What is the most powerful acid?

[WarmNPrickly]

Hydrofouric acid is not a strong acid. What that means is that in water, HF does not completely dissciate into H+ and F-. It is the flouride that does the damage. Flouride forms very strong bonds with both Silicon and Calcium. This is why HF eats through glass (silicon dioxide). This is also the reason Flouride is used in toothpaste since it bonds with the calcium in your teeth thereby preventing them from dissolving in your mouth. The calcium factor is also the reason that HF is so deadly. It will deplete your body of calcium. Spill enough on you and you won’t just lose your fingers, you will be dead. It is not treatable.

The strongest acid in water is H3O+. Anything stronger than that will lose a proton to H20 and make H3O+. In non-aqueos solutions, pH has less meaning. Instead, chemists would talk about pKa wich is the -log of the dissociation constant. The compounds with the lowest pKa that I know of are carboranes studied at UC riverside. Its doubtfull they would be usefull as a weapon, since the minute they are exposed to water (even the water in the air) they would turn into H3O+ wich is not stronger than concentrated HCl.

[WarmNPrickly]

Hydrofouric acid is not a strong acid. What that means is that in water, HF does not completely dissciate into H+ and F-. It is the flouride that does the damage. Flouride forms very strong bonds with both Silicon and Calcium. This is why HF eats through glass (silicon dioxide). This is also the reason Flouride is used in toothpaste since it bonds with the calcium in your teeth thereby preventing them from dissolving in your mouth. The calcium factor is also the reason that HF is so deadly. It will deplete your body of calcium. Spill enough on you and you won’t just lose your fingers, you will be dead. It is not treatable.

The strongest acid in water is H3O+. Anything stronger than that will lose a proton to H20 and make H3O+. In non-aqueos solutions, pH has less meaning. Instead, chemists would talk about pKa wich is the -log of the dissociation constant. The compounds with the lowest pKa that I know of are carboranes studied at UC riverside. Its doubtfull they would be usefull as a weapon, since the minute they are exposed to water (even the water in the air) they would turn into H3O+ wich is not stronger than concentrated HCl.

[MrFantsyPants]

@vetbridge

I recently filled a battery with the supplied acid (lawn tractor battery). There were numerous warnings, which i generally followed. A few drops of acid flicked onto my jeans. When I later removed the jeans from the wash, there were four holes where the droplets had struck. Guess the safety goggles were a good idea.

Funny story…

A friend in university spilled some acid on her jeans in the lab. She had some shorts handy, so she quickly changed, and dropped the jeans into a bucket of water to dilute it. The next day they had dried out, so she wore them to school again.

Unfortunately, the acid had degraded the thread far more than the denim, and over the course of the morning, every seam on her pants had started to unravel. It was, apparently, a little embarrassing.

[cruel_butterfly]

@Christopher

<snip> The calcium factor is also the reason that HF is so deadly. It will deplete your body of calcium. Spill enough on you and you won’t just lose your fingers, you will be dead. It is not treatable.

I watch ER reruns on TNT in the mornings, and they did a story about this. A guy came in with chemical burns on his body. The doctors found out it had been hydrofluoric acid. The guy didn’t feel sick at all, but the doctors told him that the acid was breaking down his body’s calcium and that he was going to die.

I don’t know how accurate a lot of the jargon was. I am neither a medical professional nor a chemist. But I remember that the mere possibility that a chemical could infiltrate our bodies and cause it to systematically break down was kinda creepy.

[robby]

@Cagey Drifter

I was told in college chemistry that pure Hydrogen Peroxide is the strongest, by definition (the kind in stores is only 1%, I think). My chemistry is rusty now, so don’t ask me to explain.

You were told wrong, then. Hydrogen peroxide is a very weak acid, regardless of its concentration.

Cite.

(The higher the pK[sub]a[/sub] of an acid, the weaker it is.)

This has nothing to do with it’s capabilities as an oxidizing agent, though. The concentration of the hydrogen peroxide makes a big difference, there.

[iamthewalrus_3]

@Padeye

What are the normal safety measures for handling HF acid? I’m thinking the butyl gloves i get at Harbor Freight for mixing mortar aren’t going to cut it.

I handled HF acid in a chemistry class in college. I worked under a fume hood that blocked any splashes from getting to my face. I wore a thick rubber apron and gloves. Really thick. I did actually spill some on the gloves at one point because they were so unwieldy and I could actually see the acid slowly eat away at the glove material as I finished the experiment.

[rbroome]

@iamthewalrus(:3=

I handled HF acid in a chemistry class in college. I worked under a fume hood that blocked any splashes from getting to my face. I wore a thick rubber apron and gloves. Really thick. I did actually spill some on the gloves at one point because they were so unwieldy and I could actually see the acid slowly eat away at the glove material as I finished the experiment.

and you know what is a strange thing (to me)? You can go down to Walmart and buy a bottle of HF acid. Way up high on the the top shelf in the back, but if you know what to ask for, it is there. Apparently it is just the thing for cleaning rust stains off surfaces :eek:

I had a rust stain in my carpet after a professional cleaning. I called the people that did the work and they, after a bit of hesitation, told me what and where to get the cleaner. Of course the label didn’t say anything about HF, but being the curious type I read the ingredients. Surprise! I only used it once (it works as one can imagine) and put it on the top shelf way in the back in my utility room…

[chemistrydork]

The question of what is the strongest acid is sort of nebulous.

Traditionally, the strongest acid is measured by its pKa. The lower the pKa, the stronger the acid. However, as Christopher pointed out, outside of the pH range of -7 to +22, the question of pKa(H2O) is irrelevant. The strongest acid that can exist in water is H3O+ (pKa -1.7) and the strongest base that can exist in water is OH- (whose conjugate base, H2O, has a pKa of 16). So to measure any pKa far outside of that range is incredibly difficult. Hydrogen iodide, hydrogen bromide, and sulfuric acid are all pushing that limit of detection on the bottom end.

In non-aqueous solvents, acids can have different pKa’s, and the range in which a pKa can be measured is also different. But the problem is that pKa’s for different acids shift differently depending on the polarity of the solvent relative to water, and the polarity of the molecule relative to solvent. In relatively non-polar solvents, pKa’s of charged acids go down (NH4+ is more acidic in ethanol than in water), but pKa’s of neutral acids go up (CH3CO2H, acetic acid, is less acidic in ethanol than in water).

A second meaning for “strongest” could be which acid will dissolve the most in water – which would involve looking up various solubilities or densities. I know that sulfuric acid is a liquid and can be distilled to near purity, hence, it may be strong in the sense that you can get very, very concentrated sulfuric acid, regardless of its pKa. Someone also mentioned phosphoric acid, which is polyvalent and can donate 3 protons per molecule. So if your question is what acid will titrate a base the fastest per mole, you may want to look at H3PO4.

Aside from pKa and concentration, however, the word “strongest” can also mean the acid that causes the most damage – for instance, everyone’s favorite example, HF, despite its relatively high pKa (+2?), is incredibly corrosive towards glass, because fluorine reacts with the silicon-oxygen bonds in glass. HF is also very toxic, precisely because its pKa is high – it tends to stay associated as H-F rather than disassociate into H+ + F-, and hence, moves very easily through the oils on top of your skin and through the hydrophobic cell membranes. Inside your bloodstream, HF disassociates, and then F- precipitates Ca2+ ions, and then crystals of CaF2 start plugging up your blood vessels.

If your question is academic, then the answer you are probably looking for is the Superacid formula (or Magic Acid, as it may be marketed). Its formula is HF*SbF5, and its extreme acidity comes from SbF5 ripping that fluorine away from HF. Of course, this acid is completely useless in most aqueous solvents.

If your question is practical, then the answer you’re probably looking for is sulfuric acid or phosphoric acid.

If your question is experimental (what is the strongest acid you can buy commercially), then sulfuric acid is probably the best bet. It’s a component in battery acid. Phosphoric acid is manifactured by the ton and put into soft drinks, and is readily available to non-chemists as well.

[spingears]

As an apprentice I was assigned to the acid dipping dept. for a stint.
Not only full goggles but a transparent face shield to to protect surrounding skin.
Gauntlet rubber gloves over long sleeves and apron.
Concentrated nitric, sulphuric, hydrochloric acids as well as cyanide solution.
Emergency showers, wash stations, eye wash stations and all.
I once saw the experienced “Dipper” accidently drop an item in the conc. sulphuric.
He reached in with a bare hand and arm and retrieved it as it could not be picked up with the normal hook.
He calmly washed off his arm and hand under a wash station and showed no sign of acid burn. The concentated suphuric doesn’t act as fast on flesh as it does on some metals.
CAUTION - Don’t try this at home!

[Mr.Blue_Sky]

What is the most powerful acid?

The boiling acid of my hate?

Kidding!

[Excalibre]

@chemistrydork

The question of what is the strongest acid is sort of nebulous.

Traditionally, the strongest acid is measured by its pKa. The lower the pKa, the stronger the acid. However, as Christopher pointed out, outside of the pH range of -7 to +22, the question of pKa(H2O) is irrelevant.

Could you explain this some? I did well in my introductory college chem classes, and I remember that some pHs could be outside the 0 to 14 range, but I don’t quite understand how it all works. As far as I remember, 0 to 14 is sorta the “standard.”

[Waterman]

@Excalibre

Could you explain this some? I did well in my introductory college chem classes, and I remember that some pHs could be outside the 0 to 14 range, but I don’t quite understand how it all works. As far as I remember, 0 to 14 is sorta the “standard.”

pH is the negative logarithm of the hydrogen ion concentration. So if you have a hydrogen ion concentration of 10-7 (ten to the minus seventh power) moles per liter then:

pH = - (-7) = 7

For a 10 molar solution of an acid (several come to mind such as sulfuric acid) the hydrogen ion concentration is 10+1 moles per liter so:

pH = - (1) = -1

[matt]

@Padeye

What are the normal safety measures for handling HF acid? I’m thinking the butyl gloves i get at Harbor Freight for mixing mortar aren’t going to cut it.

HF doesn’t attack polymers as far as I know, so your butyl gloves will be fine.

I’m going to use HF to etch aluminium today, if I can ever get the sample polished properly. Fume cupboard, lab coat, new latex surgical gloves under long-arm rubber gloves, and a lot of care. I hate handling the stuff. If anyone knows a decent non-HF metallurgical etchant for aluminium alloys please let me know. (I’ve tried all the ones in the Metals Handbook.)

HF is probably good at taking off rust stains - I don’t know because I’d never dare slopping around large quantities of it. HCl works very well at taking rust stains off glassware and stainless steel sinks, and it’s a LOT safer.

Sulphuric acid has a very strong affinity for water, which it locks up within it. Concentrated sulphuric acid will rip the water out of sucrose and other carbohydrates to leave a porous lump of “sugar charcoal” - pure carbon. Quite a fun experiment! Since cellulose is a polymerised carbohydrate, sulphuric acid will put a hole through cotton or denim distressingly fast, although it’s slower to burn skin. It also generates a lot of heat when water is added - water droplets added to concencentrated sulphuric acid can flash to steam, which is hazardous.

Liquid HCl fumes HCl gas, which will make your eyes water and irritate your nose. If you leave an open container of HCl in a room and the humidity gets high, a thin film of rust will form on every bit of bare steel around. FWIW.

[antechinus]

The strength of an acid is determined by how easily it donates protons (protons are the H+ bit in the acid).

Strong acids are difficult to differentiate, in terms of acidity, in water. The water flattens out (levels) the strengths of each acid. However, in an acidic solution the strong acids can be differentiated from one an other.

It really depends on the environment the acid is in to determine its relative strength.

Spingears - the conc sulfuric acid your colleague put his hand in was only slightly ionised because there was little water present. There was little H[sup]+[/sup] (or rather H[sub]3[/sub]O[sup]+[/sup]) due to the absence of water. It is because of this that conc sulfuric can be transported in metal containers. Add some water and you are in strife. The water allows the acid to dissociate and makes the protons available to do their damage. Leave your hand in the acid too long and the sulfuric will draw out water and start to ionise.

[kidchameleon]

@Chronos

And kidchameleon, I had always heard that Aqua Regia was a mixture of nitric and sulfuric, not hydrochloric.

Naw, we make it daily to dissolve all of our thallium. We don’t use much sulfuric.

[Waterman]

@rbroome

and you know what is a strange thing (to me)? You can go down to Walmart and buy a bottle of HF acid. Way up high on the the top shelf in the back, but if you know what to ask for, it is there. Apparently it is just the thing for cleaning rust stains off surfaces :eek:

I had a rust stain in my carpet after a professional cleaning. I called the people that did the work and they, after a bit of hesitation, told me what and where to get the cleaner. Of course the label didn’t say anything about HF, but being the curious type I read the ingredients. Surprise! I only used it once (it works as one can imagine) and put it on the top shelf way in the back in my utility room…

Are you sure that it is not hydrochloric acid that you can buy at Wal-Mart?

Many hardware stores sell hydrochloric acid (usually under it’s more common industrial name of Muriatic Acid) which is commonly used for cleaning off rust and also for cleaning mortar off of new brick surfaces.

Hydrochloric acid can be stored and sold in glass bottles whereas, as pointed out above, hydrofluoric acid cannot be stored in glass bottles.

[Waterman]

@spingears

As an apprentice I was assigned to the acid dipping dept. for a stint.
Not only full goggles but a transparent face shield to to protect surrounding skin.
Gauntlet rubber gloves over long sleeves and apron.
Concentrated nitric, sulphuric, hydrochloric acids as well as cyanide solution.
Emergency showers, wash stations, eye wash stations and all.
I once saw the experienced “Dipper” accidently drop an item in the conc. sulphuric.
He reached in with a bare hand and arm and retrieved it as it could not be picked up with the normal hook.
He calmly washed off his arm and hand under a wash station and showed no sign of acid burn. The concentated suphuric doesn’t act as fast on flesh as it does on some metals.
CAUTION - Don’t try this at home!

Reading this reminded me of my high school chemistry teacher who actually washed his hands in concentrated sulfuric acid and then proceeded to quickly wash them off with large quantities of water. He then placed a piece of filter paper in the same beaker and left it there for some time and when he returned to the beaker the filter paper had its water removed and the only thing remaining was some charred carbon. He stated that the only reason he could do it was that he did not perspire and therefore could put his hands into the acid for a short period (like 10 seconds).

As stated elsewhere, concentrated sulfuric acid has such an affinity for water that it can actually remove it from other sources such as paper or skin.

And again as you have pointed out Don’t Try This At Home (or Work or School, etc.)

[Jinx]

@Padeye

IIRC from hs chem, most acids work on metal but some will etch glass. Acids also have to be in solution with water to work.

Is this true? IIRC, 100% HF is in a vapor form. It is common to weaken by dissolving in water. Acidic vapor clouds are nasty! Unless it is the cloud + humidity that drives the reaction? Unsure… But also, since F has the highest electron affinity, the HF bond is the strongest bond, as I was taught…

Also, someone mentioned a quality called normality? Never come across that term. As for “molarity”, how can it be said that HF has the greatest molarity??? Isn’t molarity simply a measurement of concentration on a molar basis? Similarly, molality is on a volumetric basis, IIRC.

[robby]

@Waterman

Are you sure that it is not hydrochloric acid that you can buy at Wal-Mart?

You can buy “Wink” rust stain remover at Wal-Mart (and grocery stores) which contains a dilute solution of hydrofluoric acid. It comes in a small brown plastic bottle. The whole bottom front of the bottle is covered with warnings. When we use it, we ALWAYS wear protective gloves.

It works fantastically at removing iron rust stains from bathroom fixtures and clothing. (We have high iron in our well water.)

[Jinx]

@bouv

…You see, every fluid in the world has a pH.

I don’t believe this is a true statement. If a fluid’s atomic composition lacks hydrogen atoms, then wouldn’t it be said the pH is “n/a” as opposed to a value of pH=0? Also, it would be just as incorrect to say it is “neutral” at a ph=7.

Also, this thread begs the question: If an acid needs water to react, does it need to be in an aqueous solution for the pH to be measured, such as by reacting with litmus or pH paper??? For example, if HF is in vapor form in dry air or vacuum, does it have a pH?

Tree falling in the forest…

• Jinx