Question

Oxalic acid is present in spinach, chard, rhubarb, kale, and some other leafy green vegetables. Design an experiment to qualify the oxalic acid content in a one-cup helping of spinach. Give specific experimental details.

Answer 1

Step 1 : Dissolve one cup of spinach in 300mL of 6M concentrated Na₂CO₃ solution.
Na₂CO₃ (aq) + (COOH)₂ (s) --------> (COONa)₂ (aq)+ H₂O (l) + CO₂ (g)
In this step the oxalic acid present in the spinach gets soluble in the form of sodium oxalate.
Step 2 : Separate the water and the other green residue using separatory funnel and filter paper,
remember that the sodium oxalate is present in water since it is soluble in it .
Step 3 : Now acidify this solution with strong acid like HCl
HCl (aq) +  (COONa)₂ (aq)  -------> (COOH)₂ (aq) + NaCl (aq)
The oxalic acid (COOH)₂ , NaCl are soluble in water we need to separate them based
on the solubility differences.
Step 4 : Use salts like Ca(OH)₂ to precipitate the oxalic acid, followed by separation using
funnel and evaporation, the oxalic acid can be obtained.