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Chemistry Forums for Students => High School Chemistry Forum => Topic started by: davon806 on October 23, 2012, 04:27:32 PM

Title: about KH3(C2O4)2 2H2O
Post by: davon806 on October 23, 2012, 04:27:32 PM
Hi,I am doing some molarity calculation.One of the questions mention a compound:
KH3(C2H4)·2H2O,
and it is used to neutralize NaOH
I have never heard a such compound before.
Obviously it is an acid
But the formula of acid is HaXb,a is the no of H,and b is the no of X.X is an anion is it is in aqueous state.
In this case,KH3(C2H4)2,using the above formula,what does K represents?
(I guess (C2H4)2 is the "X" part.)
Can anyone give some information about this compound?I have googled it but I can't find any information...
Thx a lot.
Title: Re: about KH3(C2O4)2 2H2O
Post by: Hunter2 on October 24, 2012, 01:10:53 AM
Its Potassium tetroxalate dihydrate.

http://www.chemicalbook.com/ChemicalProductProperty_EN_CB8477350.htm

It is an acidic salt by adding of two molecules of oxalatic acid one half neutralised by potassium.

In water you would have C2O42- anions.

KH3(C2O4)2 x 2 H2O => K+ + 3 H+ + 2 C2O42- + 2 H2O
Title: Re: about KH3(C2O4)2 2H2O
Post by: Borek on October 24, 2012, 04:02:12 AM
So is it KH3(C2O4)2·2H2O as you put in the thread subject, or KH3(C2H4)2·2H2O as you consistently wrote in the question?

HaXb is not a general formula of acid. What about sulfuric acid? Or acetic?
Title: Re: about KH3(C2O4)2 2H2O
Post by: AWK on October 24, 2012, 11:54:16 AM
Quote from: Hunter2 on October 24, 2012, 01:10:53 AM
Its Potassium tetroxalate dihydrate.

http://www.chemicalbook.com/ChemicalProductProperty_EN_CB8477350.htm

It is an acidic salt by adding of two molecules of oxalatic acid one half neutralised by potassium.

In water you would have C2O42- anions.

KH3(C2O4)2 x 2 H2O => K+ + 3 H+ + 2 C2O42- + 2 H2O
Only traces of C2O42-
Title: Re: about KH3(C2O4)2 2H2O
Post by: Hunter2 on October 24, 2012, 12:35:34 PM
Bad soloubility?
Title: Re: about KH3(C2O4)2 2H2O
Post by: Borek on October 24, 2012, 12:39:38 PM
No, equilibrium.
Title: Re: about KH3(C2O4)2 2H2O
Post by: Hunter2 on October 24, 2012, 12:42:50 PM
the equilibrium is on the salt side?
Title: Re: about KH3(C2O4)2 2H2O
Post by: Borek on October 24, 2012, 12:46:02 PM
Think about pH of the solution. You have a weak acid.
Title: Re: about KH3(C2O4)2 2H2O
Post by: davon806 on October 24, 2012, 01:16:31 PM
Thx for all replies.
HaXb means,for example,
H2SO4,a = 2,X = SO4 2-, b =1
CH3COOH, a = 1, X = CH3COO- , b=1
So,I can't substitute the above formula in the case KH3(C2O4)

And consider the equation
KH3(C2O4)2·2H2O + NaOH --> NaH3(C2O4)2 + 2H2O + KOH
so H3(C2O4)2 is an anion with charge 1-?
and the resultant solution is strongly alkaline?
I don't quite understand why neutralization will give out strong alkali(KOH),usually,weak acidic/weak alkaline or neutral salt is given out.
Title: Re: about KH3(C2O4)2 2H2O
Post by: Hunter2 on October 24, 2012, 01:42:02 PM
I thought you would get sodium- and potassium  oxalate.
Title: Re: about KH3(C2O4)2 2H2O
Post by: Borek on October 24, 2012, 01:55:05 PM
Quote from: davon806 on October 24, 2012, 01:16:31 PM
KH3(C2O4)2·2H2O + NaOH --> NaH3(C2O4)2 + 2H2O + KOH

No.

Quote
so H3(C2O4)2 is an anion with charge 1-?

No.

Quote
and the resultant solution is strongly alkaline?

No.

Quote
So,I can't substitute the above formula in the case KH3(C2O4)

To some extent you can, you just have to understand what you are looking at.

Have you ever heard about sodium bicarbonate (AKA sodium hydrogen carbonate), NaHCO3? It is in some aspects quite similar to the compound in question.