Video Transcript
Reaction of 1.274 grams of aqueous copper sulfate with excess zinc metal produced 0.392 grams of copper metal, according to the equation shown. CuSO₄ aqueous plus Zn solid forming Cu solid plus ZnSO₄ aqueous. Calculate to two significant figures the percentage yield of this reaction.
The percentage yield of a reaction is equal to the actual yield of the reaction, that is what you actually got by performing the reaction, divided by the theoretical yield, which is what you should’ve gotten given the amount of reactants that you started with, times 100 percent. The problem tells us that we produced 0.392 grams of copper metal during the reaction. So, this is our actual yield of copper. However, we aren’t given the theoretical yield, so we’ll have to calculate it given the amount of our reactants.
The problem tells us that we did this reaction with excess zinc metal, which makes the copper sulfate the limiting reactant, so we can use the amount of copper sulfate to determine the theoretical yield of the copper metal. We started with 1.274 grams of copper sulfate. So, our first step to find the grams of copper that we produced in this reaction will be to convert this grams of copper sulfate into moles of copper sulfate. Which we can do by dividing by the molar mass.
Copper has a relative atomic mass of 63.546, and we have one of them in copper sulfate. Sulfur has a relative atomic mass of 32.06, and we also have one of them. And finally, oxygen has a relative atomic mass of 15.999, and there’s four of those in copper sulfate. So if we add all of that up, the molar mass of copper sulfate is 159.609 grams per mole.
Now, we can find the moles of copper sulfate. Now, we’re in units of moles of copper sulfate, and we want to get to moles of copper. According to our balanced chemical equation, for every one mole of copper sulfate, we can make one mole of copper. We can use this ratio to convert from moles of copper sulfate to moles of copper. Now that we’re in moles of copper, our final step is to find the amount of copper in grams, which we can do by multiplying by the molar mass. The molar mass of copper is 63.546 grams per mole. If we multiply everything out, we’ll get 0.50722 grams of copper, which is our theoretical yield.
Now that we’ve found the theoretical yield of copper, let’s find the percentage yield for this reaction. Doing the calculation, we’ll get 77.28 percent. Rounding to two significant figures, the percentage yield for this reaction is 77 percent.
