Worked Solutions to Textbook Questions 4

Worked solutions to textbook questions 1

Chapter 11 Biochemical fuels

Q1. Write a balanced equation for the combustion of hydrogen in air. A1.

2H2(g) + O2(g)  2H2O(g) Q2. a Why can ethanol for use as a biofuel be produced from a variety of different plant souces? b Write a balanced equation, including subscripts, for the combustion of ethanol in a good air supply. c Explain why the use of ethanol as fuel can be considered to be carbon neutral. A2. a Production of bioethanol utilises starch and cellulose which is found in all plants. b C2H5OH(l) + 3O2(g)  2CO2(g) + 3H2O(g) c Bioethanol is derived from plants which consume carbon dioxide during photosynthesis. This carbon dioxide is then released as a by-product of combustion. Q3. It is possible to make biodiesel from animal fat as well as from vegetable oils. a Assuming that the animal fat consists only of tristearin, which can be hydrolysed to make stearic acid, C17H35COOH, write a balanced equation to represent how this substance can react with methanol to form an ester. b Write a balanced equation to represent the combustion of this biodiesel in a good air supply. A3. a C17H35COOH(l) + CH3OH(l)  C17H35COOCH3(l) + H2O(l) b 2C17H35COOCH3(l) + 55O2(g)  38CO2(g) + 38H2O(g)

Chapter review

Q4. The world has become very dependent on the products of the petrochemical industry but the raw materials of crude oil and natural gas are likely to be virtually exhausted by 2100. Assuming that current production remains unchanged and no alternative sources are available, suggest the impact of the lack of raw materials on our lifestyle. A4. Apart from the difficulties in daily travel, lack of crude oil and natural gas will make transport of manufactured goods difficult and costly. It will also stop the production of all the products that are derived from crude oil—plastics, synthetic fibres, dyes, paints, solvents, detergents and pharmaceuticals.

Heinemann Chemistry 2 (4th edition) © Harcourt Education, a division of Pearson Australia Group Pty Ltd Worked solutions to textbook questions 2

Q5. The fact that global warming is taking place is now generally accepted. Use the Internet to research some of the consequences. Give one example each of the effect on: a the polar ice caps b changing weather patterns c crop production d extinction of plant or animal species A5. All of the points are inter-related. Many other valid responses are possible. a Polar ice caps are shrinking, causing sea levels to rise worldwide. Local effects on the wildlife adapted to polar conditions. Melting ice adds cold, fresh water to the ocean with the possibility of altering the major ocean currents, resulting in climate changes, e.g. to Western Europe. b Changed weather patterns causing droughts, floods, hurricanes and resulting in changed growth patterns in plants that might lead to both plant and animal extinctions. c The changed weather patterns can result in crops failing, affecting the economy and driving some people to starvation. d Some plants and animals that are dependent on particular weather conditions for propagation or for key parts of their life cycle may become extinct. Q6. a Explain what is meant by E10 petrol. b How will the introduction of E10 help with the potential shortage of crude oil? A6. a E10 petrol is a mixture of 10% ethanol and 90% conventional petrol. b Use of E10 petrol will extend the availability of petrol as a fuel and will allow more of the larger fractions from crude oil to be used as a feedstock for other uses rather than being burnt as a fuel. Q7. What advantages does biodiesel have over petrodiesel? Are there any disadvantages to its use? A7. Use of biodiesel does not add to the overall levels of carbon dioxide in the atmosphere. It is also biodegradable, non-toxic and produces fewer pollutants when burnt. No real disadvantages other than the need to ensure a consistent supply for large-scale use.

Heinemann Chemistry 2 (4th edition) © Harcourt Education, a division of Pearson Australia Group Pty Ltd Worked solutions to textbook questions 3

Q8. Syngas contains a mixture of carbon monoxide and hydrogen. Write a balanced equation for the combustion in a good air supply of: a carbon monoxide b hydrogen A8. a 2CO(g) + O2(g)  2CO2(g) b 2H2(g) + O2(g)  2H2O(g) Q9.

Assuming that SunDiesel consists of molecules such as C18H38, write a balanced equation for the combustion of this substance in a good air supply. A9.

2C18H38(l) + 55O2(g)  36CO2(g) + 38H2O(g) Q10. What might be the advantages and disadvantages of using SunDiesel in place of petrodiesel? A10. Advantages of SunDiesel – behaves like normal diesel but is derived from a renewable source that does not add to overall atmospheric carbon dioxide levels. Disadvantage – is a costly process involving inorganic catalysts. Q11. The reactions that produce ethanol can be summarised as: A B CO2 + H2O  C6H12O6  CH3CH2OH What are the names of the reactions represented by the letters A and B? A11. A: photosynthesis. B: fermentation. Carbon dioxide and water are converted to glucose and oxygen by photosynthesis. During fermentation glucose is converted to ethanol and carbon dioxide. Q12. Currently hydrogen is produced by steam reforming of alkanes such as methane.

CH4 (g) + H2O (g)  CO (g) + 3 H2 (g) a Why is hydrogen produced by this method not considered a renewable source of energy? b What more sustainable methods could be used to produce hydrogen? c List some of the advantages and disadvantages of using hydrogen as a fuel now.

Heinemann Chemistry 2 (4th edition) © Harcourt Education, a division of Pearson Australia Group Pty Ltd Worked solutions to textbook questions 4

A12. a Hydrogen is produced using a non renewable fossil fuel, methane. b Hydrogen can be produced by the electroysis of water. The electricity used to electrolyse the water could be derived from wind turbines, solar cells or some other renewable energy source. c Advantages: Hydrogen burns to produce water. It does not generate greenhouse gases if it is generated by electrolysis using electricity generated by renewable energy sources. Disadvantages: Current industrial production by steam reforming uses fossil fuels and generates greenhouse gases. Its explosive nature make it difficult to store. There is no infrastructure for large scale distribution of the gas. The term hydrogen economy is sometimes used by those supporting the use of hydrogen as a fuel. Use the Internet to find out more about the hydrogen economy. Q13. Ethanol is produced industrially by reacting ethene with water using a phosphoric acid catalyst at 300°C:

C2H4(g) + H2O(g)  CH3CH2OH(g) a Is ethanol produced by this method a biochemical fuel? Explain. b Describe how ethanol classified as a biochemical fuel can be produced. A13. a Biochemical fuels are derived from renewable resources such as plants. Ethene, the feedstock used for the industrial production of ethanol, is derived from the distillation and cracking of crude oil, a non-renewable resource. b Ethanol can be produced from the fermentation of sugar by yeasts. Sugar may be derived from sugar cane or by the hydrolysis of starch from grains such as maize. Q14. Draw a concept map that includes the following terms: biochemical fuel, biodiesel, ethanol, fermentation, sustainable. A14.