Polyhydric alcohols
how molecules of alcohols are built;
how to write down the alcohol functional group;
what is the valency of alcohol functional group;
what is the valency of carbon in organic compounds.
note formulas of polyhydric alcohols on the example of glycerol and ethylene glycol;
use common and systematic names of known polyhydric alcohols;
explain why glycerol is used as ingredient of cosmetics;
examine the properties of glycerol.
Structure of polyhydric alcohols
GlycerolGlycerol, commonly called glycerineglycerine, is a propane derivative in which three hydrogen atoms have been replaced with hydroxyl groups. Hence the name propanetriol. The first component (propane-) originates from a hydrocarbon whose chain is part of the alcohol, tri- means three groups , and -ol ending is characteristic of alcohols.
Propane‑1, 2, 3‑triol is the systematic name of glycerine. As explained above, propane - indicates that this compound is a propane derivative, numbers: 1, 2, 3, so‑called. locantslocants, inform that each hydroxyl group (hydroxyl group)hydroxyl group) is connected to another carbon atom, numeral tri- defines the presence of three hydroxyl groups, and -ol ending confirms that glycerol is part of alcohols.
Ethylene glycol
Ethylene glycol is a derivative of ethane, in which two hydrogen atoms have been replaced with hydroxyl groups. The systematic name of this compound is ethanediol.
Watch the presentation „Structure of a model of erythritol molecule”. What can you say about the structure of polyhydric alcohols by analysing another example of this group of alcohols? Write down your suggestion.
Physical properties of glycerol
Physical property | Glycerol |
state of matter | liquid |
taint | colourless |
solubility in water | no limits |
boiling point | 290°C |
density | 1.26 g/cmIndeks górny 33 |
Before the movie „Mixing glycerol with water”, formulate a research question and hypotheses. Pay attention to what happens with glycerol and water during the experiment. Write down your observations and conclusions.
Film dostępny na portalu epodreczniki.pl
Nagranie filmowe przedstawiające eksperyment mieszania glicerolu i wody. Do przeprowadzenia eksperymentu potrzebne są probówka z bezbarwną cieczą, glicerolem, glycerol, probówka z czarną cieczą, woda z atramentem, water with ink. Do probówki z wodą i atramentem laborant wlewa po ściance glicerol. W probówce glicerol spływa na dno probówki, obserwuje się dwie warstwy cieczy. W górnej warstwie widoczna jest czarna ciecz, woda z atramentem, natomiast w dolnej warstwie widać bezbarwną ciecz, glicerol. Laborant wstrząsa zawartością probówki. Obserwuje się wymieszanie obu warstw i powstaje mieszanina jednorodna.
What is the density of the glycerol with respect to the density of water?
Select one of the presented hypotheses, and then verify it.
Glycerol floats on the surface of the water.
Water of lower density floats on the surface of glycerol. Glycerol does not dissolve in water.
glycerol,
test tube,
water coloured with blue ink.
Slowly add glycerol down the side of the test tube containing water coloured with blue ink so that the liquids do not mix.
Observe which liquid is in the bottom layer of the mixture.
Shake the tube vigorously.
Observe whether glycerol dissolved in water.
We notice two distinct layers of liquid. The upper layer contains water with ink and in the bottom - colorless glycerol. After mixing the two liquids, the boundary between the layers disappears.
Glycerol (glycerine) is a colourless liquid, freely soluble in water. The boiling point and the density of the liquid are the substance‑specific quantities and allow the identification of the alcohol in question.
Chemical properties of glycerol
By conducting further experiments, we will see what the chemical properties of glycerol are. Does it react like ethanol? Does the presence of three hydroxyl groups affect the reaction of aqueous glycerol solutions? Are warning signs placed on the glycerol labels?
The smell and taste of glycerol
Glycerol has no smell. It has a sweet taste and this feature is of great importance for its various applications.
Combustion of glycerol
Before the movie „Testing combustibility of Glycerol”, formulate a research question and hypotheses. Pay attention to what is emitted during glycerol combustion. What does it mean?
Film dostępny na portalu epodreczniki.pl
Nagranie filmowe przedstawiające eksperyment badanie palności glicerolu. Do eksperymentu potrzebne są parownica z glicerolem, drewniane łuczywko, toothpick, palnik, torch. Laborant podpala koniec łuczywka i umieszcza go w parownicy, w której na dnie znajduje się glicerol. Nie obserwujemy efektów reakcji. Koniec wykałaczki cały czas pali się taki samym, małym płomieniem. Następnie laborant umieszcza parownicę z glicerolem nad palnikiem i ogrzewa. Po czym ponownie podpala koniec łuczywka i umieszcza go w parownicy, w której na dnie znajduje się glicerol. Tym razem płomień na wykałaczce gwałtownie się powiększa. Na ścianach parownicy osadza się sadza.
How to recognize incomplete combustion of glycerol?
The emission of soot during the combustion of glycerol will confirm that there is a partial combustion reaction.
glycerol,
evaporating dish,
tripod with a ceramic mesh,
burner.
Pour approximately 2 cmIndeks górny 33 of glycerol into porcelain evaporating dish.
Examine its flammability.
Gently heat up the evaporating dish containing glycerol.
Examine its flammability again.
During the combustion of glycerol smoky flame is produced which indicates that the soot is emitted.
The product of incomplete combustion of glycerol is carbon and water.
The products of complete combustion of glycerol are carbon dioxide and water.
Glycerol, like other alcohols, undergoes combustion. It is necessary to preheat glycerol in order to start the reaction. Depending on the amount of available oxygen, the glycerol combustion may be complete or incomplete.
pH of glycerol
Before you watch the movie „Testing the pH of an aqueous solution of glycerol”, formulate a research question and hypotheses. Pay attention to what happens to the indicators during the experiment. What does it mean?
Film dostępny na portalu epodreczniki.pl
Nagranie filmowe przedstawia eksperyment - badanie odczynu glicerolu. Potrzebne będą, trzy probówki wypełnione glicerolem (glycerol), probówka ze wskaźnikiem wywarem z czerwonej kapusty (decoction of red cabbage) oraz probówka ze wskaźnikiem fenoloftaleiną (phenolphthalein), pipeta (pipette), papierek wskaźnikowy (indicator paper). Do pierwszej probówki z glicerolem dodano wywar z czerwonej kapusty, do drugiej probówki z glicerolem dodano fenoloftaleinę do trzeciej probówki z glicerolem zanurzono papierek wskaźnikowy. Wskaźniki dodane do roztworów glicerolu nie zmieniły koloru. Odczyn wodnego roztworu glicerolu jest obojętny.
Is the glycerol pH the same as the pH of methanol and ethanol?
Polyhydric alcohols have the same pH as monohydric alcohols.
The colour of indicators will not change. There are no ions in the glycerol solution.
three test tubes,
aqueous solution of glycerol,
red cabbage brew,
phenolphthalein,
universal indicator strip.
Pour approximately 3 cmIndeks górny 33 of glycerol into 3 test tubes.
Add a few drops of a red cabbage brew to one tube, a drop of phenolphthalein to the other, and immerse the universal indicator strip in the last one.
Observe test tubes.
The indicators added to the glycerol solutions did not change their colour. The pH of the aqueous glycerol solution is neutral.
Watch the demonstration or conduct the experiment „Testing the electrical conductivity of an aqueous solution of glycerol”. Pay attention to what happens to the bulb of the electrical conductivity meter.
Does aqueous solution of glycerol conduct electricity?
Select one of the presented hypotheses, and then verify it.
The aqueous solution of glycerol conducts electricity well.
The aqueous solution of glycerol does not conduct electricity.
glycerol,
water,
beaker, device – electric conductivity indicator.
Fill the beaker with glycerol mixed with water.
Immerse the electrode of the electrical conductivity meter in the liquid.
Pay attention to whether the light bulb has turned on.
The bulb of the electrical conductivity meter did not light up. It indicates that there is no electrical conductivity, and thus – no ion in the solution.
There are no HIndeks dolny 33OIndeks górny ++ (HIndeks górny ++) and no OHIndeks górny –– ions in the aqueous solution of glycerol. Glycerol does not undergo electrolytic dissociation, so it is not an electrolyte.
Application of glycerol
In cosmetics there are two types of glycerol – natural and of petrochemical origin. Glycerol is obtained, among others from coconut oil.
Glycerol has hygroscopichygroscopicproperties and naturally protects the skin by binding the water necessary to maintain proper skin hydration. Effectively moisturizes dry skin. It smoothens skin, improves elasticity, regulates skin renewal processes. It is added to almost all hand creams, face creams and balms.
Glycerol is used as a sweetener in antitussive syrups. It is also used in the production of explosives (nitro glycerine). It has many applications in medicine because it is easily absorbed into the gastrointestinal tract. Oral glycerol preparations have a mild laxative effect.
Crude glycerine obtained from vegetable fats is used as an additive to cattle feed (for cows and pigs). It is tasty, maintains feed moisture, provides energy and affects e.g. cow's milk yield and pig mass gain.
Properties and application of ethylene glycol
Ethylene glycol is a colourless liquid with a high viscosity. It dissolves well in water. It is a poisonous substance. It is used in the manufacture of artificial fibres, paints and anti‑freezing engine coolants.
Ethanediol is toxic for humans. After consumption, it causes metabolic acidosis and damages to many organs, kidneys, liver and brain.
Summary
Glycerol and glycerine are common names of the same chemical compound – propanetriol.
The glycerol molecule consists of three hydroxyl groups.
Glycerol is a thick oily, colourless and odourless liquid with a sweet taste. It is not a poisonous substance.
Glycerol is widely used in the cosmetics, food and textile industries.
Write the glycerol burning reaction equation if one of the products will be a gas causing clouding of the limestone water.
Keywords
glycerol, glycerine, ethylene glycol, ethanediol, erythritol, polyhydric alcohol
Glossary
glicerol – nazwa zwyczajowa alkoholu o nazwie systematycznej propano‑1,2,3‑triol
gliceryna – nazwa zwyczajowa alkoholu o nazwie systematycznej propano‑1,2,3‑triol
grupa hydroksylowa – inaczej grupa wodorotlenowa
lokant – liczba przypisana atomom węgla w łańcuchu węglowym
substancja higroskopijna – substancja pochłaniająca wodę lub parę wodną z otoczenia