# What happens to the bleach after mopping?

At home, I clean the tiled floors by mopping with highly diluted bleach. After mopping, I let the floor dry. What happens to the acid in the bleach?

Will it crystallize on the floor, stay there invisibly in solid form, and get solved again next time the floor gets wet? Will it instead evaporate, or turn to fine dust that floats in the air and leaves through the window? Will it decompose in some sort of chemical reaction?

• This depends largely on the acid we’re talking about. – Jan Dec 25 '15 at 22:43
• What makes you say there is an acid in bleach? "Pure" bleach, sodium hypochlorite, is highly alkaline - with a pH of 12.6 for a 6% solution source – Floris Dec 25 '15 at 23:00
• Do you have the package label of the product? – Koba Dec 25 '15 at 23:17

What happens to the acid in the bleach?

First of all there is no acid in bleach. In fact bleach uses base, the antithesis of acid. and is essentially chlorine dissolved in a solution of sodium hydroxide.

Will it crystallize on the floor, stay there invisibly in solid form, and get solved again next time the floor gets wet? Will it instead evaporate, or turn to fine dust that floats in the air and leaves through the window? Will it decompose in some sort of chemical reaction?

In the short term residual bleach will remain on the floor as a crystalline film that can re-dissolve and can become dust in the most literal way. This should not be of concern though, as carbon dioxide in the atmosphere acidifies and reacts with the sodium hypochlorite and sodium chloride, releasing chlorine from the bleach forming sodium carbonate and eventually sodium bicarbonate (baking soda).

Sodium hypochlorite decomposes by a couple of different pathways:

$\ce{NaOCl\leftrightharpoons Na^+ + OCl^-\\ 2OCl^- \leftrightharpoons O_2 + 2 Cl^-}$

In that case, the oxygen escapes (if it didn't react with "things to bleach", which is of course how bleach works in the first place), and you are left with ordinary salt.

The other pathway is

$\ce{3 OCl^- -> ClO_3 + 2 Cl^-}$

In that case you get some sodium chlorate, and again some ordinary NaCl salt.

Both NaCl and NaClO3 are crystalline solids that may be blown around like fine dust; some NaOCl may also remain behind. Note that according to wikipedia most commercial bleach solutions contain a small amount of sodium hydroxide to slow down the decomposition along the pathways mentioned above.