CE : Section 5 Fossil Fuels
Alkenes can be obtained from petroleum fractions by a process called ‘cracking’. Using a suitable petroleum fraction, a student carried out this process in the laboratory and collected the gaseous product over water.
(i)What is ‘cracking’ ?
(ii)Draw a labelled diagram of a laboratory set-up that can be used for carrying out the process and collecting the gaseous product.
(iii)An important safety precaution in the experiment is to prevent sucking back.
(1)What is the potential hazard if sucking back occurs ?
(2)How can sucking back be prevented ?
(iv)If the gaseous product decolorizes a solution of bromine in tetrachloromethane, can you conclude that the gaseous product in ethene ? Explain your answer.
When chemical wastes such as methylbenzene and tetrachloromethane are burnt in the incinerator in the plant, several pollutants including sulphur dioxide are produced.
(1)Explain why sulphur dioxide is emitted from the incinerator.
(2)Name TWO pollutants other than sulphur dioxide which are emitted from the incinerator and state ONE harmful effect for each pollutant. (5 marks)
The following experimental set-up was used to determine the empirical formula of an oxide of copper.
In the experiment, 8.58 g of an oxide of copper, after complete reaction, produced 7.62 g of copper.
(i)*Deduce the empirical formula of the oxide of copper.
(ii)Write an equation for the reaction that occurred in the combustion tube.
(iii)State TWO potential hazards associated with this experiment, and suggest a safety precaution for each hazard.
(iv)At the end of the reaction, heating was stopped. However, it was necessary to continue passing the town gas through the combustion tube until the tube had cooled down. Explain why.
(Relative atomic masses : Cu = 63.5, O = 16.0)
The fumes emitted from a factory using diesel fuel contain several gaseous pollutants. One of these pollutants, Z, has a choking smell and can decolourize bromine water.
(i)(1)What is Z ?
(2)What is the effect of Z on the environment ?
(3)Suggest ONE way to reduce the amount of Z in the fumes.
(ii)(1)Suggest ONE other pollutant that is present in the fumes.
(2)Explain how this pollutant is formed.
(3)What is the effect of this pollutant on the environment ?
(4)Suggest ONE way to reduce the amount of this pollutant in the fumes.
(iii)If a fire is caused by the burning of diesel fuel, what type of fire extinguisher should not be used to put out the fire ? (8 marks)
A student suggested the following immediate actions to deal to three domestic accidents. However, these actions are considered inappropriate.
(1)Some drain cleaner, which contains mainly concentrated sodium hydroxide solution, is split onto the hand. Use vinegar to neutralize the sodium hydroxide solution left on the hand. (2)During cooking, some oil in a cooking pan catches fire.
Use water to put out the fire.
(3)Leakage of town gas occurs in a kitchen.
Turn on an exhaust fan in the kitchen to remove the town gas.
In each case, explain why the action is inappropriate and suggest a proper action. (8 marks)
‘Fossil fuels’ such as petroleum and coal constitute the world’s major source of energy. However, many countries have been developing alternative energy sources.
(a)Why are petroleum and coal called ‘fossil fuels’?
(b)give TWO reasons why it is necessary to develop alternative energy sources.
(c)Nuclear power is used as an alternative to fossil fuels in many countries. Suggest ONE advantage and ONE disadvantage of using nuclear power.
(d)Suggest ONE energy sources, other than nuclear power, that can be used as an alternative to fossil fuels. (6 marks)
The diagram below shows a longitudinal section of a fire extinguisher. When the extinguisher is being used, solution X is allowed to mix with the sodium hydrogencarbonate solution and a reaction immediately occurs. A jet of aqueous solution will then be forced out of the extinguisher.
(i)Suggest what solution X may be.
(ii)(1)Write an ionic equation for the reaction between solution X and the sodium hydrogencarbonate solution.
(2)Explain why a jet of aqueous solution is forced out of the extinguisher.
(iii)The diagram below shows a ‘fire triangle’.
(1)Complete the ‘fire triangle’ by writing a suitable word for ‘Y’.
(2)Using the concept of ‘fire triangle’, give TWO reasons why the fire extinguisher mentioned previously can be used to put out a fire.
(iv)In the Mass Transit Railway, bromochlorodifluoromethane (BCF) fire extinguisher, rather than the type of fire extinguisher shown on the
previous page, is used to put out electrical fire.
Suggest ONE advantage and ONE disadvantage of using a BCF fire extinguisher to put out electrical fire. (8 marks)
In March 1989, the oil tanker Exxon Valdex was wrecked off the coast of Alaska and spilt a large amount of crude oil into the sea. The oil spillage caused serious environmental problems.
Briefly explain why oil spillage in the sea can cause serious environmental problems and suggest ONE method of treating the spilt oil. (8 marks)
The photograph below shows a gas burner with a can of fuel. The can contains 250 g of liquefied butane.
(i)Write the structural formula of butane.
(ii)(1)Write the chemical equation for the complete combustion of butane.
(2)Suggest a chemical test for EACH of the products formed when butane is completely burnt in air.
(3)Calculate the volume of the gaseous product formed, measured at room temperature and pressure, if all the butane contained in the can is completely burnt in air.
(iii)Explain why it is dangerous to use such gas burners in a poorly-ventilated room.
(Relative atomic masses : H = 1.0, C = 12.0, O = 16.0;
molar volume of gas at room temperature and pressure = 24.0 dm3) (9 marks)
On a hot summer day, the engine of a moving bus suddenly caught fire. When the firemen arrived, they used foam, instead of water, to put out the fire. After the fire was extinguished, the firemen sprayed a lot of water onto the hot engine.
Discuss the conditions required for the fire to occur and explain the underlying principles of the actions taken by the firemen. (6 marks + 3)
The illustration below shows the exhaust from a motor car using unleaded petrol:
(a)Explain why the exhaust contains carbon monoxide.
(b)(1)Write TWO chemical equations for the formation of acid rain from nitrogen oxides.
(2)State ONE undesirable effect of acid rain.
(c)State ONE health hazard associated with particulates.
(d)Suggest ONE other pollutant that may be found in the exhaust.
(e)Suggest a device that can be installed in the motor car to reduce the emission of carbon monoxide and nitrogen oxides. (7 marks)
The diagram below shows a bottle of chemical waste in a school laboratory.
Describe and explain how you would remove kerosene and iron(III) ions from the chemical waste.
(You may use any apparatus and chemicals available in a school laboratory.) (5 + 3 marks)
(a)Crude oil is a mixture consisting mainly of alkanes. Fractional distillation of crude oil gives different petroleum fractions. The table below lists the length of carbon chain of the alkanes in some of the fractions.
Length of carbon chain
C5 – C10
C11 – C18
C18 – C25
C20 – C34
(i)Describe the principle underlying the fractional distillation of crude oil.
(ii)(1)Explain why the global demand for petrol is greater than that for kerosene.
(2)Cracking kerosene can produce petrol. State the conditions required for the cracking process.
(iii)In Hong Kong, naphtha instead of coal is used to manufacture town gas.
(1)State ONE advantage of using naphtha instead of coal to manufacture town gas.
(You are NOT required to consider the price of the materials)
(2)Explain why an additive with a foul smell is added to town gas before it is delivered to the consumers.
(iv)Give ONE use of fraction X in cars.
(b)In some countries, ‘gasohol’ (a mixture of petrol and ethanol) is used as fuel for cars.
(i)Explain why burning gasohol causes less air pollution than burning petrol.
(ii)Ethanol can be manufactured from a petroleum product. Name the manufacturing process and write the chemical equation for the reaction involved.
(iii)Ethanol can also be manufactured by another process. Name this process.
(iv)Of the two processes you have mentioned in (ii) and (iii), which one is better for the manufacture of ethanol in gasohol? Explain your answer. (5 marks)
Carbon dioxide constitutes about 0.03% of the atmosphere. Over millions of years, the concentration of carbon dioxide in the atmosphere has remained almost constant because of a number of processes.
(i)Suggest ONE process by which carbon dioxide is added to the atmosphere.
(ii)Suggest ONE process by which carbon dioxide in the atmosphere is consumed.
(iii)Carbon dioxide is one of the greenhouse gases in the atmosphere.
(1)Explain why carbon dioxide can cause the greenhouse effect.
(2)State the importance of the greenhouse gases in the atmosphere to living things on earth.
(3)Increasing the concentration of the greenhouse gases in the atmosphere leads to global warming. State ONE harmful effect of global warming. (6 marks)
The photograph below shows a burning candle:
(a)The candle wax is a petroleum product. What type of compounds is mainly present in the wax?
(b)(i)In which of the following states does wax act as the fuel in a burning candle?
solid, liquid, vapour
(ii)State the conditions required for the combustion of wax.
(iii)Suggest a reason why a burning candle can be extinguished by a strong wind.
(c)Explain why it is hazardous to add cold water to a tray containing molten wax at a higher temperature. (7 marks)
For environmental reasons, the Hong Kong Government has launched a plan for taxis to switch from using diesel to using liquefied petroleum gas (LPG).
(i)Both LPG and diesel are petroleum products. State the origin of petroleum.
(ii)With reference to their chemical constituents, explain why LPG is a cleaner fuel than diesel.
(iii)State ONE problem that may occur in the initial stage in launching this plan. (5 marks)
Using alkenes as an example, describe the characteristics of members of a homologous series. (6 + 3 marks)
Sulphur dioxide is formed when coal is burnt in a power station.
(i)The coal used in the power station contains 1.5 % of sulphur by mass. Calculate the volume of sulphur dioxide released, measured at room temperature and pressure, when 1.0 kg of the coal is burnt.
(You ma assume that all the sulphur in coal is converted to sulphur dioxide upon burning.)
(ii)State ONE environmental problem associated with the emission of sulphur dioxide into the atmosphere.
(iii)Suggest ONE measure to reduce the emission of sulphur dioxide from the power station.
(iv)Particulates are also present in the flue gas generated in the power station.
(1)State ONE environmental problem associated with the discharge of particulates into the atmosphere.
(2)Suggest ONE way to remove particulates from the flue gas.
(Relative atomic masses: O = 16.0, S =32.0; molar volume of gas at room temperature and pressure = 24 cm3) (7 marks)