CLIL for Chemistry_2 - Didattica della Chimica

 MODULE
CLIL for Chemistry - Associazione
culturale
CHIMICARE AUTHOR: Teresa Celestino
THE CARBOHYDRATES
How food and beverages can be analysed utilizing chemical and physical
properties of the carbohydrates.
1441, 3
Moduli CLIL per il quinto anno degli Istituti Tecnici e dei Licei 02 OVERVIEW
GENERAL INFORMATION
VOCABULARY WORDS
ADDRESSED TO STUDENTS 18-19 YEARS OLD
CLASS TIME: 10 HOURS OR MORE
Carbohydrates,
epimer,
ENGLISH LEVEL: B1/B2 (EUROPEAN
monosaccharide,
disaccharide,
polysaccharide, mutarotation, glycoside, glycosidic bond,
epimerization,
anomer,
Fisher
projection,
Haworth projection, glucose, gluco-furanose, gluco-
FRAMEWORK)
pyranose, aldose, ketose, pentose, hexose, fructose,
CO NTENTS
ribose, xylose, arabinose, mannose, galactose, ribulose,
maltose, lactose, sucrose, saccharose, homoglycan,
- MONOSACCHARIDES
heteroglycan, glycogen, amylose, amylopectin, murein,
- DISACCHARIDES
inulin, chitin, agarose, carrageenan, cellulose, fibril,
- POLISACCHARIDES
microfibril, starch, amyloplasts, cyanogenic glycosides,
LABORATORY EXPERIENCES
optical rotation, polarimetry, cherries, apricots, peaches,
cassava, bitter almonds, cherry laurel, flax seed, picric
- DETECTION OF HCN RELEASED FROM
acid, photosynthesis,
PLANTS
twigs, buds, rhizomes, tubers,
Lugol’s iodine, Fehling’s solution, inversion of sucrose,
- TESTING FOOD FOR STARCH
inverted
- TESTING FOOD FOR SUGARS
microwave,
- INVERSION OF SUCROSE
sugar,
pastry-making,
povidone–iodine
popping
solution,
process,
overwrap,
susceptor, toothpick, gelatinisation, retrogradation …..
- THE POPPING PROCESS
OBJECTIVES
SKILLS
BY THE END OF THIS MODULE, STUDENTS
COMMUNICATION IN ENGLISH LANGUAGE (NOTE
SHOULD BE ABLE TO DEFINE VARIOUS
TYPES OF CHEMICAL COMPOUNDS AND
EXPLAIN IN ENGLISH LANGUAGE (SPEAKING
OR WRITING) SOME OF THEIR CHEMICAL AND
PHYSICAL PROPERTIES IN THE BIOLOGICAL
TAKING,
ORAL
AND
WRITTEN
COMPREHENSION (LISTENING, READING)
SYSTEMS. THEY SHOULD BE ABLE TO
OBSERVATION - MANIPULATION
FOOD&BEVERAGES
EXPERIMENTATION
CARRY OUT EXPERIMENTS RELATED TO
ANALYSIS
AND
HOMEMADE FOOD PROCESSING, USING AN
ENGLISH TECHNICAL LANGUAGE.
SUBJECTS
EXPOSITION,
INCLUDING SUMMARIZATION)
(CONDUCTING DATA ANALYSIS)
USEFUL HINTS
In this module, practical activities have more space than
ANALYTICAL CHEMISTRY
PHYSICAL SCIENCE
GENERAL SCIENCE
the theory, which needs to be investigated by additional
lessons and researches, in order to answer the questions
posed. Questions sheets could be used by the teacher
to assign homework or as exercise to assess students’
level. If the teacher uses questions sheets during the
lesson time, it is advisable to organize students two by
two or in groups of three.
INTRODUCTION
The carbohydrates are carbonyl compounds that also
contain
several
hydroxyl
groups.
They
include
monosaccharides, oligosaccharides and polysaccharides.
These compounds are important components of food.
Many organisms use polysaccharides as building materials.
In the gut, oligosaccharides and polysaccharides are
broken down into monosaccharides (the glucose is the
form in which carbohydrates are distributed by the blood
of vertebrates). Then, the glucose is utilized to obtain
energy by the glycolysis or converted into other
metabolites. The liver and muscles store glycogen as a
polymeric reserve carbohydrate.
Oligosaccharides
and
polysaccharides
are
often
covalently bound to lipids or proteins, making glycolipids
and glycoproteins respectively (they are, for example, in
the cell membranes).
MONOSACCHARIDES
The most important natural occurring monosaccharide is
the D-glucose. The Figures 1, 2, 3 show different form of
representation of the glucose by: Fisher projection,
Haworth projection, conformation (pag 35, fare relative
domande).
CLIL for Chemistry - Associazione culturale CHIMICARE
3 Figure 1
Fischer projection
Some
important
Figure 2
Ring forms (Haworth projection)
conversions
related
Figure 3
Conformation
to
sugars
(monosaccharides) are listed below, using D-glucose as
an example (see Figure 4):
Mutarotation
The mutarotation involves the cyclic form; it is the reaction
that interconverts anomers into each other (in the αanomer the OH at the chiral center C-1 and the CH2OH
group lie on the same side of the ring ; in the β-anomer the
OH at the C-1 and the CH2OH are on different sides).
Glycoside formation
When the anomeric OH of the glucose reacts with an
alcohol eliminating water, it yields an α–methylglycoside.
The glycosidic bond is not a normal ether bond, because
of its particular properties.
Reduction and oxidation
The reduction at C-1 produces an alcoholic group (see the
open-chained form in the Figure 1), making the sugar
alcohol sorbitol. Oxidation of the aldehyde group at C-1
goves an intramolecular ester (generally called lactone,
gluconolactone if the sugar glucose is involved). When
glucose is oxidized at C-6, glucuronic acid is formed, a
strongly polar compound playing an important role in
some biotransformations.
Epimerization
In weakly alkaline solutions, glucose is in equilibrium with
the ketohexose D-fructose and the aldohexose Dmannose (the reaction isn’t shown). The only difference
between glucose and mannose is the configuration at C-2.
Pairs of sugars of this type are referred to as epimers, and
their interconversion is called epimerization.
Esterification
The hydroxyl groups of monosaccharides can form esters
with acids. In metabolism, phosphoric acid esters such as
glucose 6-phosphate are very important.
CLIL for Chemistry - Associazione culturale CHIMICARE
5 Figure 4 -­‐ Reactions of the monosaccharides Monosaccharides are classified according to the number
of C atoms (into pentoses, hexoses, etc.) and
according to the chemical nature of the carbonyl function
into aldoses and ketoses (Figure 5).
Figure 5 -­‐ Classification of the monosaccharides DISACCHARIDES
When
the
anomeric
hydroxyl
group
of
one
monosaccharide is bound glycosidically with one of the
OH groups of another, a disaccharide is formed. As in all
glycosides,
the
glycosidic
bond
does
not
allow
mutarotation. Since this type of bond is formed
stereospecifically by enzymes in natural disaccharides,
they are only found in one of the possible configurations
(α or β). The best known disaccharides are maltose,
lactose, sucrose, shown in the following Figures 6, 7, 8.
Figure 6 – Maltose Figure 7 – Lactose Figure 8 -­‐ Sucrose CLIL for Chemistry - Associazione culturale CHIMICARE
7 Questions Sheet
1. What is the meaning of the letters D or L used in the
monosaccharide nomenclature?
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2. Give the R,S configuration of each stereogenic center in
the following Fischer projection. Is this a D or L sugar?
3. What is the meaning of “pyranose” or “furanose” forms?
Select the β-pyranose form of the following aldohexose
derivative in Haworth projection
4. The following sugar derivative is written in Haworth
projection. Select a Fischer projection of the open form of
this compound.
5. Which is the most stable aldohexose? Why?
6. Connect the two columns:
Fructose
Glucose
Pentose
Hexose
Galactose
Arabinose
Mannose
Ketose
Ribulose
Aldose
Xylose
CLIL for Chemistry - Associazione culturale CHIMICARE
9 3. Explain the meaning of the term “mutarotation”.
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4. What is the difference between anomers and epimers?
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5. Classify each of the following monosaccharides as the α
or β anomer
6. Classify each of the following disaccharides as having
an α or β glycosidic bond.
POLYSACCHARIDES
Polysaccharides
formed
from
only
one
type
of
monosaccharide are called homoglycans, while those
formed from different sugar constituents are called
heteroglycans. Both forms can exist as either linear or
branched chains. Many molecules consist of α1è3, α1è4,
α1è6, β1è4, etc… linked monomer residues. For example,
glycogen
and
amylopectin
are
both
branched
homoglycans α1è4 linked glucose residues . In glycogen,
on average every 8th to 10th residue carries — via an α1è6
bond — another 1,4-linked chain of glucose residues
( Figure …). On the contrary, murein is a linear
heteroglycan, with a more complex struxture.
Figure 9 -­‐ Glycogen Figure 10 -­‐ Murein
CLIL for Chemistry - Associazione culturale CHIMICARE
11 Other important polisaccharides are amylose, inulin,
chitin and those derived from algae (e.g. agarose and
carrageenan).
Two glucose polymers of plant origin are of special
importance among the polysaccharides: cellulose (β1è4
linked polymer) and starch (mostly α1è4 linked).
Cellulose is the most abundant organic substance in
nature.
Naturally
occurring
cellulose
is
extremely
mechanically stable and is highly resistant to chemical and
enzymatic hydrolysis. These properties are due to the
conformation of the molecules and their supramolecular
organization. The unbranched β1è4 linkage results in
linear chains that are stabilized by hydrogen bonds within
the chain and between neighboring chains. Elementary
fibril is an association of 50-100 cellulose molecules with a
diameter of 4 nm; about 20 elementary fibril form a
microfibril. Starch, a reserve polysaccharide widely
distributed in plants, is the most important carbohydrate
in the human diet; it is composed by amylose and
amylopectin In plants, starch is present in the chloroplasts
in leaves, as well as in fruits, seeds, and tubers. In these
plant
organs,
starch
is
present
in
the
form
of
microscopically small granules in special organelles known
as amyloplasts. Some 15–25% of the starch goes into
solution in colloidal form when boiling is prolonged. This
proportion is called amylose (“soluble starch”). Amylose
consists of unbranched α1è4 linked chains of 200–300
glucose residues. Due the α configuration at C-1, these
chains form a helix with 6–8 residues per turn. Unlike
amylose, amylopectin, which is practically insoluble, is
branched. On average, one in 20–25 glucose residues is
linked to another chain via an α1è6 bond.
Figure 11 -­‐ Structural motifs of cellulose CLIL for Chemistry - Associazione culturale CHIMICARE
13 Figure 12 – Starch: structural motifs of amylose and amylopectin Resources from “Color Atlas of Biochemistry”, J. Koolman and K.H. Roehm (second
edition, 2005)
Questions Sheet
1. Connect the two columns:
Glycogen α1è4 Starch β1è4 Cellulose α1è6
Murein
Amylose
Amylopectin
2. Write in short origin and use of inulin, chitin, agarose e
carrageenan
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CLIL for Chemistry - Associazione culturale CHIMICARE
15 Read the information below trying to understand the referring substance. Connect
every number (on the left) with one or more letters (from left to right)(e.g.: 1 à e, f).
1. Physical properties
a. OSHA PEL: 15 mg/m3 (total dust)
2. Storage requirements
b. ACGIH TLV: 10 mg/m3
3. Hazardous characteristics
c. If inhaled, coughing, choking, shortness of
breath.
4. Principal target organ(s)
or system(s)
d. In the eyes, irritation.
5. Typical symptoms of acute exposures
e. Fine, white, water-insoluble powder
6. Exposure limits
f. Vapor pressure at 20 °C: negligible
7. Additional remarks
g. Incompatible with air, when dispersed. When
starch powder is dispersed in the air, for example as
Express your considerations about it:
-----------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------List the necessary precautionary measures:
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a “cloud” of starch dust, it explodes violenty if it is
ignited by a flame or spark. A spark from a static
electrical charge that develops as a consequence of
the dispersion is often the source of ignition in such
explosions. When heated in bulk form however,
starch burns and chars slowly.
h. Except for inhalation involving the respiratory
system,
laboratory
exposures
of
sufficient
magnitude to adversely involve target organs or
systems are not foreseeable.
i. Store with other chemicals in a cool, dry, wellventilated general storage location.
l. Starch is a mixture of the carbohydrate polymers,
amylose and amylopectin. In the laboratory, starch
from potatoes is commonly used; however, this
CLIP pertains to starch in finely powdered form
potatoes or any other source.
m. SHA PEL: 5 mg/m3 (respirable fraction)
Abbreviations:
OSHA
PEL: Occupational Safety and Health Administration
ACGIH TLV : American Conference of Governmental Industrial Hygienists – Threshold Limit Value
CLIP: Chemical Laboratory Information Profile
From:
Jay A. Young, “CLIP: Chemical Laboratory Information Profile” - Journal of Chemical Education, Vol.
85 - No. 10, October 2008.
The teacher reads slowly the following paragraph. Students are
organized two by two: every student listens and takes notes; then, the
couple of students write a short summary.
Cyanogenic glycosides
A disproportionately large number of the most important human
food plants is cyanogenic. The accumulated research of numerous
people working in several different disciplines now allows a tenable
explanation for this observation. Cyanogenesis by plants is not
only a surprisingly effective chemical defence against casual
herbivores, but it is also easily overcome by careful pre-ingestion
food processing, this latter skill being almost exclusive to humans.
Moreover, humans have the physiological ability to detoxify
cyanide satisfactorily, given an adequate protein diet. It appears
that early in the domestication of crop plants the cyanogenic
species would have been relatively free of pests and competitive
herbivores, as well as having good nutritional qualities, and thus
ideal candidates for cultivation by the first farmers.
Fruit having a pit (such as cherries, apricots and peaches, cassava,
bitter almonds, cherry laurel, flax seed, among many others) slowly
release hydrogen cyanide from cyanogenic glycosides.
From:
“Plant Biodiversity and Health” Comenius course – Laboratory session (Faculty of
Pharmacy, University of Barcelona, July 2008).
Post: http://urtoefficace.linxedizioni.it/tag/acido-cianidrico/ (in Italian)
CLIL for Chemistry - Associazione culturale CHIMICARE
17 The teacher reads slowly the following brief paragraph. Students are
organized two by two: every student listens and takes notes; then, both
students answer the related questions.
Sugar solutions and polarimetry
Sugar solutions can be analyzed by polarimetry, a method based
on the interaction between chiral centers and linearly polarized
light. It can be produced by passing normal light through a special
filter (a polarizer). A second polarizing filter of the same type (the
analyzer), placed behind the first, only lets the polarized light pass
through when the polarizer and the analyzer are in alignment. In
this case, the field of view appears bright when one looks through
the analyzer. Solutions of chiral substances rotate the plane of
polarized light by an angle α, either to the left or to the right. When
a solution of this type is placed between the polarizer and the
analyzer, the field of view appears darker. The angle of rotation, α,
is determined by turning the analyzer until the field of view
becomes bright again. A solution’s optical rotation depends on the
type of chiral compound, its concentration, and the thickness of
the layer of the solution. This method makes it possible to
determine the sugar content of wines, for example.
Figure 13 – The polarimetry allows the determination of the α and β glucose content. Questions Sheet
1. Observe the Figure 13 (on the left side) and comment
upon the three steps of the instrumental analysis.
- Step 1
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- Step 2
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- Step 3
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2. Observe the Figure 13 (on the right side). Explain the
meaning of the graph shown.
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CLIL for Chemistry - Associazione culturale CHIMICARE
19 The
teacher
reads
slowly
paragraph-by-paragraph.
Students
are
organized two by two: every student listens and takes notes; then, both
students write together a summary of every paragraph. The day after,
teacher asks students to expose the summary orally, without reading.
The starch
Foods as rice, potatoes or bread contain a large amount of starch.
Produced in plants by the photosynthesis of carbon dioxide,
starch granules are made out of glucose polymers and serve as
energy stores. Towards the end of the growing season, starch
accumulates in twigs of trees, close to the buds. It is also found in
fruits, seeds, rhizomes and tubers. Starch granules are very
suitable for such long-term storage, because of their compactness,
relative dryness and high stability.
In order to increase its digestibility, starch needs to be cooked, so
it becomes water-soluble and edible. The transformation of raw
starch in hot water is called gelatinisation: the granules swell and
burst, forming a paste. During cooling, the starch paste often
thickens
due
to
a
phenomenon
called
retrogradation.
Gelatinisation and retrogradation affect the behaviour of starchcontaining systems.
Consequently, starch is excellent for modifying the texture of
many home-cooked foods (for example, to thicken sauces), and
has also been used for centuries for other purposes, including the
manufacture of paper (sizing), glues or fabric stiffener. Today,
new applications of starch are emerging, including low-calorie
dietary fibres, biodegradable packaging materials, thin films and
thermoplastic materials.
From:
Dominique Cornuéjols, “Starch: a structural mystery” – Science in school, Issue 14, p.
22-27, Spring 2010 http://www.scienceinschool.org/repository/docs/issue14_starch.pdf
LABORATORY
DETECTION OF HCN RELEASED FROM PLANTS
Materials:
Filter Whatman 3 mm
Sodium carbonate
Water
Picric acid (1,0 g)
Plant material (about 1 g or more)*
Test glass tubes
Cork or rubber stoppers
Xylene (0,5 ml)
Mixer machine
Bath at 60 °C
* Each group has 3 test tubes and uses the drugs corresponding to the
number written on the tube:
Test tube n.
1: cassava pulp (about 10 g) boiled in c. a. 200 ml of water for 30 minutes
2: cassava pulp (raw)
3: flax seeds
4: cassava bark (about 10 g) boiled in c. a. 200 ml of water for 30 minutes
5: cassava bark (raw)
6: peach seeds
7: cassava pulp (about 10 g) boiled in c. a. 200 ml of water for 30 minutes
8: cassava pulp (raw)
9: flax seeds
10. cassava bark (about 10 g) boiled in c. a. 200 ml of water for 30 minutes
11: cassava bark (raw)
12: tapioca (cassava starch)
CLIL for Chemistry - Associazione culturale CHIMICARE
21 13: cassava pulp (about 10 g) boiled in c. a. 200 ml of water for 30 minutes
14: cassava pulp (raw)
15: peach seeds
16: cassava bark (about 10 g) boiled in c. a. 200 ml of water for 30 minutes
17: cassava bark (raw)
18: flax seeds
19: cassava pulp (about 10 g) boiled in c. a. 200 ml of water for 30 minutes
20: cassava pulp (raw)
21: flax seeds
Procedure:
The picric acid paper was prepared beforehand by
dipping filter Whatman 3 mm in a water solution of 1,0 g of
picric acid in 100 ml of 10% (w/v) sodium carbonate. The
paper was allowed to air dry and was cut into strips about 1
cm by 10 cm. Store dried strips avoiding sunlight contact.
Finely chop or crush with knife or hands a small quantity
of plant material (about 1 g) and place it in a test glass
tube that can be sealed with a cork or rubber stopper
(even with cotton). Put one end of the stopper to hold a
picrate paper strip.
If plant material is dry, moisten with about 0,5 ml of xylene,
mix by the mixer machine; add 3 ml of water using the mixer
again and allow hydrolyzing several minutes in stoppered
tube in a bath at 60 °C degrees.
If the paper changes from yellow to brick red within 30
minutes, HCN is present. The redness is proportional to
the HCN contents. HCN reacts with sodium picrate
producing isopurpurate (red color).
Cautions:
Picric acid is explosive and toxic. Modern safety precautions recommend
storing picric acid wet. Dry picric acid is relatively sensitive to shock and
friction, so laboratories that use it store it in bottles under a layer of water,
rendering it safe. Glass or plastic bottles are required, as picric acid can easily
form metal picrate salts that are even more sensitive and hazardous than the
acid itself.
Hydrocyanic acid developed irritates seriously the eyes and the respiratory
tract. Avoid all contact! Wear safety goggles or eye protection in combination
with breathing protection.
From:
“Plant Biodiversity and Health” course – Laboratory session (Faculty of Pharmacy,
University of Barcelona, July 2008).
Post http://urtoefficace.linxedizioni.it/tag/acido-cianidrico/
CLIL for Chemistry - Associazione culturale CHIMICARE
23 Questions Sheet
1. Observe the following draft related to the laboratory
experience and explain it.
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2. Describe the experiment’s steps related to the following
pictures.
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25 mmmmm m
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TESTING FOOD FOR STARCH
Iodine reacts with starch to form starch/iodine complex which has a blue-black
colour. The appearance of blue-black colour confirms the presence of starch in the
given food sample.
Materials:
Test tubes
Test tubes support
Glass rods
Lugol’s iodine
Water
Food samples
Dropper
Knife
Pestle and mortar
Funnel and gauze
Procedure:
Prepare the referring sample: introduce a small quantity of
soluble starch in a test tube. Add some ml of water in
order to solubilize it; then, add from 2 to 5 drops of
Lugol’s Iodine. Wait the formation of a blue complex
intensely colored.
Mince finely every food sample and put the same quantity
in every test tube labeled with the corrisponding number.
CLIL for Chemistry - Associazione culturale CHIMICARE
27 Add 5-10ml of water filling all the test tubes until the same
level. Mix well.
Add some drop of Lugol’s iodine by the dropper.
Note in a table the color of every test tube content,
comparing with the referring sample.
Write the results in the following table:
FOOD
COLOR
after adding Lugol’s iodine
POSITIVE
NEGATIVE
Pasta
Sugar
(saccharose)
Salt (sodium
chloride)
Wheat flour
Bread
Rice
Milk
Vegetables
Fruits
Cautions:
Elemental iodine is toxic if inhaled; it is also a skin irritant. Lugol's solution is
capable of causing tissue damage if the exposition is prolonged.
Observations
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Conclusions
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Questions
1. Describe the composition of the Lugol’s iodine
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2. Why does Lugol’s iodine react with starch?
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CLIL for Chemistry - Associazione culturale CHIMICARE
29 TESTING FOOD FOR SUGARS
Fehling's solution is a chemical test used for monosaccharides. It is always prepared
fresh in the laboratory, made initially as two separate solutions, Fehling's A and
Fehling's B. Fehling's A is a blue aqueous solution of copper(II) sulfate, while
Fehling's B is a clear and colorless solution of aqueous potassium sodium tartrate
and a strong alkali (commonly sodium hydroxide). Fehling's can be used to determine
whether a carbonyl-containing compound is an aldehyde or a ketone . This test
works with reducing sugars.
Materials:
Test tubes
Test tubes support
Glass rods
Fehling’s solution
Water
Food samples
Dropper
Knife
Pestle and mortar
Bunsen burner
Beaker
Procedure:
Prepare the referring sample: put in the test tube 2 ml of
glucose solution, add 4 ml of Fehling’s A e B, shake the
test tube and warm it. Observe and take notes.
Mince finely and put the same quantity of every food
sample in a labeled test tube.
Add 5-10 ml of water (fill all the test tubes until the same
level) and mix well.
Add some drops of Fehling’s A and Feheling’s B by the
dropper.
Observe the color of the content in every test tube. Heat
the test tubes in a double boiler (using a beaker).
Wait some minutes and take note of the changing colors.
Complete the table.
FOODS
COLOR
COLOR
obtained by adding
after some
Fehling’s solution
minutes
POSITIVE
NEGATIVE
Pasta
Sugar
(saccharose)
Salt (sodium
chloride)
Wheat flour
Bread
Rice
Milk
Vegetables
Fruit juices
CLIL for Chemistry - Associazione culturale CHIMICARE
31 Notes:
It is opportune to filter the fruit juice in order to eliminate the suspended particles .
Add 3 or 4 ml of vinegar to 10 ml of milk before testing lactose in the milk. So, the
proteins can precipitate. Filter and carry out the test utilizing the clear solution.
If sugars are in small quantity, the final content could begin cloudy green rather than
yellow or red.
Either sugars or proteins react with the copper sulfate, so in the starting phase
sugars could be masked by proteins’ reaction. For this reason, it is necessary a
prolonged heating of the test tube until the formation of thebrick- red precipitate.
Cautions:
Fehling’s solution is made with sodium hydroxide, caustic at high
concentrations. Precautions should be taken as such not to come into direct
contact with it. Another component, copper(II) sulfate, is toxic if ingested.
Observations
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Conclusions
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Questions
1. Describe the preparation of the Fehling’s solution.
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CLIL for Chemistry - Associazione culturale CHIMICARE
33 2. How does the Fehling’s solution work? Write the
reaction with a generic monosaccharide.
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3. Explain the result obtained when testing the sucrose.
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INVERSION OF SUCROSE
When saccharose reacts with a strong acid,
the molecule is separated into its two
components, fructose and glucose. This
process
is
called
“inversion”.
Inverted
saccharose reacts with Fehling’s solution.
Materials:
Test tubes
Test tubes support
Sucrose
Hydrochloric acid 37%
Feheling’s solution
Bunsen burner
Procedure:
Dissolve in 5 ml of distilled water one spatule of commercial
sucrose in a test tube, one spatule in another test tube.
Add to the second test tube 2 or 3 drops of hydrochloric
acid 37%. Heat both the test tubes by the bunsen burner.
Add 3 ml of Fehling’s solution in every test tube.
Cautions:
Hydrochloric acid is irritant and corrosive, use protective equipment.
CLIL for Chemistry - Associazione culturale CHIMICARE
35 Observations
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Conclusions
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Questions
1. Why the term “inversion” is used?
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2. The inversion of sucrose can be home-made using, for
example, lemon juice or vitamin C. Why these ingredients?
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3. The inversion of sucrose is commonly used in pastry
making laboratories. Why?
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For more information, see: http://www.chefeddy.com/2009/11/invert-sugar/
THE POPPING PROCESS
Nearly everyone has popped popcorn in a
microwave oven. Microwave heating is the
result of the friction created as polar
molecules, such as water molecules inside an
unpopped kernel of popcorn, oscillate at the
microwave frequency. When a kernel bursts
in response to the vapor pressure of
superheated water, the hot gelatinous starch
inside the kernel first expands and then
cools to form a solid foam as water
evaporates.
Materials:
Two bags of “high-fat” microwave popcorn
Microwave oven
Scissors
Small container
Large bowl
Toothpicks
Clear, colorless, or light-colored cup
Hot water
Paper plate
Gloves and goggles
Povidone–iodine solution
Procedure:
STEP 1. Remove the plastic overwrap from a bag of “highfat” microwave popcorn. What purpose might the
overwrap serve?
CLIL for Chemistry - Associazione culturale CHIMICARE
37 STEP 2. Examine the inner and outer surfaces of the bag.
Locate the “This Side Up” and “Open This End”
instructions on the outside of the bag and a dark
rectangle (the susceptor), on the inside of the bag. The
susceptor is vacuum-deposited aluminum on a polyester
film. What purpose do you think the susceptor
serves?
STEP 3. Using a microwave oven, pop a second,
unopened bag of “high-fat” microwave popcorn according
to
the
package
instructions.
Carefully
touch
the
susceptor; what do you notice about its temperature?
Examine the adhesives that seal the top and bottom of the
bag. Pour the contents into a large bowl. Record your
observations.
STEP 4. Fill a clear, colorless, or light-colored cup with
hot water. Add about a dozen popcorn flakes from step 3,
one at at ime, to the water. Listen! Look! Mix the water and
flakes with a toothpick. Record your observations.
STEP 5. While wearing gloves and goggles, add a few
drops of povidone–iodine solution to the flake/water
mixture. Stir the mixture with a toothpick and allow it to
stand for a few minutes. Starch turns blue-purple in the
presence of iodine. Record
What’s it happen?
your
observations.
STEP 6. Transfer flakes to a plastic bag before disposal
in a trash can. Pour the remaining liquid into a sink for
disposal.
Cautions:
Be Safe! When popcorn is heated in a microwave oven, the bag and its
contents get very hot. Use caution when handling the bag. Heating popcorn
too long in a microwave oven can cause the popcorn and/or the bag to burn.
Wear gloves and goggles when handling the povidone–iodine solution.
From:
Marissa B. Sherman and Thomas A. Evans, “Popcorn—What's in the Bag?” - Journal
of Chemical Education, Vol. 83 - No. 3, March 2006.
CLIL for Chemistry - Associazione culturale CHIMICARE
39