August 31, 2005
At least one person who reads me knows something about science. This is from somebody who must have stayed awake in school.
pH is all about the concentration of Hydrogen ions, you know. I love science.
Posted by GORDON at August 30, 2005 07:51 PM
Gordon is correct. The pH scale measures how acidic or alkaline a substance is, using a scale from 0 to 14, with 7 being neutral. The pH scale isn't linear--- it works in multiples of 10. In other words, a substance with a pH of 5.0 is TEN TIMES more acidic than a substance with a pH of 6.0. It works that way up and down the scale and it's all based on the arrangement of hydrogen ions (hydroxyls) in the substance.
When I ran the Acid Plant, we made three basic "flavors" of sulfuric acid: 98%, 93% and 77%. 98% sulfuric acid freezes at around 45 degrees F. But if you add water to it and knock it down to a 93% concentration, the freezing temperature drops to something like 30 below zero. If you add some MORE water, and lower the strenth to 77%, the freezing temperature rises again, up to around the freezing temperature of water.
At first, I thought that was PURE FUCKING MAGIC! But--- it's not. It's pure fucking chemistry. By changing the strength of the acid, you rearrange the hydrogen ions and change its chemical characteristics.
There's a short and sweet science lesson for you.
All right. I went back and reviewed some old chemistry studies, cause I was still a bit foggy on some of this shit, but here goes.
pH means power of 'H', or the amount of H+ ions in a solution. pH is expressed using a negative log scale, ie. pH= -log(H+). For example, ph 14 means the concentration of H+ ions in solution is 10 to the -14th power.
Acids and bases are ionic solutions, meaning that they are atoms with electron imbalances, either gaining an electron, (acids) or losing an electron (bases).
Acids and bases, when mixed with water give up ions, either positive or negative. Acids give up positive ions (H+), and bases negative, such as soduim hydroxide (NaOH), the negative ion being given up is (OH-), the positive is (Na+).
"But if you add water to it (sulfuric acid)." You know better than that Rob! Adding water *to* 98% sulfuric acid would be a most unpleasant experience, to say the least!
Hoo boy. No, you don't want to add water to sulfuric acid. Better you should add the sulfuric acid to the water, if you have to mix them...and be sure to keep stirring.
That stuff will get hot enough to boil, and you do NOT want boiling acid spattering all over you. Mars the complexion, dontcha know.
What many people don't know is that a mixture of sulfuric acid and water - especially if it's 98 parts by weight of acid to 36 parts water - is a much stronger acid than pure sulfuric. That's because the presence of the water allows the acid to disassociate into its ionic components. You're talking pH below 1...and that is a strong-ass acid.
Damn - an Acidman and a Pigmenteer! Meet Rob Smith, Renaissance Man!
In the pump tanks at the Acid Plant, you ALWAYS added water to the acid to keep it from becoming too strong. You can make oleum, which is MORE that 100% sulfuric acid and it fumes like crazy if you don't water it down. Yes. We added water TO the acid. That generates a lot of heat and I wouldn't recommend doing it on your kitchen counter.
But the pump tanks were constructed for adding water to acid. If you did that shit in a lab, you did it the other way around in a beaker.
You bastards can't talk acid over my head. I handled that shit for too long.
Yep, and a base is just as bad. That's why I laugh at folks who think they can just rinse the salt water off their fishing reels and line guides and they will not rust. Hell, a gallon of salt water in a 500 gallon tank of pure fresh water is enough to make all 500 gallons corrosive. Any one who lives around the heat and salt of the Florida coast has seen the shit put pits in stainless steel!
Back in my phosphate mining days, we used a caustic soda solution to raise the pH in the flotation cells. Some of the operators started calling it "pH concentrate." I decided after a while that life's too short to be forever correcting people, so the name stuck. I just had to be careful not to let it slip in a meeting or talking to the "white hats.".
Fine, fine. I don't make the shit, I just use it, but I am curious about why you added water to the acid to keep it from becoming too strong. I forget the exact formula for creating say a 10% solution v/v of sulfuric acid and DI water. Doesn't it work the same way? Enlighten me, I am more than willing to go to school on this.
And yeah, fumes are a bitch. We make up process baths with muriatic acid, and it always looks like someone lit a bonfire in the room until the ventilation system clears it out.
Let me try this one, Acidman. Anthony, suppose you have a 400 ton tank of 99.5 % acid, and you want to cut it to 98%. It would take 6.12 tons of water, or 1,470 gallons. Would it make more sense to put the water in an empty tank and spend the afternoon pumping the acid in, or pump the water into the acid tank?
Another interesting fun-fact about H+ is that it is a prime player in cellular repiration. All cellular respiration.
(I love biology in particular.)
Reminds me of my better than average public education days; specifically a lab dealing with 28 Molar Hydrofluoric acid.
I never want to so much as be in the same zip code as that shit ever again.
I'm wondering what kind of tank can hold that strong a solution of acid? What's it made of and how long does it last? And if it starts leaking what do you do? I mean other than run like a mf.
Terry, mild steel tanks and cast iron pipes are materials of choice for 98% sulfuric acid. As long as the acid is strong (over 93%), it ties up the hydrogen ions so they can't attack the steel. The worst sulfuric acid would be around 70%. You would need very expensive alloys. Even ordinary stainless steel wouldn't last long.
What do you do in case of trouble? For tanks at risk, they run routine tests with thickness gauges and other instruments. The idea is to drain the tank and do maintenance before a leak occurs. If a small leak does occur, drain the tank and fix it, and perhaps condemn the tank if the corrosion is too extensive. A catastrophic acid tank failure is too terrible to contemplate. They have occurred, and the industry has learned from them, just as the aircraft industry has learned from plane crashes.
Ernie confirmed something I said earlier.
70% sulfuric acid is a stronger acid than 100% sulfuric. It's less concentrated, but since there's enough water to let those hydronium ions dissociate, it's more acidic. That's why it'll eat through mild steel, whereas 100% or 98% sulfuric won't.
I'm pretty sure you need nickel-lined vessels and pipes for that 70% stuff...but Rob knows that better than I do. For really nasty acids, you may need glass-lined equipment.
Except for hydrofluoric, which eats up glass...and most everything else.
When I was in college, I used to keep a bottle of 70% nitric acid in my dorm room. To entertain people, I'd dissolve pennies and nickels in it.
I was a fucking idiot.
98% sulfuric acid does not attack carbon steel pipe. There's not enough MOISTURE in it to cause a corrosive chemical reaction.
77% acid must be handled with ALL 316 stainless steel.
You want to know the MOST corrosive form of acid? Water it down to 20% and get that on your clothes or any steel.
It'll eat the fuck out of it.