A % yield < 100 can be explained by losses and side reactions. How could you account for a % yield > 100? Cu has two common oxidation states: +1 and +2. How could you explain an empirical formula of Cu2Cl3?
The Correct Answer and Explanation is:
Correct Answer:
A percent yield greater than 100 can be explained by experimental errors such as incomplete drying of the product, contamination with impurities, or the presence of leftover solvents. These factors can artificially inflate the measured mass, making the calculated yield exceed 100 percent.
An empirical formula of Cu₂Cl₃ cannot be explained by standard copper oxidation states alone because copper typically exhibits +1 and +2 states. However, this formula suggests an unusual oxidation state or a mixed valency compound involving both Cu⁺ and Cu²⁺ ions.
Explanation:
Percent yield is a measure of how efficiently a chemical reaction produces the desired product. It is calculated by dividing the actual yield by the theoretical yield and multiplying by 100. In most cases, percent yield is less than 100 due to losses from transfer steps, incomplete reactions, or side reactions. However, a percent yield greater than 100 is possible and often results from experimental errors rather than an actual increase in product formation.
One common reason for a yield over 100 percent is improper drying of the product. Residual water, solvents, or other volatile substances can remain in the final solid, increasing its measured mass. Contamination by impurities, such as leftover reactants, byproducts, or atmospheric materials like dust, can also contribute. Miscalculations in the theoretical yield, such as using incorrect molar masses or measurement errors, can further cause this issue.
As for the empirical formula Cu₂Cl₃, it appears inconsistent with the common oxidation states of copper, which are +1 (cuprous) and +2 (cupric). The ratio of two copper atoms to three chlorine atoms suggests an average oxidation state of copper that does not match either of these individually. One possible explanation is the existence of a mixed valency compound where both Cu⁺ and Cu²⁺ coexist within the same structure. Such compounds are known in coordination chemistry and solid-state materials, where different oxidation states stabilize the structure, leading to unusual empirical formulas like Cu₂Cl₃, even though they may not represent a simple ionic salt.
