I want to just discuss a question you had in the original post
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Mine is a powder... does this matter? If not, would I add it as a powder or mix it with something to make it a liquid... and how much?
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The reaction would probably work with the powder
but maybe not at the optimum.
I posted the ingredients in a Dawn dish soap earlier in the thread.
I think you will find that the first ingredient is water (search the internet further) but how much is in the company's recipe'.
It still should be a major constituent
So even though you might only use 5 mL of dish soap, it has lots of water in it.
The hydrogen peroxide is about 70% water and 30% hydrogen peroxide.
So if you had 30 mL of Hydrogen peroxide, it would contain about 20 mL of water.
After seeing that the sodium iodide dissolve pretty readily in water at room temperature,
it is likely that it would disperse throughout the mixture fairly quickly.
But if the sodium iodide was in solution already, it would disperse faster.
Of course we do not want the sodium iodide to be too dilute in solution.
That is why I suggested something close to a concentrated solution of sodium iodide.
The faster the sodium iodide disperses the more likely it would come in contact with the hydrogen peroxide quicker.
In a lab setting I have found using liquids are easier to pour into a container.