Question

Calculate the pH at 25°C of a 0.65 M aqueous solution of oxalic acid (H2C2O4). (Ka1 and Ka2 for oxalic acid are 6.5 × 10−2 and 6.1 × 10−5, respectively.

Answer 1

Using ICE table and Ka1 expression for equilibrium calculate the concentrations of hydronium/hydrogen ion for 1st dissociation.

Then for 2nd dissociation follow the same steps.

We see that the concentrations of hydronium ions in 2nd dissociation is very very less than the Concentration of hydronium ion in first dissociation at EQUILIBRIUM.

So we can ignore the concentrations of hydrogen in 2nd dissociation.

Then apply :

So pH = 0.76

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