Chemistry
Biofuels: The carbon
equation
This chemistry lesson is all about biofuels, as a sustainable alternative to
fossil fuels, and the chemical reactions involved in making them.
In this lesson you will investigate the following:
• Are biofuels really that different from fossil fuels?
• What makes ethanol an alcohol?
• How does the carbon cycle illustrate the law of conservation of matter?
• What makes yeast ferment?
This lesson will sustain your interest and renew your enthusiasm for
chemistry.
This is a print version of an interactive online lesson.
To sign up for the real thing or for curriculum details
about the lesson go to www.cosmosforschools.com
Introduction: Biofuels (P1)
Making ethanol from plants to use as fuel for cars and trucks sounds like it should be an eco-friendly thing to do, but so far
it’s been disappointing. One reason is you need to grow a lot of crops to make the fuel – crops that could otherwise be used for
food.
This type of fuel is called bioethanol, and it produces too little energy to justify the cost of producing it – dirty old fossil fuels are a
lot cheaper.
But scientists have just worked out how they might be able to convert plants to ethanol a lot more efficiently, and that could tip the
scales to make it a viable alternative to petrol.
Making bioethanol is all about chemistry. Plants contain cellulose, which can be broken down into sugars. Those sugars can then be
fermented and turned into ethanol – a type of alcohol. But the biggest problem is getting to the cellulose in the first place, as it is
cemented together by a stringy molecule called lignin that must be broken down first.
Up until now, ethanol producers have tried using plants with cellulose that is easier to get to, but a new group of researchers is now
looking at the problem in a different way. They have modified the genes of a plant to produce a form of lignin that breaks down
more easily than the natural version, making the cellulose more accessible, which could produce more energy more efficiently.
Their technique is still a work in progress, but the early tests are promising.
Read or listen to the full Cosmos magazine article here.
Credits: iStock.
Question 1
List: Think about your typical weekday morning routine, from when you get up to arriving at school. Identify as many activities as
you can that require you to use a fuel, either directly or indirectly.
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Gather: Biofuels (P1)
Credits: iStock & Chappatte in "International Herald Tribune".
Question 1
Match: Draw lines to match the following terms from the article with their definition.
Fuels
The two short media clips below provide useful information about biofuels and fossil fuels. The ideas presented in the media
clips will help you compare and contrast these two types of energy resources.
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Credit: Biofuels - the Green alternative / YouTube.
Credit: Formation of Fossil Fuels / YouTube.
Question 2
Identify: Use the information in the media clips to help you decide whether the statements in the table below apply either to
biofuels or fossil fuels, or both. Indicate your choices by typing "yes" or "no" into the relevant columns.
Statement
Applies to fossil fuels
Applies to biofuels
Renewable
Non-renewable
Formed over millions of years
Formed from currently living plant material or
animal wastes
Needs to be refined or processed
Natural gas, oil, coal
Ethanol, biodiesel, biogas
Supplies energy for more than 90% of the world's
energy needs
Helps reduce greenhouse gas emissions
Requires more sophisticated technology
Technology already very well established around
the world
Undergoes combustion to release carbon
dioxide, water and heat energy
Production can have damaging environmental
consequences
Alcohols
Ethanol is a member of a large family of chemical compounds called alcohols. It is a simple molecule containing only nine atoms. It
has many everyday uses ranging from solvents, cleaning products, fuel for camping stoves, industrial applications and even medical
uses.
The International Union of Pure and Applied Chemists (IUPAC) prescribes the following rules for naming alcohols:
The number of carbon atoms in the chain is described by a special prefix, as shown in the following table:
Number of carbon
atoms​
1
2
3
4
5
6
7
8
Prefix
meth
eth
prop
but
pent
hex
hept
oct
The presence of the –OH group, substituting for an H atom on one of the carbons, is indicated by the suffix 'ol' and makes the
molecule a member of the alcohol family.
The middle syllable 'an' indicates the fact that the carbon atoms are ‘saturated’ so that all of the carbon atoms are bonded to
each other by a single covalent chemical bond.
A number is used to indicate which carbon has the –OH group attached to it, when there is a choice (start counting from the
end of the molecule which results in the smallest number).
Question 3
Name: Complete the gaps to correctly name the following alcohol molecules.
Question 4
Solve: Assume that using conventional petrol as a fuel in a motor vehicle results in 90 units of CO2 emissions for a given amount of
use. The use of E10 fuel in the same vehicle and the same amount of use results in only 71 units of CO2 emissions (E10 is
formulated with 90% conventional petrol and 10% ethanol).
Calculate the percentage reduction in CO2 emissions achieved by using the E10 fuel over conventional petrol for the vehicle. Show
your working.
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Process: Biofuels (P1)
Credits: iStock.
From photosynthesis to combustion
There are three main chemical processes associated with generating and burning ethanol as a biofuel. These are:
Photosynthesis, the process by which plants and algae use sunlight to synthesise carbohydrates from carbon dioxide and
water.
Fermentation, the process by which bacteria and yeast convert carbohydrates into carbon dioxide and ethanol (and
sometimes other chemicals).
Combustion, the process by which a fuel (such as ethanol) reacts with oxygen to produce carbon dioxide, water and heat
energy.
Question 1
Analyse: Balance the following chemical equations by writing whole number coefficients in front of the chemical formulae as
needed.
The carbon cycle
Carbon plays a critical role in sustaining life on Earth. The carbon cycle describes the movement of carbon through the atmosphere,
the oceans, the soil, animals and vegetation.
Carbon dioxide and other carbon-containing compounds in the Earth's atmosphere have a substantial effect on the Earth's
climate – they absorb infrared radiation and maintain our planet's surface at temperatures suitable for sustaining life. This balance
is disrupted when more carbon dioxide is added into the atmosphere than can be naturally absorbed by the oceans and plant life.
The extra carbon dioxide contributes to the enhanced greenhouse effect, and in turn, global warming.
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Credit: The Carbon Cycle / YouTube.
Question 2
Organise: Use the information in the media clip above, and an internet search if necessary, to draw arrows onto the carbon cycle
diagram below. The arrows should illustrate the flow of carbon from photosynthesis, respiration, combustion and decomposition.
Distinguish between the different processes by using arrows of different colours:
Photosynthesis - green arrow
Respiration – blue arrow
Combustion – red arrow
Decomposition – purple arrow
Question 3
Plan: Imagine you are a chemical engineer who has been given the responsibility of strategically developing a new biorefinery
complex to make ethanol from cellulose. Brainstorm the factors you and your team would have to consider during the planning,
construction and operation stages of the project. Classify each of these factors as environmental, social and/or economic
considerations.
Hint: The table builder will help you with this task. Place the factors you can think of in the first column, and then use the second, third and
fourth columns to indicate the classifications of your factors.
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Apply: Biofuels (P2)
Experiment: Fermentation of sugar using yeast
Background
Yeast is a single-celled, microscopic fungus. Yeast uses sugar as a source of energy in a process that produces methanol and carbon
dioxide gas. This process is called fermentation, and is represented by the following chemical equation:
C6H12O6
→
2C2H5OH + 2CO2
Fermentation has been used for thousands of years to make bread, beer, wine and other alcoholic products. In bread, the carbon
dioxide causes the dough to rise to make a light, slightly spongy loaf of bread. In beer production, the carbon dioxide produced
from sugar fermentation is trapped in the solution to make a fizzy or carbonated drink.
Aim
To determine the effect of sugar concentration on yeast fermentation.
Materials
Spherical balloons
Permanent marker
Funnel
Electronic mass balance
14 g dry yeast
33 g sugar
50 mL graduated cylinder
350 mL tap water
String
Flexible tape measure
Paper towel
Ice bath
Warm water bath maintained at approximately 37°C
Procedure
1. Label seven balloons A - G with a permanent marker.
2. Add 2 grams of dry yeast to each balloon using the funnel.
3. Add sugar to the balloons using the funnel in the following manner:
2 grams to balloon A
3 grams to balloon B
4 grams to balloon C
6 grams to balloon D
8 grams to balloon E
10 grams to balloon F
0 grams to balloon G
4. Add 50 mL of water to each balloon and tie securely shut with string, squeezing as much air from the balloons as possible.
Work quickly and as soon as each balloon is secure, add to an ice water bath for at least 5 minutes.
5. Once all balloons have been prepared, dry them with a towel, and determine the volume of each balloon by measuring the
circumference (at the widest part) using the flexible tape measure (if you do not have a flexible tape measure, you may use
string and a ruler instead). Calculate the approximate volume of each balloon using the following formula:
volume =
circumference3
6π 2
6. Return all balloons to the ice water bath for at least 2 minutes.
7. Place all balloons into the 37°C water bath for 30 minutes.
8. After 30 minutes, remove each balloon, dry them with a towel, and re-calculate their volumes.
9. Use the project space below to record your results.
10. Plot your results.
Safety Information
You must wear a lab coat and safety glasses at all times.
Experiments should be carried out in a well ventilated area.
While the amount of ethanol produced is minimal and very dilute, the ethanol should be disposed of properly and carefully.
Variables
Question 1
Identify: Write down the independent, dependent and controlled variables for this experiment.
Hint: The independent variable is what is being changed each time, the dependent variable is what you are measuring or testing and the
controlled variables are all of the factors that remain constant throughout the experiment
Hypothesis
Question 2
Hypothesise: Predict what you think the outcome of the experiment will be, and why, by writing a hypothesis.
Results
Question 3
Collect: Use the project space below to present your results. You should construct a table of results which best suits the data but
you may also include photos, video or other representations.
Hint: You may wish to take a photo of your experiment, upload it into a sketchpad and then label it.
Question 4
Plot: Visualise your data by plotting the balloon volumes against the quantity of sugar added below.
Title
auto
Series 1
Y-Axis
x
y
This graph needs some data!
auto
auto
auto
X-Axis
Discussion
Answer the following discussion questions to help you analyse your data and evaluate your experiment.
Question 5
Justify: Explain why balloon G did not contain any sugar.
Question 7
Interpolate: Use your graph to predict the volume of a balloon
containing 5 g of sugar.
Question 6
Justify: Explain why you needed to quickly tie the balloons shut.
Question 8
Assess: Explain whether or not you think fermentation is taking
place to the same extent in each balloon. Use your results to
support your answer.
Question 9
Evaluate: Identify some limitations of the experimental design
that prevent you from collecting more reliable and accurate
data.
Question 10
Evaluate: Suggest changes that you could make if you were to
repeat this experiment. Address the limitations you identified.
Conclusion
Question 11
Conclude: Write a concluding statement that addresses the aim of the experiment and your hypothesis.
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Career: Biofuels (P2)
When most people look at a plant, they are taken with the colour of its leaves and the shape of its branches. But when
Professor John Ralph looks at a plant, he’s thinking about what is happening inside its cell walls!
Growing up in New Zealand, John always thought he would like
to be an entomologist and study insects, just like his father. But
all that changed when his high school chemistry teacher
introduced him to the wonderful world of chemistry, with its
colourful reactions, explosions and interesting odours.
Today, John works at the University of Wisconsin-Madison in the
United States. He specialises in the structure and chemistry of
plant cells, in particular, a tough molecule called lignin that
reinforces the cellulose in cell walls. Plant cellulose can be
broken down into sugar and then fermented to produce ethanol
and other biofuels. However, there is a problem – breaking
down lignin to extract cellulose takes a lot of energy.
John and his colleagues are working to improve this process.
Using genetic engineering, they have discovered a way to grow
plants with lignin that breaks down more easily. This saves a lot
of energy and may make biofuels more economically
competitive with fossil fuels.
John says that working collaboratively with other scientists is
incredibly satisfying. He and his colleagues love the challenge of
what they do; they solve problems together in ways that would
not be possible working alone. Even though John has been
researching lignin for the last forty years, he says that it still
contains many mysteries and surprises.
In his spare time, John enjoys nature on a larger scale – he
loves stand-up paddle boarding, snowboarding, hiking in the
mountains, and travelling with his wife of 34 years.
John Ralph in his second-favorite work environment,
working on nuclear magnetic resonance (NMR)
instruments; his favorite is interacting with his research
group! Credit: University of Wisconsin-Madison.
Question 1
Propose: John has been using genetic engineering techniques to manipulate plant cells into manufacturing a modified form of
lignin. Imagine, like John, you are also a plant cell chemist. If you had the choice, what product might you genetically engineer plant
cells to manufacture? What benefits could your genetically engineered product bring to society? What might be some of the ethical
issues associated with your research?
Cosmos Live Learning team
Education director: Daniel Pikler
​Education editor: Bill Condie
Art director: Robyn Adderly
Profile author: Edwina Berry
​ esson authors: Hayley Bridgwood and Kathryn Grainger
L
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