Sulfuric acid at 33% is about 6 molar, so if a liter of that leaked into the barrel you’d have 50 mM sulfuric acid, and pH would be about 1.3.
If only 20% of that acid leaked into the barrel, the pH would be around 2.
I’ve used white (distilled) vinegar to neutralize the pH of antifreeze (the surfactant used to prevent cavitation damage in my Diesel raises the pH causing the Aluminum water pump to corrode and fail if not neutralized). It takes a bit…2-3 quarts to bring a 12 gallon system from 8.5 down to 7.
I would also consider using diluted hydrochloric (muriatic) acid.
Wouldn’t using a weak lye (sodium hydroxide) solution be a safe/reasonable way to raise pH?
You could probably also use the chemicals made for pools/spas to adjust PH. My spa is usually has a PH that is too low, so I use a product which for some odd reason has the name spa up. They also make a spa down.
Just out of curiosity what would happen if you let the water in the can evaporate? Bad idea?
Bad idea. Sulfuric acid has a boiling point of 338°C, so it doesn’t evaporate nearly as fast as water. This is one of the reasons that even dilute solutions of H[sub]2[/sub]SO[sub]4[/sub] will burn holes in clothing. As the water evaporates, the acid left behind becomes more and more concentrated.
I’d probably go with Acetic or Sulphuric if it was just to neutralise.
I don’t know where to get concentrated acetic acid. For mildly basic things such as the antifreeze previously mentioned vinegar might work. The problem with using sulfuric or hydrochloric acid to neutralize a base is that the difference between neutral and strongly acidic is too small. You are more likely to end up with a strongly acidic solution than a neutral solution. i suppose you could bring the solution to strongly acidic then neutralize with sodium bicarbonate.
Similarly, one doesn’t use sodium hydroxide (lye) to neutralize something, because you are more likely to end up with a strongly basic solution than you are a neutral solution. Technically it is possible, but realistically it’s not.
It used to be possible to get glacial acetic acid at camera stores. It was used to make stop bath.
Citric acid can be had in the bulk spices section of most food coops. Being triprotic, and not very strong, it’s a good choice for neutralizing bases of all sorts.
Citric acid is definitely the one to use. Thanks.
Which is exactly the use I used to put it to.
IANA Chemist, nor did I stay at Holiday Inn Express last night.
It appears the concensus is that a single fully charged car battery holds ~1 quart of ~33% pure sulfuric acid ~= 1-1/3 cups of pure sufuric acid.
Are you really asserting that if I wanted to dilute that acid to the “background” acidity of open fresh water, I’d need to use 118 billion gallons of water? That any less water would leave the pH above background?
I’m in no position to disagree; I’m just flabbergasted the volume is so large, and I wanted to make sure I understood before I declared my ignorance fought.
Nothing wrong with dilute NaOH, but by the time you’re using that, you might as well be using NaCO[sub]3[/sub], which will git 'er done just as effectively without needing to worry about how you’re going to get your dilute hydroxide in the first place, and may be cheaper and easier to come by.
Someone mentioned glacial acetic acid - does that offer worthwhile safety benefits over sulphuric?
No, the figure quoted is just what’s needed to dilute the whole amount to the same degree that the homeopathic dilution would do for the amount so treated. You long since passed the point at which you were pretty much dealing with plain water.
No, that was just the dilution factor Rick specified in post# 17.
Acetic acid is a weak acid. Sulfuric acid is a strong acid. Safer yet is citric acid, which has the added benefit of being a solid.
Boil distilled vinegar? It’d take a while I suppose.
Sure, but “weak acid” as a specific technical term only means that it does not fully dissociate in solution - I see that glacial acetic acid has some safety implications of its own. Interesting to see that latex gloves are useless against it.
You have me mixed up with Rico. He is taller, I am better looking. That and he carrys a ban stick and I don’t. 
Weak acid may be a technical term but it means exactly what it says it means. Acetic acid is not wihout it’s hazards though. Strong solutions of acetic acid are corrosive and they will burn. Latex gloves have very poor chemical resistance, so it is not suprising that acetic acid goes through them.
If you are using a weak acid to neutralize a strong base, you will get a buffered solution of the weak acid and it’s conjugate base. The conjugate base of a strong acid on the otherhand, is to weak to act as a buffer, so you end up with very steep titration curves where only a small amount is the difference between neutral and acidic.