How to Make Iodine From an Alkali Metal Iodide, Hydrochloric Acid and Hydrogen Peroxide.




Introduction: How to Make Iodine From an Alkali Metal Iodide, Hydrochloric Acid and Hydrogen Peroxide.

About: NurdRage is a dedicate group of science nerds trying to further amateur science with direct how-to instructions in video format. We saw what was already online and we thought "we could do better".....

Make iodine from an Alkali metal iodide, hydrochloric acid and hydrogen peroxide.

Warning: This reaction makes small amounts of chlorine gas and should be performed outside or in a fumehood.

Our previous iodine making video:

Simply get some potassium or sodium iodide and dissolve in a minimal amount of water. Then add an equal amount of concentrated hydrochloric acid. Check this new volume and measure out five times more 3%hydrogen peroxide. Mix together the two solutions and let stand for ten minutes. Filter the iodine.

You can then purify by vaporization and crystallization.



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    19 Discussions

    this reaction shouldnt generate any chlorine gas.
    a sign your hydrochloric acid is contaminated is that if you mix it with hydrogen peroxide the peroxide will neutralise the acid and form chlorine gas, as well as also changing a redish orange.
    these are often contaminants found inside pool muriatic acid or pool brand hydrochloric acid, and are not filterd out as they dont need to be. also use distilled water as it acts as normal water contaminants act as a catalyst to form chlorine gas in hydrochloric acid and hydrogen peroxide.

    1 reply

    I love many of the videos the folks at Nurdrage produce, though sadly I often have trouble carrying out certain experiments since I dislike buying chemicals from suppliers besides acids. With that in mind, do any suggestions where I can acquire a metal iodide? I don't mind if I need to purify it, since I love chemistry so much. So would I be able to somehow obtain a metal iodide through store-bought materials or will I have to order it offline? Thanks! :)

    muriatic acid is another name for hydrochloric acid isn't it? And you can get that for pools, would that work here?

    1 reply

    I'm not sure that this reaction will produce chlorine gas. Most likely aqueous Cl- ions. Considering that:

    2NaI(aq) + 2HCl(aq) -----> 2I(s) + 2NaCl(aq) + H2(g)

    I think this is correct.


    NaI(aq) + HCl(aq) + 2H2O2(aq) -------> I(s) + NaCl(aq) + 4H2O(L)

    Tell me if this is wrong, in fact I'm sure most of it is. I just don't think any Cl gas will be produced.

    5 replies

    If everything is done in a perfect stoichiometric ratio, then no gas will be produced. But not everyone has precision weigh-scales and volumetric flasks. A lot of people will just eyeball it. The danger is when someone uses excess hydrogen peroxide and excess hydrochloric acid. Then this reaction takes place: H2O2 + 2HCl --> 2 H2O + Cl2 I tell people to do the reaction assuming chlorine will be produced not because it should be produced under ideal conditions, but to cover those situations where an accidental excess is used. Not everyone is as precise as we are.

    That's true, you can never be too safe, especially if you have little experience with chemistry.

    But wouldn't the Cl produced by the H2O2 + HCl be aqueous? Although the HCl is in excess wouldn't the reaction be:

    H2O2(aq) + HCl(aq) -----> H2O(L) + O2(g) + Cl(aq)

    Then the excess HCl would react with the H2O, and that reaction would go to equilibrium:

    HCl(aq) + H2O(L) <------> HCl(aq) + H2O(L)

    The HCl being the acid, "donates" a H atom (or proton) to the Hydrogen Peroxide to produce H2O, O2 gas and aqueous Chlorine ions.

    I think the energy required to transform the Cl ions in the HCl to gaseous chlorine is far more than any amount produced in this reaction.(I think)

    You're equations aren't balanced.

    Also, free monoatomic chlorine can never exist in aqueos solution. Only chloride ions or molecular chlorine.

    And hydrogen peroxide *CAN* oxidize chloride ions into chlorine under acidic conditions. The table of reduction/oxidation potentials pegs its power at 1.8 volts, while chlorine is 1.4 volts. Clearly it can oxidize chlorine.

    In fact, this is a known danger in the electronic industry when copper/hydrochloric acid solutions are regenerated using hydrogen peroxide. Excessive addition by an inexperienced operator results in a surge of chlorine gas that poses an extreme danger to the workers. This is why those etching solutions are not use often, not because they don't work, but because a mistake can result in a fatality.

    I knew I forgot something! But yeah, I meant chlorine ions, not monoatomic chlorine. Thanks for clearing that up.

    I wouldn't be worried about small amounts of chlorine gas, but if you're going to issue warnings - breathing iodine vapour isn't healthy either. L

    2 replies

    Ya... That is a problem. How much warning to give. The acid, the peroxide and the salt are all dangerous in their own way. Ah well, as long as the experimenters do it outside, that should cover most invisible dangers. The painfully obvious dangers like corrosiveness of the acid is already listed on the bottles of the chemicals

    I've handled plenty of hazardous chemicals in my time - "why do my eyes sting? Oh that's probably residual benzene, now I know why it's got an eye-irritant warning on the bottle.." (The funnest were pyrophoric) I only meant that chlorine isn't a 'top' hazard in this. (keep up the good work!) L

    Not something I'd want to do (my days of experimenting with nitrogen tri-iodide are long ago), but it's fascinating to watch chemistry done like this - all the good bits compressed down to a couple of minutes. Nice one, NurdRage.

    1 reply