95% Sulphuric Acid On Sale In Diy Stores

[NiceCupOfTea]

I was horrified to see this on sale at my local little DIY store as a drain unbloker. This is seriously scary stuff, should it not be restricted?

[theprof]

Even small quantities of water added suddenly to acid of this concentration, will indeed cause the acid to get hot and there is a severe risk of the acid/water mix erupting out of the pipe with predictable consequences. Incidentally, the other missing 5% can be regarded as water in the case of 95% acid, but most manufacturers use a method of manufacturing the acid to this strength which obviates the need to “water-down” 100% acid.
It is not true to state that sulphuric acid liberates hydrogen on contact with metals. Not all metals react with the acid. Furthermore, I think that some posters are recalling their knowledge of the reactivity of metals with dilute sulphuric acid. Concentrated sulphuric acid reactions are often completely different. To complicate matters further, I’d refer readers to any table on the internet showing the Reactivity Series.
By and large, Caustic Soda is indeed safer to use in domestic situations as long as you take common sense precautions and remember that it too is exothermic.

[theprof]

Many years ago, carboys were indeed stoppered using corks. Cork was just about the only non-reactive, reliable, stoppering material in use and was used for everything from medicinal vials to carboys and the like.

My lab life was transformed in the sixties when I used Quickfit and Quartz laboratory equipment, all of which was ground-glass stoppered. I was so impressed, I acted as an adviser to the company years later at their request and have fond memories of Stone in Staffordshire, their UK headquarters

[jomifl]

/It is not true to state that sulphuric acid liberates hydrogen on contact with metals./
It is not untrue either. Bear in mind that concentrated sulphuriv acid poured down a drain will be diluted by the water already present in the drain. Zinc, a protective coating used on steel pipework, readily produce hydrogen in the presence of dilute sulphuric acid. My warning was based on the principle that if it is not known for certain what materials the acid might come in contact with then one should assume the worst feasible case and the worst outcome.

[theprof]

jomifl, your scenario assumes that a fairly large volume of water remains in the pipe. This is far from the case. The majority of blockages are of solid consistency and any water will have drained away. Therefore, it is unlikely the acid will be diluted.

Furthermore, you have to realise that these single or double dose packages of concentrated acid amount to something like 500ml or 1000ml of the concentrated acid being poured down the sink in one action. The exothermic behaviour of these volumes of concentrated acid will nullify any reasonable quantity of water remaining in the pipe, resulting in the spluttering and boiling of any residual water. You are then left with what you can continue to call concentrated acid but of lower concentration than the original 95% strength. Nevertheless, it can hardly be called dilute acid

Believe me, I've seen quantities of concentrated acid of this strength being poured rapidly on 100/200ml of water in fume cupboard. You are not left with anything you could call dilute acid in these circumstances. The reaction will behave identically in domestic plumbing pipework.

[Bazile]

Hello prof - long time no see

[theprof]

Correct me if I'm mistaken, but I remain unaware of where precisely in a domestic plumbing situation one comes across steel pipework with a zinc coating.

UK pipework is made from predominantly various plastics and copper along with brass fittings and connectors, sometimes chromium plated.

[theprof]

Hi Bazile. Nice to hear from you. I'm all over the place at the moment having just come back from Los Alamos and then back to my part-time secondment at the MOD and suchlike. I've not had much time to post but I'm hoping to stay here in my uni at least for the next few months!

[jomifl]

prof, if the acid is being poured into the pipe because the water hasn't drained away..
Re. the matter of reactive metals, best to err on the side of caution.

[theprof]

Overall, I concur jomifl. That's why I said that drain cleaners containing caustic soda are safer. Strong alkalies are far better at removing grease, hair, fat etc than strong acids.