Question

Before going to lab, a student read in his lab manual that the percent yicld for a difficult reaction to be studied was likely to be only \(40 . \%\) of the theoretical yield. The student's prelab stoichiometric calculations predict that the theoretical yicld should be \(12.5 \mathrm{~g}\). What is the student's actual yield likely to be?

Short answer

The student's actual yield is likely to be 5 grams, based on the given percentage yield of 40% and theoretical yield of 12.5 grams.

Step-by-step solution

Understand the given information

We have the following information: Percentage Yield = 40% Theoretical Yield = 12.5 grams

Use the percentage yield formula

The formula to calculate the actual yield from the percentage yield is: Actual Yield = (Percentage Yield / 100) * Theoretical Yield

Substitute given values into the formula

Plug in the given values into the formula: Actual Yield = (40 / 100) * 12.5 grams

Calculate the actual yield

Perform the calculation: Actual Yield = 0.4 * 12.5 grams Actual Yield = 5 grams The student's actual yield is likely to be 5 grams.

Key concepts

Stoichiometry

Stoichiometry is a fundamental concept in chemistry that involves the calculation of reactants and products in chemical reactions. It is based on the balanced chemical equation and allows us to predict the quantities of substances consumed and produced. The principle behind stoichiometry is the conservation of mass, where the mass of the reactants equals the mass of the products.

In our specific exercise, stoichiometry plays a crucial role in determining the theoretical yield. By using stoichiometric calculations, a student can ascertain how much product should be formed during the reaction, assuming complete conversion and perfect conditions. This will serve as a benchmark against which the actual yield can be compared.

• In any chemical equation, coefficients represent the stoichiometric ratios of the substances involved.
• Stoichiometric calculations enable us to convert between moles of different substances.
• Theoretical yield is often directly calculated using stoichiometric coefficients from a balanced chemical reaction.

Understanding stoichiometry is essential for predicting yields and planning laboratory work, allowing the student to efficiently use resources and confirm their experimental results.

Theoretical Yield

The theoretical yield is the maximum amount of product that could be formed from given amounts of reactants under ideal conditions. It is the yield predicted by stoichiometric calculations based on the balanced chemical equation.

In our example, the theoretical yield is calculated to be 12.5 grams. This number is derived from the ideal assumption that every molecule of reactant will be converted to product, with no loss, inefficiencies, or side reactions. Theoretical yield sets the bar for what to expect when everything goes perfectly.

• Theoretical yield is always calculated beforehand, guiding experiments.
• It assumes perfect conditions, no impurities, and complete reaction.
• Theoretical yield usually exceeds the actual yield due to real-world constraints.

Accurate calculation of theoretical yield forms the basis for determining other key quantities in reaction yields, such as percent yield and actual yield.

Actual Yield

Actual yield is the amount of product actually obtained from a chemical reaction, which is usually less than the theoretical yield due to various practical factors. These factors might include incomplete reactions, side reactions, or losses during product recovery.

From the given problem, the actual yield is calculated to be 5 grams based on the provided percent yield of 40%. Actual yield gives a more realistic picture of a reaction's success under practical conditions. It's calculated by multiplying the theoretical yield by the percent yield (converted to a decimal).

• Actual yield can vary significantly based on reaction efficiency and conditions.
• Comparison of actual and theoretical yields helps identify practical constraints.
• Improvements in methods might be needed if the actual yield is very low compared to the theoretical yield.

Understanding actual yield is crucial for optimizing reaction conditions and improving overall laboratory processes, allowing scientists to achieve more efficient and effective results.