fertilizer

c. Pesticides and insecticides

d. Green manure

iii. Which of the following is the source of nitrogen?

a. Triple super phosphate c. Ammonium nitrate

b. Potassium carbonate d. Amophus

iv. Which of the following is not the function of potassium?

a. It helps in fast maturity of the fruits and seeds.

b. It helps in protein synthesis and cell division.

c. It increases disease resistant capacity of plants.

d. It promotes the flowering of plants.

v. Which of the following is used to produce green manure?

a. Asuro b. Dhaincha c. Titepati d. All of these

2. Answer these questions in brief.
1. What is meant by chemical fertilizers? Give examples.
2. What is organic fertilizer? Explain in brief.
3. What is the importance of nitrogen for the plants? What
happens if there is deficiency of nitrogen in the plants?
4. What is NKP fertilizer? How is it prepared?
5. How is organic fertilizer prepared? Write down the steps
involved.
6. Write down three sources each of nitrogen, phosphorus and
potassium containing fertilizers.

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7. What happens if there is deficiency of potassium in the
plants? Write the effects.

8. Explain the relationship between organic fertilizer and
chemical fertilizers.

9. Write down the advantages and disadvantages of organic
fertilizers.

10. What are the disadvantages of chemical fertilizers?

3. Write down differences between:
1. Compost manure and green manure
2. Organic fertilizers and chemical fertilizers

Project Work

Visit a vegetable farm or the crop field nearby your school. Ask the
farmers or the concerned persons about types of fertilizers they use in
the field or farm, time gap for use of fertilizers, amount of fertilizers
and the method of their use. Also discuss the advantages of such
fertilizers to the plants. Prepare a report and present in the class.

Glossary
Organic fertilizer : fertilizers prepared from the wastes of animals
as well as dead animals and plant parts
Inorganic fertilizer : fertilizer prepared from different minerals
Pesticides : the chemicals that are used to kill harmful insects and
worms

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