You first treated your unknown solution with 1 M K2C2O4 and 1 M CH3COOH and a yellow precipitate formed. The liquid remaining atop this precipitate was removed after centrifugation, and to it was added 1M H2SO4. No new precipitate formed. Next, a solution of 0.25 M (NH4)2C2O4 was added to the unknown solution which had been treated in the fashion described. A white precipitate formed. This mixture was centrifuged and separated, and the clear solution was then treated with 1 M Na2Co3. No Preceipitate formed. Which metal ions were present in your unknown? Which metal ions were absent?