[mookxi]

A 1.0 mol L^-1 aqueous solution of H2C2O4 was prepared at 25 degrees celcius. The equation for the hydrolysis reaction is:

H2C2O4(aq) + H2O(l) <=> H3O+ + HC2O4-

Ka(298K) = 6.4 x 10^-5 M

Which of the following species is present in the lowest concentrations?

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I found that the [H30+] to be .008 - & the answer is [HC2O4-] but i thought that that is the same as the concentration of [H30+]? So why is [HC2O4-] the answer instead of [H3O+]?

[AWK]

H₂O > H₂C₂O₄ > H₃O⁺ > HC₂O₄^- > C₂O₄^2- > OH^-

[Borek]

The equation for the hydrolysis reaction is:

H2C2O4(aq) + H2O(l) <=> H3O+ + HC2O4-

That's dissociation, not hydrolysis.

I found that the [H30+] to be .008 - & the answer is [HC2O4-] but i thought that that is the same as the concentration of [H30+]? So why is [HC2O4-] the answer instead of [H3O+]?

They are ALMOST identical, but H⁺ concentration is always slightly higher due to water autodissociation. Difference is in this case in the 10^-12M range, but it exist.

[mookxi]

Ahh.. I see. Thanks Borek. It's a dissociation?

The equation for the hydrolysis reaction is:

H2C2O4(aq) + H2O(l) <=> H3O+ + HC2O4-

That's dissociation, not hydrolysis.

I found that the [H30+] to be .008 - & the answer is [HC2O4-] but i thought that that is the same as the concentration of [H30+]? So why is [HC2O4-] the answer instead of [H3O+]?

They are ALMOST identical, but H⁺ concentration is always slightly higher due to water autodissociation. Difference is in this case in the 10^-12M range, but it exist.

[anarchron]

No it's also a hydrolysis as you have water smashing into the other thing.

[Borek]

No it's also a hydrolysis as you have water smashing into the other thing.

Going further that way - HCl doesn't dissociate, it hydrolise:

HCl + H₂O -> H₃O⁺ + Cl^-

and same holds for all other acids...

On the other hand, bases dissociate:

KOH -> K⁺ + OH^-

unless you believe those that state there is no OH^- ion, but some larger conglomerates like H₃O₂^-, in which case KOH hydrolise too:

KOH + H₂O -> H₃O₂^- + K⁺

Somehow I find it hard to believe that I was wrong for so many years

[Will]

No it's also a hydrolysis as you have water smashing into the other thing.

Going further that way - HCl doesn't dissociate, it hydrolise:

HCl + H₂O -> H₃O⁺ + Cl^-

and same holds for all other acids...

On the other hand, bases dissociate:

KOH -> K⁺ + OH^-

unless you believe those that state there is no OH^- ion, but some larger conglomerates like H₃O₂^-, in which case KOH hydrolise too:

KOH + H₂O -> H₃O₂^- + K⁺

Somehow I find it hard to believe that I was wrong for so many years

I think it is perfectly acceptable to say HCl_(aq) dissociates, and so does my organic chem book I keep quoting! (see below)

The solvation of OH^- and H₃O⁺ is quite cool- below is a pic and description.

[Borek]

I think it is perfectly acceptable to say HCl_(aq) dissociates

Well, if we assume that oxalic acid hydrolises, why do we call HCl decomposition into ions dissociation?

[Will]

I think it is perfectly acceptable to say HCl_(aq) dissociates

Well, if we assume that oxalic acid hydrolises, why do we call HCl decomposition into ions dissociation?

I don't know!