The solution in the small cylinder takes on a blue/green colour and bubbles rise to the surface. At the end of the experiment, the watch has completely disintegrated and the remaining metal pieces are thin and brittle. The caustic soda corrodes the pig's trotter slightly, the solution becomes cloudy. The trotter in the Hydrochloric acid dissolves completely, leaving behind a dark solution and a shapeless, pale mass.



Further images relating to this experiment can be found here: (continue...)



Attention: These images are not for the faint hearted!



Acids react with metal, such as the iron contained in the stainless steel watch, forming metal salts and Hydrogen:



Reduction: 2 H3O+ + 2e- -> H2 + 2 H2O



Oxidization: Fe -> Fe2+ + 2e-



2 H3O+ + Fe -> H2(g) + Fe2+(aq)



The watch contains metals other than iron, and it is these that are responsible for coloring the solution.



The reactions of the acid and alkalies with the pig's trotters are manifold. A few of the possible reactions are listed here:



The cells of living bodies such as ours mainly consist of proteins, which are degenerated by the acid, meaning that their angular structure changed irrevocably. The bigger protein constructs in the cells are destroyed in this process. Enzyme activity is now taking place in an uncoordinated and chaotic way, so that the body's own enzymes speed up the process of degeneration. The high concentration of the acid also breaks up the peptide bonds between the amino acids making up the proteins, thus destroying the proteins further. Bones consist of carbonates and proteins. Proteins are destroyed as shown above, and carbonates in the presence of strong acids change into Carbon Dioxide and water. At the end of the process, only the fat is left, which will be found floating on the solution.



The alkali has a much less spectacular reaction with the pig's trotter, but a degree of destruction is visible. The strong caustic soda first neutralizes the natural, acidic protective layer and then forms a soapy coating with the fat � this may be what protects the trotter from further destruction. A few proteins are also hydrolyzed (disintegrated) by the alkali.



The alkali is decidedly not as harmless as it may seem in comparison to the acid. Just a few drops of highly diluted caustic soda on the retina of the eye can lead to blindness! The corrosive effect of alkalies can be much stronger in other circumstances and it is very difficult to wash it off in case of a laboratory accident.



As we come into contact daily with concentrated acids and alkalies in our homes (essence of vinegar, drain blockage remover, etc.) we should be most careful to comply with any safety notifications on the packaging!



Learn more about this experiment here: http://www.science-tube.com/index.php?c=chemie§ion=091



Source: http://www.science-tube.com/

Views: 14,346
Added: 16 years ago.
Topic: Acids and Bases