Answer to Question #71975 in General Chemistry for Riece

Question

What happens on a molecular level with the chemical reactions when Potassium Iodide, a mixture of sodium sulfite, sulfuric acid, and starch, and water are combined to make a chemical clock? How are the reactions altered to make the reaction happen at different times?

Answer 1

In the course of this reaction, several processes occur:
1) Oxidation of potassium iodide to free iodine:
8KI +5H2SO4 = 4I2 + 4K2SO4 + H2S + 4H2O
With this reaction, iodine (I2) is formed which binds to starch in a complex, forming a solution of dark blue color.
2) Along with the process described above, another process is taking place: the reduction of iodine to iodide with the help of a sulfite ion.
I2 + Na2SO3 + H2O = Na2SO4 +2HJ
In the course of this reaction, an iodide ion is formed which does not bind to the starch, i. E. does not form a colored solution.
In general, there are 2 processes: First iodine is formed from iodide, which forms a dark blue solution with a solution of starch, then iodine passes into iodide, while the blue solution turns into a colorless solution, then iodide goes back to iodine and everything repeats over the cycle many times .