Question

In order to get as much copper as possible from a reaction, one usually adds an excess of zinc. Why? We already have a set amount of zinc needed to reduce all the copper(II) ions. Why should we add an excess of zinc? Is it to make sure that there's enough zinc to react with the copper, or will there be a loss of electrons during the reaction?

Answer 1

An excess of zinc is used to guarantee the complete reduction of copper(II) ions because zinc is more reactive than copper, as per the activity series. The excess ensures that all copper ions react despite potential losses or measurement inaccuracies.

Step-by-step explanation:

Adding an excess of zinc to a reaction involving copper(II) ions helps ensure the complete reduction of copper due to the relative activity of metals.

Since zinc is listed above copper on the activity series, it is more easily oxidized than copper. This means that zinc atoms are oxidized to zn2+ ions, while Cu2+ ions are simultaneously reduced to metallic copper.

The excess zinc compensates for any potential inaccuracies in measurement and ensures that all copper ions are fully reduced.

During the reaction, if the exact stoichiometric amount of zinc is used, there might not be enough to drive the reaction to completion if any zinc is lost or not fully reacted.

Thus, having an excess of zinc ensures that there is a sufficient amount to react with all of the copper ions available, without considering potential losses.

Further, this reaction is spontaneous, meaning that when zinc metal and copper ions are mixed, they react without the need for additional energy.