Comenius Math and Science Studio

Experiments using common materials Experiments using common materials

Coloured milk PRINCIPLE ◦ Reduction of surface straint of a milk by the help of detergent. TOOLS ◦ 3 types of milk (with different content of fat) ◦ detergent ◦ colours (ink, food dye) ◦ ear cleaning sticks PROGRESS OF WORK ◦ We put a few drops of each colour into prepared plates of milk. We put the ear cleaning stick with detergent in the middle of each plate. The colours on the milk surface start “to move“ and make coloury patterns. EXPLANATION ◦ The course of experiment is different according to content of fat in the milk. The detergent causes the reduction of surface straint of the milk and causes “the dissolving“ of fat in the water and molecules start to move in the milk. The more content of fat is in the milk in which the fat melts slower and the molecules move slower too, that's why the making of coloury patterns is slower too.

Coloured milk

Acid-base indicators PRINCIPLE ◦ Pigments in some food (stuff) are sensitive to change of pH. TOOLS ◦ solution of acid ◦ solution of base ◦ fruit tea PROGRESS OF WORK ◦ We pour the same quantity of fruit tea into two test-tubes. We pour an acid into first test-tube and then the same quantity of base into the second test-tube. We watch both test-tubes and the change of colours in solutions with different pH. EXPLANATION ◦ It includes pigments which are sensitive to the change of pH. The pigments change their colour depending on the pH solution like substances: phenolphtalein, litmus.

Acid-base indicators PRINCIPLE ◦ Neutralization of solution of NaOH by CO2 in exhaled air. TOOLS ◦ destilled water ◦ Phenolphtalein ◦ NaOH PROGRESS OF WORK ◦ We put 1 drop of NaOH solution into a bulb with the destilled water. Than we also put 1 drop of phenolphtalein. The colour of phenolphtalein turns purple – in basic. While mixing the bulb and breathing out into it the phenolphtalein quickly decolorizes. EXPLANATION ◦ 2NaOH + H 2 CO 3 → Na 2 CO 3 + 2H 2 O ◦ CO 2 in exhalted air partly melts while H 2 CO 3 is coming up. Phenolphtalein decolourizes by neutralization of all NaOH in the solution.

Acid-base indicators

Flubber PRINCIPLE ◦ „Coagulative“ reaction of glue and borax. TOOLS ◦ Glue (100 ml) ◦ water (the same quantity as glue) ◦ Borax – ( sodium tetraborate ) ◦ pigment (ink or food colour) PROGRESS OF WORK ◦ We mix the glue and a half of water (properly!). Put some colour (ink or food colour) to the mixture. Now warm up the second half of the water and melt ½ of teaspoon of borax in it. Than put the solution of borax into the mixture. ◦ Take a fork and mix it till it’s consistant. You can also form it with hands – dont’t worry ;-). ◦ You should create consistant and elastic matter, which is not sticky and it´s workable.

Flubber

What's inside the battery? PRINCIPLE ◦ Manganese dioxide speeds up the decomposition of hydroperoxide. TOOLS ◦ hydrogen peroxide ◦ a battery PROGRESS OF WORK ◦ We pour a dark powder from a battery into a bulb. We add a concentrated hydrogen peroxide. EXPLANATION ◦ MnO 2 from the battery decomposes H 2 O 2. It acts as catalyst. MnO 2 works in a common battery with a salmiac as an electrolyte.

Chemistry in baby nappies PRINCIPLE ◦ Prooving the absorber properties of sodium polyacrylate. TOOLS ◦ plastic cups ◦ a baby nappy ◦ water PROGRESS OF WORK ◦ We pour sodium polyacrylate from a nappy into a plastic cup and we add 5 ml of water. Sodium polyacrylate absorbs the liquid immediately and increases the volume. ◦ Turn the cup upside-down. Thereś no liquid in the cup.

The hollywood blood PRINCIPLE ◦ Coagulative reaction with a rise of a dark red coloured complex compound. TOOLS ◦ solution of KSCN ◦ solution of FeCl 3 EXPLANATION ◦ Dark red coloured complex compound comes up by the coagalative reaction of FeCl 3 and KSCN. ◦ We can simply write down the reaction like this: 3KSCN + FeCl 3 → Fe(SCN) 3 + 3KCl

The hollywood blood