Why is it difficult to identify all the ions in a mixture than to identify the cation and anion in a binary ionic compound?

Because ions in the same mixture can have similar physicochemical properties generating interference in the methods used for such separation.

Explanation:

When we have only 2 ions present in a solution, and also one has a positive charge (cation) and the other one has a negative charge (anion), its separation is very easy since there are multiple methods to separate ions of opposite charge. Example we have the Cl- and Na + present in the water.

But in the case that we have many ions in solution, for example protons in which we do not know their identity, we will need several identification methods since there are multiple possibilities that generate interference, that is, erroneous readings during their identification, since these protons they have similar physicochemical properties. For example K +, Na +, Li +