3. Experiment – Chemical Cleaning of Water
Water that is beneath the ground is called groundwater. Groundwater is often so clean that you can drink it, but in cities or other densely populated areas it is not enough. Then water from lakes, rivers or other currents is used. That water is called surface water and to make it drinkable you have to clean it in a waterworks.
The surface water is often polluted with particles that are hard to clean. In this experiment we will analyze what happens when we add a water cleaning chemical.
Materials: 0,5 ml sodium bicarbonate, 1 ml ‘Oboy’ chocolate powder, 1 ml PAX-XL19 solution, 1,5 liters PET-bottle, ml measurement, Water
First we will pollute the water so that it looks like water could look in a lake. A little brown, but not too dirty.
Pour 1 liter tap water into the PET-bottle. Add 0,5 ml sodium bicarbonate. Add 1 ml ‘Oboy’. Seal the bottle and shake until it is completely solved (No lumps).
Now it’s time to add the water cleaning chemical.
Open the bottle and add 1 ml of the PAX-solution. Seal the bottle and shake for about 5-10 seconds. Slowly roll the bottle on the table and try to see what happens (about 1-2 minutes). Put the bottle at a place where you can observe what happens inside of it.
Experiment 2 – Dialysis
The dialysis tube lets certain molecules and ions through. It can be used to clean the blood of people who are kidney sick. Now let’s examine what happens when two different liquids are placed inside respectively outside of the dialysis tube.
Plastic Cup, Sodium bicarbonate solution dyed with black carrot, Citric acid solution, 15cm dialysis tube, 2 wire twists
Rinse the dialysis hose with water (eases opening). Open the tube and fold one end. Then fold the folded end double to tighten it. Close it with a wire twist. Fill the tube with the colored bicarbonate solution with a pipette. Close the second end the same way as the first one. Use wire twist. Rinse off eventual spilling from the outside of the dialysis tube with water. Put the dialysis tube in the plastic cup. Pour the citric acid solution in the cup until it completely covers the dialysis tube. What happens?
Short explanation of what happens
The dialysis tube is made of a so called semipermeable membrane, a membrane that lets water and smaller molecules such as ions through, but not bigger molecules. The citric acid and the anthocyans are too big to pass through the dialysis hose, but the carbonate ions that are created when sodium bicarbonate are solved in water are small enough. When the bicarbonate ions penetrate out they react with the citric acid and create carbon dioxide. It bubbles.
After approximately 10 minutes it still bubbles and then you can see that the contents in the top of the dialysis tube have changed color from purple to pink. That is because the anthocyans in black carrot are natural pH-indicators, they change color when the solution gets less basic.
After half an hour it still bubbles and the color shift has become clearer. If you let the experiment stand the tube’s content will become completely pink.