Sapling HW question

[Janna Shakiba]

Consider the nucleophilic addition reaction of 2‑butanone with excess propyl magnesiumbromide, made in situ by reacting 1‑bromopropane with metallic magnesium, to make 3‑methyl‑3‑hexanol.

Reaction scheme where 2-butanone (d = 0.81 g/mL), 1-bromopropane (d=1.35 g/mL), and magnesium react to form 3-methyl-3-hexanol (d = 0.82 g/mL)

A reaction was performed in which 0.45 mL of 2‑butanone was reacted with an excess of propyl magnesiumbromide to make 0.41 g of 3‑methyl‑3‑hexanol. Calculate the theoretical yield and percent yield for this reaction.

[Kelly Ha 1K]

1) Calculate theoretical yield
Using the given density for 2-butanone, first convert the volume of 0.45 mL of 2-butanone into grams to find the mass of the reactant. After you find that value, calculate the number of moles of 2-butanone by dividing the value by the molar mass. Since 2-butanone and 3-methyl-3-hexanol (product) have a molar ratio of 1:1, you find that the number of moles of 3-methyl-3-hexanol is the same as the number of moles of 2-butanone. Finally, calculate the amount of grams of 3-methyl-3-hexanol by multiplying the number of moles of 3-methyl-3-hexanol by the molar mass to find the theoretical yield.

2) Calculate percent yield
To calculate percent yield refer to the equation (actual yield)/(theoretical yield) x100. Use the given actual yield (0.41 g) and the theoretical yield you calculated in the previous step to find the percent yield. Hope this helps!

[IreneGi2I]

I also had problem with this one because I had no idea how to calculate the molar masses of 2-butanone and 3-methyl-3-hexanol. I actually looked them up on the internet, and according to TA, we would not have to know how to calculate these molar masses! I think those molar masses will be given in the question if this type of question shows up on the exam.

[Alejandro Gonzalez 2G]

Yeah I was also confused about finding the molar masses, and I tried to solve it multiple times but I was finally able to realize that the molar ratios of the reactant and the product were equal so finding them at first was not totally necessary.

[Ayesha Aslam-Mir 3C]

For this question, you should multiply the mL of the reactant you know (2-butanone) by density to get the grams of this compound. you should also find out how many mol of product were created using the molar mass. When solving this for the yield, I assumed 2-butanone and the product given were in a 1:1 proportion as both were the only mentioned components with oxygen (but this may not always be the case, especially in this problem where the rest of the products are not necessarily mentioned). Using the mol of reactant, you can calculate the max yield, and using the given amount of product created, you can divide by the theoretical yield to get your true percent yield.