Using A Natural pH Indicator to Measure Household Chemicals?

Question

Some household chemicals, such as hydrogen peroxide and chlorine bleach, break down many organic molecules. Do you think it would be wise to try to measure the pH of these types of solutions using a natural pH indicator? Why or why not?

Answer 1

Hi Nevaeh P.,

If you did try to measure, bear in mind that the colors generated are likely to rapidly disappear due to oxidation of the indicator. A flow-through spectrophotometer cell, with pumped solutions mixed immediately upstream, would be a fix for that. Maybe. Give you some data on relative rate of oxidation (the indicator color is instantaneous upon mixing), at any rate, maybe even hint at possibility of intermediates, etc.

But, overall, deliberately mixing oxidizable molecules with oxidizers, is not a good idea unless you are 1) observing safety precautions, against splashes, inhalation of vapors, and explosions, and 2) you want to get the oxidation products.

If you ever get the chance, boil up some elderberries (Sambucus canadensis) and observe the colorant as you dilute it in a stainless-steel bowl. It's a just gorgeous purple (makes a fine jelly, too). But add a dash of ammonia, it goes instantly green, its basic indicator color. Lots of other flavenoid colors are indicators, too, as well as making colored complexes with metals (such as tannins + iron).

-- Cheers, -- Mr. d.