Climate Change Experiments

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Fuelling interest: climate change experiments

Image courtesy of alohaspirit / iStockphoto

Dudley Shallcross, Tim Harrison, Steve Henshaw and Linda Sellou offer chemistry and physics experiments harnessing alternative energy sources, such as non-fossil fuels.

iscussions of climate change in 1) Measuring fuel efficiency (·OH) to form predominantly alco- Dthe science classroom can be Unburned fuel evaporating into the hols and carbonyls. Levels of atmos- very wide-ranging, but will probably atmosphere, during either storage or pheric ·OH are important, as these involve different sources of energy combustion, is an air pollutant, and radicals remove greenhouse gases and their consequences. Relevant top- also plays a role in determining the that contain the C-H bond, such as

ics are likely to include different fuels lifetime of greenhouse gases. One CH4. Computer simulations have that can be used, how effective they way to limit the damage is to use shown that releasing alcohols into the are and how they are produced, and alcohols instead of more standard atmosphere has a less damaging effect alternatives to combustion. We sug- hydrocarbon fuels such as petrol and than releasing hydrocarbons, because gest a couple of laboratory activities diesel. fewer oxidation steps take place, to support physics and chemistry les- Hydrocarbons in the atmosphere removing smaller amounts of ·OH. sons on climate change. are oxidised by the hydroxyl radical Therefore, using alcohols instead of

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Teaching activities

hydrocarbons as fuels has a positive dren’s chemistry sets and are readily The energy released in the combus- effect on both air quality and the available from schools equipment tion, used to raise the water tempera- removal of greenhouse gases. companies. They can be used to deter- ture, can be calculated using equation (1) r r Moreover, the smaller alcohols mine the energy released in the com- HC = -c Mwater TR (1) released into the atmosphere can be bustion of shorter primary alcohols where:

removed, to a small extent, by physi- such as methanol, ethanol, propan- HC = heat of combustion [kJ] cal processes such as dry (taken up by 1-ol, butan-1-ol and pentan-1-ol. c = the specific heat capacity of a surface) and wet (rain, fogs, The students can set up the experi- water = 4.187 kJ kg-1 °C-1 aerosols) deposition, whereas their ment (see image on page 40), in M = mass of water [kg] hydrocarbon counterparts cannot. which the alcohol burner is filled with water T = temperature rise of water [°C] Alcohols are used in fuel a known alcohol. First, R cells (see graph ‘Fuel cells: weigh the burner The combustion energy can then be energy from elec- and its contents. expressed as energy per gram or ener- trolysis’ gy per mole of the alcohol burnt, in order to compare the results obtained by several groups with the same alcohol or with different alcohols. Energy of combustion per gram =

HC / MB (2) Energy of combustion per mole = r HC Mr / MB (3) where: Mr is the relative molecular mass of the alcohol being burnt,

MB is the mass of the burnt alcohol. Further Measure investigations that out 150 ml of water accurate- can be carried out by ly and place it in a 250 ml the students include: glass beaker. We assume that · Change the alcohol that the burner 1.0 ml of water weighs uses. In practice, it is best to have 1.0 g. Measure the water tem- sets of alcohol burners that use dif- perature at the beginning of the ferent alcohols, as it is very difficult experiment and clamp the beaker to replace the alcohol in a wet wick. on page 42) which have a wide range above the burner, leaving a space of An alternative to comparing several of potential applications, for example about 5 cm between the wick and the different alcohols is to compare just in short-range vehicles. base of the beaker. Ignite the burner one alcohol with a night light (a small Of course, a good fuel is not only and place it centrally under the water wax candle in a metal holder) environmentally friendly – it must container until the temperature has · Change the material that the beaker also be an efficient source of energy. risen by 30 to 40 °C. Determine the is made from, for example to cop- The following experiment allows stu- temperature rise by recording the per or a galvanised steel food can dents to determine the energy final temperature of the water. Weigh · Change the thickness of the materi- released by burning different types of the final mass of the alcohol burner al that the water container is made alcohols, and to compare their effec- and its contents. It is at this stage that from tiveness with that of more standard the students will not remember if · Compare an insulated container fuels. they originally weighed the alcohol (made from a heatproof material!) Alcohol burners are the small burn- burner with the lid on or off! with a glass beaker ers made of glass, complete with a Calculate the mass of alcohol burned Compare the open glass beaker wick, which usually come with chil- (M ). · B being heated to one with a lid fitted

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Alcohol burner set up under a beaker to which a known volume of water is to be added

Close-up of an alcohol burner

Images courtesy of Bristol ChemLabS

on top, through which the ther- · Does the height at which the beaker duction of biofuels, however, also mometer is placed. is clamped above the flame make generates CO2; the life-cycle emission any difference to the amount of heat · Does it make a difference whether (amount of CO2 generated during the water in the container is stirred absorbed by the water? production, use and waste disposal) or not? · Does it make a difference to have of some first-generation biofuels even boards / heatproof mats placed exceeds that of traditional fossil fuels. around the burner to reduce So far, three generations of biofuels Table 1: Heats of combustion for small draughts? primary alcohols (Handbook of chem- have been developed: first-generation istry and physics, 57th edition, CRC Press) · Does the length of wick that is biofuels are made from sugar, starch, and some common fuels (Wikipedia, exposed make any difference? vegetable oil, or animal fats. Besides http://en.wikipedia.org/wiki/Heat_of_ having sub-optimal emission levels, combustion, accessed 17/03/09) Note that it is too dangerous to use first-generation biofuels have other petrol or diesel in these burners. Even important limitations: there is a Name of Standard heat of without testing conventional fuels or threshold above which their produc- alcohol/fuel combustion [MJ/kg] different alcohols to compare the tion threatens food supplies and bio- energies released by ‘green’ fuels, diversity. Moreover, they are more these experiments can be used to dis- expensive than existing fossil fuels. Peat (damp) 6.0 cuss experimental error and accuracy This led to the development of sec- Peat (dry) 15.0 of measurement in general. It will be ond-generation biofuels, which can Wood 15.0 obvious from comparing the class- supply a larger proportion of our fuel Coal (Lignite) 15.0 room experimental results with supply sustainably, affordably and Methanol 22.7 the textbook data or those available with greater environmental benefits. Coal (Anthracite) 27.0 w1 Ethanol 29.7 on Wikipedia (see table) that there They use a variety of non-food crops, Carbon 32.8 are significant errors. including waste biomass, the stalks of Propan-1-ol 33.6 wheat, corn, and wood. Butan-1-ol 36.2 2) Producing biofuels from Still, land-based biofuels occupy Pentan-1-ol 37.7 vegetable oil land that could otherwise be used to Diesel 44.8 Biofuels are solid, liquid or gaseous grow food. Algae fuel, also called oil- Paraffin 46.0 fuels derived from relatively recently gae, is being developed as a third-gen- Kerosene 46.2 dead biological material, as opposed eration biofuel to avoid this problem. Gasoline 47.3 to fossil fuels, which are derived from These fuels can be produced in a low- Butane 49.5 long-dead biological material. input, high-yield manner, since algae Propane 50.4 Whereas burning fossil fuels releas- produce 30 times more energy per Ethane 51.9 es CO2 which has been trapped for a acre than land crops such as soybeans. Natural gas 54.0 long time, burning biofuels should Theoretically, biofuels can be pro- (average, varies only release CO2 that has been recent- duced from any biological carbon depending on ly captured from the atmosphere dur- source, although the most common source country) ing photosynthesis and converted to sources are photosynthetic plants and Methane 55.5 fuel. In theory, the process should plant-derived materials. One advan- Hydrogen 141.8 therefore be carbon neutral. The pro- tage of many biofuels over most other

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Teaching activities

out O O

H2C O R1 H2C OH R4OR1

O O in

HC O R2 + 3 x R4OH HC OH + R4OR2

O O

Image courtesy of Bristol ChemLabS Reflux

H2C O R3 H2C OH R4OR3 condenser

Transesterification of vegetable oil triglycerides heat

fuel types is that they are biodegrad- small ball bearing (readily available, able, and so relatively harmless to the symmetric shape, smooth and dense) environment if spilled. to drop through a defined depth of There are a number of ways to the mixture in the tube every 5 min- make biofuels from a range of veg- utes at regular intervals for up to 2 etable oils, but the reaction is essen- hours. The larger triglyceride is bro- tially the same. A biofuel is made by ken down to smaller subunits (see alkaline hydrolysis of the triglycerides image above), which will then have a in a vegetable oil (see image above), smaller mass than the compound and the following re-esterification of from which they are formed. Since the the triglycerides to the methyl ester. viscosity of a liquid is directly propor- In practice, both steps can take place tional to the mass of its molecules, the in the same preparation, provided a reaction will lead to a less viscous mixture of methanol in alkali is used, mixture. Furthermore, you can leave a as is done commercially. This mixture sample for a whole day in these con- Image courtesy of Bristol ChemLabS contains the methoxide ion. During ditions to qualitatively observe the Electricity generated from gin in a mini hydrolysis, a fatty acid is liberated extent of hydrolysis. fuel cell from the triglyceride. Together with Although the biofuel produced in the methoxide ion, the methyl ester of this experiment still contains the the fatty acid is then formed. glycerol formed as a waste product not the only way. Fuels can also be Glycerol (propan-1,2,3-triol) is a of the reaction, the change in viscosity oxidised by electrolysis, as demon- waste product of this last reaction. can nevertheless be observed. If strated in the following experiment. The disposal or use of the glycerol is using a reflux condenser for the Fuel cells produce electricity from a one of the challenges for this growing reaction, the biofuel can be separated reaction between a fuel such as an industry. from the glycerol by solvent extrac- alcohol or hydrogen at the anode, and For the experiment described below, tion. an oxidising agent such as oxygen or you can either use a boiling tube or a The biofuel produced by either chlorine at the cathode. The fuel and reflux method involving QuickfitTM method can then, for example, be the oxidising agent react in the pres- laboratory glassware. used to run a small diesel engine. ence of an electrolyte. The reactants In the simpler preparation without Note: if using vegetable oil that has flow into the cell, and the reaction a reflux, 12-13 ml of a vegetable oil of already been used for cooking, please products flow out of it, while the elec- choice are put into a boiling tube with remember to filter out any food trolyte remains within it. A fuel cell 2 ml of potassium hydroxide in residues first! works by catalysis, separating the methanol (5% w/w). The liquids are component electrons and protons of mixed without shaking to prevent 3) Fuel cells: energy from the reactant fuel, and forcing the elec- trapping air and foaming. The mix- electrolysis trons to travel through a circuit, hence ture is left to stand in a water bath at Both the previous experiments are converting them to electrical power. 60ºC. The reaction rate can be fol- based on the release of energy through A fuel cell is different from a chemi- lowed by measuring the viscosity: combustion. While this is one way of cal battery because its reactants can be you can time how long it takes for a oxidising a fuel to release energy, it is replenished (representing a thermo-

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dynamically open system), whereas the chemicals being methanol to pentan-1-ol, the secondary or tertiary iso- consumed in a battery are not, as it is sealed (thermody- mers of these alcohols (where they exist) and different namically closed). A fuel cell will continue to work as long sources of alcohol, such as methylated spirits, car wind- as its reactants are replaced. screen wash, antifreeze or even alcoholic drinks like vodka or gin. What effect does the type of alcohol have A typical fuel cell produces a voltage from 0.6 V to 0.7 V on the voltage produced? at full rated load. However, fuel cells can be combined in series and parallel circuits; series yield higher voltage, · Students can investigate the effect of changing the initial while parallel allows a stronger current to be drawn. Such concentration of alkali on the output voltage. They may a design is called a fuel cell stack. Furthermore, the cell also analyse whether the type of alkali used, for example sodium versus potassium hydroxide, makes any differ- surface area can be increased to allow stronger current ence to the voltage produced by the fuel cell. from each cell. Fuel cells are very useful as power sources in remote · Investigating the change in concentration of the alkali or locations, such as spacecraft, remote weather stations, the alcohol while the fuel cell is running can also be large parks and rural locations. In the future, they could interesting. also power vehicles. · The whole setup can be placed in a cooled/heated water There are several demonstration fuel cells available for bath to change the temperature at which the reaction purchasew2 (for about €20 each), to show the principle to takes place. By measuring the output current, the effect students. The one we use is an alcohol/air fuel cell (see of temperature on the rate of reaction can be investi - image on page 41), which consists of two parts: an adapt- gated. ed plastic beaker with a conductive pad connected to a ter- Suggestions for further experiments can be found in a cou- minal (the anode), and an insert containing the catalyst. A ple of books or onlinew3. defined volume of a source of alcohol (such as antifreeze), or of an alcohol itself (such as propan-1-ol) is mixed with Acknowledgement 55 ml of alkali (such as sodium hydroxide) as an elec- The authors wish to thank Will Davey at Sheffield trolyte, and put into the plastic beaker. The insert is put University for the basis of the biofuel production experi- into the beaker to complete the cell. Air can pass through ment. the insert into the alkaline alcohol mixture. The chemical reaction that generates a current is the Web references oxidation of the alcohol by the oxygen in the air – to a w1 – For heat of combustion tables of various fuels and carbonyl or a carboxylic acid, depending on the degree of organic compounds on Wikipedia, see: oxidation. The reaction is catalysed by platinised graphite http://en.wikipedia.org/wiki/Heat_of_combustion# in a pad at the base of the beaker. Heat_of_combustion_tables w2 – One of many suppliers specialising in fuel cell tech- At the cathode: nology for both industry and education is h-tec: www.h- - r - tec.com 4e + O2 + 2H2O 4 OH At the anode: w3 – h-tec has also published a book on using fuel cells in - r - the classroom: CH3CH2OH + 2OH CH3CHO + 2H2O + 2e Voigt C, Hoeller S, Kueter U (2005) Fuel Cell Technology The aldehyde CH CHO is also capable of being oxidised 3 for Classroom Instruction (Basic Principles, Experiments, to a carboxylic acid, so it can continue to release an electric Work Sheets). Luebeck, Germany: h-tec current. Incidentally, an alternative fuel for this particular A collection of safe, inexpensive, educational and fun type of fuel cell, which gives a greater voltage than an projects focusing on fuel cell technology is: alcohol, is sodium tetrahydroborate (III) (sodium borohy- Harper G (2008) 101 Fuel Cell Projects for the Evil Genius. dride, NaBH4). According to the manufacturer, only New York, USA: McGraw-Hill Professional minute quantities (about 20 mg of NaBH4) are required to

run the fuel cell for one hour. Note NaBH4 is toxic, harmful For further experiments using fuel cells, see: and an irritant. www.ectechnic.co.uk/exps.html The voltage produced by the fuel cell can easily be measured using a cheap multimeter. These are some of the investigations that can be carried out by students using the fuel cells: · Different types of alcohol may be used, as long as they are water-soluble: these include the alcohol series from

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Teaching activities

Resources Dudley Shallcross is the professor in atmospheric chem- Harrison T, Shallcross D, Henshaw S (2006) Detecting CO2 – the hunt for greenhouse-gas emissions. Chemistry istry, Tim Harrison is the school teacher fellow and Linda Review 15: 27-30 Sellou and Steve Henshaw are both postdoctoral teaching Pacala S, Socolow R (2004) Stabilisation wedges: solving assistants at the School of Chemistry, University of Bristol, the climate problem for the next 50 years with current UK. The school teacher fellowship is a position for a sec- technologies. Science 305: 968-972. doi: 10.1126/ ondary-school teacher that was created to bridge the gap science.1100103 between secondary schools and universities, and to use Shallcross D, Harrison T (2008) Climate change modelling the resources of the School of Chemistry to promote chem- in the classroom. Science in School 9: 28-33. istry regionally, nationally and internationally. For more www.scienceinschool.org/2008/ information about modelling climate change or about the issue9/climate post of school teacher fellow, please contact Dudley Shallcross ([email protected]) or Tim Harrison Shallcross D, Harrison T (2008) Practical demonstrations to ([email protected]). augment climate change lessons. Science in School 10: 46-50. www.scienceinschool.org/2008/ issue10/climate For a full list of Science in School articles about climate change, see: www.scienceinschool.org/ climatechange

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