Strong/Weak acid (1 Viewer)

[namburger]

I have contradicting definitions of a weak/strong acid

Is it acid pressent in solution ionise to form hydronium ions or hydrogen ions?

Thx

 

[undalay]

hydronium or hydrogen ions are effectively the same thing.
To be specific, hydrogen ions don't ever exist on there own.
They are always in the form of hydronium.

A strong acid is one which readily forms hydronium ions.
For example in HCl, 100% of the hydrogen will combine with water to form the hydrogen ions, completely being detached from the Chlorine ions.
The equilibrium is completely to the right.
HCl + H2O -> H3O + Cl-

A weak acid is one in which where the hydrogen ions will shift between being attached to the water and the anion. I.e. the equilibrium is not completely to the right (more to the left).

 

[Cleft]

Hmmm, my understanding is that both weak and strong acids ionise in solution, it's just that strong acids ionise more completely.
As for the hydrogen and hydronium ions. Acids ionise to make hydrogen ions (or protons) which can then bond with water molecules to make hydronium ions.

 

[namburger]

shit jimmy too good
thanks =D

 

[me121]

Source: Harvey, A. (2007) HSC Chemistry Syllabus Notes 2007. http://hscphysics.googlepages.com/HSC_Chem_Notes.pdf

Hmmm, my understanding is that both weak and strong acids ionise in solution, it's just that strong acids ionise more completely.
As for the hydrogen and hydronium ions. Acids ionise to make hydrogen ions (or protons) which can then bond with water molecules to make hydronium ions.

That's correct.

 

[Slidey]

Concentration does, however, change the pH of an acid. As such, pH is not always an effective measure of acid strength, as the acid in question may have a low pH without actually dissociating completely, among other factors.

An interesting one is HF. It is swiftly lethal as, it seeps into the blood stream upon contact. Inhalation contact (e.g. of fluoride, hydrogen fluoride, or hydrofluoric acid vapour) requires fairly significant amounts (but don't think that means small amounts are safe; they're just not as deadly). Skin contact has a high fatality rate, but if the solution is dilute you might have time to wash it off before it seeps into the bloodstream. The trouble is, if it is seeping into your blood, you won't know, as it is usually painless.

Interestingly, stomach acid has a pH of 0.7

 

[midifile]

Strong acids are those that completely ionise in solution ie HCl + H20 --> H30+(aq) + Cl-(aq)
Weak acids do not completely ionise, and when dissolved in solution form an equilbrium H2CO3 + 2H2O <--> CO3 2- + 2H30+
Be careful not to get these confused with concentrated and dilute, as many people use the term 'strong' to describe a concentrate solution and 'weak' to discribe a dilute solution.

H+ and H30+ tend to be used interchangebly, although H+ ions do not really exist as they combine to water to form H3O+ ions

 

[brenton1987]

To be specific, hydrogen ions don't ever exist on there own.
They are always in the form of hydronium.

That is really only true at the HSC level.

There are a number of superacids which have bare protons in solution. One of them, Fluoroantimonic acid, which is 2×10¹⁹ times stronger than 100% sulfuric acid contains naked protons which accounts for its extreme acidity. A sample of fluoroantimonic acid can have a pH as low as -25.

Isn't that interesting?

 

[Undermyskin]

That is really only true at the HSC level.

There are a number of superacids which have bare protons in solution. One of them, Fluoroantimonic acid, which is 2×10¹⁹ times stronger than 100% sulfuric acid contains naked protons which accounts for its extreme acidity. A sample of fluoroantimonic acid can have a pH as low as -25.

Isn't that interesting?

OH shit! (sorry) Now I have a specific example. OH man, can you give me a specific example proving HSO4- is amphiprotic by reacting with an acid, please? H3O+ is too general and not convincing! How can H2SO4 exists on its own in an aqueous solution? Ludicrous!

By the way, which base has a pH greater than 37?

 

[rooeys2]

haha superacids i learnt about that in tutoring its pretty hectic

 

[brenton1987]

By the way, which base has a pH greater than 37?

Lithium diisopropylamide, sodium amide and n-butyllithium have pH's of 34, 33 and 35 respectively which are close enough.

 

[Undermyskin]

Thanks heaps!

The last question:.....don't worry./