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 farit’s been disappointing. One reason is you need to grow a lot of crops to make the fuel – crops that could otherwise be used forfood.

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 alot 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 thescales 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 befermented and turned into ethanol – a type of alcohol. But the biggest problem is getting to the cellulose in the first place, as it iscemented 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 nowlooking at the problem in a different way. They have modified the genes of a plant to produce a form of lignin that breaks downmore 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.

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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 asyou can that require you to use a fuel, either directly or indirectly.

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.

The two short media clips below provide useful information about biofuels and fossil fuels. The ideas presented in the mediaclips will help you compare and contrast these two types of energy resources.

Fuels

Credit: Biofuels - the Green alternative / YouTube.

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Credit: Formation of Fossil Fuels / YouTube.

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Question 2

Identify: Use the information in the media clips to help you decide whether the statements in the table below apply either tobiofuels 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 oranimal wastes

Needs to be refined or processed

Natural gas, oil, coal

Ethanol, biodiesel, biogas

Supplies energy for more than 90% of the world'senergy needs

Helps reduce greenhouse gas emissions

Requires more sophisticated technology

Technology already very well established aroundthe world

Undergoes combustion to release carbondioxide, water and heat energy

Production can have damaging environmentalconsequences

Ethanol is a member of a large family of chemical compounds called alcohols. It is a simple molecule containing only nine atoms. Ithas many everyday uses ranging from solvents, cleaning products, fuel for camping stoves, industrial applications and even medicaluses.

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:

Alcohols

Number of carbonatoms

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 themolecule 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 toeach 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 theend 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 CO emissions for a given amount ofuse. The use of E10 fuel in the same vehicle and the same amount of use results in only 71 units of CO emissions (E10 isformulated with 90% conventional petrol and 10% ethanol).

Calculate the percentage reduction in CO emissions achieved by using the E10 fuel over conventional petrol for the vehicle. Showyour working.

2

2

2

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Process: Biofuels (P1)

Credits: iStock.

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 andwater.

Fermentation, the process by which bacteria and yeast convert carbohydrates into carbon dioxide and ethanol (andsometimes other chemicals).

Combustion, the process by which a fuel (such as ethanol) reacts with oxygen to produce carbon dioxide, water and heatenergy.

From photosynthesis to combustion

Question 1

Analyse: Balance the following chemical equations by writing whole number coefficients in front of the chemical formulae asneeded.

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'sclimate – they absorb infrared radiation and maintain our planet's surface at temperatures suitable for sustaining life. This balanceis 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.

The carbon cycle

Credit: The Carbon Cycle / YouTube.

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Question 2

Organise: Use the information in the media clip above, and an internet search if necessary, to draw arrows onto the carbon cyclediagram 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 biorefinerycomplex 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 economicconsiderations.

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.

Apply: Biofuels (P2)

Experiment: Fermentation of sugar using yeast

Yeast is a single-celled, microscopic fungus. Yeast uses sugar as a source of energy in a process that produces methanol and carbondioxide gas. This process is called fermentation, and is represented by the following chemical equation:

C H O 2C H OH + 2CO

Fermentation has been used for thousands of years to make bread, beer, wine and other alcoholic products. In bread, the carbondioxide causes the dough to rise to make a light, slightly spongy loaf of bread. In beer production, the carbon dioxide producedfrom sugar fermentation is trapped in the solution to make a fizzy or carbonated drink.

To determine the effect of sugar concentration on yeast fermentation.

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

Background

6 12 6 → 2 5 2

Aim

Materials

Paper towel

Ice bath

Warm water bath maintained at approximately 37°C

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 thecircumference (at the widest part) using the flexible tape measure (if you do not have a flexible tape measure, you may usestring and a ruler instead). Calculate the approximate volume of each balloon using the following formula:

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.

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.

Procedure

volume =circumference3

6π2

Safety Information

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 butyou 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

X-Axis

auto

Y-A

xis

auto auto auto

Series 1

x y

This graph needs some data!

Answer the following discussion questions to help you analyse your data and evaluate your experiment.

Discussion

Question 5

Justify: Explain why balloon G did not contain any sugar.

Question 6

Justify: Explain why you needed to quickly tie the balloons shut.

Question 7

Interpolate: Use your graph to predict the volume of a ballooncontaining 5 g of sugar.

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Question 8

Assess: Explain whether or not you think fermentation is takingplace to the same extent in each balloon. Use your results tosupport your answer.

Question 9

Evaluate: Identify some limitations of the experimental designthat prevent you from collecting more reliable and accuratedata.

Question 10

Evaluate: Suggest changes that you could make if you were torepeat 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.

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 whenProfessor 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 liketo be an entomologist and study insects, just like his father. Butall that changed when his high school chemistry teacherintroduced him to the wonderful world of chemistry, with itscolourful reactions, explosions and interesting odours.

Today, John works at the University of Wisconsin-Madison in theUnited States. He specialises in the structure and chemistry ofplant cells, in particular, a tough molecule called lignin thatreinforces the cellulose in cell walls. Plant cellulose can bebroken down into sugar and then fermented to produce ethanoland other biofuels. However, there is a problem – breakingdown 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 growplants with lignin that breaks down more easily. This saves a lotof energy and may make biofuels more economicallycompetitive with fossil fuels.

John says that working collaboratively with other scientists isincredibly satisfying. He and his colleagues love the challenge ofwhat they do; they solve problems together in ways that wouldnot be possible working alone. Even though John has beenresearching lignin for the last forty years, he says that it stillcontains many mysteries and surprises.

In his spare time, John enjoys nature on a larger scale – heloves stand-up paddle boarding, snowboarding, hiking in themountains, 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 researchgroup! Credit: University of Wisconsin-Madison.

Question 1

Propose: John has been using genetic engineering techniques to manipulate plant cells into manufacturing a modified form oflignin. Imagine, like John, you are also a plant cell chemist. If you had the choice, what product might you genetically engineer plantcells to manufacture? What benefits could your genetically engineered product bring to society? What might be some of the ethicalissues associated with your research?

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Cosmos Live Learning team

Education director: Daniel PiklerEducation editor: Bill CondieArt director: Robyn AdderlyProfile author: Edwina Berry

Lesson authors: Hayley Bridgwood and Kathryn Grainger