6
$\begingroup$

In my experience, most of the commercial products intended for removing soap scum from bathroom surfaces are ineffective. No matter how long you leave it on or how hard you scrub, the soap scum doesn't come off. The only successful way I've found is to scrub it with a stiff brush using elbow grease. The better cleaning products are have mild abrasives, which results in a dull surface finish.

I read some of the bathroom cleaning product labels and most contain primarily soaps and other high pH-level chemicals such as ammonia. Since soap has a high pH-level, shouldn't the soap scum respond better to an acid such as citric or acetic acid?

It's also common to add salt or hydrogen peroxide to an acid. Can they increase the strength of the acid, making it more effective? If so, how?

Improve this question
$\endgroup$

3 Answers 3

Reset to default
7
$\begingroup$

Soap is a combination of a metal (e.g. sodium) and a fatty acid (e.g., palmitic acid). If you use acid to break the metal off (e.g., $\ce{CH3(CH2)14COONa + HCl -> CH3(CH2)14COOH + NaCl}$) you're left with salt water and a slimy fatty acid stuck to the surface. Sort of counterproductive.

Alkaline bathroom cleaners work by re-forming soap from fatty acids, which is soluble.

These cleaners may also contain chemicals to chelate or sequester metals that form poorly-soluble salts with fatty acids, such as magnesium and calcium in "hard" water.

Regrettably, they may take some time to loosen soap scum, and watery cleaners may drip off a vertical surface before they can be effective. To help the cleaner stay in place, wet a paper towel (or filter paper -- this is a site for chemists! ;-) with the cleaner and adhere it to the surface.

BTW, strong alkaline cleaners are more effective, but:

  • They're dangerous.
  • The alkali attacks glass (e.g., shower doors) and glazed porcelain, leaving the surface permanently damaged.
Improve this answer
$\endgroup$
3
$\begingroup$

The white deposits may be limescale or soap scum, or a combination of both. Is there a high level of hardness in the water in your area? Therefore, one cannot generalize that acidic cleaners are ineffective. As long as the correct product is used, they are pretty effective. The soap scum is composed of calcium or magnesium salts of fatty acids. The substance is insoluble in water. Salts of sodium are soluble in water. As you may be aware, soap scum is greasy, and low quality acid cleaners simply bead up and flow downwards when sprayed on walls. A quality acid cleaner will contain wetting agents as well as a mixture of mild acids, such as lactic and gluconic acids. As a result, soap scum as well as limescale are wetted effectively while acid helps to dissolve the insoluble product. Calcium and iron are well chelated by glutonic acid. Lactic acid is a mild acid.

Improve this answer
$\endgroup$
4
  • $\begingroup$ Soap scum is noticeably different from limescale which leaves a white dry haze or a in extreme cases a cement like deposit. The two almost always exist in combination and varies depending on the water source, so we should assume it's both with soap scum being the majority of its content. Your answer seems to disagree with the first one which claims soap scum will respond better to a base than an acid. Am I reading this wrong? For the record, your answer is what I would have guessed, but science always has a surprise in store. $\endgroup$
    – user148298
    Commented Oct 3, 2022 at 4:04
  • $\begingroup$ Btw, lye is the main active ingredient in commercial drain cleaners which dissolves slimy concretions composed of organic matter, lime scale and soap scum. Lye is such a powerful base it is essentially a solvent with the benefit of not corroding pipes as would an equally power acid. $\endgroup$
    – user148298
    Commented Oct 3, 2022 at 4:22
  • $\begingroup$ I don't think that soap scum is better removed by lye than acids alone. One needs chelating agents plus surfactants and pH (low or high). The acids I mentioned such as lactic and gluconic acid along with surfactants are mild yet act on soap scum effectively. These acids do not corrode metals. One should not use strong acids or strong bases for scum removal or even lye. Both are damaging to the tiles and grit. $\endgroup$
    – ACR
    Commented Oct 3, 2022 at 4:53
  • $\begingroup$ How about using an oxalic, acetic or citric acids? They're relatively mild and while they can corrode metal, as long as they're not applied directly to metal surface, it should be OK. Can you recommend a good household surfactant? $\endgroup$
    – user148298
    Commented Oct 4, 2022 at 17:23
2
$\begingroup$

I conducted an experiment where I collected soap scum by shaving it off the glass using safety blades. Our water is very light, almost like distilled water. I divided the material into different batches and tried a few different chemicals on them. The worst one was water, and the best one to dissolve it was an alkaline drain opener. However, using a household spray with 2.5 percent lactic acid and a nylon brush cleaned it faster and better. So, I guess mechanical agitation is the key.

Improve this answer
$\endgroup$
1
  • $\begingroup$ Wonderful! What inspired you to conduct this experiment? I'm curious as to why the alkaline drain opener worked, considering soap scum is presumably basic. $\endgroup$
    – user148298
    Commented Aug 1 at 17:46

Your Answer

By clicking “Post Your Answer”, you agree to our terms of service and acknowledge you have read our privacy policy.

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