Beatty 7.1 Fuels WS1 2023 Answers

1 Beatty Secondary School Science Department (Chemistry Unit) Chemistry 6092 Name: ___________________________________ ( ) Date: _______________ Class: 4E1 TOPIC: FUELS AND CRUDE OIL (WORKSHEET 1) Learning Objectives: (a) Name natural gas, mainly methane, and petroleum as sources of energy. (b) Describe petroleum as a mixture of hydrocarbons and its separation into useful fractions by fractional distillation. (c) Name the following fractions and state their uses. (i) petrol (gasoline) as a fuel in cars (ii) naphtha as the feedstock and main source of hydrocarbons used for the production of a wide range of organic compounds in the petrochemical industry (iii) paraffin (kerosene) as a fuel for heating and cooking and for aircraft engines (iv) diesel as a fuel for diesel engines (v) lubricating oils as lubricants and as a source of polishes and waxes (vi) bitumen for making road surfaces (d) Describe the issues relating to the competing uses of oil as an energy source and as a chemical feedstock. Multiple-Choice Questions 1 Petroleum can be separated by fractional distillation because its constituents A are immiscible B have different densities C are highly flammable D have different boiling points ( D ) 2 Which of the following fractions of petroleum has the highest boiling point? A diesel B kerosene C bitumen D petroleum gas ( C ) 3 Which fuel, on combustion, does not form a pollutant? A petrol B natural gas C hydrogen D diesel ( C ) 4 Which of the following are arranged in order of increasing boiling points? A kerosene, petrol, diesel, bitumen B bitumen, diesel, kerosene, petrol C petrol, diesel, kerosene, bitumen D petrol, kerosene, diesel, bitumen ( D )

2 5 Which of these fractions has the most number of carbon atoms per molecule? A naphtha B diesel C petrol D lubricating oil ( D ) 6 The main constituent of natural gas is _____________. A butane B ethane C methane D petroleum gas ( C ) 7 The fractions obtained by fractional distillation of petroleum have different uses. Which fraction and use are correct? fraction use A bitumen fuel for lorries and buses B kerosene aircraft fuel C petrol making waxes D lubricating oil surfaces of roads ( B ) 8 At which outlet of the fractionati ng column below is the fuel used in gas cookers collected? ( A ) 9 Which statement about petroleum is true? A Petroleum can be separated by simple distillation. B Natural gas is a renewable source of energy. C Biodiesel is an alternative fuel to petroleum. D Biogas is produced when organic matter decays in air. ( C ) 10 Petroleum can be s eparated into f ractions using f ractional distillation. Which statements about petroleum are correct? 1 Alkanes used in polis hes and waxes have a higher boiling point than those used as diesel fuel. 2 Any of the fractions could be used a s fuels because their enthalp y changes of combustion are negative. 3 The fraction used for petrol is extracted from higher up the fractionating column than the fraction used for paraffin. 4 The fraction obta ined at a particular point in the fractionating colum n always contains the same compounds in the same ratio. A 1, 2 and 3 B 1 and 4 C 2 only D 3 and 4 ( A )

3 Structured Questions 11 The diagram shows the fractional distillation of petroleum. (a) Label the fractions obtained at A to D. A: fuel gas / petroleum gas B: naphtha C: diesel D: bitumen (b) State a use for the fractions obtained at A and D. use of fraction A: fuel for cooking and heating use of fraction D: making / paving road surfaces (c) Propane and butane leave the column in the same fraction labelled A. Explain why. Both propane and butane have similar low relative molecular masses and boiling points. As such, both fractions condense within the same range of temperatures in the fractionating column, leaving at A. 12 Petroleum (crude oil) is a mixture of hydrocarbons wh ich is separated into usef ul fractions by fractional distillation. The table shows the percentages of various fractions obtained by fractional distillatio n (the supply) and the percentages req uired (the demand) for the petroleum from a Middle East oil field. fraction percentage produced (supply) percentage required (demand) petroleum gases 4 4 petrol 13 26 naphtha 10 5 kerosene 14 8 diesel 13 20 bitumen and other heavy hydrocarbons 46 37 (a) What physical property enables petroleum to be separated by fractional distillation? difference in boiling points

4 (b) (i) For which fraction does the demand exceed the supply by the greatest amount? petrol (ii) For which fraction does the supply exceed the demand by the greatest amount? bitumen and other heavy hydrocarbons (c) Describe how the different fractions can be separated by fractional distillation. As the petroleum is heated, all of the fractions boil and the vaporised crude oil enters the fractionating column as a gas. The temperature is the highest at the bottom of the fractionating column and the lowest at the top of the column. As the vapour rises up the column, each fraction is cooled down and condenses at different parts of the column through selective condensation. Fractions with lower boiling point condense and are collected at the upper part of the column while fractions with higher boiling point condense and are collected at the lower part of the column. (d) Some cars use diesel f uel while so me use petrol. A car will travel a greater distance in kilometres using one litre of diesel than one litre of petrol. Suggest why. Diesel has a greater number of carbon atoms compared to petrol. As such, the enthalpy change of combustion increases with the number of carbon atoms. This leads to more energy released from the combustion of diesel than petrol, l eading to a greater distance travelled. (e) Name two fuels, suitable for cars, which does not come from crude oil. hydrogen and ethanol and biodiesel 13 Methane is a fuel obtained from natural gas. Methane completely burns in air to form carbon dioxide and water. An equation for this reaction is shown below. (a) Explain in terms of the bonds broken and made why this reaction is exothermic. The total am ount of thermal energy absorbed to break the (C−H) bonds in methane and the (O=O) bonds in oxygen is lesser than the thermal energy released to form the (C=O) bonds in carbon dioxide and the (O−H) bonds in water.

5 (b) Calculate the energy released when 0.96 g of methane is completely burnt in air No of mol of methane = 0.96 16 = 0.06 mol Total amount of energy = 0.06 × 890 = 53.4 kJ (c) Name all the possible products in the inc omplete combustion of methane. Explain how this incomplete combustion can be harmful. Water vapour, carbon monoxide and soot (carbon). Carbon monoxide is a toxic gas can bind to ha emoglobin to form carboxyha emoglobin which prevents blood from transporting oxygen around the body and may lead to death. 14 Natural gas consists mainly o f methane (CH 4). Hydrogen sulfide (H 2S) is a common contaminant of natural gas and must be removed before natural gas is used as a fuel. (a) Construct the equation to show the combustion of hydrogen sulfide in air t o form sulfur dioxide and water. 2H2S + 3O2 → 2SO2 + 2H2O (b) Suggest why it is necessary to remove the hydrogen sulfide before natural gas is used as a fuel. Sulfur dioxide formed from the combustion of hydrogen su lfide is an air pollutant t