Combustion and Flame quiz

The gas necessary for combustion is:

The hottest part of a candle flame is the:

Which of the following fuels has the highest calorific value?

The most suitable fire extinguisher for a fire in electrical equipment is:

Which of the following is an example of spontaneous combustion?

The unit of calorific value is:

Which of the following is an inflammable substance?

Incomplete combustion of fuels produces the poisonous gas:

The middle zone of a candle flame is:

The head of a safety match contains:

Define combustion. What are the products formed when charcoal burns in air? (2 marks)

Explain ignition temperature with the help of an example. (2 marks)

Why does a burning candle go out when it is covered with an inverted glass tumbler? (2 marks)

Why is carbon dioxide the best extinguisher for fires involving electrical equipment and inflammable materials like petrol? (2 marks)

Why should water not be used to put out a fire in a pan of hot oil? (2 marks)

How do forest fires sometimes start, and why do they spread rapidly in hot, dry weather? (2 marks)

Give two reasons why LPG is a better domestic fuel than wood. (2 marks)

What is acid rain? Name the gases released by burning fuels that cause it. (2 marks)

What do you observe when a magnesium ribbon is burnt in air? Name the product formed. (2 marks)

Why does a goldsmith use the outermost zone of a flame for melting gold? (2 marks)

When 3 kg of a liquid fuel is burnt completely, 1,35,000 kJ of heat is produced. Calculate its calorific value and suggest which common liquid fuel it could be. (3 marks)

A family uses 12 kg of LPG (calorific value 55,000 kJ/kg) in a month. Find the total heat produced. How much wood (calorific value 17,000 kJ/kg) would give the same amount of heat? Give your answer to one decimal place. (3 marks)

Biogas has a calorific value of about 35,000 kJ/kg and cow dung cake about 6,000 kJ/kg. Find the heat produced by burning 10 kg of each, and how many times more heat biogas gives. (3 marks)

Compare the heat produced by burning 0.25 kg of hydrogen (calorific value 1,50,000 kJ/kg) with that produced by burning 1 kg of coal (calorific value 25,000 kJ/kg). Which gives more heat and by how much? (3 marks)

A student covered identical burning candles with glass jars of 250 mL, 500 mL and 1000 mL. The candles went out after 10 s, 20 s and 40 s respectively. Describe the relationship shown, explain it, and predict how long a candle would burn under a 2000 mL jar. (3 marks)

Read the passage and answer the questions. While frying puris, the oil in Radha's pan caught fire. Her brother was about to throw a mug of water on it, but their mother stopped him, quickly turned off the gas and covered the pan with a tight lid. (i) Why was it wrong to throw water on the burning oil? (ii) How did covering the pan with a lid put out the fire? (iii) Which side of the fire triangle was removed by turning off the gas, and which by the lid? (5 marks)

Read the passage and answer the questions. On a cold winter night, a family in a hill town kept a coal stove burning in a closed room with all the windows shut. In the morning, some members felt dizzy and were taken to hospital. (i) Name the poisonous gas that was likely formed and explain why it formed. (ii) Why is this gas especially dangerous? (iii) Suggest two precautions to avoid such accidents. (5 marks)

Read the passage and answer the questions. Early matches used white phosphorus, which was dangerous for both the workers and the users. Today, safety matches have a head containing antimony trisulphide and potassium chlorate, while the rubbing surface on the side of the box contains powdered glass and a little red phosphorus. (i) Why was white phosphorus dangerous? (ii) What happens when a safety match is struck on the side of the box? (iii) Why is a safety match called "safe"? (5 marks)

Read the passage and answer the questions. In summer, a forest fire spread across several hectares of a hill forest. Firefighters cleared a strip of land of all trees and dry grass ahead of the fire, and helicopters dropped water on the burning area. (i) Give two possible natural causes of the forest fire. (ii) Which requirement for combustion was removed by clearing the strip of land? (iii) How does dropping water help to control the fire? (5 marks)

Read the passage and answer the questions. In a village, most families burn cow dung cakes and wood for cooking, and the kitchens are often filled with smoke. The panchayat plans to set up a community biogas plant that will supply gas through pipes. (i) Why are cow dung cakes a poor fuel? (ii) Give two advantages of biogas over cow dung cakes. (iii) How will the change improve the health of the women and children in the village? (5 marks)

Draw a labelled diagram of a candle flame showing its three zones. Describe the colour, temperature and type of combustion in each zone, and describe the experiments with a glass plate held in the luminous zone and a copper wire held in the non-luminous zone that support your description. (6 marks)

Draw the fire triangle. Explain the three conditions necessary for combustion with one activity for each, and describe how water, sand and carbon dioxide extinguishers put out fires, stating which type of fire each is best suited for. (6 marks)

Draw a labelled diagram of the activity in which water in a paper cup is heated over a candle or burner. Explain why the cup does not burn, and use the idea of ignition temperature to explain why a matchstick lights only when struck, and why wet wood is hard to burn. (6 marks)

List the characteristics of a good fuel. Draw a bar graph comparing the approximate calorific values of cow dung cake (6,000 kJ/kg), wood (17,000 kJ/kg), coal (25,000 kJ/kg), petrol (45,000 kJ/kg), LPG (55,000 kJ/kg) and hydrogen (1,50,000 kJ/kg). Use the graph to discuss which fuels are most efficient and why some high-value fuels are not always used. (6 marks)

Draw a flowchart showing the harmful effects of burning fuels: carbon particles, carbon monoxide, carbon dioxide, and oxides of sulphur and nitrogen. Explain each effect on human health or the environment, including global warming and acid rain, and suggest ways to reduce these effects. (6 marks)