Quote: Originally posted by Smooth203 | Okay! Thanks for that, I'm doing A-Level chemistry but as far as identifying reactions goes I'm rather inept! Anyway, many thanks for both of your
help!! |
I see. In that case, it might help if it were elaborated. Sulfur dioxide, much like carbon dioxide, will react reversibly with water to form
sulfurous acid, H2SO3. Carbon dioxide forms carbonic acid, H2CO3. Both of these reactions would normally be driven in the gas-producing direction,
since when gas forms bubbles and leaves the solution, it can no longer react. To keep these ions in solution though, a base can be added, like NaOH.
This makes it so there are a lot more -OH ions in solution than there are +H ions. A free SO2 molecule that's about to leave the solution would
instead react with a -OH ion, forming a bisulfite ion again.
In fact, a similar reaction with CO2 is the reason you can smell sulfur dioxide in the first place. CO2 will slowly dissolve in the solution from the
air, and when it does, that creates more H+ ions and uses up -OH ions, acidifying the solution. Even though sulfurous acid is a stronger acid than
carbonic acid, because the concentration of bisulfite ions would be so much higher than bicarbonate ions, the species that ends up leaving solution is
more likely to be SO2. Additionally, you notice SO2 more because you can't smell CO2. If you wanted to eliminate the smell completely, you could add
NaOH to your solution, which would capture ANY acidic species entering the solution and keep it there.
Yet another chemical that behaves like this is chlorine. It reacts with water to form hypochlorous acid and hydrochloric acid. (HCl and HOCl) Both
of these acids can be neutralized by sodium hydroxide, which keeps them in solution. |