Question

Before going to lab, a student read in his lab manual that the percent yield 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 yield should be 12.5 g. What is the student's actual yield likely to be?

Short answer

The student's actual yield is likely to be 5 grams.

Step-by-step solution

Identify the given values

We are given the percent yield (\(40\%\)) and the theoretical yield (12.5 g).

Write down the formula for finding the actual yield

The formula we'll use is: Actual Yield = (Percent Yield / 100) * Theoretical Yield

Plug in the given values into the formula

Now, we plug in the given values: Actual Yield = (40 / 100) * 12.5 g

Calculate the actual yield

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

Key concepts

Stoichiometry

Stoichiometry is the section of chemistry that involves the calculation of the quantities of reactants and products involved in a chemical reaction. It's based on the conservation of mass where the total mass of reactants equals the total mass of the products. To make stoichiometric calculations, you must first understand the mole concept, because chemical reactions happen molecule by molecule but we measure substances in grams.

One mole of any chemical compound contains the same number of entities, be they atoms, molecules, or ions, as there are atoms in 12 grams of pure carbon-12. This number is Avogadro's number (\(6.022 \times 10^{23}\text{ entities/mole}\)). Stoichiometry uses the balanced chemical equation to relate quantities of reactants to products. For example, if you know how many moles of a certain reactant you have, you can determine how many moles of a product you'll get, assuming the reaction goes to completion.

Theoretical Yield

The theoretical yield is the amount of product that will be formed during a chemical reaction if every molecule of reactant is perfectly converted to product. This figure is based entirely on stoichiometry and assumes that the reaction goes to completion without any side reactions or losses.

The calculation of the theoretical yield starts with a balanced chemical equation from which the mole ratio of reactants to products can be obtained. Using this ratio and the amount of the limiting reactant, you can determine the highest possible amount of product that could be produced. In an educational setting, it's essential to note that the theoretical yield represents an ideal, maximum efficiency scenario and is rarely achieved in practice due to various practical limitations.

Actual Yield

In contrast to the theoretical yield, the actual yield is the amount of product that is actually obtained from a chemical reaction. It is typically less than the theoretical yield due to the inefficiencies of the reaction, such as incomplete reactions, side reactions, and loss of product during recovery.

To determine the actual yield, you actually have to perform the experiment and measure the amount of product produced. This measurement can be affected by how carefully you conduct the experiment and how accurately you measure your compounds. The difference between the theoretical and actual yield can be important for industrial processes, where optimizing the yield of a reaction can have significant economic implications.

Chemical Reaction Calculations

Chemical reaction calculations include determining theoretical and actual yields, but they also encompass a broader range of problem-solving strategies in the context of chemical reactions. This includes calculating the amount of reactants required for a given yield of product, understanding reaction stoichiometry, and knowing how to use the mole concept for converting between masses of substances and the number of moles.

When performing these calculations, it is important to always balance the chemical equation and to understand what is the limiting reactant that determines the theoretical yield. These calculations are based on the assumption that the chemical equation is a direct representation of the molar relationships between reactants and products and are essential for anyone who works with chemical reactions in a scientific or industrial capacity.