Ask A Scientist Chemistry Archive

name         Ian M.
status       other
age          old

Question -   Sir, I haven a substantial quantity of sulfuric acid, about 15
gallons, which I have been using to pickle (etch clean) copper parts
that I have been making into a boiler for a steam locomotive. I have
completed the work and I wish to dispose of the acid in a safe way.
The solution is dilute in the approximate ratio of 1:15 acid/water.
I tried household bleach but only succeeded in producing chlorine gas!
A litmus test came up bright red and I am unwilling to go on making
chlorine and I am asking if there is a suitable chemical alternative
for baking soda, washing soda etc. Thanking you in anticipation.
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You are correct that household bleach is not an appropriate reagent for
neutralizing sulfuric acid. Baking soda will work, but as you have already
probably discovered, CO2 gas is produced and this makes a messy foam. The
most direct method would be to neutralize the sulfuric acid with DILUTE
sodium hydroxide, which you can probably obtain from a hardware store or
industrial chemical supplier under the common name,
"caustic soda". This should be diluted carefully with water because the heat
of dilution is substantial. Add the diluted sodium hydroxide slowly to the
dilute acid until the endpoint is reached using litmus paper. The reaction
product is aqueous sodium sulfate, which can be safely discarded into the
sewer/septic system.

A word of caution: Do NOT use "old fashion" Draino as a source of "caustic
soda". It is a mixture of sodium hydroxide and aluminum flakes. When diluted
hydrogen is evolved, which is potentially explosive.

Vince Calder
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