What is purpose of sulfuric acid in iodine extraction? I am trying to extract iodine from kelp following this guide here.  It calls for sulfuric acid, but I don't see what this does do help the reaction.  I thought the reaction was simply oxidizing iodide to iodine with hydrogen peroxide, so I don't understand the purpose of the acid.  I do not have any sulfuric acid, and it is expensive to purchase, I do have a large supply of sodium bisulfate.  Could this be used as a substitute to the sulfuric acid if all that is needed is a low pH.
You need a strong acid to provide hydrogen (technically hydronium) ions, which is true for most aqueous oxidation reactions:

$\ce{2I- +H2O2 +2H+ -&gt; I2 +2H2O}$

Unfortunately, bisulfate ion appears to be a weaker acid than water $(K_{\mathrm{a}} =  10^{-2})$, so it may not work unless you use a very concentrated amount to obtain enough hydrogen ions. Try it!

A fairly cheap alternative could be hydrochloric acid, which may be available in hardware stores as muriatic acid, and is stronger than sulfuric acid. But read the MSDS, as hydrochloric acid fumes and is nasty stuff.

Best of luck, it’s a cool experiment!