Document 6533566

40 Experiment
Reactions and properties of some organic compounds
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Practical activity 05 Reactions and properties of some organic compounds.
Duration
Purpose
45 minutes
To investigate the reactions and properties of saturated and
unsaturated hydrocarbons, chloroalkanes, alkanols and carboxylic
acids.
Materials
Procedure
Part A—Reactions of saturated and unsaturated hydrocarbons
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1 Shake five drops of cyclohexane with 10 drops of water in a test-tube. Note whether
the saturated hydrocarbon is soluble in water. Repeat using the unsaturated
hydrocarbon, cyclohexene.
2 Place two drops of cyclohexane on one watch glass and two drops of cyclohexene
on another. Light the two liquids with a match and record the appearance of each
flame (colour, smoke, soot, etc.).
3 Using a fume cupboard, place cyclohexane to a depth of 1 cm in one test-tube
and cyclohexene to the same depth in another tube. Add two drops of a solution of
iodine in hexane to each liquid. If there is no immediate reaction, stopper the tube
and place it in sunlight for five minutes. Record your observations.
• small dropping bottles of:
– cyclohexane
– cyclohexene
– iodine in hexane
– 2-chloro-2-methylpropane (tertbutyl chloride)
– ethanol
– 0.1 M silver nitrate solution
– concentrated sulfuric acid
– glacial ethanoic (acetic) acid
– 0.02 M potassium
permanganate solution
– 2 M nitric acid
– 1 M sulfuric acid
• potassium hydroxide
• sodium hydrogen carbonate
• de-ionised water
• 3 × strips of blue litmus paper
• 2 × strips of red litmus paper
• 250 mL beaker
• 8 × semi-micro test-tubes
• 2 × stoppers
• semi-micro test-tube stopper
• semi-micro test-tube rack
• semi-micro test-tube holder
• semi-micro spatula
• 2 × dropping pipettes
• 2 × small watch glasses
• matches
• beaker of hot water (almost boiling)
• disposable plastic gloves
• safety glasses
Part B—Reactions of chloroalkanes
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Use a fume cupboard during all of Part B.
1 Shake five drops of the chloroalkane, 2-chloro-2-methylpropane, with 10 drops of
water. Note whether the chloroalkane is soluble in water.
2 Mix two drops of 2-chloro-2-methylpropane and five drops of ethanol with half
of a small pellet of solid potassium hydroxide. (The ethanol helps to dissolve the
potassium hydroxide.) Warm the mixture in a beaker of hot water for one minute.
3 Test for the presence of Cl– ions by acidifying the mixture with 2 M nitric acid, using
litmus paper to test the acidity, and adding three drops of silver nitrate solution.
Note whether a white precipitate of silver chloride forms.
Part C—Reactions of alkanols
1 Add five drops of ethanol with 10 drops of de-ionised water in a test-tube and
shake. Note whether the saturated alkanol is soluble in water. Test the solution with
red and blue litmus paper.
2 Add four drops of glacial ethanoic (acetic) acid to eight drops of ethanol in a dry
test-tube. Carefully add one drop of concentrated sulfuric acid. Heat the mixture in
a beaker of hot water for two minutes and then pour it into a beaker of cold water.
Note the fruity odour of the chemical formed.
3 Place five drops of ethanol, 10 drops of 1 M sulfuric acid and two drops of
potassium permanganate solution in a test-tube. Heat the mixture in the beaker
of hot water for two minutes and note the colour change due to the formation of
colourless Mn2+ ions.
Part D—Reactions of carboxylic acids
1 Shake five drops of glacial ethanoic acid with 10 drops of de-ionised water in a
test-tube. Note whether ethanoic acid is soluble in water. Test the solution with red
and blue litmus paper.
2 Add a small quantity of sodium hydrogen carbonate to the solution of ethanoic acid
from step 1. Record your observations.
© Pearson Education, a division of Pearson Australia Group Pty Ltd 2007
ISBN 978 1 74081 656 4
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Part 2: Experiments, demonstrations and exercises
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Theory
CH2
H2C
H2C
CH2
CH2
H2C
CH2
H2C
CH
CH
CH2
Cyclohexane
Cyclohexene
Figure 40.1
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CH2
(a) Cyclohexane (b) Cyclohexene
The reactions of organic compounds are described in Heinemann Chemistry 2,
Chapter 10.
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Question
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Construct a table to show:
a details of each test performed
b observations
c inferences drawn from the observations
d equations, where appropriate
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• Wear safety glasses, a laboratory
coat and gloves throughout this
experiment.
• Concentrated sulfuric acid.
Extremely corrosive, causes severe
burns. Highly toxic. Harmful by
inhalation, ingestion and skin
contact.
• Glacial ethanoic acid. Strongly
corrosive, causes serious burns.
Very harmful if swallowed.
• Iodine solution in hexane. Harmful;
danger of serious damage to health
by prolonged exposure; harmful
by inhalation. Use small quantities;
avoid contact of eyes or skin with
iodine solution; work in a fume
cupboard; avoid breathing vapour.
• 2-chloro-2-methylpropane. Harmful
if inhaled or absorbed through the
skin. Use a fume cupboard.
• 2 M nitric acid. Contact with
combustible materials may cause
fire. Corrosive—causes burns;
eye and skin irritant. Use small
quantities.
• Potassium hydroxide. Corrosive and
can cause severe burns; harmful if
swallowed. Use small quantities.
• Organic chemicals used in this
experiment. Highly flammable.
Keep bottles firmly stoppered and
keep away from flames.
• 0.1 M silver nitrate solution. Stains
skin, clothes and benchtops.
Handle with care.
• 0.2 M potassium permanganate is
harmful if swallowed.
The organic chemicals used in this experiment demonstrate reactions typical of
different classes of organic compounds. The chemicals and the classes they represent
are cyclohexane (saturated hydrocarbon), cyclohexene (unsaturated hydrocarbon),
2-chloro-2-methylpropane (chloroalkane), ethanol (alkanol) and ethanoic acid
(carboxylic acid).
The structures of cyclohexane and cyclohexene are shown in Figure 40.1.
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Safety
Waste disposal: After each
experiment, organic wastes should
be disposed of in an organic waste
container in a fume cupboard.
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Part 2: Experiments, demonstrations and exercises
© Pearson Education, a division of Pearson Australia Group Pty Ltd 2007
ISBN 978 1 74081 656 4
23/6/08 10:48:50 AM
41 Exercise
Modelling and naming alkanes
Purpose
• To build models of simple straight chain and branched chain alkanes
• To represent the structures by writing structural and semi-structural formulae
• To develop an understanding of the use of systematic nomenclature.
Duration
45 minutes
Procedure
Materials
Part A—Straight chain alkanes
• Molecular model building kit
• Optional—computer molecular
modelling software
Alkanes have the general molecular formula Cn H2n+2. Carbon atoms are bonded to
other carbon atoms and hydrogen atoms complete the remaining bonds. When the
appearance of the atoms is represented by realistic relative sizes, a molecule of
propane would look something like that shown in Figure 41.1. When we use kits to
build molecular models, the ‘atoms’ show the relative positions of the nuclei and the
plastic straws indicate the orientation of the bonds between the atoms.
Because all the carbon atoms are joined directly to each other, these substances are
referred to as straight chain alkanes. However, as the molecular chain gets longer, the
orientation of the bonds between carbon atoms becomes quite ‘wavy’.
When these molecules are represented on paper in two dimensions, it is usual to draw
either:
• the structural formula – showing every bond between every atom, or
• the semi-structural formula – showing the atoms grouped around every carbon
atom.
1 Construct molecular models of CH4, C2H6 and C3H8.
2 Draw the structural and semi-structural formulae for:
C2H6
C3H8
CH4
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H
C
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Figure 41.1
H
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C
H
H
H
H
H
C
C
H
H
H
H
C
C
C
C
H
H
H
H
Figure 41.3
H
H
H
H
H
C
C
C
C
H
H
H
H
H
H
H
H
C
C
C
H
H
C
H
H
H
H
Figure 41.2
H
C
C
C
H
H
H
I
H
Cl
H
C
C
C
H
H
H
C
C
C
H
Br
Cl
H
H
H
Cl
H
H
H
H
Cl
H
C
C
C
C
C
C
C
C
H
Cl
H
Cl
Br
H
H
Cl
H
v
H
Cl
and
Structural formulae
Cl
H
H
H
H
H
H
C
Cl
H
and
H
H
H
and
H
H
I
Isomers
© Pearson Education, a division of Pearson Australia Group Pty Ltd 2007
ISBN 978 1 74081 656 4
Untitled-1 63
H
C
and
H
H
C
and
H
Cl
Propane molecule
and
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3
C
H
H
1 Identify which pairs of substances are isomers. You may find that building molecular
models may help if you are unsure.
2 Write semi-structural formulae for:
H
Cl
H
H
H
H
H
CH
i
ii
iii
iv
C
H
C
H
When the alkane chain has 4 or more carbon atoms it is possible to form molecules
of different shapes. These are different substances, with different physical properties.
The substances are known as structural isomers.
1 Build molecular models of the possible structural isomers of C4H10.
2 For each structural isomer, draw its structural and semi-structural formula and
give its systematic name.
3 Build molecular models to represent the structural formula shown in Figure 41.2.
4 Do these structures represent molecules that are isomers of each other?
H
H
C
H
Part B—Branched chain alkanes and structural isomers
Questions
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Part 2: Experiments, demonstrations and exercises
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a 3-ethyloctane
b 2-methylpentane
3 For the compounds in Figure 41.4:
a Deduce the systematic names.
b Build molecular models.
i CH
CH
CH
CH
CH
3
2
2
CH3
CH
CH2
CH3
CH2
CH2
CH3
2
CH3
iii
CH3
CH3
CH
CH2
CH3
CH3
CH2
CH2
CH3
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ii
Alkanes
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Figure 41.4
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Part 2: Experiments, demonstrations and exercises
© Pearson Education, a division of Pearson Australia Group Pty Ltd 2007
ISBN 978 1 74081 656 4
23/6/08 10:48:52 AM
42 Experiment
Modelling functional groups and organic reactions
Purpose
• To examine the bonding, shape and nomenclature of a number of organic molecules
with common functional groups.
• To investigate the concept of structural isomers.
• To model reactions involving common functional groups.
Duration
up to 90 minutes, depending on the
number of molecules constructed
Procedure
Materials
Part A—Functional groups
• molecular model building kit
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For each of the molecules listed below:
1 Construct a three-dimensional model.
2 Draw the three-dimensional model in your log book.
3 Draw a diagram of the structural formula.
4 Write the semi-structural formula.
Alkanes: methane, ethane, propane, butane
Alkenes: ethene, propene, but-1-ene, but-2-ene
Chloroalkanes: chloromethane, 1,2-dichloroethane, 1,e-dichloroethane
Alkanols: methanol, ethanol, butan-2-ol, hexan-3-ol
Carboxylic acids: methanoic acid, ethanoic acid, propanoic acid
Esters: methyl ethanoate, ethyl propanoate
Amines: methylamine, ethylamine
Part B—Isomers
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Part C—Reactants
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Construct models and draw the structural formulae of all possible isomers of the
following molecules. Provide the systematic name of each.
1 dichloroethane
4 chloropropane
2 dichloroethene
5 butanol
3 pentane
For each of the pairs of reactants listed below:
1 Construct a three-dimensional model of each organic reactant.
2 Rearrange the ‘atoms’ in the reactants to form models of the products.
List of reactants
a ethane and chlorine
b ethene and hydrogen chloride
c chloroethane and aqueous sodium hydroxide solution
d ethanol and acidified potassium dichromate solution
e ethane and oxygen
f ethanol and ethanoic acid
Theory
Refer to Heinemann Chemistry 2, Chapters 9 and 10, for a discussion of functional
groups, structural isomers and organic reactions.
Questions
1
2
3
4
5
What type of bonding is present within the molecules?
Name the functional groups present within the molecules constructed in Part A.
What are structural isomers?
Draw structural formulae to show the reactants and products for each reaction.
Construct flowcharts to show how ethyl ethanoate can be prepared from either:
a ethane
b ethene
© Pearson Education, a division of Pearson Australia Group Pty Ltd 2007
ISBN 978 1 74081 656 4
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Part 2: Experiments, demonstrations and exercises
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43 Experiment
Preparing artificial fragrances and flavours
This experiment is also included in Heinemann Chemistry 2 Student Workbook as
Practical activity 04 Preparing artificial fragrances and flavours.
Duration
Purpose
30 minutes
To prepare several esters that are widely used as artificial fragrances and flavours.
Procedure
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Theory
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1 Label two semi-micro test-tubes ‘A’ and ‘B’. Place 10 drops of pentan-1-ol in each
tube.
2 Wearing gloves, add 10 drops of glacial ethanoic acid to test-tube A and a similar
volume of salicylic acid to test-tube B. Then add two drops of concentrated sulfuric
acid to each tube.
3 Heat the mixtures for 10 minutes in a beaker of boiling water and then pour each
one into a 250 mL beaker containing 200 mL of cold water.
4 Try to identify the odour of the esters produced by cautiously wafting the vapour
from the ester towards you. Note the name of the carboxylic acid and alkanol used
in this test and describe the smell of the ester.
5 Wash out the beakers thoroughly and repeat steps 1–4 using clean semi-micro
test-tubes and other combinations of alcohols and carboxylic acids.
Esters are commonly used as artificial flavourings in foods such as ice-cream and
sweets. They are partially responsible for many familiar odours, including those
of coffee, perfumes and fruit. An ester is formed when an alkanol undergoes a
condensation reaction with a carboxylic acid. For example, an ester is formed during
the condensation reaction between ethanol and ethanoic acid:
CH3CH2OH(l) + CH3COOH(l) → CH3COOCH2CH3(l) + H2O(l)
The ester produced during this reaction is known as ethyl ethanoate. The formation of
esters is discussed in Heinemann Chemistry 2, Chapter 10.
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• small volumes of the alkanols
pentan-1-ol (n-amylalcohol),
methanol and ethanol
• small amounts (in small plastic
dropper bottles) of various
carboxylic acids: octanoic acid,
glacial ethanoic (acetic) acid and
decanoic acid
• salicylic acid
• dropping bottle of conc. sulfuric acid
• 6 × semi-micro test-tubes
• semi-micro test-tube rack
• small tongs
• 250 mL beaker containing 100 mL
of boiling water
• 2 × 250 mL beakers
• marking pen
• safety glasses
• gloves
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Materials
Questions
1 Salicylic acid has the formula C6H4(OH)COOH. Write an equation for the reaction
between methanol and salicylic acid.
2 Write equations for each of the other reactions you performed in this experiment.
3 Name the esters that you have made in this experiment.
4 What is the role of the concentrated sulfuric acid in these reactions?
Safety
• Wear safety glasses, gloves and a laboratory coat for this experiment.
• Concentrated sulfuric acid. Extremely corrosive, causes serious burns. Highly toxic.
Harmful by inhalation, ingestion and skin contact.
• Glacial acetic acid. Strongly corrosive and causes serious burns. Very harmful if
swallowed.
• Salicylic acid. Harmful by inhalation, ingestion and skin absorption.
• Decanoic acid. Eye, skin and respiratory irritant. Harmful by ingestion or skin contact.
• Pentan-1-ol. Harmful if swallowed, inhaled or absorbed through the skin. Severe eye
and skin irritant. Flammable.
• Methanol. Toxic by inhalation, ingestion or skin absorption. Flammable.
• Ethanol. Skin and eye irritant. Flammable.
• Esters. Eye, skin and respiratory system irritant.
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Part 2: Experiments, demonstrations and exercises
xercises
© Pearson Education
Education, a division of Pearson Australia Group Pty Ltd 2007
ISBN 978 1 74081 656 4
23/6/08 10:48:53 AM
44 Experiment
Fractional distillation of an alcoholic drink
Fractional distillation is a separation technique widely used industry and laboratories
to separate liquids with fairly close boiling points. In a refinery, fractional distillation is
used to separate the components of crude oil.
45 minutes
Purpose
•
•
•
•
Duration
To correctly assemble fractional distillation apparatus
To observe and identify physical processes occurring in a fractionating column
To recognise when a particular compound is separated
To calculate the percentage of alcohol in the original drink.
Procedure
•
•
•
•
•
•
•
•
•
•
fractionating column
condenser
100 mL boiling flask
thermometer (0–120°C)
delivery tube
silicone grease
heating mantle
2 retort stands
boiling chips
50 mL whisky, wine or ethanol/
water mixture
• 50 mL measuring cylinder
• 2 × 100 mL conical flasks
• 10 mL measuring cylinder
thermometer
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1 Assemble the fractional distillation apparatus as shown in Figure 44.1. Lightly
grease all joints with silicone grease for a tighter fit.
2 Add a few boiling chips to a clean, dry boiling flask.
3 Measure 50 mL alcoholic drink or ethanol/water mixture and pour it into the
reaction flask.
4 Position a conical flask under the delivery tube.
5 Heat the flask gently then increase heating until the temperature of the distillate
reaches 75°C.
6 Position another conical flask at this temperature and collect this fraction until the
temperature reaches 80°C.
7 Using a small measuring cylinder, measure the volume of the fraction that was
distilled between 75°C and 80°C.
8 Draw a labelled diagram of your apparatus.
9 Place 10 drops of the ethanol collected between 75°C and 80°C into a clean
evaporating basin and light it.
10 Record your observations.
Materials
Safety
• Ethanol is a flammable liquid.
• All liquids can be washed down the
sink in the fume cupboard.
delivery tube
condenser
fractioning column
boiling flask
Figure 44.1
© Pearson Education, a division of Pearson Australia Group Pty Ltd 2007
ISBN 978 1 74081 656 4
Untitled-1 67
Fractional distillation apparatus
Part 2: Experiments, demonstrations and exercises
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Theory
Fractional distillation is based on the principle that the vapour above a mixture of volatile
liquids will be richer in the more volatile component. A series of evaporations and
condensations occurs as the vapours rise up the fractionating column, progressively
increasing the proportion of the more volatile component (refer to Figure 10.32 in
Heinemann Chemistry 2 ). At the top of the column the vapour will ideally be of only
the more volatile component, which is condensed as it enters the condenser. However,
it is not possible to achieve complete separation in all cases. The distillate from the
fractional distillation of an ethanol/water mixture will at best contain 95% ethanol.
Fractional distillation is discussed in Heinemann Chemistry 2, Chapters 10 and 23.
Questions
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Calculations
1 Calculate the percentage by volume of ethanol in the fraction collected at
75–80°C.
Alcohol
ethanol
propan-1-ol
butan-1-ol
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Table 44.1 Boiling point
of different alcohols
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General questions
2 How does the percentage of alcohol you distilled compare with the content of
alcohol shown on the label of the original bottle? Account for any difference.
3 Using your observations, explain the function of the fractionating column and
condenser.
4 The boiling point of pure ethanol is 78.3°C. Comment on the purity of your fraction
collected between 75°C and 80°C.
5 What difference would it make to the products if you removed the fractionating
column and continued with ordinary distillation?
6 Write a phase change equation for the process occurring in the fractionating
column at 75–80°C.
7 Refer to Table 44.1.
a What is the relationship between the size of the molecules and their respective
boiling points?
b Explain this trend in terms of the molecular forces.
8 On the molecular level, water is a smaller molecule than ethanol. Why does ethanol
have a lower boiling point than water?
9 The volatility of hydrocarbons is directly proportional to their boiling points and
melting points. Explain the difference between volatility and boiling point.
10 What is the basis for separation of components of crude oil?
11 Highly volatile carbon compounds are easily ignited and present a fire hazard. The
ignition temperature and flash point of a compound are good indicators of a fire
hazard. Use the internet to find a definition of each term and explain how these
indicators are used in the fire rating of a compound.
12 Write a balanced chemical equation for the complete and incomplete combustion
of ethanol.
Boiling point (°C)
78.3
97.2
117.7
Part 2: Experiments, demonstrations and exercises
© Pearson Education, a division of Pearson Australia Group Pty Ltd 2007
ISBN 978 1 74081 656 4
23/6/08 10:48:55 AM
45 Experiment
Fermentation
A recent use of the age-old process of the fermentation of sugar is to
use the ethanol produced as a biochemical fuel for motor vehicles. In this
investigation you will design your own procedure to make ethanol from
sucrose and test the product using a known reaction of ethanol.
This experiment is also included in Heinemann Chemistry 2 Student Workbook as
Practical activity 06 Fermentation—student-designed investigation.
Purpose
• To design an experiment to produce ethanol by fermenting sugar and to verify the
product by testing with acidified potassium permanganate solution.
• To monitor the reaction by measuring the mass of the fermentation vessel and
determine when the process is complete. (Fermentation will take about five days.)
• To identify the gas produced in the reaction.
Materials
As required.
Safety
As required.
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1 Using secondary sources for information, write a description of
how you will perform this experiment. Include a labelled diagram of
the experimental set-up. List the materials and submit your procedure
and materials list to your teacher for approval.
2 Complete a risk assessment for your chosen method. Show it to your teacher.
3 Set up your experiment so you can monitor the mass changes and identify the
gaseous products formed.
Questions
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What gas was produced during fermentation and how did you identify it?
Write a balanced equation for the fermentation reaction.
What is the function of yeast in fermentation?
How long did the reaction take to reach completion? Explain your reasoning.
Calculate an approximate percentage of ethanol by mass in the reaction mixture
produced in your experiment.
6 Explain how you would expect ethanol to react when tested with potassium
permanganate solution. Write half equations and an overall equation for the
reaction.
7 In Australia, petrol is now being produced with up to 10% ethanol. Explain the
advantage of using this type of fuel.
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2
3
4
5
25 minutes to set up and up to 5 days
for completion of fermentation
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Procedure
Duration
© Pearson Education, a division of Pearson Australia Group Pty Ltd 2007
ISBN 978 1 74081 656 4
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Part 2: Experiments, demonstrations and exercises
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46 Experiment
Breaking down the starch polymer
Purpose
To examine the breakdown of starch by dilute hydrochloric acid, and by an enzyme.
Duration
Procedure
40 minutes
Part A—Acid hydrolysis
•
•
•
•
•
•
•
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Part B—Enzyme hydrolysis: saliva
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•
•
•
•
•
•
•
•
•
•
•
1 Add 1–2 mL of your saliva (or 1% diastase solution) to 5 mL of starch solution in a
large test-tube. Label it with your name and leave it to stand at room temperature
for 5 minutes.
2 Using a dropping pipette, place a few drops of the mixture into a semi-micro testtube. Test the mixture for the presence of starch using iodine solution.
3 Place a small sample of the saliva and starch mixture in another semi-micro testtube and test for the presence of sugars using Benedict’s reagent as in step 4 of
Part A. Record your observations.
4 Place a small cube of potato or dry biscuit in your mouth for 5 minutes. Note and
record any change in taste.
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•
6 mL 1% starch solution
5 mL 0.05 M iodine solution
15 mL 2 M hydrochloric acid
5 mL 2 M sodium hydroxide
solution
2 mL 1% diastase solution
(Diastase contains amylase and can
be used as a substitute for saliva;
see Procedure.)
15 mL Benedict’s reagent
litmus paper or pH paper
2 × small pieces unripe banana
2 × small pieces ripe banana
potato, approximately 1 cm cube
5 × large test-tubes
test-tube rack
4 × semi-micro test-tubes
semi-micro test-tube rack
10 mL measuring cylinder
hot-water bath (250 mL beaker of
boiling water)
2 × dropping pipettes
Bunsen burner
bench mat
marking pen
trough of disinfectant solution
(shared by class)
disposable plastic gloves
safety glasses
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•
•
•
•
1 Place 1 mL starch solution in a large test-tube with 15 mL 2 M hydrochloric acid.
Heat the test-tube in a boiling water bath for 5 minutes.
2 Using a dropping pipette, place a few drops of the mixture in a semi-micro testtube and test with iodine solution. If the result of the test is positive, heat the
contents of the large test-tube in a boiling water bath for a further 5 minutes and
re-test.
3 In a semi-micro test-tube neutralise a small sample of the mixture of starch solution
and hydrochloric acid using 2 M sodium hydroxide solution, testing with litmus or
pH paper.
4 Test for the presence of sugars such as maltose or glucose by pouring about 2 mL
of the neutralised mixture into a large test-tube. Add about five drops of Benedict’s
reagent and boil gently. Observe and record any change of colour. Maltose and
glucose cause a red precipitate of copper(I) oxide (Cu2O) to appear.
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Materials
Refer to the next page for safety
information related to this experiment.
Part C—Enzyme hydrolysis: banana
1 Place one drop of iodine solution on a sample of ripe banana and another drop on
a sample of unripe banana. Record your observations.
2 Place a small piece of the ripe banana in a large test-tube, and a small piece of
the unripe fruit in another large test-tube. Test with Benedict’s reagent for the
presence of sugars. Record your observations.
Theory
Starch is a polymer of glucose. It is broken down into simpler molecules during hydrolysis
(reaction with water). The products formed depend upon the reaction conditions. If the
hydrolysis of starch is catalysed by hydrochloric acid the monosaccharide glucose is
formed, whereas when hydrolysis occurs in the presence of an enzyme both glucose
and the disaccharide maltose are produced.
In acid hydrolysis, each of the glycosidic bonds between the glucose units in the starch
polymer is broken. This non-selective hydrolysis yields glucose as the only product.
In contrast, the enzyme usually present in saliva, called amylase, attacks the starch
polymer randomly; glucose and maltose are products of the reaction. As amylase is
not able to catalyse the hydrolysis of maltose further, maltose produced in the mouth
remains intact until it reaches the stomach.
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Part 2: Experiments, demonstrations and exercises
© Pearson Education, a division of Pearson Australia Group Pty Ltd 2007
ISBN 978 1 74081 656 4
23/6/08 10:48:56 AM
Questions
1 Using hexagons to represent glucose units, draw a simple diagram of the structure
of starch and show how breakdown occurs via acid and enzyme hydrolysis.
2 Account for any change in the taste of the potato.
3 Explain the significance of the results of the tests performed on the samples of ripe
and unripe banana. How are these results related to the taste of ripe and unripe
banana?
Extension activity
• Wear safety glasses and a
laboratory coat for this experiment.
• To avoid risk of infection, do not
perform this experiment using
someone else’s saliva. Place
equipment containing saliva in
disinfectant solution immediately
after use and wear disposable
plastic gloves when handling such
equipment.
• Sodium hydroxide solution and
hydrochloric acid are corrosive.
• Iodine stains skin, clothing and
bench surfaces.
• Benedict’s reagent may cause
irritation to skin and eyes. Avoid
contact.
• Because the potato in this
experiment is to be tasted, it must
be stored away from chemicals
and handled only after hands have
been washed.
Sa
m
pl
e
pa
ge
s
Use thin-layer chromatography and the mixtures from parts A and B of the experiment
to identify the products of the hydrolysis of starch. The method for this is described
in Experiment 49 Separation of monosaccharides and disaccharides using thin-layer
chromatography.
Safety
© Pearson Education, a division of Pearson Australia Group Pty Ltd 2007
ISBN 978 1 74081 656 4
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