Chapter 4: Combustion and Flame with this engaging Class 8 quiz! Test your knowledge with thoughtfully crafted questions and answers designed to make learning fun and interactive. Perfect for students seeking a deeper understanding of combustion, flame structure, and related concepts. Sharpen your science skills and ace your studies with this exciting educational challenge!
1) What are some common fuels used in homes?
Answer: Common fuels used in homes include cow dung, wood, coal, charcoal, petrol, diesel, and compressed natural gas (CNG).
2) Can you name some fuels used in trade and industry?
Answer: Fuels used in trade and industry include coal, petrol, diesel, and compressed natural gas (CNG), among others.
3) What fuels are used for running automobiles?
Answer: Fuels used for running automobiles include petrol, diesel, and compressed natural gas (CNG).
4) What is the difference between the burning of a candle and the burning of coal?
Answer: A candle burns with a flame, whereas coal does not burn with a flame.
5) Can all materials burn with a flame?
Answer: No, not all materials burn with a flame. Some burn without a flame.
6) What is combustion?
Answer: Combustion is a chemical process in which a substance reacts with oxygen to give off heat. Sometimes, light is also produced, either as a flame or as a glow.
7) What is a combustible substance?
Answer: A combustible substance is a material that undergoes combustion. It is also called fuel.
8) What are the different states in which fuels can exist?
Answer: Fuels can exist in solid, liquid, or gaseous states.
9) What did we learn from the activity of burning magnesium ribbon?
Answer: We learned that magnesium burns in the air to form magnesium oxide and produces heat and light.
10) What happens when charcoal is brought near the flame of a candle or a Bunsen burner?
Answer: Charcoal burns in the air, producing carbon dioxide, heat, and light.
11) What are some examples of combustible substances?
Answer: Examples of combustible substances include magnesium and charcoal.
12) How is food considered a fuel for our body?
Answer: In our body, food is broken down by a reaction with oxygen, which produces heat and energy. Food is considered a fuel for our body as it provides energy, similar to how fuel provides energy for combustion.
13) How do you identify if a material is combustible or non-combustible?
Answer: If combustion takes place, the material is marked combustible; otherwise, it is marked non-combustible.
14) Can you list some combustible materials?
Answer: Combustible materials include wood, paper, kerosene oil, straw, charcoal, and matchsticks.
15) Can you list some non-combustible materials?
Answer: Non-combustible materials include iron nails, stone pieces, and glass.
16) Can you name additional substances that are combustible?
Answer: Additional combustible substances can include items like natural gas, ethanol, or wax.
17) Why candle burn freely in the chimney?
Answer: The candle burns freely because air can enter the chimney from below.
18) For the combustion of any material which thing is necessary?
Answer: For combustion to occur, air (specifically oxygen) is necessary.
19) Is the heat and light produced by the sun a result of combustion?
Answer: No, the heat and light produced by the sun are the result of nuclear reactions, not combustion.
20) What happens when a piece of burning wood or charcoal is covered with a jar?
Answer: The charcoal or wood stops burning after some time because the supply of air (oxygen) is cut off, which is essential for combustion.
21) Why does a blanket extinguish fire when wrapped around a person?
Answer: A blanket extinguishes fire by cutting off the supply of air (oxygen), which is necessary for the fire to continue burning.
22) Can a matchstick burn by itself?
Answer: No, a matchstick cannot burn by itself. It needs to be struck against a surface to ignite.
23) Does paper burn when a burning matchstick is brought near it?
Answer: Yes, paper burns easily when a burning matchstick is brought near it.
24) Can wood burn when a burning matchstick is brought near it?
Answer: No, wood does not ignite easily with a burning matchstick. It requires additional materials like paper or kerosene to start burning.
25) Why do we use paper or kerosene oil to start a fire in wood or coal?
Answer: Paper and kerosene oil catch fire easily and help to increase the temperature, which is necessary to ignite materials like wood or coal.
26) What causes forest fires?
Answer: During extreme heat in summer, dry grass catches fire. The fire then spreads to trees, and eventually, the entire forest can catch fire.
27) Why are forest fires difficult to control?
Answer: Forest fires are difficult to control because they spread quickly over large areas due to the abundance of dry vegetation and wind.
28) Do these experiences tell you that different substances catch fire at different temperatures?
Answer: Yes, the provided experiences strongly suggest that different substances have varying ignition temperatures. Some substances, like kerosene oil, ignite at relatively lower temperatures compared to others, such as wood.
29) What is the lowest temperature at which a substance catches fire called?
Answer: The lowest temperature at which a substance catches fire is called its ignition temperature.
30) Can you tell now why a matchstick does not catch fire on its own at room temperature?
Answer: A matchstick doesn't ignite spontaneously at room temperature because its temperature is below its ignition temperature.
31) What is the condition for a combustible substance to catch fire or burn?
Answer: A combustible substance can only catch fire or burn when its temperature reaches or exceeds its ignition temperature.
32) Can cooking oil catch fire when a frying pan is left on a burning stove for an extended period?
Answer: Yes, cooking oil can catch fire if a frying pan is left on a burning stove for a prolonged time.
33) Kerosene oil and wood do not catch fire on their own at room temperature. But, if kerosene oil is heated a little, it will catch fire. But if the wood is heated a little, it would still not catch fire. Does it mean that the ignition temperature of kerosene oil is lower than that of wood?
Answer: Yes, the observation that kerosene oil ignites with minimal heating while wood requires significant heating suggests that kerosene oil has a lower ignition temperature than wood.
34) Does it mean that we need to take special care in storing kerosene oil?
Answer: Yes, the fact that kerosene oil has a relatively low ignition temperature necessitates careful storage to prevent accidental fires.
35) What happens to the empty paper cup? What happens to the paper cup with water? Does water in this cup become hot?
Answer: The empty paper cup will catch fire and burn when heated with a candle.
The paper cup containing water will not burn easily. The water absorbs heat from the candle, preventing the paper cup from reaching its ignition temperature.
Yes, the water in the cup will become hot.
36) What happens if we continue heating the paper cup containing water?
Answer: We can even boil water in a paper cup.
37) Can you think of an explanation for the boiling water in the paper cup?
Answer: The heat supplied to the paper cup is transferred to the water through conduction. This heat transfer prevents the paper from reaching its ignition temperature, thus preventing it from burning.
38) What are inflammable substances?
Answer: Inflammable substances are those that have very low ignition temperatures and can easily catch fire with a flame.
39) Give some examples of inflammable substances.
Answer: Some examples of inflammable substances include petrol, alcohol, and Liquified Petroleum Gas (LPG).
40) What actions do firefighters typically take when they arrive at a fire scene?
Answer: Firefighters typically pour water on the fire.
41) What are the three essential requirements for producing fire?
Answer: The three essential requirements for producing fire are fuel, air (to supply oxygen), and heat (to raise the temperature of the fuel beyond its ignition temperature).
42) How do fire extinguishers help control fire?
Answer: Fire extinguishers work by cutting off the supply of air, bringing down the temperature of the fuel, or both.
43) What is the most common type of fire extinguisher?
Answer: The most common fire extinguisher is water.
44) When is water effective in extinguishing fires?
Answer: Water is effective in extinguishing fires involving materials like wood and paper.
45) Why is water not suitable for extinguishing fires involving electrical equipment?
Answer: Water can conduct electricity, posing a risk of electrocution to those attempting to extinguish fires involving electrical equipment.
46) Why is water not suitable for extinguishing fires involving oil and petrol?
Answer: Water is denser than oil and petrol, causing it to sink below the flammable liquid, allowing the fire to continue burning on the surface.
47) What type of fire extinguisher is best suited for fires involving electrical equipment and flammable materials like petrol?
Answer: Carbon dioxide (CO2) is the best extinguisher for such fires.
4. CO2, being heavier than oxygen, covers the fire like a blanket. Since the contact between the fuel and oxygen is cut off, the fire is controlled.
48) How does carbon dioxide extinguish fires?
Answer: CO2, being heavier than oxygen, blankets the fire, cutting off the supply of oxygen to the fuel and thus controlling the fire.
49) What is an added advantage of using CO2 as a fire extinguisher?
Answer: In most cases, CO2 does not damage electrical equipment.
50) How is carbon dioxide stored for use in fire extinguishers?
Answer: Carbon dioxide is stored at high pressure as a liquid in cylinders.
51) In what form is LPG stored in cylinders?
Answer: LPG is stored in cylinders as a liquid.
52) What happens when CO2 is released from a cylinder?
Answer: CO2 expands significantly in volume and cools down upon release from a cylinder.
53) What is another method of obtaining CO2 for fire extinguishing purposes?
Answer: Releasing dry powders of chemicals like sodium bicarbonate or potassium bicarbonate can produce CO2 near the fire.
54) What happens when a burning matchstick or gas lighter is brought near a gas stove and the knob is turned on?
Answer: The gas burns rapidly, producing heat and light. (This question requires a practical observation.)
55) What is the term for the type of combustion observed when a gas burns rapidly, producing heat and light?
Answer: Such combustion is known as rapid combustion.
56) Are there substances that can burn in air at room temperature?
Answer: Yes, there are substances like phosphorus that can burn in air at room temperature.
57) What is spontaneous combustion?
Answer: Spontaneous combustion is a type of combustion where a material suddenly bursts into flames without any apparent external cause.
58) What can cause spontaneous combustion fires in coal mines and forests?
Answer: Spontaneous combustion of coal dust can cause fires in coal mines. In forests, spontaneous fires can be caused by the heat of the sun or lightning strikes. However, most forest fires are due to human carelessness.
59) What's an important safety measure to take after using a campfire in the forest?
Answer: It's crucial to completely extinguish campfires before leaving a forest after a picnic or visit.
60) What kind of reaction occurs when a firework cracker is ignited?
Answer: When a firework cracker is ignited, a rapid reaction takes place, releasing heat, light, and sound. A large amount of gas is also produced during this reaction.
61) What other way can a firework explode besides ignition?
Answer: Applying pressure to a firework cracker can also cause it to explode.
62) What is the color of an LPG flame?
Answer: When LPG burns completely, the flame is typically blue.If the flame is yellow, orange, or red, it signifies incomplete combustion.
63) What is the color of a candle flame?
Answer: A candle flame typically appears yellow.
64) Does a kerosene stove produce a flame when lit?
Answer: Yes, a kerosene stove produces a flame when lit.
65) If a flame is observed, what is the likely cause of this flame?
Answer: The vapors of wax coming out of the glass tube are likely the cause of the flame.
66) What happens to the wax near the heated wick of the candle?
Answer: The wax near the heated wick melts quickly.
67) What happens when a clean glass plate/slide is held in the luminous zone of a candle flame for about 10 seconds?
Answer: (This requires observation) A circular blackish ring is likely to form on the glass plate/slide.
68) What type of substances produce flames during burning?
Answer: Substances that vaporize during burning produce flames.
69) Give an example of substances that produce flames during burning.
Answer: Kerosene oil and molten wax are examples of substances that produce flames during burning.
70) Why doesn't charcoal produce a flame?
Answer: Charcoal does not vaporize during burning and therefore does not produce a flame.
71) What is observed on the glass plate/slide after being held in the luminous zone of the flame?
Answer: A circular blackish ring is formed on the glass plate/slide.
72) What does the blackish ring on the glass plate/slide indicate?
Answer: The blackish ring indicates the deposition of unburnt carbon particles present in the luminous zone of the flame.
73) What happens to a thin copper wire when held just inside the non-luminous zone of a flame for about 30 seconds?
Answer: The portion of the copper wire just outside the flame gets red hot.
74) Does the fact that the copper wire gets red hot indicate that the non-luminous zone of the flame has a high temperature?
Answer: Yes, the fact that the copper wire gets red hot when placed in the non-luminous zone of the flame strongly indicates that this zone has a high temperature.
75) Which part of the flame is the hottest?
Answer: The outermost zone of the flame is the hottest part.
76) What is the color of the outer zone of the candle flame?
Answer: The outer zone of the candle flame shows complete combustion and its color is blue.
77) What is the color of the middle zone of the candle flame?
Answer: The middle zone of candle flame shows partial combustion and its color is yellow.
78) What is the color of the innermost zone of the candle flame?
Answer: The innermost zone of candleflame shows unburnt wax vapors and its color is black.
80) Why do goldsmiths use the outermost zone of a flame for melting gold and silver?
Answer: Goldsmiths use the outermost zone of the flame because it is the hottest part, which is necessary for melting metals like gold and silver.
81) What are fuels?
Answer: Fuels are substances used as sources of heat energy for domestic and industrial purposes, such as wood, charcoal, petrol, and kerosene.
82) What are the characteristics of a good fuel?
Answer: A good fuel should be readily available, cheap, burn easily at a moderate rate, produce a large amount of heat, and not leave behind any undesirable substances.
83) Is there an ideal fuel that fulfills all requirements?
Answer: No, there is probably no single fuel that can be considered an ideal fuel for all purposes.
84) How do fuels differ?
Answer: Fuels differ in their cost, with some being cheaper than others.
85) List some familiar fuels and categorize them as solid, liquid, and gaseous fuels.
Answer: Solid Fuels: Coal, Wood, Charcoal
Liquid Fuels: Kerosene oil, Petrol, Diesel
Gaseous Fuels: Natural gas, LPG (Liquefied Petroleum Gas)
86) Do cow dung, coal, and LPG produce the same amount of heat?
Answer: No, these fuels do not produce the same amount of heat.
87) What is the calorific value of a fuel?
Answer: The calorific value of a fuel is the amount of heat energy produced on the complete combustion of 1 kg of that fuel.
88) What is the unit of calorific value?
Answer: The unit of calorific value is kilojoule per kilogram (kJ/kg).
89) What is the calorific value of wood?
Answer: The calorific value of wood is 17000-22000 kJ/kg.
90) Which fuel has the highest calorific value?
Answer: Hydrogen has the highest calorific value at 150000 kJ/kg.
91) What is the calorific value of Cow dung cake, Coal, Petrol, Kerosene, Diesel, Methane, CNG, LPG, and Biogas?
Answer: Cow dung cake-6000-8000 kJ/kg.
Coal-25000-33000 kJ/kg.
Petrol-45000 kJ/kg.
Kerosene-45000 kJ/kg.
Diesel-45000 kJ/kg.
Methane-50000 kJ/kg.
CNG-50000 kJ/kg.
LPG-55000 kJ/kg.
Biogas-35000-40000 kJ/kg.
92) What are some of the harmful effects of increasing fuel consumption on the environment?
Answer: Increasing fuel consumption can lead to harmful effects on the environment, including the release of pollutants and greenhouse gases.
93) What are some of the disadvantages of using wood as fuel?
Answer: Burning wood produces a lot of smoke, which is harmful to human health and can cause respiratory problems.
Wood provides useful substances that are lost when it is burned as fuel.
Cutting trees for fuel leads to deforestation, which has harmful environmental consequences.
94) How does the burning of carbon fuels like wood, coal, and petroleum affect the environment?
Answer: Burning carbon fuels releases unburnt carbon particles, carbon monoxide, carbon dioxide, and other pollutants into the environment.
95) What are unburnt carbon particles, and what are their effects?
Answer: Unburnt carbon particles are fine particles released during the combustion of carbon fuels. They are dangerous pollutants that can cause respiratory diseases like asthma.
96) What is carbon monoxide, and why is it dangerous?
Answer: Carbon monoxide is a poisonous gas produced by the incomplete combustion of fuels. Burning coal in a closed room can release carbon monoxide, which can be fatal for those sleeping in the room.
97) What is the effect of increased carbon dioxide concentration in the atmosphere?
Answer: Increased carbon dioxide concentration in the atmosphere is believed to cause global warming.
98) What are the consequences of global warming?
Answer: Global warming can lead to the melting of polar glaciers, causing a rise in sea levels and resulting in floods in coastal areas.
99) What are the effects of burning coal and diesel?
Answer: Burning coal and diesel releases sulfur dioxide gas, which is a suffocating and corrosive gas. Petrol engines release oxides of nitrogen. Both sulfur dioxide and nitrogen oxides can dissolve in rainwater to form acid rain, which is harmful to crops, buildings, and soil.
100) Why is CNG considered a cleaner fuel compared to diesel and petrol?
Answer: CNG produces significantly fewer harmful products compared to diesel and petrol, making it a cleaner fuel option.
