How to Spot a Psychopath

A reader writes:

My mom's always been a strong proponent of vinegar as a miracle cleaner for almost anything, floors, windows, clothes, you name it. She recently discovered bicarbonate of soda, too, and has been using that for all sorts of stuff too, like in the dishwasher instead of the special powder.

When I visited the other day, she was washing the floors with a bucket that had hot water, bicarbonate of soda AND vinegar in it. Apparently the fizz when you add the vinegar gives you more "scrubbing bubbles". Except I vaguely remember from elementary school that an acid and a base cancel each other out, the example given having been exactly this, vinegar and washing soda.

So was my mom just washing the floor with salty water?

Joseph

Almost.

Vinegar and bicarbonate of soda are indeed the standard boringly-safe-science demonstration of an acid and a base neutralising, and the reaction does produce a salt, but not table salt.

Bicarb is NaHCO₃, acetic acid is CH₃CO₂H. Acetic is the acid in vinegar - cheap "white vinegar", which is rather more economical for cleaning things than 50-year-old balsamic, contains nothing but nice clean industrial acetic acid and water.

The reaction is:

NaHCO₃ + CH₃CO₂H -> CH₃COONa + H₂O + CO₂

Those products are sodium acetate, water and carbon dioxide. The CO₂ is invisible but heavier than air, and can be poured out of the reaction container to extinguish a candle, said candle being the most dangerous thing that exists in boringly-safe-science demonstrations.

Sodium acetate is sometimes used as a flavouring, because it tastes like salt and vinegar all by itself. ("Salt and vinegar" snacks in the USA are apparently likely to be flavoured with sodium acetate; here in Australia I think that's illegal for some reason. I don't think it's toxicity; sodium acetate is pretty innocuous.)

If you mix sodium bicarbonate and hydrochloric acid, HCl, then the reaction is the same except instead of sodium acetate, you get sodium chloride, which is everyday table salt.

(For this reason, bicarb is a very effective antacid. A teaspoon full of bicarb can turn nasty acid-reflux indigestion into a series of hugely satisfying CO₂ belches in seconds. You'll have a pretty darn high-sodium diet, though, if like me you end up eating several spoonfulls of the not-that-bad-tasting-when-you-get-used-to-it substance per day. In that case, hie thee to a doctor and get yourself a prescription for one or another acid-production-reducing drug.)

You'd want to be careful making salt from bicarb and hydrochloric acid, though, because if you don't get your stoichiometry right and not add balanced amounts of the reagents, then there'll be left-over bicarb or hydrochloric acid at the end. This is also what will happen if someone decides to make a cleaning product out of bicarb and vinegar; they probably won't titrate the mixture, and so will have a surplus of one substance or the other. Surplus bicarb, as a base, will clean greasy things by, essentially, turning the grease into soap. Surplus vinegar, as an acid, will clean things by dissolving various kinds of dirt, like mineral deposits ("scale"), or rust.

For these reasons, and also the fact that plain water plus elbow grease can clean a lot of things pretty effectively (the basis for the popularity of "laundry balls", which don't actually do anything), people may come to the conclusion that a vinegar-and-bicarb concoction is a super cleaner, when in fact they'd be better off using a smaller amount of only one of the ingredients.

(At least, in this case, mixing the compounds will do no harm. Mixing bleach and ammonia, on the other hand, may greatly reduce the amount of time you spend doing household chores, on account of how you may now be dead.)

Oh, and sodium bicarbonate is not "washing soda"; that's sodium carbonate, Na₂CO₃, which is commonly used to "soften" hard water, which contains dissolved minerals that prevent soap from working properly. Sodium bicarbonate is "baking soda", named for its use as a leavening agent; if you mix bicarb into batter that's slightly acidic, the fizzy-neutralisation reaction occurs and creates lots of little CO₂ bubbles in the batter. "Baking powder" contains dry bicarb and acid powder (usually tartaric acid). Add water, and the components react and fizz.

(See also, the delightfully popular recipe for "Swedish Lemon Angels".)

Getting back to sodium acetate, a supersaturated solution of it is used in "phase change" heat packs...

...which "freeze", liberating heat, when disturbed with the little clicker device inside, or when otherwise slapped around. You put the pouch in boiling water to re-liquefy its contents; the things can be used over and over indefinitely, as long as they don't spring a leak.

You can do something similar to this with numerous other fluids, but sodium acetate's properties suit it very well to the purpose. Even if you don't actually need a hand-warmer, I strongly recommend you buy one as a toy, since you can get them on eBay for about $5 delivered.

Psycho Science is a regular feature here. Ask me your science questions, and I'll answer them. Probably.

And then commenters will, I hope, correct at least the most obvious flaws in my answer.