To gravimetrically analyze the silver content of a piece of jewelry made from an alloy of $\ce{Ag}$ and $\ce{Cu}$, a student dissolves a small preweighed sample in $\ce{HNO3(aq)}$. $\ce{Ag+(aq)}$ and $\ce{Cu^{2+}(aq)}$ ions form in the solution. Which of the following should be the next step in the analytical process?

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In order to isolate silver, we need to be able to precipitate it out using the correct anion. The anion should not form a salt with the undesired copper ion.

The other choices could also be eliminated. Centrifuging works only when there are immiscible (non-mixing) liquid phases. In our case the heterogenous solution contains all of the ions.

Evaporation would not help us obtain the silver content.

Changing the pH does not help us obtain the silver content either.