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CBSE Questions for Class 8 Chemistry Combustion And Flame Quiz 1 - MCQExams.com
CBSE
Class 8 Chemistry
Combustion And Flame
Quiz 1
Middle zone is the hottest zone of a flame.
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True
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False
Explanation
The outermost zone or the non-luminous part of the flame is the hottest zone of a flame. It is blue in colour. This is because of complete combustion.
Hence, the given statement is "False".
Lubricant oil is used as fuel in vehicles and kitchen.
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True
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False
Explanation
Lubricating oil is a class of oils used to reduce the friction between mechanical components that are in contact with each other. It is neither used as fuel in vehicles nor used in kitchen.
Nitrogen gas supports burning.
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True
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False
Explanation
Nitrogen gas is a non-supporter of combustion (burning). It is a non-flammable gas.
The lowest temperature at which a substance catches fire?
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Flammable temperature
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Ignition temperature
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inflammable temperature
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None of above
Explanation
Ignition temperature is the lowest temperature at which a combustible substance when heated (as in a bath of molten metal) takes fire in the air and continues to burn. It is also called also autogenous ignition temperature.
The difference between combustible over non-combustible substances is:
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it cannot ignite
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it can ignite
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need low activation energy
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need high activation energy
Explanation
Combustible substances:- Substances which burn in air to produce heat and light are called combustible substances. Eg:- wood, coal, charcoal, kerosene, petrol, diesel, liquefied petroleum gas (LPG), compressed natural gas (CNG) etc.
Non-Combustible substances:-
Substances like stone, glass, iron nails, etc. do not burn on being exposed to flame.
Combustion is a process involving:
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oxidation
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reduction
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liberation of heat
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all of the above
Explanation
Combustion is a process involving o
xidation, r
eduction and l
iberation of heat.
The component of air which controls combustion is __________.
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Water vapour
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Oxygen
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Nitrogen
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Carbon monoxide
Explanation
Combustion is a chemical process in which substance reacts rapidly with oxygen and gives off heat. The original substance is fuel and the oxygen source is oxidizer. Oxygen is essentially required to carry the process of combustion.
Magnesium is a _______________metal.
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non-combustible
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combustible
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non
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None of the above
Explanation
Magnesium is a
combustible metal.
It burns to form magnesium oxide and produces heat and light.
Hence the correct option is B.
The non-combustible substance among the following is ______.
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Coal
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Glass
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Wood
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Paper
Explanation
Glass is the non-combustible substance among the given options.
Combustion is a reaction in which a substance reacts with:
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Hydrogen
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Nitrogen
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Oxygen
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Chlorine
Explanation
Combustion is a chemical process where substance reacts with Oxygen to give off a lot of heat. So combustion reactions involve molecular oxygen $$O_2$$. When wood burns, it must do so in the presence of $$O_2$$.
Combustion is a:
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physical process
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chemical process
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biological process
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mechanical process
Explanation
$$\bf{Hint:}$$ It is an irreversible process.
$$\bf{Correct \ answer:}$$ Option $$B$$
$$\bf{Explanation \ for \ correct \ option:}$$
A combustion reaction is a type of chemical reaction in which a compound and oxygen are reacted to produce heat and a new product.
It is considered a chemical reaction because once it is completed we cannot revert it into the initial stage as well we get a new product in this reaction.
For example combustion of methane gas.
$$\bf{CH_{4} + 2O_{2} \rightarrow CO_{2} + 2H_{2}O}$$
As here in this reaction methane react with an excess of $$O_2$$ it forms gas $$CO_2$$ and water vapors.
$$\bf{Explanation \ for \ incorrect \ options:}$$
A physical process only changes the appearance of a substance, not it's chemical composition. For example
Heating of water
$$\bf{2H_{2}O(l) \rightarrow H_{2}O(g)}$$
In a biochemical process the transformation of one molecule to a different molecule inside a cell.. For example
$$\bf{O_{2} + Glucose \rightarrow ATP + CO_{2}}$$
In a mechanical process, the transformation of one particular object into a different shape takes place. For example - Heating plastics
The substance which is expected to have the highest ignition temperature out of the following is _________.
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coal
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kerosene
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petrol
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alcohol
Explanation
Ignition temperature of a substance is the least temperature at which the substance starts combustion. We all know coal requires more temperature to start burning or to start combustion.
Substances Ignition temperatures (in Celsius)
Coal
580
Kerosene 295
Petrol 400
Alcohol
365
Hence the
highest ignition temperature is of coal.
The zone of no combustion is _______.
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The middle zone
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Outermost zone
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The base of the flame
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Innermost zone
Explanation
Innermost zone is t
he zone of no combustion. It is also called as dark zone which is formed around the wick of the candle flame.
Burning of coal and wood causes _____________.
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pollution of air
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decrease of non-renewable source of energy
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Both A and B
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Neither A nor B
Explanation
The burning of coal and wood causes air pollution and because of the burning of coal and wood, there is decrease in the amount of non-renewable sources.
Which one of the following is combustible?
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Iron nail
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Glass
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Stone pieces
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Paper
Explanation
Paper is combustible because the paper is made from wood pulp which is an organic matter, it burns in presence of air.
Innermost zone is the _______.
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hottest part
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moderately hot part
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least hot part
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cold part
Explanation
The innermost zone is the least hot part black in colour. This is due to the unburned wax vapor.
Substance which vaporize during burning gives ____________.
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sound
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flame
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combustion
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none of these
Explanation
Substances which vaporize during burning gives flame.
For example, combustion of kerosene oil produces a flame. On the other hand, certain substances like coal do not vaporize and hence does not produce a flame.
Explosion is the evolution of:
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heat
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light
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sound
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all of these
Explanation
Combustion that occurs very rapidly with the evolution of heat, light, and sound is known as explosion.
Example - Crackers.
Good fuel is:
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Readily available
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Cheap
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Burn easily in air
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All of these
Explanation
A fuel is considered good or valuable if it has a low ignition temperature and it produces a large quantity of heat and has high calorific value. Ideal fuels should be easy to store, leave behind no ash after being burnt and burn easily. They are cheap, easily available, produce no harmful odor while burning and can be transported easily and their combustion can be controlled.
Fossil fuels are found in the earth's crust.
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True
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False
Explanation
Fossil fuels are made from decomposing plants and animals. These fuels are found in the Earth's crust.
On burning fuel produces _________ amount of heat.
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large
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less
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very less
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no heat
Explanation
Coal, petroleum and Natural gas all these considered as fossil fuels.
When combustion takes place, the hydrocarbons present in the fossil fuel create energy. The heat that is used to burn fossil fuels causes molecules of hydrogen and carbon to react and produce a large amount of heat.
Which one of the following is non-combustible?
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Stone piece
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Paper
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Straw
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Matchsticks
Explanation
Stone piece is composed by small pieces of rocks and clay. So it does not have organic matter in it to burn in presence of air. Hence, it is a non combustible.
Yellow colour in the flame denotes __________.
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outermost part
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middle zone
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innermost zone
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none of these
Explanation
The middle zone is moderately hot and is yellow in color. This is because of partial combustion.
Solid fuels among the following are _____________.
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coal
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coke
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cow dung
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All
Explanation
All the above are fuels and solid in nature. Hence, option $$D$$ is correct.
Which type of energy is produced during an explosion?
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Heat
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Light
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Sound
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All of the above
Explanation
An explosion is a sudden reaction during which there is a release of a high amount of heat along with light and sound energy.
Why water cannot control fire caused by oil or petrol?
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Water reacts with oil
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Water is denser than oil
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Water is less denser than oil
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Water mixes with oil
Explanation
Water is denser than oil. So it sinks below the oil and oil keeps burning on top and fire cannot be controlled.
Water does not react with the oil and it does not mix with oil.
Hence, option $$B$$ is correct.
The characteristics of non-combustible substances is/are:
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They do not ignite
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They do not support combustion
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They are not volatile
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All of the above
Explanation
Non-combustible substances are the one which possess all the above qualities.
In combustion, heat is ______________.
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absorbed
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released
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reduced
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All of the above
Explanation
In combustion, heat is $$\text{released}$$.
Combustion reactions are the chemical reactions in which substances react with oxygen. In this process, heat is given off or released.
A chemical process in which a substance reacts with oxygen to give off heat is called:
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ignition
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combustion
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Both A and B
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None of the above
Explanation
A chemical process in which a substance reacts with oxygen to give off heat is called combustion. The substance that undergoes combustion is known as a combustible substance.
The lowest temperature at which a substance catches fire is called its ignition temperature.
So the correct option is $$B$$.
What type of materials gives flame?
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All materials
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Materials which vaporise on heating
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Materials which melt on heating
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None of the above
Explanation
The material which vaporizes on burning is capable of producing flame.
Hence the option B is correct.
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