adding water to acid

[calgoldrecyclers]

now, i have always read and learned that you never add water to acid, always add acid to water. as adding water to acid can produce an exothermic reaction. yet, earlier, i read that you can add cold water in small ( four tablespoons and less ) amounts.
anyone know of any situation as this?
thanks

 

[Harold_V]

While it does no harm to be safe, water most certainly can be added to acids without problems, but not all of them. You can introduce water in any volume to tech grade nitric or HCl with no reactions to speak of.

If one observes the rule of putting acid in water, not water in acid, there's nothing more to remember, so play it safe so you don't form bad habits.

While there may be other acids that would react violently by adding water---the one that is of concern to the home refiner is sulfuric. As you alluded, the reaction is exothermic, which can turn the water to steam instantly, causing what is, for lack of a better description, a steam explosion.

Even when introducing acid to water, when it's sulfuric, it should be stirred well while introducing the acid in a small stream, to avoid localized heating.

Lou or Irons may well add their comments to this subject. I'm reporting only that which I have experienced.

Harold

 

[calgoldrecyclers]

ok. thanks for the information harold. i will stick with what i have read and learned.
thanks again,
Ezra

 

[Irons]

adding small amounts of water to Sulfuric can be very dangerous.

If you need to dilute concentrated Sulfuric, take the water you wish to add and slowly add small amounts of Sulfuric to the water, let it cool and add a little more Sulfuric until you have added all of the concentrated Sulfuric. If you were to add it all at once, the resulting reaction would spray you and everything nearby with hot, concentrated acid.

If you see the water getting hot, STOP.

Here, patience is a virtue.


On another note, The affinity of Sulfuric Acid for water can be a problem if you want to keep your acid concentrated. Leaving it in an open tank or container with a loose-fitting lid will allow the acid to absorb water from the air, thus diluting it.

 

[Lou]

Typically speaking, the more concentrated the acid, the greater the danger in dilution.

Concentrated 95%+ HNO3 will act just like sulfuric acid when water is added to it, if not worse in some ways (as the nitric's vapours are far more prolific, and dangerous). It is also much more likely to boil than sulfuric.

Irons, ever worked with an oleum or neat SO3 before?

 

[Irons]

Typically speaking, the more concentrated the acid, the greater the danger in dilution.

Concentrated 95%+ HNO3 will act just like sulfuric acid when water is added to it, if not worse in some ways (as the nitric's vapours are far more prolific, and dangerous). It is also much more likely to boil than sulfuric.

Irons, ever worked with an oleum or neat SO3 before?

It's best to dissolve SO3 in Sulfuric Acid not water. The Sulfuric Acid mist formed in contact with Water is almost as bad as the SO3.

A lung full of SO3 is a good way to drown in your own body fluids.

Another student on the other side of my lab bench pushed some books on the top shelf and knocked a liter of white fuming Nitric onto the bench in front of me. It exploded like a tear gas grenade. Lucky for me I was wearing safety goggles and was standing a few feet from an emergency shower. In the few seconds it took me to pull the ring on the shower, the skin not protected by clothing or glasses peeled away. Another few seconds and it might have been the end of me, once the acid soaked through my clothing.

I stripped down so fast, I forgot there were ladies present. I didn't care.

 

[Lou]

It's best to dissolve SO3 in Sulfuric Acid not water. The Sulfuric Acid mist formed in contact with Water is almost as bad as the SO3.

A lung full of SO3 is a good way to drown in your own body fluids.

Remember who you're talking to about SO3 :wink: hence the reason I asked if you've ever worked with it. Commercially, sulfuric acid is made by burning sulfur to SO2 then oxidizing with V2O5 catalyst at 500C to get SO3 then dissolved in concentrated sulfuric acid (still exothermic!). The oleum formed is then diluted with cold water--straight SO3 into water does not work because it immediately forms a clinging sulfuric acid mist. I have done the contact process.

As for me, I once had some 98% nitric acid drip from the lid of the bottle onto the underside of my right wrist as I was pouring some out. It felt like someone put a cigarette out on me. By the time I got to the sink, the skin came off. Point being, just because the 67% stuff turns your skin yellow in a few minutes, it does not mean that the concentrated stuff is of like temperament.

Lou

 

[Anonymous]

OK here is a dumb reply by a newbie.
I thought Sulphuric acid is in car batteries.
And I always add water to my batteries. :!:

 

[Harold_V]

OK here is a dumb reply by a newbie.
I thought Sulphuric acid is in car batteries.
And I always add water to my batteries. :!:

The acid in batteries is quite dilute, so the heat generated is not excessive. Should you pour water in concentrated sulfuric, it's a whole different world.

Harold