CALCULATING DENSITY in a PEMAR classroom

Another task I ask the students, is the application of the scientific method to a problem or a doubt that they may have: to calculate the density of three different objects.

Click on the image to continue reading this activity:

FOOD ANALYSIS TO FIND THE PRESENCE OF CARBOHYDRATES

Shared by: Yolanda Ruiz

Starch Test
1. Chop up each food.
2. Add a little water to each food so that the nutrients are released from the food material.
3. Add three drops of iodine solution to each food suspension.
4. A change of colour of the iodine to blue-black indicates the presence of starch.

A test for reducing sugar

1. Chop up each food.
2. Add a little water to each food so that the nutrients are released from the food material.
3. Add Benedict’s reagent to each food suspension to a depth of 2 cm.
4. Shake the test tube gently.
5. Place it in a water bath of boiling water for 3 minutes and record the colour change.

Colour change:
• A sample that does not contain a reducing sugar will remain blue.
• A sample that contains reducing sugar will turn green, yellow, red or brown, depending on the increasing amount of reducing sugar.

This video shows how to test food for the presence of reducing sugars. This would indicate that sugar is present in food.
1. Bread
2. Nut
3. Grape juice

HOW TO MAKE PLASTIC SHAPES FROM MILK

Provided by Mª Carmen Santamaría:

With a little bit of milk and vinegar, you can create a material similar to plastic. The experiment is completely safe and you can make whatever you would like out of the plastic once it’s made."

This experiment shows the movement of particles through a membrane

For this experiment you will need:

• Water • Starch solution • Iodine • Dropper • Zipper plastic bag PROCEDURE: • Mix the starch solution in the water in a beaker. • With the help of the dropper put some iodine solution in the zipper bag. • Zip the plastic bag. • Now turn up side down to check whether there is any leak. • Submerge the plastic bag into the beaker with starch solution. • Leave the arrangement for half an hour. • A layer of deep purple-black color layer is formed on the membrane of the plastic bag and the color slowly diffuses into the starch water.

EXPLANATION:

Iodine is used to test for the presence of starch. When Iodine reacts with starch, it turns deep purple-black. The iodine molecules are small enough to pass through the membrane of the plastic bag, however starch and water molecules are too big to pass through the membrane.

The movement of the iodine through the plastic membrane is functionally the same as movement of molecules through biological membranes, that is, any cell membrane.

The molecules will move from higher concentration to lower concentration. Osmosis is the net movement of solvent molecules (in this case, iodine) through a partially permeable membrane (like a plastic bag) into a region of higher solute (water) concentration, in order to equalize the solute concentrations on the two sides.

Here, by partially permeable membrane or semi-permeable membrane, we mean a permeable to the solvent, but not the solute. Diffusion is that physical process in which any solvent moves, without input of energy, across a semi permeable membrane separating two solutions of different concentrations.

ADDING SULPHURIC ACID TO SUGAR

By Tomás Isla,

This is a video which shows the effect of adding sulphuric acid to sugar.

Sulphuric acid is a strong dehydrating agent and transforms sugar in coal with a very soothing effect.

The heat involved in the reaction is so high that makes the liberated water boil. You can do this experiment at your lab, but be careful because the vapours are very hot and irritating. Take care of the hot released even when touching the beaker or the coal. After some minutes, pupils can touch and take pieces of the coal, always wearing gloves because of the remaining sulphuric acid.