Which of the following is a reason why the percent yield of a chemical reaction might be less than 100%?

• A. Some product is lost during purification or transfer.
• B. All reactants are completely converted to products.
• C. The reaction is performed under ideal conditions with no errors.
• D. No side reactions occur during the process.

Answer: (A)

Verified step by step guidance

1. Understand that percent yield is calculated by comparing the actual amount of product obtained to the theoretical maximum amount possible, using the formula: \(\text{Percent Yield} = \left( \frac{\text{Actual Yield}}{\text{Theoretical Yield}} \right) \times 100\%\).
2. Recognize that a percent yield less than 100% means the actual yield is less than the theoretical yield, indicating some loss or inefficiency in the process.
3. Consider common reasons for yield loss, such as product loss during purification or transfer steps, incomplete reactions, side reactions, or measurement errors.
4. Evaluate the given options and identify that 'Some product is lost during purification or transfer' is a valid reason for a percent yield less than 100%, because physical handling can cause loss of product.
5. Note that the other options describe ideal or complete scenarios (all reactants converted, no side reactions, ideal conditions), which would not cause a percent yield less than 100%.