German version
Supermarket products:
| red cabbage juice
| vinegar essence
| Bullrich Salt Powder - medicament against heartburn, active component: sodium bicarbonate
| |
Glass wares:
| 3 conical measures, graduated, 350 mL
| Petris dish d = 9 cm
| 2 snap-cap vials 20 mL
| 2 glass stirring rods | |
Experimental procedure:
150 mL of water and 3 mL of concentrated red cabbage juice are placed in each of three conical measures. Two of these solutions are mixed with
10 mL of vinegar essence. The third solution serves as reference solution. Three spatula full of Bullrich Salt are added to one of the two acidified solutions.
Result:
The purple cabbage juice turns red when it is acidified. When Bullrich Salt is added the color changes from red to purple to blue while foaming.
Videoclip (Download RealPlayer .rm file)Discussion and background:
The color change of the indicator shows that the vinegar has been neutralized by Bullrich Salt. The release of carbon dioxide causes the solutions to foam.
Gastric juice contains hydrochloric acid and an enzyme called pepsin, by which the proteins in the food are converted into polypeptides. The gastric juice is highly acidic with a pH of about 2. The HCl in the gastric juice serves to kill off micro-organisms and also to denature proteins. Furthermore it creates the right pH for the enzymes to work efficiently. This acid is so strong that it has the capacity to dissolve not only the food but also the stomach walls. The stomach walls are protected by the epithelial cells, which produce and secrete a bicarbonate-rich solution that coats the mucosa. Secreted bicarbonate neutralizes the stomach acid, and raises the pH in the small intestine to just slightly acidic (about 5.5), which is the chemical environment in which the pancreatic enzymes work best.
