2
$\begingroup$

I have a clogged pipe in my bathroom so I went to the store to get something to unclog it. Basically there are two types that you can find in my area:

  • Sodium hydroxide pellets
  • "Liquid plumber" mixtures. The components for those are mainly surfactants, sodium hydroxide and sodium hypochlorite.

As far as I recall from the water treatment courses I took in college, hypochlorite's oxidizing activity is heavily dependent on pH, as the active form is hypochlorous acid, not the hypochlorite ion. At high pH values the oxidizing activity becomes really low whereas low pH will make it stronger.

Does it make sense to buy a product that mixes a strong base, such as sodium hydroxide, with sodium hypochlorite? Wouldn't it be a waste of money?

| improve this question | |
$\endgroup$
3
$\begingroup$

Lye is very corrosive, just like acid, except opposite (hope that makes sense). Although lye is a very powerful chemical, and it is sufficient for many blockages, oxidizing agents (like bleach) may be helpful for breaking down paper/cellulose blockages.

Mixing bleach with acid will cause chlorine gas evolution... bad, bad, bad.

EDIT- The oxidative powers of hypochlorous acid and hypochlorite ion(s) compared:

enter image description here

Source: Descriptive Inorganic Chemistry, Third Edition (By Geoff Rayner-Canham, Tina Overton)

So in terms of power, yes hypochlorous acid is a stronger oxidizer, but it's not wildly different.

On a related note (see comments below) hypochlorous acid is a much better microbicide than the hypochlorite ion, because it penetrates cell walls more easily. However, regarding a drain cleaner, the oxidative difference is much less pronounced. And it's worth mentioning that at above pH 12, a cell will lyse (burst open) and become saponified, so that obviates whatever microbial effect hypochlorite or hypochlorous acid might have on bacteria... like being thrown into a poisonous wood chipper.

| improve this answer | |
$\endgroup$
  • $\begingroup$ All your facts are right, but I don't think this answers my question. I am aware of the effects of strong acids over hypochlorite, what I wanted to know is if bleach would mantain any oxidizing power in a very basic solution (I'm guessing pH 12 or above) as to be worth using it, or I might as well get enough lye to last a lifetime of clogged toilets for the same price. $\endgroup$ – Variax Aug 10 '16 at 14:51
  • $\begingroup$ @Variax I would expect pH of no less than 14 from a drain cleaner. Houshold bleach typically has a pH of 11. Although I've never tested the function of oxidizing power of bleach with respect to pH, I do understand the question and will say that at above pH11 all of the bleach exists as (-OCl); none of it exists at HOCl and straight houshold bleach (pH 11) is a plenty "powerful" oxidizer (eats holes in tee shirts). As an interesting experiment, you could test the amount of time for say a 99:1 dilution of bleach to turn a piece of black craft paper white at various pH levels, for example. $\endgroup$ – Ben Welborn Aug 10 '16 at 15:34
  • $\begingroup$ I found some sources for the effect of pH on bleach. They refer to water treatment, but the science is there: cdc.gov/safewater/chlorination-faq.html (Point 6), oregonstate.edu/dept/larc/sites/default/files/pdf/…. This second one stated that ClO- is two orders of magnitude less oxidizing than its acid counterpart. So if 100 is the maximum and 1 the minimum, the oxidizing power of hypochlorite is: pH 5: 99.68 pH 6: 96.89 pH 7: 75.79 pH 8: 24.37 pH 9: 3.96 pH 10: 1.30 pH 11: 1.03 pH 12: ~1.00 pH 13: ~1.00 pH 14: ~1.00 $\endgroup$ – Variax Aug 10 '16 at 16:11
  • $\begingroup$ @Variax Your links are not working $\endgroup$ – Ben Welborn Aug 10 '16 at 16:13
  • 1
    $\begingroup$ There's table here showing oxidation power: Hypochlorous acid mechanism Also, the second link still doesn't work. Ok here's the PDF. $\endgroup$ – Ben Welborn Aug 10 '16 at 16:18

Your Answer

By clicking “Post Your Answer”, you agree to our terms of service, privacy policy and cookie policy

Not the answer you're looking for? Browse other questions tagged or ask your own question.