Class 6 - Chemistry - Introduction to Chemistry - Exercise and Solutions

EXERCISE

BE PROMPT

A. Fill in the blanks

1. Alchemists were regarded as early chemists.

2. Antoine Laurent de Lavoisier is considered as the ‘Father of Modern Chemistry’.

3. John Dalton is credited for proposing modern atomic theory.

4. Carbaryl is an insecticide.

5. Cheese and breads are examples of processed food.

6. Penicillin and Ampicillin are examples of antibiotics.

B. Identify the error in the given statement. Circle the incorrect

word and write the correct word in the blank.

1. Science has two main branches: Chemical science and natural  
science.          Physical science

2. By the late seventeenth century the field of chemistry had completely 

 separated from traditional alchemy. Eighteenth

3. J.J. Thomsom discovered the proton.        Electron

4. Urea and sodium nitrate are insecticides.    Fertilizer

5. Manufacturing of cloth involves the combination of fibres 
in to fabrics.     Transformation

6. Paracetamol is an antibiotic used to treat infections.     Penicillin

C. Choose the correct option.

1. Chemistry is a _________ science

(a) Social           (b) Physical       (c) Life       (d) None of these

2.   Which of the following metals was considered the purest 

according to alchemy?

(a) Potassium    (b) Silver   (c) Sodium         (d) Gold

3. Who gave the ‘Law of conservation of mass’?

(a) Dmitri Mendeleev            (b) Niels Bohr

(c) Antoine Lavoisier           (d) John Dalton

4. Which of the following is not a pesticide?

(a) Ammonium phosphate         (b) Malathion   

(c) Parathion                                 (d) Aldrin

5. Which of the following come under the category of cosmetics?

(a) Skin cleansers       (b) Moisturizers    

(c) Perfumes               (d) All of these

6. Which of the following is a synthetic fibre?

(a) Cotton                   (b) Nylon    (c) Silk     (d) Wool

D. Match the columns.

        Column A                                    Column B

1.      Alchemy                               (a) Fungicide

2.      Plum pudding model            (b) Food preservative

3.      Ethylene oxide                     (c) Philosopher’s stone

4.      Yogurt                                  (d) Treat moderate pain

5.      Sodium benzoate                  (e) J.J.Thomson

6.      Aspirin                                  (f) Processed food

Ans.   1 – (c), 2 – (e), 3 – (a), 4 – (f), 5 – (b), 6 – (d).

SHORT AND PRECISE

A. Show the given text in the form of flowcharts.

(i) Alchemy   (ii) Benefits of chemistry

(i) Alchemy

(ii) Benefits of Chemistry

B. Give reason for the following statements.

1. Science is both a body of knowledge as well as a continuous ongoing

Process.

Science refers to the knowledge attained through study or practice.

Science is the system of gaining knowledge using observation and

Experimentation to describe various natural processes around us. So

science is both a body of knowledge as well as a continuous ongoing

process.

2. Chemistry is of vital importance and plays a fundamental role in all

aspects of life.

Chemistry is everywhere around us. It helps us understand the world

in a better way and answer questions about how thing work. The air

we breaths, the food we eat, the clothes we wear and a lot more,

everything based on chemistry.

3. Alchemy is considered of importance.

Alchemy is considered important as it made a significant contribution

in the evolution of modern science. Alchemy was an early philosophical

and spiritual field of study that integrated chemistry with metalwork.

It was also seen as an investigation of nature.

4. Chemistry plays a significant role in the development of cosmetics.

All the cosmetics we use are made from combination of different

chemical ingredients. For example lipsticks are made from combination

of oils, waxes. Pigments and skin softeners called emollients. So chemistry

plays a significant role in the development of cosmetics.

C. Answer in short.

1. State the main aim of alchemy.

The main aim of alchemy was to find the ‘philosopher’s stone’.

2. How did Mendeleev use the modern periodic table of elements?

Mendeleev used the table to predict the existence and properties of

new chemical elements which were not existing in the table.

3. What is the use of fertilizers?

Fertilizers are the chemicals which provide the required nutrients for a

proper growth of crops. Fertilizers increases the yield.

4. Why do we use sugar and salt often to preserve food?

Sugar and salt help in preventing the growth of bacteria in food items.

So we use sugar and salt to preserve food.

5. What are processed foods? Give examples.

The food products which are made suitable for consumption, cooking,

or storage are called processed food. For example, cheese, bread,

butter, jam, jelly, snacks, soft drinks, tinned food and ice cream etc.

6. What are cosmetics? Give examples.

Cosmetics are the products that enhance the appearance of external

parts of human body. These cosmetics are used to cleanse, beautify or

promote attractiveness without affecting the body’s structure or

function. Some examples of cosmetics are skin cleansers, lotions,

shampoo, moisturizers, lipsticks, deodorants and perfumes etc.

AT LENGTH

A. Explain the following terms.

1. Chemistry.

Chemistry is the branch of physical science that deals with the study of

composition and properties of substances and how they react when

combined with one another. Chemistry is everywhere around us. It helps

us understand the world in a better way and answer questions about

how thing work. The air we breaths, the food we eat, the clothes we

wear and a lot more, everything based on chemistry.

2. Alchemists.

Alchemists were the people who practiced alchemy. These people

were regarded as early chemists. They contributed in laying the

foundation for modern chemistry and medicine. Alchemists used

chemicals in metal working, inks, paints, and cosmetics etc. These

people were the first to learn the process of isolating zinc and

phosphorous.

3. Preservatives.

Preservatives are the chemicals used to preserve food and control its

wastage. Different types of preservatives are used to preserve different

food items.

Sodium benzoate is used to preserve food items such as fruit products,

beverages and salads.

Sorbic acid, sodium and potassium are used as preservative in diary

products, fish and seafood.

Sugar, salt and vinegars are also used as preservatives.

4. Food processing

Food processing is the process of transforming raw materials into

marketable food products by physical or chemical method. Various

additives are added to these products to increase their self life. Various

vitamins and minerals are also added to enhance the nutritional value

of these food products. These food products which are made suitable

for consumption, cooking,or storage are called processed food. For

example, cheese, bread, butter, jam, jelly, snacks, soft drinks, tinned food

and ice cream etc.

B. Differentiate between the following.

1. Science and Chemistry.

Science	Chemistry
Science is both the body of knowledge as well as a continuous ongoing process.	Chemistry is a branch of science that deals with the study of composition and properties of substances and how they react when combined with each other.
It forms the basis of our modern civilization.	Chemistry is of vital importance and plays a fundamental role in all aspects of life.

   

 2. Insecticides and pesticides.

  

Insecticides	Pesticides
These are the chemicals that are used to kill the insects that affects the growth of crops.	These are the chemicals used to kill the pests affecting the crop production and growth of fruits.
Examples: Benzene Hexachloride (BHC), Dichloridediphenyltrichlroethane (DDT)	Examples: Aldrin, Malathion and parathion.

3. Preservatives and Processed foods.

Preservatives	Processed food
These are the chemicals used to preserve the food items and control its wastage.	This is the process of transforming raw materials into packaged food products by physical and chemical method.
Example: Sodium benzoate, Sugar, Salt, Vinegar, Sorbic acid, Sodium metabisulphite etc.	Example:  cheese, bread, butter, jam, jelly, snacks, soft drinks, tinned food     and ice cream etc.

4. Natural fibres and Synthetic fibres.

Natural fibres	Synthetic fibres
These are the fibres that we get from the nature through plants  and  animals	These are the fibres which are man made by various chemical processes.
These fibres are not wrinkle free and takes time to dry.	These are wrinkle free and dry quickly.
Example: Cotton, Linen, Jute, Wool and Silk.	Example: Nylon, Terylene

C. Answer in detail.

1. Write a note on alchemy.

Alchemy was an early philosophical and spiritual field of study that

integrated chemistry with metalwork. Alchemy was scientific but spiritual

as well.  It was also seen as an investigation of nature. Alchemy is

considered important as it made a significant contribution in the

evolution of modern science. The physical aspect of alchemy was the

experimental study of the transformation of base metal into silver or

gold. The main aim of alchemy was to find the ‘philosopher’s stone’.

2. Write about the contributions of these notable scientists.

(a) Antoine Lavoisier (b) Dmitri Mendeleev

(a) Antoine Lavoisier is considered as the ‘Father of Modern Chemistry’.

Lavoisier is credited for discovering the role of oxygen in combustion.

He also gave the ‘Law of conservation of Mass’ that states that the

mass neither can be created not destroyed in a chemical reaction.

He also named oxygen and hydrogen.

(b) Dmitri Mendeleev was the first scientist who formulated the

‘Modern Periodic Table of Elements’. Mendeleev used this table to

predict the existence and properties of new chemical elements

which were not existing in the table.

3. How has chemistry helped to meet the increased demand of food

Due to an increase in population?

Chemistry has helped in the development and application of new

techniques in the field of food and agriculture. It has helped to

increase the food production and provided ways to produce

disease free crop. Chemistry has developed fertilizers which give

the crops proper growth. Pesticides, Insecticides and fungicides

help in producing disease free crops. Preservatives help us to

preserve the food and control the wastage of food. In this way

chemistry has helped us to meet the increased demand of food.

4. Write a note on how chemistry plays a role in the development of

cosmetics.

Chemistry plays a significant role in the development of cosmetics. All the

cosmetics are made from various chemical ingredients. For example

lipsticks are made from combination of oils, waxes, pigments and skin

softners. Similarly all other cosmetics like skin cleansers, lotions,

deodorants and perfumes are also made from the combination of

different chemicals. So it can be understood that chemistry plays a role

in the development of cosmetics.

5. What is the role of chemistry in the development of medicines?

Chemistry has helped us in developing a vast range of new medicines.

Antibiotics like penicillin and ampicillin are developed and used to treat

infections. Medicines like aspirin and Paracetamol help to cure moderate

pain and fever. Discovery and development of medicines is due to the

knowledge of chemistry of various molecules and how they are

associated with life processes.

6. How has chemistry contributed to the development of different

industries?

Chemicals are used to make different products in various industries.

Industries manufacture various products such as dyes, plastic, fertilizers,

textile, paper, glass, soaps, detergents etc. with the help of chemicals or

various chemical processes. Preparation of common salt from sea water, 

extraction of sugar from sugarcane, extraction of metals, preparation of 

alloys and development of drugs are possible because of the application 

of various chemical processes. We can hence concluded that chemistry has 

contributed to the development of different industries.

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Extra Questions and Answers

A. Objective Questions

1. Fill in the blanks

a) Aspirin is used to reduce fever.

b) Fungicides are used to prevent crops from fungi.

c) Science is the knowledge attended through study or practice.

d) Chemistry is a branch of physical science.

e) Alchemy aimed at finding philosopher’s stone.

f)  Dmitri Mendeleev was the first one to formulate the modern periodic

table of elements.

g) Ernest Rutherford performed the famous gold foil experiment .

h) Niels Bohr proposed that the energy levels of electrons are discrete.

i)  The book Rasaratnakara was written by Nagarjuna.

j)  Philosopher’s stone was considered as a mythical and magical

substance.

k) Alchemists were the people who practiced alchemy.

l)  J.J. Thomson discovered the electron and proposed the

plum Pudding Model.

m) Niels Bohr proposed that the electrons revolve in orbits around the

nucleus of an atom.

n) India’s first pharmaceutical company was founded by P.C.Ray.

o) Structure and functions of ribosomes was suggested by

Venkatraman Ramakrishnan.

p) Nitrogen was discovered by Daniel Rutherford.

q) Hydrogen was discovered by Henry Cavendish.

r)  Oxygen was discovered by Joseph Priestley.

s)  Radium was discovered by Marie curie.

t)  Acharya Prafulla Chandra Ray developed mercury compounds.

u) Paracetamol is used to relieve mild to moderate pain.

v) Ampicillin is an antibiotic used to treat infections such as pneumonia,

bronchitis and urinary tract infections caused by bacteria.

2. Answer in one word:

a) Name any one preservative – Sodium benzoate.

b) Chemicals which provide nutrients to crops for proper growth –

Fertilizers.

c) Substances or products used to enhance the appearance of external

parts of the human body –  Cosmetics.

d) Scientist who gave the ‘Law of conservation of mass’ – Antoine Lavoisier.

e) The Iron pillar near Qutub Minar is made up of – Wrought iron

f)  The model which represents that electrons are surrounded by positive

charges in order to balance negative charges – Plum Pudding Model.

g) Scientist who discovered radioactive half life – Ernest Rutherford.

h) A food preservative used in fruit products, beverages and salads –

Sodium benzoate.

3. Correct the underlined words.

a) The natural fibres are strong, wrinkle resistant and dry quickly.

The synthetic fibres are strong, wrinkle resistant and dry quickly.

b) Physical processes take place to produce numerous useful substances.

Chemical processes take place to produce numerous useful substances.

c) Pesticides are used to kill insects that affect the growth of crops.

Pesticides are used to kill pests that affect the growth of crops.

d) Preservatives are used to prevent the crops from fungi.

Fungicides are used to prevent the crops from fungi

e) Malathion and Parathion are two examples of insecticides.

Malathion and Parathion are two examples of pesticides.

f) Sodium benzoate is used to preserve fish, sea food and fat based products.

Sorbic acid is used to preserve fish, sea food and fat based products.

 4. Match the columns:

Column A                                             Column B

1. Dmitri Mendeleev                     (a) Law of partial pressure

2. Antoine Lavoisier                     (b) Radioactive half-life

3. John Dalton                               (c) Bohr atomic model

4. Niels Bohr                                 (d) Modern periodic table

5. Ernest Rutherford                      (e) Role of oxygen in combustion

(Ans.) 1-(d), 2-(e), 3-(a), 4-(c), 5-(b)

B. Short Questions

1. Define the following:

a) Science:

Science refers to the knowledge attained through study or practice. In

simple terms science is the system of gaining knowledge using

observations and experiments to describe various natural processes

around us. It is both a body of knowledge and a continuous ongoing

process. Science is the basis of our modern civilization.

b) Philosopher’s stone:

It was considered as a mythical and magical substance. It was

believed that this substance would turn into gold on heating with the

base of iron and copper.

c) Fungicides:

Fungicides are the chemicals that prevent crops from being affected

by fungi. Sulphur, calcium polysulphide and ethylene oxide are

examples of fungicides.

d) Penicillin:

It is an antibiotic used to treat infections caused by bacteria.

e) Aspirin:

Aspirin is used to reduce fever and treat moderate pane from

conditions such as common cold, muscle aches and headaches.

2. Answer the following:

a) What are fertilizers?

Fertilizers are the chemicals which provide nutrients required by crops

for proper growth. Use of fertilizers help in increasing the yield. Urea,

Sodium nitrate, Potassium and Ammonium phosphates are some

examples of fertilizers.

b)  Name any two food preservatives and state why they are used.

Sugar and salt are two food preservatives. They are used to prevent

the food by preventing the growth of bacteria in the food items.

c) What are cosmetics? Why do we use cosmetics?

Cosmetics are the beauty products that enhance the appearance of

external part of human body. We use cosmetics to cleanse, beautify

or promote attractiveness without affecting the bodies structure or

function.

d) Name two natural fibres and two synthetic fibres.

Two natural fibres are cotton and jute. Two synthetic fibres are nylon

and Terylene.

e) What is the importance of chemical industry?

The chemical industry is the most important industry and is very diverse.

It produces a huge variety of products that are used by other industries.

Without chemical industry it is almost impossible to run other industries.

f) Discuss the contribution of John Dalton.

John Dalton proposed the modern atomic theory. He also gave the law

of Multiple proportions and the Law of partial Pressures.

g) Discuss the contribution of Niels Bohr.

Niels Bohr developed the Bohr atomic model. He proposed that energy

levels of electrons are discrete and electrons revolve in orbits around

the nucleus of an atom.

h) How chemistry has contributed in space research?

Chemistry has contributed significantly in space research by producing

better quality and more powerful fuel, which help in launching space

satellites.

C. Long Questions

a) Discuss some harmful effects of chemistry.

Chemistry has the following harmful effects.

Pollution: Smoke from the vehicles cause air pollution. Use of

insecticides and pesticide cause  water and soil pollution. Combustion

of petrol and diesel emit out harmful gasses which affect the ozone

layer and all these pollutions resulted in global warming.

Destructive chemical weapons: Chemistry has a role in the

development of destructive chemical weapons, which can cause

massive destruction of human lives.

Side effect of drugs: Drugs can disturb the hormonal cycle and cause

conditions like anxiety, insomnia, and other unwanted physiological

effects.

b) Write about the contribution of J.J.Thomson.

J.J.Thomson discovered the electron and proposed the ‘Plum pudding

Model’ according to which electrons are embedded in a cloud of

protons. The model represents that electrons are surrounded by positive

charges in order to balance the negative charges. Thomson helped us

to have a better idea of the atom and it’s structure.

c) Write about the contribution of Ernest Rutherford.

Ernest Rutherford performed the famous ‘Gold foil experiment’. He

proposed that protons and neutrons lie at the centre of an atom in

the nucleus, and are surrounded by electrons. He also discovered

the concept of radioactive half-life.

d) List some common medicines and their uses.

Some common medicines and their uses are as follows.

Aspirin: Aspirin is used to reduce fever and treat moderate pain from

conditions such as common cold, muscle aches and headaches.

Paracetamol: This is used to relieve mild to moderate pain. It is also

used to reduce fever.

Penicillin: Penicillin is an antibiotic that is used to treat infections

caused by bacteria.

Ampicillin: Ampicillin is an antibiotic used to treat infections such as

pneumonia, bronchitis and urinary tract infections caused by bacteria.

e) How did the contribution of the alchemists helped in the advancement

of the civilization?

Alchemists were regarded as early chemists. They used chemicals in

metal working, inks, paints, cosmetics and to prepare extracts and

liquors. Their work contributed in laying the foundation of modern

chemistry and medicine. They had the knowledge of isolating zinc

and phosphorous. In this way their contribution helped in the

advancement of the civilization.

f) Why do the farmers use insecticides and pesticides?

Insecticides are the chemicals which kill insects that affect the growth

of crops. Pesticides are the chemicals which kill the pests affecting the

production and growth of crops and fruits. So the farmers use

insecticides and pesticides to produce diseases free crops as well as to

increase the crop yield.

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