HF (weak or strong acid)

[H2SO4]

Ive heard from people that hydrofluoric acid is actualy pretty weak, but i know it can dissolve certain types of glass. I thought that the the stronger the halogen, the stronger its acid. Is this true, is this the same for the alkali metals and there bases. Is cesium hydroxide the strongest base known to man?

[BenSon]

hydrofluoric acid is a weak acid because it is not totally dissociated into ions in solution. I believe the reason it attacks glass it the F- ions attack impurities in glass its not to do with the concentration of H+ ions.

 

Edit: Your right cesium hydroxide is the strongest base.

~Scott

[jdurg]

HF is a paradoxically weak acid. I say that because it is scientifically 'weak', but it's INCREDIBLY toxic and dangerous to work with. For the hydrohalic acids, acid strength increases as you move down the group. So HI is stronger than HBr which is stronger than HCl which is stronger than HF. HF is weak because the fluorine atom does NOT want to dissociate and form H+ and F-. The hydrogen-fluorine bond is fairly strong, so very little of the acid dissociates when dissolved in water. The exact reason why it attacks glass I'm not really sure about. It's most definitely not because of the F- ion for multiple reasons. Number one is that HF is a very weak acid and there isn't a heckuva lot of F- ions in a solution of HF. Number two is that the F- ion does not attack glass. A solution of sodium fluoride, no matter how concentrated, can safely be stored in glass containers.

[budullewraagh]

HF attacks glass in an acid-base reaction: the fluoride anions actually displace oxygen and bond to silicon. the oxygen bonds to the hydrogen.

 

-O-Si-O-Si-O-Si-O-

___|____|____|

-O-Si-O-Si-O-Si-O- etc

___|____|____|

 

H-F

 

___O

___|

-O-Si-F + -O-H

___|

___O

^intermediate

 

-O-H

___F

___|

-O-Si-F + -O-H

___|

___O

 

^intermediate

 

you get the drift.

[H2SO4]

so is HI the strongest of the "halogen " acids? and is LiOH the strongest of the Bases.

[budullewraagh]

HI is the strongest of the halide acids. CsOH is the strongest of the alkali hydroxide bases.

 

there are other strong bases like alkali metals dissolved in ammonia.

 

grignard reagents, organolithium reagents, anions of terminal alkynes, alcohols, thiols, amines and ammonia are all nucleophiles

[jdurg]

CsOH is actually the strongest base that mankind knows about at this moment. It's just very expensive so any of these 'strongest base' uses are better taken care of with cheaper, 'less strong' bases.

[akcapr]

flourine is the strongest oxidizer. you can even burn oxygen in it. In some cases that should lead to quite a strong acid/oxidizer.

[jdurg]

Not for bi-atomic acids. (Which basically means the hydro-halides). For the hydro-halogen acids, the strength of the anion as a reducing agent will help determine the strength of the acid. F- is a VERY poor reducing agent as the fluorine nucleus does not want to give up its electron. As a result, HF is a weak acid. I- is a pretty good reducing agent as the nucleus is very well shielded and will give up that 'extra' electron pretty easily. So HI is a very strong acid.

[H2SO4]

i thought that only tungsten fluoride oxidized oxygen.

[budullewraagh]

well, oxygen oxidizes oxygen to form ozone, usually under a catalyst, namely a fluoride. also, fluorine oxidizes oxygen.

[H2SO4]

ultraviolent light also creates ozone.

[budullewraagh]

somebody's been reading a clockwork orange too many times.

you mean ultraviolet, not ultraviolent

certain wavelengths of radiation can cause O2 to break apart and form O3

[akcapr]

im right

[BenSon]

I didn't know a clockwork orange was a book...I've only seen the movie.

 

~Scott

[H2SO4]

ya, simple mistake, hahahaha.

[YT2095]

that`s TWO mistakes within 24 hours, and in Chemistry, that can make you Infra-Dead

[H2SO4]

haha very funny, remind me again weres the second one, was it the KNO3 instead of NaNO3 or the potassium carbonate decomposes to CaO (typing error). Im just kinda tired lately, so my spelling and typing have been screwin up lately.

[collector]

The difference in base strength of the alkali hyrdoxides is small. Even LiOH is a strong base, and attacks glass.

 

Alkali metal oxides are stronger bases than the hydroxides. And nitrides are stronger bases than imines, which are stronger than amines, which are stronger than ammonia.

 

Another group of strong bases (base strength approx as alkali metal hydroxides) in water solution is tetraalkyl ammonium hydroxide, R4NOH, R=alkyl group.

[budullewraagh]

yeah, a clockwork orange was originally a novel by anthony burgess i believe.

 

oh, btw, that was downright dreadful, yt

[jdurg]

Yes, LiOH and NaOH will attack glass, but over a MUCH longer period of time than CsOH and RbOH will. (Hence why the ground glass stoppers of bottles of lithium and sodium hydroxide tend to annoyingly fuse shut). But CsOH will visibly attack glass. I.E. you can see it happening. It's just as effective as HF is, but hydrogen fluoride is sooooooooooooo much cheaper than CsOH that using CsOH to etch glass would be a very costly mistake.

[folded]

Yes, LiOH and NaOH will attack glass, but over a MUCH longer period of time than CsOH and RbOH will. (Hence why the ground glass stoppers of bottles of lithium and sodium hydroxide tend to annoyingly fuse shut). But CsOH will visibly attack glass. I.E. you can see it happening. It's just as effective as HF is, but hydrogen fluoride is sooooooooooooo much cheaper than CsOH that using CsOH to etch glass would be a very costly mistake.

 

What is more dangerous to your naked skin.

HF or CsOH?

 

Is there a big difference in the damage of getting ~10%HF and ~70%HF on your skin?

[jdurg]

HF is far more dangerous. Not only will HF burn through your skin, but HF itself is violently toxic and will make you violently ill and potentially end your life. Many, many, many scientists lost their lives or severely crippled themselves when trying to isolate fluorine gas and had accidents with HF. The fluoride ion is quite toxic, and when HF attacks things it generates a good deal of F-. While CsOH will cause great physical damage to your skin, the Cs+ ion isn't all that toxic.

[YT2095]

another Nasty effect of HF, is that you don`t feel it burning you, it kills the nerves effecting pain instantly, you`de probably not notice until it was too late

[woelen]

I want to put a few things right.

 

CsOH is not the strongest known base. It is not stronger than NaOH or KOH. If you dissolve CsOH, then you simply get Cs(+) ions and OH(-) ions. It might be that CsOH attacks glass more quickly than NaOH does, but this does not need to be due to stronger alkalinity.

 

Stonger bases are the amides (e.g. NaNH2), alkoxides (e.g. the methoxide CH3OK), but also certain oxides (e.g. Na2O). All of these bases are so strong, that they cannot exist in water, but they can exist in more basic solvents.

 

This strength of alkalinity (and also of acidity) can only be fully understood if the concept of acidity is generalized to non-aqueous solvents. For now, it suffices to say here, that each compound on its own has an intrinsic acidity or alkalinity and the observed alkalinity or acidity is limited to what a solvent can accomodate. In water, any compound more basic than hydroxide and any compound more acidic than hydronium seems equally strong. In liquid ammonia, any compound more basic than amide and any compound more acidic than ammonium seems equally strong. So, the observed acidity is limited by the solvent.

As an example of this: HI is a stronger acid than HBr. In water, they look equally acidic, because both are fully ionized. In more acidic solvents (e.g. pure CH3COOH) the difference can be observed. HI ionizes more easily than HBr. The reason that HI and HBr differ, while NaOH and KOH and CsOH are not really different is that the latter already are fully ionized. E.g., liquid NH3 can discriminate between alkali strength of hydroxides and amides. In liquid NH3, all the above mentioned hydroxides are equally strong as well. In any solvent they are equally strong, simply because they always are fully ionized, regardless the solvent in which they are dissolved.

 

---------------------------------------------

 

The compound NaF does attack glass (and I can say this, because I have experience with this:D ). The attack is not really fast, but it certainly happens. The reason of this is that NaF hydrolyses to a fairly large extent:

 

NaF ---> Na(+) + F(-)

F(-) + H2O <---> HF + OH(-)

 

The HF, which exists with the F(-) in equilibrium, slowly attacks the glass. So, you can do test tube experiments with NaF without ruining the test tubes, but storing it in a glass bottle for days certainly results in etching of the glass.