The EPA has a handy online chart giving the pH levels of various common substances. As a refresher: the pH scale ranges from 0-14, with 0 being battery acid, 7 bring neutral, and 14 being highly alkaline caustic soda.
(The chart is in the form of a one-page PDF)
Anyway, the chart gives pH values of 7-10 for shampoo, 9 for hand soap, and 10 for “mild detergent” (Laundry? Household surface degreaser? Unsure here). And then it shows “soapy water” as straddling the 11-12 line.
The FQ: Why does adding close-to-neutral water to an alkaline substance like soap yield something more alkaline than the soap?
Something I thought I knew from homebrew pool maintenance was that mixing bleach and water yielded a liquid that was less alkaline than just plain bleach – but maybe that’s incorrect?
One common measure of pH is the relative amounts of OH- and H+ ions in solution.
Potential acids and bases ionize when they are dissolved in water. Solvation in water breaks them up. The water molecules surround and attract out the OH- ions in the case of bases and H+ ions in the case of acids. If the materials aren’t solvated with water, fewer of these ions exist.
You can also consider solid acids like citric acid. If you tried to take the pH reading of it in solid form, you’d pretty much get no where because the ions aren’t there to migrate. Only when you dissolve them do you get the acidic effects.
Thanks, Sigene. And it makes some sense – a given measure of pure acid or base can only produce so many ions. So maybe, for example, 100g of Ivory bar soap and (I don’t know) 500g of water produce a mixture that is more alkaline than the soap alone.
But that same 100g of Ivory soap with, say, 1,000 kg of water … I’m guessing all the ions produced get ‘used up’ or attenuated or something, and the resulting solution is only slightly more alkaline than the water was alone.