The dissolved copper then binds to one of the sulfate ions to make copper (II) sulfate, which lends the persulfate etchant solution a familiar blue-green tinge as etching proceeds. Another etchant ...

5. Add the reaction mixture from the beaker to the filter paper. 6. Collect the filtrate, which is the copper(II) sulfate solution. Dispose of the residue, which is the unreacted copper(II ...