1. Comprehensive School “M. Buonarroti“
Marina di Carrara
Secondary school
Presents
SCIENTIFIC WORKSHOP
Scientific project: Tiziana Perfetti
Text translated by : Maria Antonietta Caporale
2. LET’S DISCOVER THE CHEMICAL REACTIONS
We have a chemical reaction when we observe phenomena that testify the
disappearance of the substances used and/or the formation of new ones.
In particular :
bubbles
the formation and the disappearance of a solid
spontaneous heating or cooling
the colours changes
are evidence of chemical reactions
The substances that give rise to the transformation are called reagents and
the substances that are formed are called chemicals (products)
Reagents Chemicals
Chemical reactions can be faster or less fast
However we may act to increase or decrease the speed of a reaction in a lot of
ways , for example using catalysts. Almost all the reactions that occur in living
organisms are activated by biological catalysts, the enzymes.
3. Even the stones breathe
( breathe out)
Marble
and hydrochloric acid
You need:
• a plastic spoon • hydrochloric acid
• a glass rod • distilled water
• marble powder • a beaker
Process:
o With the spatula take a small amount of marble powder, add
water and a few drops of hydrochloric acid until all the solid
has not disappeared.
Observations:
What do you observe? What do you think
happened?
Does the acid dissolve the marble in the
4. same manner in which water dissolves salt and sugar?
Has a new substance formed or not?
5. Can it be stated that there has been a chemical reaction? Give an
explanation
What happened?
The effervescence observed in the test tube with the marble powder
is due to the development of another gas, the carbon dioxide. The
chemical reaction is:
hydrochloric acid + marble calcium chloride + carbon dioxide
+ water
6. Accadue
HYDROGEN PRODUCTION
(be careful !)
The use of the match requires proper precautions and the
completion of the experiment by the teacher.
Targets
To recognize a very fast and effect chemical reaction.
You need:
• Pieces of aluminum foil • A match
(for food) • A wood pliers
• Hydrochloric acid • A glass rod
solution (muriatic)
• Two test tubes
• A test tube rack
• a pipette
Process:
o Put some pieces of aluminum in a test tube
o Add a few drops of hydrochloric acid
7. What do you observe?
In the test tube with aluminum effervescence is observed , the solution
becomes darker and aluminum corrodes and disappears. You must wait
a few minutes to allow reaction to develop, fragments are surrounded
by bubbles of hydrogen that keep them afloat.
o Place above the test tube the second inverted test tube, that is
with the opening facing downwards, to collect the hydrogen which
is lighter than air.
o After a few minutes move away the second test tube, always
keeping it inverted, from that in which hydrogen is generated and
approach the entrance to a lighted match.
What happens?
We will hear a slight explosion and, if you look carefully, you can see
a flame inside the test tube, while the blast of the explosion will turn off
the match. The effervescence observed in the test tube with the
aluminum is due to the development of a gas, the hydrogen. In the
reaction we can also see that the hydrogen reacted with the oxygen in
the air producing water vapor ( after the reaction we will find some
condensation on the inner walls of the test tube).
The chemical reaction is :
6HCI + 2AI 2 +3
( Hydrochloric acid + aluminum aluminum chloride+
hydrogen)
8.
9. Balloon
Let’s inflate a balloon without blowing
You need :
• an Erlenmeyer flask
• a balloon
• baking soda
• graduated cylinder
• vinegar
• a funnel
• a teaspoon
Process:
1. Using a graduated cylinder pour 30ml of vinegar in the
Erlenmeyer
flask.
2. Stick a balloon to the mouth of the funnel.
3. Put a teaspoon of baking soda in the balloon .
4. Take off the funnel from the balloon.
5. Adjust the opening of the balloon around the neck of the
flask, being careful not to fall into the baking soda.
6. Keep the flask still, raise the balloon in such a way to allow
the
10. baking soda to come into contact with the vinegar.
Reflections
What do you observe inside the flask?
What happens to the balloon?
What conclusions do you draw?
What happens?
After the baking soda has been dropped in vinegar, a chemical reaction
starts for which we can note the development of foam and the balloon
that is inflated. A gas called carbon dioxide develops. Since gases expand
until they occupy all the space available , the carbon dioxide inflates the
balloon. Touching it the bottle is cooled and at the end a deposit may
remain.
Baking soda + acetic acid = sodium acetate + water+ carbon dioxide
The vinegar that remains ( if it is in excess of the amount of baking soda)
is now diluted. If a white deposit remains on the bottom, it means that
the vinegar was not sufficient to react all the baking soda.
11. A volcano of foam
(be careful !)
TARGETS
To recognize an exothermic reaction and the function of a catalyst
You need:
• An empty glass bottle (preferably with a narrow
neck)or a graduated cylinder
• 1/2 cup of hydrogen peroxide at 20 volumes
• liquid detergent
• 3-4 drops of food coloring
• Potassium iodide
• A funnel
• A large and low container
Process
1. Put the bottle in the centre of the container. Insert
the funnel in the bottle and pour the peroxide.
12. 2. Add the detergent to the peroxide in the bottle.
What happens?
3. Add 3-4 drops of food coloring.
4. Dissolve two teaspoons of sodium iodide in a few millimeters of
warm water in a beaker.
5. Quickly pour the sodium iodide in the bottle ( and move away).
6. The students can touch the bottle to feel all the changes that
occur.
What do you observe?
The reaction creates foam which is shot out of the bottle. After about a
minute a moving flow is formed. The bottle will feel warm to the touch
as it is an exothermic reaction.
To obtain the volcano of foam we have to use a catalyst, a substance
that accelerates the rate of the reaction and that it is found unchanged
at the end, without transformations.
How does it work?
The decomposition reaction of hydrogen peroxide into water and
oxygen is the following:
2 2 O+
When we pour KI in the hydrogen peroxide / liquid detergent mixture,
the volcano of foam starts. We will also recognize other phenomena
such as the release of oxygen, the production of H2O in addition to
changes in ph.
A lot of reactions of industrial importance take place with the aid of
suitable catalysts, all the reactions of biological importance take place
with the aid of enzymes, active catalysts in living organisms.
13. SECRET MESSAGES
First message
You need:
• Lemon juice
• A blank sheet of paper
• A glass stick
• A candle
Process:
14. o Take the stick and dunk it in the lemon juice
o Write on a paper what you want or make a small drawing
o Let the ink dry and wait till the writing disappears
o Now let the paper pass over the flame of a candle being
careful not to burn it.
What do you observe?
The writing reappears and it is perfectly legible
What do you
deduce?
The heat makes
the lemon juice
react so that it
darkens and makes visible the writing
15. SECRET MESSAGES
Second message
You need:
• A wad of cotton • A sheet of paper
• Very diluted tincture of • Lemon juice, brush
iodine
What to do
o Write a message on the white paper using a brush dipped in the
lemon juice.
o Let the writing dry till it becomes invisible.
o Rub a wad of cotton soaked in a dilute solution of iodine on the
sheet where it says.
What do you observe?
The writing reappears, white on a blue/purple background
What do you deduce?
The starch of the paper is combined with iodine by changing colour to
the sheet of paper which becomes blue/purple. Also the vitamin c in
lemon combines with the iodine but it forms a colourless molecule. So
the area covered by the lemon juice stands on a colored background.
16. Let’s change the colours
The colour change may indicate the formation of new
substances
You need:
o Two test tubes
o Two pipettes
o Solution of ferric chloride
o Solution of potassium ferrocyanide
Process:
o Take a few ml of solution of ferric chloride ( a yellow-
orange colour solution) by a pipette and put it into the two
test tubes
o Add some drops of a reactive called
potassium ferrocyanide to the first
test tube
• What do you observe?
17. The second solution, light yellow, added to
the solution of ferric chloride determines a
marked change in colour : the content of the
test tube becomes blue ( also called Prussian
blue) due to the formation of a new substance
( the ferric ferrocyanide)
o Add some drops of potassium thiocyanate
( colourless solution) to the second test tube
What do you observe?
o The solution becomes dark red even if precipitate
doesn’t form: the new formed red substance is soluble
in water. Some chemical reactions occurred: the initial
substances are transformed and they have given rise to
new substances that there weren’t before, with their
own evident characteristics ( a different coloration).
Rubber egg
How can an egg bounce like a ball without breaking
You need:
o A raw egg
o A glass or a glass jar
o Vinegar
o (time)
Process:
1) Put the egg into the glass jar and cover the egg with vinegar
2) After some hours look closely the egg. What do you observe? Do
you see the bubbles formation around the eggshell?
3) Let the egg into the vinegar for 24-48 hours
4) On the second day, carefully pour the old vinegar down the drain
and cover the egg with fresh vinegar
18. 5) Don’t disturb the egg but pay attention to the bubbles that are
formed on the surface of the eggshell ( or what’s left of it).
6) Pour the vinegar and rinse thoroughly the egg with water
7) What do you observe?
The egg looks translucent because the outer shell has disappeared! The
only thing that remains is the delicate membrane of the egg.
What happened?
The bubbles that cover the shell are carbon dioxide bubbles. Vinegar
is an acid called acetic acid. ( White vinegar is usually made up of about
5% of acetic acid and 95% of water). The egg shells are composed of
calcium carbonate. Vinegar reacts with the calcium carbonate giving
origin to a substance called calcium acetate and carbon dioxide.
The egg shell is reduced to a very thin layer and the egg is flexible. The
shelled membrane remains . The semi-impermeable membrane in
contact with the external solution begins to flow solvent ( the vinegar)
inside the egg from the outside so that the concentration of particles
inside balances the outside one. This flow of a liquid through a semi-
impermeable membrane from a less concentrated solution to a more
concentrated one is called osmosis.
The volume of the egg has visibly increased showing the effect of
osmotic pressure. If you shake the egg, the yolk can be seen splashing
19. around the egg white. If the egg reacts with the carbon dioxide in the
air it will harden.
