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Mixing sodium bicarbonate with vinegar (and sometimes adding dishwasher detergent) is quite a common tip on the internet. But I have never understood the reason.

I saw there was a question about using sodium bicarbonate and vinegar here to unclog drains, where the answer referred to the production of $\ce{CO2}$ being able to push whatever gunk blocking the drain.

However, for cleaning, the reaction is done when you use the mixture. Is there something I am missing? I am not a chemist, but my intuition is that using either bicarbonate or vinegar + dishwasher detergent alone would be more effective? Can somebody explain if the cleaning tip actually makes sense?

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    $\begingroup$ Mixing vinegar and bicarbonate is a non-sense. Bicarbonate destroys the acetic acid contained in the vinegar. The only advantage is that this mixture produces a huge amount of foam, as if this foam would unclog the drain. It does not. Adding detergent would still increase the volume of the foam. Only vinegar may unclog a drain. Either bicarbonate or vinegar + dishwasher is more effective $\endgroup$ – Maurice Dec 25 '20 at 9:10
  • $\begingroup$ The advantage is that you're adding an abrasive to a weak acid, which neither mars most surfaces nor affects their color fastness when used as a cleaning solution. $\endgroup$ – Mazura Dec 27 '20 at 8:52
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Your intuition is on point. Pretty much all the "lifehacks" praising cleaning abilities of vinegar and sodium bicarbonate are ineffective. The reaction appears vigorous due to the formation of carbon dioxide gas, but what is left is a diluted solution of sodium acetate:

$$\ce{CH3COOH(aq) + NaHCO3(aq) -> NaCH3COO(aq) + H2O(l) + CO2(g)}$$

Sodium acetate doesn't have any pronounced cleaning abilities. It doesn't act like a surfactant, doesn't drastically increase solubility of the impurities, or participate in complexation helping to dissolve metal-containing compounds.

As for unclogging abilities—yes, this is something that my grandmother used to use, but these days there are much better alternatives. The idea was to pour some hot water into the system and then put a couple of spoons of baking soda into the drain creating warm concentrated solution in the siphon. This solution would also be mildly basic due to hydrolysis and help to dissolve some fat and thin hair:

$$\ce{HCO3^-(aq) + H2O(l) <=> H2CO3(aq) + OH-(aq)}$$

After some time (approx. 30 min) it would make sense to add some vinegar hoping the reaction would cause mixing up the constituents of the clog and excessive pressure would help to push the waste further down the drain.

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Better is using washing soda alone first ( instead of baking soda ), pouredby boiling water and kept there overnight. Next day vinegar may be used to make some bubbles desintegrating the clogging.

Washing soda has cleaning ability by itself and has better solubility than baking soda. Adding vinegar later is not to produce some extra powerful chemical cleaner, but it's effect is mechanical. It is producing CO2 bubbles and pressure to tear and push clogging, hopefully weakened by prior soda action.

Detergents then make the clog desintegration easier.

An even stronger cleaner is sodium hydroxide, that is often used as well. But is cannot be used alone, without soda, to produce CO2 with vinegar.

Note that majority of clogging is caused by protein a/o fat rich materials, like hairs, that are chemically dissolved in alkaline solutions.

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  • $\begingroup$ IANAC, but I find sodium percarbonate (e.g. oxyclean laundry powder) + boiling water to usually do well at unblocking drains (3 long-haired humans in my house). Pack the dry drain with a cup or so of Na2H3CO, then pour a liter or more of boiling water over it. I think the heat of the water amplifies the alkaline properties of the Na2H3CO, and the water causes it to release H2O2 which does some good oxidising. It all washes away cleanly with no need for vinegar. Na2H3CO works for 90% of blocked toilets too if given some time to react. $\endgroup$ – Digital Trauma Dec 25 '20 at 21:39
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    $\begingroup$ What exactly is "washing soda"? $\endgroup$ – Lawnmower Man Dec 25 '20 at 21:54
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    $\begingroup$ @LawnmowerMan Is not faster to google "washing soda" ? It is a common household name for $\ce{Na2CO3 . 10 H2O}$, being part of washing powder formulas and, mainly in past, used even separately to prevent coagulation of insoluble calcium and magnesium salts of fatty acids. Baking soda is $\ce{NaHCO3}$ $\endgroup$ – Poutnik Dec 26 '20 at 7:55
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    $\begingroup$ @DigitalTrauma You must mean $\ce{Na2H3CO6}$, more properly written as $\ce{2 Na2CO3 . 3 H2O2}$ $\endgroup$ – Poutnik Dec 26 '20 at 8:02
  • $\begingroup$ @Poutnik yes you’re right $\endgroup$ – Digital Trauma Dec 26 '20 at 18:11

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