Exemplar:
A substance which reacts with oxygen giving heat is
called a combustible substance.
Which, one of the following is a combustible
substance?
(a) Iron nail
(b) Glass
(c) Stone piece
(d) Wood
d
Which one of the following has the highest calorific
value?
(a) Kerosene
(b) Biogas
(c) LPG
(d) Petrol
c
Magnesium ribbon on burning in air produces:
(a) Magnesium oxide, water and light
(b) Magnesium oxide and heat
(c) Magnesium oxide, heat and light
(d) Magnesium oxide, water and heat
c
Which of the following is not a combustible substance?
(a) Camphor
(b) Glass
(c) Straw
(d) Alcohol
b
The substance that does not burn with flame is:
(a) LPG
(b) Camphor
(c) Dry grass
(d) Charcoal
d
On placing an inverted tumbler over a burning candle,
the flame extinguishes after some time.
This is because of non-availability of:
(a) Oxygen
(b) Water vapours
(c) Carbon dioxide
(d) Wax
a
If a person’s clothes catch fire, the best way to
extinguish the fire is to:
(a) Throw water on the clothes.
(b) Use fire extinguisher.
(c) Cover the person with a woollen blanket.
(d) Cover the person with a polythene sheet.
c
The substance expected to have the highest ignition
temperature out of the following is:
(a) Kerosene
(b) Petrol
(c) Coal
(d) Alcohol
c
Choose the correct statement about inflammable
substances from the following.
They have:
(a) Low ignition temperature and cannot catch fire
easily.
(b) High ignition temperature and can catch fire
easily.
(c) Low ignition temperature and can catch fire
easily.
(d) High ignition temperature and cannot catch fire
easily.
c
Choose the incorrect statement from the following.
Forest fires are usually due to:
(a) Carelessness of humans
(b) Heat of sun
(c) Cutting of trees
(d) Lightning strike
c
The calorific value of a fuel is expressed in a unit
called:
(a) Kilojoule per litre
(b) Kilogram per mililitre
(c) Kilojoule per gram
(d) Kilojoule per kilogram
d
In villages, people use wood as fuel because:
(a) It is considered to be an ideal fuel.
(b) Of its easy availability and low cost.
(c) It is environment friendly.
(d) It catches fire easily.
b
Which among the following is considered as the
cleanest fuel?
(a) Cow dung cake
(b) Petrol
(c) Kerosene
(d) Hydrogen gas
d
Choose the incorrect statement from the following.
A good fuel is one which:
(a) Is readily available.
(b) Produces a large amount of heat.
(c) Leaves behind many undesirable substances.
(d) Burns easily in air at a moderate rate.
c
Shyam was cooking potato curry on a chulha.
To his surprise he observed that the copper vessel was
getting blackened from outside.
It may be due to:
(a) Proper combustion of fuel.
(b) Improper cooking of potato curry.
(c) Improper combustion of the fuel.
(d) Burning of copper vessel.
c
VERY SHORT ANSWER QUESTIONS (5)
Fill in the blanks in the following sentences.
a)
A ____________ process in which a substance reacts
with__________ to give off heat is called combustion.
b)
When the clothes of a person catch __________, the
person is covered with a __________ to extinguish fire.
c)
The __________ temperature at which a substance
catches fire is called its
__________ temperature.
d)
The substances which have very ________________
ignition temperature and can easily catch fire with a flame are
called__________ substances.
e)
The substances which vaporise during __________, give
flame.
(a) Chemical, Oxygen;
(b) Fire, Blanket
(c) Lowest, Ignition;
(d) Low, Inflammable
(e) Burning.
Some words (underlined) in the following sentences are
jumbled up.
Write them in their correct form.
(a)
Seldie is a combustible substance.
(b)
Slags is a non-combustible material.
(c)
Chittsmack does not burn by itself.
(d)
Some substances on combustion produce thea and mafel.
(e)
The amount of heat energy produced on complete
combustion of 1 kg of a fuel is called its ficalroic value.
(a) Diesel
(b) Glass
(c) Matchstick
(d) Heat, flame
(e) Calorific
Two glass jars A and B are filled with carbon dioxide
and oxygen gases, respectively. In each jar a lighted candle is placed simultaneously.
In which jar will the candle remain lighted for a longer
time and why?
The candle will remain lighted for a longer time in
jar B, because oxygen gas is a supporter of combustion.
Anu wants to boil water quickly in a test tube. On
observing the different zones of the flame, she is not able to decide which
zone of the flame will be best for boiling water quickly. Help her in this
activity.
In order to boil water quickly in a test tube, Anu
should keep her test tube in the outermost zone of the flame, which has the
highest temperature, and hence is the hottest zone.
Why is the use of diesel and petrol as fuels in
automobiles being replaced by Compressed Natural Gas (CNG) in big cities?
It is because CNG produces much smaller amount of harmful
products and is a cleaner fuel, compared to diesel and petrol.
SHORT ANSWER QUESTIONS (10)
Boojho wants to separate the following materials as
combustible and non-combustible. Can you help him?
Charcoal, chalk, stone, iron rod, copper coin, straw, cardboard,
glass, paper, candle, wood.
(a) Combustible charcoal, straw, card board, paper,
candlewood,
(b) Non-combustible chalk, stone, iron rod, copper coin, glass.
Indicate whether the following statements are True or
False.
Also write the false statements in their correct form.
(a) Air is necessary for combustion.
(b) Magnesium is a non-combustible metal.
(c) Carbon dioxide is an excellent fire extinguisher.
(d) Calorific value of wood is higher than that of
coal.
Both (a) and (c) are true statements.
(b) Magnesium is a combustible metal.
(d) Calorific
value of coal is higher than that of wood.
Match the items of Column A with the items of Column
B.
Column A Column
B
(a) Oxides of sulphur and nitrogen (i) fire extinguisher
(b) CNG (ii)
incomplete combustion of coal
(c) Oxygen (iii)
very low ignition temperature
(d) inflammable substance (iv) acid rain
(e) carbon dioxide (v)
necessary for combustion
(f) carbon monoxide (vi)
fuel for automobiles.
(a) (iv)
(b) (vi)
(c) (v)
(d) (iii)
(e) (i)
(f) (ii)
Match the following for the flame of a candle:
Column A |
Column B (zone) |
Column C (colour) |
(a)Hottest part |
(i) Innermost zone of unburnt wax vapours |
(x) Blue |
(b)Moderately hot |
(ii) Middle zone of partial combustion |
(y) Black |
(c) Least hot |
(iii) Outer zone of complete combustion |
(z) Yellow |
(a)(iii)(x)
(b)(ii)(z)
(c)(i)(y)
If you hold a piece of iron wire with a pair of tongs
inside a candle flame or a Bunsen burner flame, what will you observe?
Will it produce a flame?
Iron wire will not produce a flame, but it will become
red hot and will glow.
Fill in the blanks using the words given in the box:
ignition, petrol, combustion, calorific value, combustible,
inflammable
(a)
A chemical process in which a substance reacts with
oxygen to give off heat is called __________.
(b)
Wood, paper, CNG are __________ substances.
(c)
The lowest temperature at which a substance catches
fire is called its
__________ temperature.
(d)
Ignition temperature of __________ is lower than that
of wood.
(e)
The substances which have very low __________
temperature and can easily catch fire with a flame are called
__________substances.
(f)
The amount of heat energy produced on complete
combustion of 1kg of a fuel is called its __________.
(a) Combustion,
(b) Combustible,
(c) Ignition,
(d) Petrol,
(e) Ignition, inflammable,
(f) Calorific value.
People usually keep Angethi/burning coal in their closed rooms during winter season.
Why is it advised to keep the door open?
Ina closed room, due to the burning of angethi or
coal, there will be insufficiency of oxygen, due to the consumption of the gas in
the process of burning. Carbon monoxide gas is produced as a result of the
burning process in the closed room and the person sleeping in that room can die
by inhaling the poisonous carbon monoxide gas. So, the door should be left open
to let the fresh air in.
Write True/False against the following statements and
also correct the false statement.
(a) A physical process in which a substance reacts
with oxygen to give off heat is called combustion.
(b) Water is the best extinguisher for fires involving
electrical equipment.
(c) Alcohol, CNG and LPG are inflammable substances.
(d) Increased concentration of nitrogen in air is
believed to cause global warming.
(e) Greater the calorific value, better is the fuel.
(f) Middle zone is the hottest zone of a flame.
(g) The substances which vapourises during burning,
give flame.
(a)
False. A chemical process in which a substance reacts
with oxygen to give off heat is called combustion.
(b)
False. Water cannot be used for controlling fires from
electrical appliances, as water is a good conductor of electricity.
(c)
True
(d)
False. Increased concentration of carbon dioxide in
air is believed to cause global warming.
(e)
True
(f)
False. The outermost zone is the hottest zone of a
flame.
(g)
True
Cracker on ignition produces sound. Why?
The burning of a cracker is a chemical reaction. When
a cracker is ignited, it produces a sound because of the sudden release of the
gases formed due to the chemical reaction.
What do you understand by fuel efficiency?
Fuels are burnt to convert its chemical energy into
other forms of energy like heat energy, light energy, chemical energy, etc. A
fuel is considered to be efficient if it has high calorific value. It means it
should produce high amount of energy when a specified amount of it is
completely burnt.
You are provided with three watch glasses containing
milk, petrol and mustard oil, respectively.
Suppose you bring a burning candle near these
materials one by one, which material(s) will catch fire instantly and why?
Amongst the provided material(s), petrol will catch
fire instantly, as it is highly inflammable.
Manu was heating oil to fry potato chips. The cooking
oil all of a sudden caught fire; he poured water to extinguish the fire. Do you
think this action was suitable, If yes, why? If not, why not? In such a
condition what should Manu have done?
Manu’s action was not suitable as water is not appropriate
to extinguish the fire when cooking oil goes up in flame.
He should have switched off the gas flame and put a
lid on the frying pan. The lid would have cut off the contact between the fuel (i.e.,
the cooking oil) and oxygen, and the fire would have extinguished soon after.
What are the three essential requirements to produce
fire? How fire extinguisher is useful for controlling the fire.
The three essential requirements to produce fire are fuel,
air and heat.
Fire extinguisher either cuts off the supply of air,
or brings down the temperature of the fuel, or does both. This helps in
extinguishing the fire.
Give two examples each for a solid, liquid and gaseous
fuel along with some important uses.
Examples of solid fuel Coal, wood, etc.
·
Coal is used as a source of energy for heating or
burning.
·
Wood is used in making furniture. Wood is burnt to
produce heat.
Examples of liquid fuel Kerosene oil, petrol, etc.
·
Kerosene oil is used for lighting lamps and burning
woods.
·
Petrol is used in automobiles as fuel.
Examples of gaseous fuel CNG, LPG, etc
·
CNG is a used as a fuel in automobiles.
·
LPG is used as a fuel in cooking.
The calorific values of petrol and CNG are 45000 kJ/kg
and50,000 kJ/kg, respectively.
If you have vehicle which can run on petrol as well as
CNG, which fuel will you prefer and why?
If I have a vehicle which can run on petrol as well as
CNG, I will prefer CNG.
Reasons for preferring CNG:
The calorific value of CNG is comparatively higher
than that of petrol. Therefore, CNG will be more economical. CNG causes lesser
pollution.
Although wood has a very high calorific value, we
still discourage its use as a fuel. Explain.
Though wood has a very high
calorific value, we will still discourage its use as a fuel.
Reasons:
(a)
Burning wood results in very high air pollution.
(b)
Wood, as a fuel, is obtained by cutting down trees.
Extensive use of wood will lead to deforestation and environmental pollution.
Forest fire produces a lot of air pollution.
Write in brief about the reasons of forest fires.
Forest fire causes air
pollution and should be prevented. Some of the causes of forest fire are given
below:
High temperature: When the temperature is very high, there are high
possibilities of dry grasses and leaves catching fire. This fire spreads
throughout the forest.
Human negligence: Human negligence, like discarded cigarettes,
camp fire left unattended, etc., results in large number of forest fire.
Natural phenomenon: Natural phenomenon,
like lighting, causes forest fire.
Complete the crossword with the help of the clues:
Across
1. Non-metal which catches fire if exposed to air (10)
3. The lowest temperature at which a substance catches
fire is called its __________ temperature. (8)
5. The most common fire extinguisher. (5)
Down
2. A chemical process in which a substance reacts with
oxygen to give off heat. (10)
4. Petrol is used as a __________ in automobiles. (4)
6. It is as hard as stone and black in colour. (4)