Animated Solution for Chemistry - Basic Concepts in Chemistry: ......... grams of 3-hydroxy propanal (MW = 74) must be dehydrated to produce 7.8 g of acrolein (MW = 56) (${\text{C}}_3{\text{H}}_4\text{O}$), if the percentage yield is 64 (Round off to the nearest integer). [Given : Atomic masses : C = 12.0 u, H = 1.0 u, O = 16.0 u]

Imagine you are a chemical engineer tasked with producing a specific amount of a valuable chemical, acrolein. You are starting with a precursor called 3-hydroxy propanal. The reaction is a simple dehydration—we heat the precursor, it loses a water molecule, and acrolein is formed.

However, the real world is messy. Reactions rarely go to completion perfectly. In this case, we are told the reaction has a 64% yield. This means for every 100 molecules you theoretically expect to produce, you only actually get 64. Our goal is to find out exactly how many grams of the starting material we need to guarantee we end up with 7.8 grams of acrolein.

First, let's figure out how many moles of acrolein we actually need. We know the mass we want is 7.8 g, and the molar mass of acrolein is given as 56 g/mol.

Now, because our reaction is only 64% efficient, we can't just use this number directly. If we only aimed for this amount, we would fall short by 36%! We need to calculate the theoretical moles—the amount we would need to aim for in a perfect world to get our desired actual amount in the real world.

Looking at the balanced chemical equation, the stoichiometry is beautifully simple: 1 mole of 3-hydroxy propanal yields 1 mole of acrolein. Therefore, the moles of reactant we must start with is exactly equal to the theoretical moles of acrolein we just calculated.

To find the final mass of the reactant, we multiply these moles by its molar mass, which is 74 g/mol.

When you crunch these numbers, you get approximately 16.10 grams. The question asks us to round off to the nearest integer, which leaves us with our final answer: 16 grams.

This problem perfectly illustrates why understanding percentage yield is so critical. If you had ignored it, you would have started with much less reactant and failed to produce the required 7.8 grams of acrolein!