3. Other resources such as ethanol, are readily
available from renewable resources such as plants
3.1.1 Describe the dehydration of ethanol to ethylene and identify the need for a catalyst in this process
and the catalyst used
 Before ethylene was produced from the cracking of petroleum, it was produced
from the dehydration of ethanol
 Dehydration: chemical reaction where a water molecule is removed from a
compound
o
 Ethanol vapours are heated over a catalyst at 350 C, leading to the OH group
and hydrogen atom to be removed from an adjacent carbon atom, which forms
a water molecule
 Catalyst is needed because the ethanol molecule does not spontaneously
break bonds to release a water molecule and form a double bond and a
catalyst increases the rate of reaction by providing an alternate reaction pathway with a lower activation
energy
 Specifically, concentrated sulphuric acid is used because it’s a powerful dehydrating agent
 In the lab, catalyst used is excess concentrated sulphuric acid. Porous ceramic crystals are also used
3.1.2 Describe the addition of water to ethylene resulting in the production of ethanol and identify
the need for a catalyst in this process and the catalyst used
 The hydration of ethylene is a chemical
process whereby a water molecule is
reacted with ethylene to produce ethanol
 The reaction is carried out at 300oC at high
pressure, in the presence of a catalyst such
as dilute sulphuric acid or concentrated
phosphoric acid
 Catalyst is needed open ethylene’s double bond, because the water molecule itself will not attack
the electrons in the double bond. Also, the catalyst is added to increase the rate of reaction, as it
provides an alternate reaction pathway with a lower activation energy
3.1.3 Describe and account for the many uses of ethanol as a solvent for polar and non-polar
substances
 Ethanol is a very important industrial solvent which can dissolve both polar and non-polar substances
 The hydrophilic, polar hydroxyl group of ethanol can interact with other polar substances by ion-dipole,
dipole-dipole interactions or even hydrogen bonding in some cases due to the high electronegativity of oxygen
(refer to diagram below). It can thus interact with other polar substances and dissolve them via the like dissolves
like principle (eg: can dissolve water).
 USE: These properties make it useful in industry where it is used to dissolve the polar compounds in vanilla
extract/essence (such as Vanillin - C8H8O3), where it interacts with this chemical through hydrogen bonding and
is able to dissolve it using the like-dissolves-like principle
 The hydrophobic non-polar ethyl chain of ethanol interacts with other non-polar substances by dispersion
forces (refer to diagram below), and can dissolve them via the like dissolves like principle(ethanol can dissolve
octane)
 USE: This property makes it useful in perfumes, where ethanol is often used to dissolve the non-polar, organic
compounds which give the perfume its fragrance through the like dissolves like principle.
 OTHER USES: It is also used as a solvent in cosmetics and toiletries, medications, antiseptics and perfumes
3.1.4 Outline the use of ethanol as a fuel and explain why it can be called a renewable source
 Ethanol can be used as a fuel as its combustion is highly exothermic. However, vehicles as yet due to the
inability of engines to cope with the fuel cannot directly use it. As such, engines require extensive modification
to use ethanol or ethanol must be present as an additive (<20%) only.
 Ethanol is considered to be a renewable source because it can be derived from non-fossil fuel sources, such as
the fermentation of glucose which is obtained from cellulose (a major component of biomass)
 Ethanol fuels with concentrations over 90% can also be used, but require engine modifications for blends above
24%
 The combustion of ethanol:
3.1.5 Describe conditions under which the fermentation of sugars is promoted
 Fermentation is the process in which glucose is decomposed into ethanol and carbon dioxide by the action of
enzymes present in microbes (especially yeast)
 Conditions for fermentation
ESSENTIAL
o
Aqueous solution of simple sugars (glucose)
o
Alcohol tolerant yeast
o
pH of about 3.7 – 4.6 (to kill pathogens that may develop)
o
Ethanol concentration under 15% (or else yeast dies)
o
Inorganic nutrients such as nitrogen or phosphorus
o
Fermentation’s optimal temperature is at about 37 C
o
distilled water is optional (ideal)
o
Anaerobic environment (exclusion of oxygen)
o
3.1.6Summarise the chemistry of the fermentation process:
1. Cane sugar waste is rich in sucrose. If water and yeast are added, the sucrose reacts with water producing
glucose. This is because the enzymes in yeast break down the larger carbohydrates (e.g. starch and sucrose from
cane sugar waste or molasses) into simple carbohydrates (glucose):
C12H22O11(aq) + H2O(l)
2C6H12O6(aq)
2. In an oxygen-free environment (see above for the other conditions), the enzymes in yeast break down glucose
into ethanol and carbon dioxide:
3. The fermentation process stops at around 15% ethanol concentration, as the ethanol starts killing the yeast.
Distillation of the mixture can achieve higher ethanol concentrations (up to 96%).
3.1.7Define the molar heat of combustion of a compound and calculate the value for ethanol from
first hand data
The molar heat of combustion of a compound is the quantity of heat released per mole of complete
combustion of a fuel under standard laboratory conditions
 REASONS FOR DIFFERENCE BETWEEN THEORETICAL AND DETERMINED VALUES
1. Incomplete combustion; can be avoided by conducting experiment in a well-ventilated area
2. Heat is lost from flame to the surrounding environment; can be avoided by using a heat shield
3. Conducting vessel absorbs heat; Use metal can rather than glass beaker as metal cans transfers heat quickly
 Molar heat is measured in kilojoules per mole (Kj/mol)
 Molar heat of combustion for ethanol = -1367Kj/mol
 In calculations, to GET AN ANSWER IN JOULES/MOL  Use mass of water in grams and 4.18
 To GET AN ANSWER IN KJ/MOL  Use mass of water in kg and 4.18
Assess the potential of ethanol as an alternative fuel a discuss the advantages and disadvantages
of its use
 Sourced from biomass (eg: Cellulose), Ethanol (C2H5OH) produced from fermentation of glucose has
significant potential for use as a replacement fuel for petroleum (as crude oil supplies are predicted to decline in
the foreseeable future).
 Ethanol is currently used in fuel blends such as E10 in Australia, but in Brazil more than 30% of cars run on>25%
ethanol blends.Countries such are China and South Africa are investigating greater use of ethanol fuels. It’s use
has numerous advantages and disadvantages
Advantages
 It's a renewable source when produced by fermentation, helping to reduce pressure on our finite supply of
crude oil
C6H12O6 (aq)2C2H5OH(aq) Yeast
+ 2CO2(g)
 Ethanol requires less oxygen to completely combust than octane for per mole of fuel. This means that
Ethanol is more likely to undergo complete combustion, reducing the production of undesirable products such
as carbon (soot) and carbon monoxide (which is toxic).Thus ethanol is a cleaner fuel than octane
C2H5OH (l) + 3O2 (g) 2CO2 (g) + 3H2O (g)
 Ethanol is a liquid at room temperature, and therefore does not need to be stored under high pressure,
unlike natural gas
 Ethanol that is sourced from biomass is
theoretically carbon-neutral, as the
carbon released in the combustion of
ethanol is absorbed during the
photosynthesis of the biomass source
 Ethanol fuels are less likely to lead to
petrochemical smog, which is a major
concern in urban environments
 Ethanol can be produced from local
biomass production, which can be
locally sourced. Conversely petroleum sources often have to be imported. Thus the transportation costs for
raw materials in ethanol production will be lower
 Returns 139% of energy invested in its production
Disadvantages
 In order to produce ethanol from crops to provide ethanol as an alternative fuel it would require twice the area
used for farmland today (arable land). This destroys the habitats of many animals, and negatively impacts the
environment
 The disposal of the waste liquors of fermentation would also cause environmental problems.
 The fermentation process is currently too expensive to operate on the large scale required for fuel use. This
is because the energy required for the distillation process in fermentation is very high and is associated with
high costs.
 At present, Ethanol is still mainly produced by the hydration of Ethylene (as fermentation is currently too
expensive) and this is a non-renewable process, placing pressure on our finite supply of crude oil. The equation
is:
 Upon complete combustion, Ethanol releases less heat per mole than octane (so ethanol is less energyefficient than octane). The combustion of octane [2C 8H18OH (l) + 25O2(g) 16CO2 (g)+ 18H2O(l)] releases ~ 5470
Kj/mol whereas the combustion of ethanol releases ~ 1367 Kj/mol
 It needs to be used in concentrations of 15% - 20% in cars as it is damaging to the engines of vehicles, or
engine modifications need to be made
Criteria: In assessing the potential of ethanol as an alternate fuel, the following factors must be considered: the
cost of production (distillation etc.), the energy efficiency of ethanol compared to octane, renewability and
potential long term use and polluting emissions
Judgement
 Ethanol has a strong potential to be used as an alternative fuel due to its renewability, complete combustion,
lower ignition temperatures and higher energy returns. However it does have disadvantages and research into
more cost effective and viable means of producing ethanol must be developed if it is to be widely used as an
alternative fuel.
3.2.2 Process information from secondary sources to summarise the processes involved in the
industrial production of ethanol from sugar cane
1. The sugar-cane crop is harvested; the whole plant is then crushed and grinded to create a pulp of cellulose and
sucrose.
o
2. The pulp is hydrolysed with dilute sulphuric acid at 100 C for two hours to hydrolyse the cellulose and sucrose
into glucose molecules
3. The mixture is then filtered to remove the glucose solution from the solid residues of lignin and unbroken
cellulose (However the solid residue is further hydrolysed with stronger acids and filtered again and the glucose
are added into the filtrate)
4. Calcium hydroxide is added to the acidic sugar solution remaining to neutralise the sulfuric acid; calcium sulfate
(a precipitate) is formed (Ca(OH)2(aq) + H2SO4(aq) CaSO4(s) + 2H2O(l)). The Calcium Sulfate is filtered off as
gypsum and is sold to the agricultural industry
5. The solution is then fermented by being placed in an oxygen-free tank, warmed to 37°C, and by adding suitable
yeast cultures
6. The CO2 that evolves in the fermentation process is captured and purified to sell to other industries (e.g. soft
drink companies)
7. After about two days, the mixture reaches around 10-12% ethanol concentration
8. The solution undergoes distillation to produce high concentration industrial grade ethanol.
3.2.3 Process information from secondary sources to summarise the use of ethanol as an
alternative car fuel, evaluating the success of current usage
 Ethanol as an alternative car fuel has had mixed successaround the world.
 In Brazil, the government introduced subsidiesto encourage the production of ethanol by sugar cane
fermentation in response to petroleum shortages in the 1980s. The program was so successful that by 1985,
96% of cars ran exclusively on ethanol. Brazil requires that ALL car engines are able to accept at least 25%
ethanol. In fact, 4 million Brazilian cars run on pure ethanol (at least 99% ethanol). It has proven to be a very
efficient fuel. Moreover, in Sweden, 85% ethanol mixtures are common.
 However, elsewhere around the world, countries such as Australia and the USA has produced limited
amountsof ethanol to use in ethanol-petrol blends. Normal cars can use about 10-20% ethanol blend fuel
without engine modifications, but beyond 20% cars require expensive modificationswhich add to its cost.
Although the use of ethanol is a renewable sourceand has environmental benefits of lower greenhouse gas
emissions (especially CO), petrol remains cheaper to produceand it is unlikely that ethanol is to be
adopted in other countries soon
 Judgement: Even though ethanol is well received in some countries, it is still more expensive to produce and
implement in most parts of the world. Further research to reduce the cost of production process
(transportation, distillation) may make ethanol an economically viable fuel in the future.
3.2.4 Solve problems, plan and perform a first-hand investigation to carry out the fermentation of
glucose and monitor mass changes
Aim: To carry out the fermentation of glucose and monitor mass changes
Apparatus: 1 x Electronic balance, 1 x Thermometer, 20mL of glucose solution 10% (w/v), 1 x 100mL conical
flask with rubber stopper and a bent glass tube, 1 x 500mL beaker, 50mL measuring cylinder, Large test tube,
and 3g of Sodium Biphosphate
Safety:
 Chemicals involved in experiment Sodium Biphosphate may splash into eyes and cause damage. For this reason,
safety goggles should be worn throughout the experiment to protect eyes
 If possible, the area where the experiment is being conducted should be sterilised with disinfectant to ensure
that no microbes develop around the apparatus, because these can cause illness. The mixture should not be
tasted for this reason
 Before disposing the mixture, an antiseptic should be added to kill any microbes and pathogenic organisms that
may be present
Method:
1.
Weight out 1 gram of yeast using an electronic balance, and add it into a 250mL conical flask
2.
Measure 20mL of glucose solution using a measuring cylinder and add the glucose solution to the flask.
3.
Add 3 grams of Sodium biphosphate (Na2HPO4) as a yeast nutrient into the flask. Mix this thoroughly
4.
Using an electronic balance, record the mass of this set-up
5.
Add a gas transferring pipe from this flask to another 250mL flask (cleaned with distilled water) half-filled with
limewater
o
6.
Place this setup in an incubating oven set at 37 C for the duration of the experiment
7.
After six hours, remove the flask and dry it before weighing it on the electronic balance. Record its mass and
note any observations (including in limewater set-up). Return the flask to the incubating oven
8.
Repeat step 7 at every six hour interval until the mass recorded for three subsequent recordings are concordant
(a stable mass has been achieved)
9.
Repeat steps 1-8 using distilled water rather than a glucose solution, this set-up will act as the control
10. Repeat experiment ten times
Discussion
Justification of the Method:
 A “closed” system (where no gas was allowed to escape) was used to ensure an accurate experiment.
 Limewater was employed to prove CO2 was produced.
o
 Using an incubating oven at 37 C and adding a yeast nutrient (sodium biphosphate) ensured that the most
optimal fermentation occurred
 A control was used to check if the mass loss was purely due to the formation of CO2, orif other processes such as
evaporation assisted in the mass loss process
 Using an electronic balance ensures that the mass lost due to the carbon dioxide was measured very accurately
Limitations of the method:
 The atmosphere in the flask was not anaerobic (oxygen-free) and this could have hampered the fermentation
process
 Some of the carbon dioxide may not have been released from the conical flask, and was rather dissolved in the
fermentation mixture
 In the control setup, a small decrease in mass was recorded, suggesting evaporation took place to a certain
extent
Accuracy:
 When weighing the apparatus, a more accurate electronic balance should have been used.
 Additionally, a rubber hose should have been attached to the bent glass tube so that no water got stuck inside
the bent glass tube, adding to the mass of the apparatus
 Additionally, the flask should have been dried before weighing
Reliability:
 The experiment was repeated ten times and the results were consistent, thus the experiment was reliable.
 To improve the reliability, the results can be compared with other members of the class who performed the
exact same experiment, to check for consistent results
Validity:
 A control should have been used to ensure validity. If the mass of the control changed, then there is a possibility
that something else was causing or contributing to the mass change. This is likely to be evaporation. However,
we are only interested in the mass change cause by fermentation. Therefore, by determining the mass change of
the control (mass change due to evaporation), the other values of mass change can be adjusted, giving more
valid (and accurate) results. The control and the actual experiment should have been treated in the exactly same
way, except for the presence of absence of glucose solution.
 Additionally, more valid results could be obtained from drying the apparatus before weighing, using the same
electronic balance for every weighing, and using a rubber hose
Results: The carbon dioxide reacted with the limewater, turning it into a milky colour (due to the formation of
calcium carbonate):
Ca(OH)2(aq)+ CO2(g)
Time (hours)
Mass of Flask
(g)
0
573.16
6
572.54
12
572.17
18
571.43
CaCO3 (s) + H2O(l)
NOTE: In questions to do with the fermentation prac, it is likely
that they will give you a graph showing the mass of the setup
slowly decreasing, and eventually reaching a stable mass. You
must assume that the mass change in the graph is due to the
formation of carbon dioxide gas. This gives you the mass of
carbon dioxide, and this allows you to calculate the moles of
carbon dioxide and the other reactants and products (use the
fermentation formula). There are limitations to this assumption
which are covered below. Volume may also be calculated using
24
571.08
30
570.92
36
570.92
42
570.92
"Volume = n(CO2) x 24.79"
Note: In the control set up, 0.5g was lost (likely due to evaporation)
Calculations:
Mass lost in Experimental setup = 2.24g
Mass lost in Control setup = 0.5g
∴ Approximate mass lost due to fermentation =
1.74g
∴n(CO2) =
=
𝑚𝑎𝑠𝑠
𝑚𝑜𝑙𝑎𝑟 𝑚𝑎𝑠𝑠
=
1.74
44.01
= 0.03953646898
𝑉𝑜𝑙𝑢𝑚𝑒 𝑜𝑓 𝑐𝑎𝑟𝑏𝑜𝑛 𝑑𝑖𝑜𝑥𝑖𝑑𝑒
24.79
∴Volume of CO2 released = 0.9801090661 L
= 0.98L (to 2 d.p)