why the change in the calcium oxalate equilibrium is produced?

Question

We hace experimented with calcium oxalate and i have some observations that could help:

First, we made a solution with 5mL of calcium chloride 0,1 M and 5 mL of sodium oxalate 0,1 M. this solution has a milky white color, corresponding to a precipitate.

Then, we add to this solution hydrochloric acid concentrated, this caused that the solution turn colorless.

 

my question is: why this changes happen with the hydrochloric acid? or why are this changes?

 

please reply :)

Answer 1

The milky white color is a result of the formation of calcium oxalate, CaC₂O₄.

CaCl₂(aq) + Na₂C₂O₄(aq) ==>2NaCl(aq) + CaC₂O₄(s)

When HCl(aq) is added, it reacts with the CaC₂O₄ to form oxalic acid and CaCl₂

CaC₂O₄(s) + 2HCl(aq) ==> CaC_l2 + H₂C₂O₄(aq)

 

In a more detailed explanation, this is a result of Le Chataelier's Principle.

Oxalic acid, H₂C₂O₄ is soluble.  Calcium oxalate, CaC₂O₄ is not.

CaC₂O₄(s) ===> Ca²⁺(aq) + C2O4^2-(aq)

Upon addition of 2HCl

C₂O₄^2-aq) + 2H⁺(aq) ==> H₂C₂O₄ (aq)