6. Oxalic acid, H2C2O4, is a diprotic acid. High levels of oxalic acid are a kno

Question

6. Oxalic acid, H2C2O4, is a diprotic acid. High levels of oxalic acid are a known cause of kidney stones.

a) Write the stepwise acid dissociation equilibrium reactions for oxalic acid, and provide the corresponding Ka values.

b) Calculate the Kb values of the hydrogen oxalate ion and oxalate ion. (Show calculations!

c) The hydrogen oxalate ion, HC2O4 - , can be described as amphiprotic. What does this mean? Write chemical reactions to support your answer.

d) Will a solution of HC2O4 - be acidic or basic?

Explanation / Answer

6. Oxalic acid is a diprotic acid

a) stepwsie dissociation reactions

First dissociation,

H2C2O4 <==> H+ + HC2O4-   Ka1 = 5.9 x 10^-2

Second dissociation

HC2O4- <==> H+ + C2O4^2-   Ka2 = 6.45 x 10^-5

b) Kb = Kw/Ka

Kb1 = 1 x 10^-14/6.45 x 10^-5 = 1.55 x 10^-10 for oxalate ion

Kb2 = 1 x 10^-14/5.9 x 10^-2 = 1.70 x 10^-13 for hydrogen oxalate ion

c) HC2O4- is amphoteric as it can loose a hydrogen to form oxalate ion and acts as an acid or it may accept a hydrogen to form oxalic acid and acts as a base.

d) A solution of HC2O4- would be acidic as it would give H+ easily and form oxalate ion. Ka2 is greater than Kb2.

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