Combustion and Flame Test

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Combustion and Flame Test - 16

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Question 1
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A substance which burn in air is __________ (combustible/ non-combustible) substance such as ____________ (hydrogen/ ammonia/ chlorine).

A
Non-combustible, chlorine

B
Combustible, hydrogen

C
Combustible, ammonia

D
Combustible, chlorine

Solution

A substance which burns in air is $$combustible$$ substance such as $$ammonia$$.
Question 2
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Stack heat losses can be minimized by ____________.

A
controlling the excess air.

B
oxygen enrichment of combustion air.

C
using low c.v. fuels.

D
maintaining proper draft in the furnace.

Solution

Stack effect is the movement of air in and out of buildings, chimneys, flue gas stacks, or other containers, resulting from air buoyancy. Stack losses typically are the largest single energy loss in boiler operations and involve both excess air and stack temperatures. The amount of heat lost will depend on the temperature and volume of gas leaving the boiler. Some stack-gas heat losses are unavoidable but controlling the excess air or lowering the gas temperature as close to the air temperature surrounding the boiler can improve overall efficiency. So, the correct answer is option A.
Question 3
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The products of a burning candle are:

A
ash and water vapour

B
$$CO_2$$ and water vapour

C
wax and water vapour

D
only melted wax

Solution

In candle burning, if there is sufficient oxygen the products are water, $$CO_2$$, light and heat.
Question 4
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A thin paper cup filled with water does not catch fire when placed over a flame. This is because:

A
water cuts off oxygen supply to the paper cup

B
water is an excellent conductor of heat

C
the paper cup does not become appreciably hotter than the water it contains

D
paper is a poor conductor of heat

Solution

Water absorbs a lot of heat. So, when you heat a paper cup containing water,
it absorbs the heat coming from the burning source and thus prevents the paper from reaching the ignition temperature. Hence it does not burn. So you will notice that water in the bowl becomes hot. This is due to the absorption of heat by the water.
So the correct option is C.
Question 5
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While cooking, if the bottom of the vessel is getting blackened on the outside, it means that __________.

A
the food is not cooked completely

B
the fuel is not burning completely

C
the fuel is wet

D
All of above

Solution

While cooking, if the bottom of the vessel is getting blackened on the outside, it means that the fuel is not burning completely. When the fuel burns completely giving a blue flame, the bottom of the vessel remains clean.

When the fuel does not burn completely then a sooty flame appears which makes the bottom of the utensil black. It is due to the air holes, which are getting blocked and the fuel does not burn completely.
Question 6
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Which of the following statements gives the correct distinction between the burning of carbon compounds and respiration?

A
The burning of carbon compounds is a slow process while respiration is spontaneous.

B
Burning of carbon compounds releases energy in form of ATP while respiration releases in form of light.

C
Burning of carbon compounds is a fast process while respiration is slow.

D
All the above statements are correct
Solution
In respiration:
Carbon and Hydrogen present in organic matter are oxidized.
Energy is released in the form of ATP and heat.
It is a slow process.
It occurs at body temperature of $$37^0C$$.

In the burning of carbon compounds:
carbon and hydrogen present in the inorganic matter are oxidized.
energy is released in the form of heat and light.
It is a fast and spontaneous process.
It occurs at higher temperatures.
Question 7
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The different zones of a candle flame are marked by the letters, A, B and C. Which of the following is correct?

A
B is the hottest part of the flame.

B
C is moderately hot.

C
A is the hottest part of the flame.

D
A is moderately hot whereas C is the coldest part.

Solution

There are three zones in a flame. They are:
A: Non-luminous zone
B: Luminous zone
C: Dark zone

The non-luminous zone is the zone of complete combustion. It is the hottest zone of the candle flame and does not produce much light.

Middle zone is the zone which is moderately hot with limited supply of oxygen.

C is a dark zone as this zone doesn't support burning. Because there is no supply of air.

Here option (C) is correct.
Question 8
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The essential requirements for producing a fire ___________.

A
fuel

B
air

C
heat

D
all of the above

Solution

The essential requirements for producing fire are fuel, air, and heat. Air supplies oxygen gas for combustion and heat is to increases the temperature of the fuel beyond ignition temperature. If one of these essential requirements is removed, fire can be controlled.
Hence, option $$D$$ is correct.
Question 9
1 / -0

Charcoal burn to produce heat, light and:

A
$$CO_2$$

B
$$O_2$$

C
$$H_2 $$

D
Both B and c

Solution

When charcoal burns in the air. We know that coal, too, burns in air producing carbon dioxide, heat and light.
Burning of fuel means burning of hydrocarbon like methane in air. It is an exothermic reaction.
$$CH_4 + 2O_2 \rightarrow CO_2 +2H_2O + heat, light$$
Question 10
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Which of the following is combustible?

A
Oxygen

B
Carbon dioxide

C
Hydrogen

D
All of these

Solution

Combustion is an exothermic reaction between a combustible substance and an oxidizer that forms an oxidized product. Exothermic means heat is released by the reaction. Hydrogen is combustible and oxygen is an oxidizer.

$$2H_2+O_2\rightarrow 2H_2O+Energy$$.
Hence option C is correct.

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Combustion and Flame Test - 16

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Combustion and Flame Test - 16

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Question 1

Non-combustible, chlorine

Combustible, hydrogen

Combustible, ammonia

Combustible, chlorine

Solution

Question 2

controlling the excess air.

oxygen enrichment of combustion air.

using low c.v. fuels.

maintaining proper draft in the furnace.

Solution

Question 3

ash and water vapour

$$CO_2$$ and water vapour

wax and water vapour

only melted wax

Solution

Question 4

water cuts off oxygen supply to the paper cup

water is an excellent conductor of heat

the paper cup does not become appreciably hotter than the water it contains

paper is a poor conductor of heat

Solution

Question 5

the food is not cooked completely

the fuel is not burning completely

the fuel is wet

All of above

Solution

Question 6

The burning of carbon compounds is a slow process while respiration is spontaneous.

Burning of carbon compounds releases energy in form of ATP while respiration releases in form of light.

Burning of carbon compounds is a fast process while respiration is slow.

All the above statements are correct

Solution

Question 7

B is the hottest part of the flame.

C is moderately hot.

A is the hottest part of the flame.

A is moderately hot whereas C is the coldest part.

Solution

Question 8

fuel

air

heat

all of the above

Solution

Question 9

$$CO_2$$

$$O_2$$

$$H_2 $$

Both B and c

Solution

Question 10

Oxygen

Carbon dioxide

Hydrogen

All of these

Solution

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