Question

What could have accounted for a percent yield of less than 100% in this lab?
Check all that apply.

The copper chloride did not fully dissolve in water before performing the reaction.

The mass of the copper was not measured with the same accuracy.

Not all of the copper was collected in the filter.

Not enough time was allowed for all of the aluminum to react.

There were impurities in the aluminum.

Answer 1

Answers: 1, 3, 4, 5.

Brief reasons:
- If CuCl2 didn’t fully dissolve, some reactant wasn’t available to react, lowering the amount of copper formed.
- If not all the copper was collected on the filter, product was lost during workup (lower measured yield).
- Insufficient reaction time can leave the reaction incomplete, giving less product.
- Impurities in the aluminum reduce the amount of reactive Al present, so less product forms.

The statement about measurement accuracy (2) describes a measurement error that could make the reported percent yield too high or too low, so it isn’t a definitive cause of a yield being less than 100%.