Let's play with reactions


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workshops Buonarroti secondary school Marina Di Carrara Italy

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Let's play with reactions

  1. 1. Comprehensive School “M. Buonarroti“ Marina di Carrara Secondary school Presents SCIENTIFIC WORKSHOPScientific project: Tiziana PerfettiText translated by : Maria Antonietta Caporale
  2. 2. LET’S DISCOVER THE CHEMICAL REACTIONSWe have a chemical reaction when we observe phenomena that testify thedisappearance 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 changesare 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 ChemicalsChemical reactions can be faster or less fastHowever we may act to increase or decrease the speed of a reaction in a lot ofways , for example using catalysts. Almost all the reactions that occur in livingorganisms are activated by biological catalysts, the enzymes.
  3. 3. Even the stones breathe ( breathe out) Marble and hydrochloric acidYou 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. 4. same manner in which water dissolves salt and sugar?Has a new substance formed or not?
  5. 5. Can it be stated that there has been a chemical reaction? Give an explanationWhat happened?  The effervescence observed in the test tube with the marble powderis due to the development of another gas, the carbon dioxide. Thechemical reaction is:hydrochloric acid + marble calcium chloride + carbon dioxide+ water
  6. 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 pipetteProcess: o Put some pieces of aluminum in a test tube o Add a few drops of hydrochloric acid
  7. 7. What do you observe?In the test tube with aluminum effervescence is observed , the solutionbecomes darker and aluminum corrodes and disappears. You must waita few minutes to allow reaction to develop, fragments are surroundedby 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 seea flame inside the test tube, while the blast of the explosion will turn offthe match. The effervescence observed in the test tube with thealuminum is due to the development of a gas, the hydrogen. In thereaction we can also see that the hydrogen reacted with the oxygen inthe air producing water vapor ( after the reaction we will find somecondensation on the inner walls of the test tube).The chemical reaction is :6HCI + 2AI 2 +3( Hydrochloric acid + aluminum aluminum chloride+hydrogen)
  8. 8. Balloon Let’s inflate a balloon without blowing You need : • an Erlenmeyer flask • a balloon • baking soda • graduated cylinder • vinegar • a funnel • a teaspoonProcess: 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
  9. 9. baking soda to come into contact with the vinegar. ReflectionsWhat 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 reactionstarts for which we can note the development of foam and the balloonthat is inflated. A gas called carbon dioxide develops. Since gases expanduntil they occupy all the space available , the carbon dioxide inflates theballoon. Touching it the bottle is cooled and at the end a deposit mayremain.Baking soda + acetic acid = sodium acetate + water+ carbon dioxideThe 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 thatthe vinegar was not sufficient to react all the baking soda.
  10. 10. A volcano of foam (be careful !)TARGETSTo recognize an exothermic reaction and the function of a catalystYou 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 containerProcess 1. Put the bottle in the centre of the container. Insert the funnel in the bottle and pour the peroxide.
  11. 11. 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 aminute a moving flow is formed. The bottle will feel warm to the touchas it is an exothermic reaction.To obtain the volcano of foam we have to use a catalyst, a substancethat accelerates the rate of the reaction and that it is found unchangedat the end, without transformations.How does it work?The decomposition reaction of hydrogen peroxide into water andoxygen 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 phenomenasuch as the release of oxygen, the production of H2O in addition tochanges in ph.A lot of reactions of industrial importance take place with the aid ofsuitable catalysts, all the reactions of biological importance take placewith the aid of enzymes, active catalysts in living organisms.
  12. 12. SECRET MESSAGES First messageYou need: • Lemon juice • A blank sheet of paper • A glass stick • A candleProcess:
  13. 13. 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 itdarkens and makes visible the writing
  14. 14. SECRET MESSAGES Second messageYou need: • A wad of cotton • A sheet of paper • Very diluted tincture of • Lemon juice, brush iodineWhat 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 backgroundWhat do you deduce?The starch of the paper is combined with iodine by changing colour tothe sheet of paper which becomes blue/purple. Also the vitamin c inlemon combines with the iodine but it forms a colourless molecule. Sothe area covered by the lemon juice stands on a colored background.
  15. 15. Let’s change the coloursThe colour change may indicate the formation of newsubstancesYou need: o Two test tubes o Two pipettes o Solution of ferric chloride o Solution of potassium ferrocyanideProcess: 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?
  16. 16. 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 eggHow can an egg bounce like a ball without breakingYou 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
  17. 17. 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! Theonly thing that remains is the delicate membrane of the egg.What happened?The bubbles that cover the shell are carbon dioxide bubbles. Vinegaris an acid called acetic acid. ( White vinegar is usually made up of about5% of acetic acid and 95% of water). The egg shells are composed ofcalcium carbonate. Vinegar reacts with the calcium carbonate givingorigin to a substance called calcium acetate and carbon dioxide.The egg shell is reduced to a very thin layer and the egg is flexible. Theshelled membrane remains . The semi-impermeable membrane incontact with the external solution begins to flow solvent ( the vinegar)inside the egg from the outside so that the concentration of particlesinside balances the outside one. This flow of a liquid through a semi-impermeable membrane from a less concentrated solution to a moreconcentrated one is called osmosis.The volume of the egg has visibly increased showing the effect ofosmotic pressure. If you shake the egg, the yolk can be seen splashing
  18. 18. around the egg white. If the egg reacts with the carbon dioxide in theair it will harden.