Combustion And Flame Test

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Combustion And Flame Test - 7

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Question 1
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Directions: Read the statements given below and select the correct option.

Statement 1: Combustion is a chemical process in which a substance reacts with oxygen to give out heat and light.
Statement 2: Heat and light are produced in the sun due to combustion.

A
Both statements are true and statement 2 is the correct explanation of statement 1.

B
Both statements are true, but statement 2 is not the correct explanation of statement 1.

C
Statement 1 is true and statement 2 is false.

D
Both statements are false.

Solution

Statement 2 is false because nuclear reactions are responsible for the heat and light produced in the sun.
Question 2
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Which of the following options correctly defines calorific value of a fuel?

A
Heat energy liberated by complete combustion of 1 g of fuel

B
Heat energy liberated by complete combustion of 1 kg of fuel

C
1 kJ of energy liberated by complete combustion of any amount of fuel

D
None of these

Solution

The amount of heat produced by the complete combustion of a material or a fuel is called its calorific value.
It is measured in units of energy per amount of material, e.g. kJ/kg.
Question 3
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Observe the image given below and answer the question that follows.

Which of the following in an incorrect statement?

A
The orange colour of the middle zone is on account of complete combustion of the fuel.

B
The outermost zone is the hottest part of the flame.

C
The wick turns black due to deposition of unburnt carbon particles.

D
The flame is the burning vapour of paraffin wax.

Solution

Complete combustion takes place in the outermost part of the flame due to the availability of oxygen, which is the reason that this is the hottest part of the flame.
Partial combustion takes place in the middle zone, because the supply of oxygen is inadequate; hence, a yellowish orange luminous flame is produced.
Therefore, option (1) is incorrect.
Question 4
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Analyse the two statements given below and select the correct option.

Statement I: Fuel are energy reserves and this energy is released by the process of combustion.
Statement II: Combustion is the process of burning the substance in the presence of a sufficient quantity of oxygen.

A
Both statements I and II are correct and statement II is the correct reason for I.

B
Both statements I and II are correct, but statement II is not the correct reason for I.

C
Statement I is correct, but statement II is incorrect.

D
Both statements I and II are incorrect.

Solution

Both statements I and II are correct, but statement II is not the correct reason for I.
The correct reason for statement I is that combustion is an exothermic process.
Question 5
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Observe the given flow chart and the statements that follow.

I. W and X are the components of water gas.
II. W, X and Y are the components of coal gas.
III. W is a rocket fuel.
IV. Z is a domestic fuel.

Which of the following options is the correct identification of W, X, Y and Z?

A
W - Hydrogen; X - Carbon monoxide; Y - Methane; Z - L.P.G.

B
W - Hydrogen; X - Methane; Y - Carbon monoxide; Z - L.P.G.

C
W - Carbon monoxide; X - Hydrogen; Y - Methane; Z - L.P.G.

D
W - L.P.G; X - Carbon monoxide; Y - Methane; Z - Hydrogen

Solution

W - Hydrogen; X - Carbon monoxide; Y - Methane; Z - L.P.G.
This is the correct identification of the combustible substances W, X, Y and Z.
W is hydrogen (rocket fuel); hence, X is the other component of water gas and is carbon monoxide.
Y will be the third component of coal gas which is methane.
Z is L.P.G, which is used as a domestic fuel.
Question 6
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Which of the following options regarding burning of coal is correct?

A
It burns with a flame.

B
It vaporises on heating.

C
It smoulders when hot.

D
It leaves no residue on burning.

Solution

Coal is a solid fuel and it does not vaporise on heating. Hence, it does not burn with a flame, but smoulders on heating.
The initial flame formed is due to the trapped impurities.
Moreover, coal on burning produces solid ash.
Question 7
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Combustion of fuels is

A
an oxidation reaction in the absence of nitrogen

B
an endothermic process

C
a process of chemical combination with atmospheric oxygen

D
an oxidation process in the absence of air

Solution

Combustion of fuel is the reaction of fuel with excess of oxygen to release energy.
Hence, the process is highly exothermic.
Question 8
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In which of the following cases is the use of water as a fire extinguisher inappropriate?

I. In an electrical appliance shop
II. In a newspaper factory
III. In a furniture house

A
Only II and III

B
Only I and II

C
Only I and III

D
Only I

Solution

Water works as a fire extinguisher by lowering the temperature of the fuel below its ignition temperature.
However, it should not be used to put off a fire caused by electric current, as water being a good conductor of electricity could cause an electric shock.
Hence, its use to put off a fire in an electrical appliance shop is inappropriate.
Question 9
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What happens when water is heated in a paper cup?

A
Paper cup burns up without any change in the temperature of water.

B
Paper cup burns up with water undergoing the boiling process.

C
There is no effect on the paper cup or water.

D
Water continues to boil without the paper cup getting burnt up.

Solution

On heating a paper cup containing water, the heat is transferred to the water which begins to boil.
Since all the heat supplied is used up to vaporise water, the paper does not acquire its ignition temperature and hence the cup does not burn up, while the water continues to boil.
Question 10
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Water is used to extinguish fire because it

A
raises the ignition temperature of the burning substance

B
cools the burning substance down to a temperature below its ignition temperature

C
lowers the ignition temperature of the burning substance

D
conducts heat

Solution

Water cools the burning substance down to a temperature below its ignition temperature and as a result, the burning process stops.
Question 11
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Directions: Read the two statements given below and select the correct option accordingly.

Statement I: Air supports the combustion process.
Statement II: Air is a homogeneous mixture of gases with 78% nitrogen and nearly 21% oxygen.

A
Both statements I and II are correct, and statement II is the correct reason for statement I.

B
Both statements I and II are correct, but statement II is not the correct reason for statement I.

C
Statement I is correct, but statement II is incorrect.

D
Both statements I and II are incorrect.

Solution

Both statements I and II are correct, and statement II is the correct reason for statement I.
Since air is a mixture, its components retain their characteristic properties.
Hence, oxygen present in the air supports combustion.
Question 12
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Consider the following statements about the combustion of fuels:

(i) Combustion of fuels occurs in the presence of oxygen.
(ii) Combustion is a slow process.
(iii) It requires an external source of ignition.
(iv) This process usually takes place at room temperature.

Which of the above statements are not correct?

A
Only (i) and (ii)

B
Only (ii) and (iv)

C
Only (iii) and (iv)

D
Only (i) and (iv)

Solution

The statements (ii) and (iv) are incorrect, because combustion is a fast process and fuels have to be heated to their ignition temperature before they start burning.
Question 13
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Which among the following are released during the process of combustion of fuels?

A
Energy + Carbon dioxide

B
Energy + Carbon dioxide + Water vapour

C
Energy + Oxygen + Water vapour

D
Energy + Water vapour

Solution

When hydrocarbons are burned as fuels, carbon dioxide and water are produced as combustion products along with the release of enormous amount of energy. Moreover, since the temperature of the reaction mixture is above 373K, the water formed is in the vapour form.
Hydrocarbons (g) + O₂(g) CO₂(g) + H₂O (g) + Energy

Question 14

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Match the combustion processes in Column I with the types of combustion in Column II.

Column I	Column II
I. A piece of phosphorus bursting into flames on its own	(i) Rapid combustion
II. Bursting of a cracker	(ii) Spontaneous combustion
III. Lighting of an LPG burner	(iii) Explosion

I - (iii), II - (ii), III - (i)

I - (ii), II - (iii), III - (i)

I - (iii), II - (i), III - (ii)

I - (ii), II - (i), III - (iii)

Solution

The correct match is: I - (ii), II - (iii), III - (i)

Column I	Column II
I. A piece of phosphorus bursting into flames on its own	(ii) Spontaneous combustion
II. Bursting of a cracker	(iii) Explosion
III. Lighting of an LPG burner	(i) Rapid combustion

Question 15
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Which of the following chemical substances are the components of a matchstick head and which are present on the striking surface (Side of the match box)?

(I) Antimony trisulphide
(II) Potassium chlorate
(III) Red phosphorus
(IV) Powdered glass

A
(I) and (IV) on the match stick head; (II) and (II) on the match box.

B
(II) and (III) on the match stick head; (I) and (IV) on the match box.

C
(III) and (IV) on the match stick head; (I),(II) and (III) on the match box.

D
(III) and (IV) on the match stick head; (I) and (II) on the match box.

Solution

The tip of a matchstick: Potassium chlorate (an oxidant), Antimony trisulphide (Source of sulphur), starch, glue and some other ingredients
Striking surface (Matchbox sides): Red phosphorus, powdered glass, and glue
Question 16
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Which of the following fuels has the highest calorific value?

A
Wood

B
Kerosene

C
LPG

D
Hydrogen

Solution

Hydrogen has the highest calorific value, which is why it is used as a rocket fuel.
Question 17
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A good fuel should have

A
a high ignition temperature

B
a low ignition temperature

C
a very low ignition temperature

D
a variable ignition temperature according to the weather conditions

Solution

A good fuel should have a low ignition temperature, but it should be safely above the room temperature.
This is important so that the fuel is safe to store.
Question 18
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Study the dichotomous key and identify the correct statements about W, X and Y:

I. (i) A fuel that does not burn with a flame
(ii) A fuel that burns with a flame Go to II
II. (i) It is a gaseous fuel.
(ii) It is a solid fuel.

A. W may be wood or kerosene.
B. X may be used for cooking.
C. Y can produce a luminous flame.
D. Y vaporises on heating.
E. X may be used in automobiles.

A
Only A, B and C

B
Only A, B, C and D

C
Only B, C, D and E

D
Only B, C and E

Solution

W may be wood or coal, which are solid fuels that do not burn with a flame. Kerosene vaporises on heating and burns with a flame. Hence, statement A is incorrect.
X may be CNG (automobile fuel) or LPG (domestic fuel), both of which are gaseous fuels and burn with a flame.
Y may be paraffin wax, which vaporises on heating and burns with a luminous flame in candles.
Hence, B, C, D and E are correct statements.

Question 19

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Match the following:

Column - I	Column - II
(a) Hottest zone of a candle flame	(i) No combustion zone
(b) Dark zone of a candle flame	(ii) Zone of unburnt wax vapours
(c) Yellow zone of a candle flame	(iii) Non-luminous zone
(d) Black, innermost zone of a candle flame	(iv) Incomplete combustion zone

(a) – (i), (b) – (ii), (c) – (iii), (d) – (iv)

(a) – (iii), (b) – (i), (c) – (iv), (d) – (ii)

(a) – (iv), (b) – (iii), (c) – (ii), (d) – (i)

(a) – (ii), (b) – (i), (c) – (iii), (d) – (iv)

Solution

Column - I	Column - II
(a) Hottest zone of a candle flame	Non-luminous zone
(b) Dark zone of a candle flame	No combustion zone
(c) Yellow zone of a candle flame	Incomplete combustion zone
(d) Black, innermost zone of a candle flame	Zone of unburnt wax vapours

Question 20
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In the flow chart given below, X and Y represent the type of combustion and P and Q represent the type of flame.

Select the option which is the correct identification of X, Y, P and Q.

A
X: Partial combustion; Y: Complete combustion
P: Non-luminous flame; Q: Luminous flame

B
X: Partial combustion; Y: Complete combustion
P: Luminous flame; Q: Non-luminous flame

C
X: Complete combustion; Y: Partial combustion
P: Non-luminous flame; Q: Luminous flame

D
X: Partial combustion; Y: Complete combustion
P: Luminous flame; Q: Luminous flame

Solution

Complete combustion (X) takes place in an LPG stove and partial combustion (Y) during the burning of a candle.
Non-luminous flame (P) is produced as a result of complete combustion and luminous flame (Q) is produced as a result of partial combustion.

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Combustion And Flame Test - 7

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Combustion And Flame Test - 7

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Question 1

Both statements are true and statement 2 is the correct explanation of statement 1.

Both statements are true, but statement 2 is not the correct explanation of statement 1.

Statement 1 is true and statement 2 is false.

Both statements are false.

Solution

Question 2

Heat energy liberated by complete combustion of 1 g of fuel

Heat energy liberated by complete combustion of 1 kg of fuel

1 kJ of energy liberated by complete combustion of any amount of fuel

None of these

Solution

Question 3

The orange colour of the middle zone is on account of complete combustion of the fuel.

The outermost zone is the hottest part of the flame.

The wick turns black due to deposition of unburnt carbon particles.

The flame is the burning vapour of paraffin wax.

Solution

Question 4

Both statements I and II are correct and statement II is the correct reason for I.

Both statements I and II are correct, but statement II is not the correct reason for I.

Statement I is correct, but statement II is incorrect.

Both statements I and II are incorrect.

Solution

Question 5

W - Hydrogen; X - Carbon monoxide; Y - Methane; Z - L.P.G.

W - Hydrogen; X - Methane; Y - Carbon monoxide; Z - L.P.G.

W - Carbon monoxide; X - Hydrogen; Y - Methane; Z - L.P.G.

W - L.P.G; X - Carbon monoxide; Y - Methane; Z - Hydrogen

Solution

Question 6

It burns with a flame.

It vaporises on heating.

It smoulders when hot.

It leaves no residue on burning.

Solution

Question 7

an oxidation reaction in the absence of nitrogen

an endothermic process

a process of chemical combination with atmospheric oxygen

an oxidation process in the absence of air

Solution

Question 8

Only II and III

Only I and II

Only I and III

Only I

Solution

Question 9

Paper cup burns up without any change in the temperature of water.

Paper cup burns up with water undergoing the boiling process.

There is no effect on the paper cup or water.

Water continues to boil without the paper cup getting burnt up.

Solution

Question 10

raises the ignition temperature of the burning substance

cools the burning substance down to a temperature below its ignition temperature

lowers the ignition temperature of the burning substance

conducts heat

Solution

Question 11

Both statements I and II are correct, and statement II is the correct reason for statement I.

Both statements I and II are correct, but statement II is not the correct reason for statement I.

Statement I is correct, but statement II is incorrect.

Both statements I and II are incorrect.

Solution

Question 12

Only (i) and (ii)

Only (ii) and (iv)

Only (iii) and (iv)

Only (i) and (iv)

Solution

X: Partial combustion; Y: Complete combustion
P: Non-luminous flame; Q: Luminous flame

X: Partial combustion; Y: Complete combustion
P: Luminous flame; Q: Non-luminous flame

X: Complete combustion; Y: Partial combustion
P: Non-luminous flame; Q: Luminous flame

X: Partial combustion; Y: Complete combustion
P: Luminous flame; Q: Luminous flame