Sapling Q #10-Balancing

Mackenzie Van Val 3E
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Joined: Wed Sep 30, 2020 9:36 pm
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Sapling Q #10-Balancing

Hi! I know there are a lot of questions about #10, so I hope mine hasn't been asked before.

When given a question like this, do we just assume that the equation is balanced before doing our limiting reagent calculations? I know that on other questions where it was not explicitly stated whether an equation was balanced, we have had to balance them before proceeding. Also, should we just assume that all stoichiometric coefficients are 1? Thanks for any responses!

For reference, here is question 10:

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 0.40 mL of 2‑butanone was reacted with an excess of propyl magnesiumbromide to make 0.38 g of 3‑methyl‑3‑hexanol. Calculate the theoretical yield and percent yield for this reaction.

Ansh Patel 2I
Posts: 103
Joined: Wed Sep 30, 2020 9:42 pm

Re: Sapling Q #10-Balancing

Hi! For this reaction I assumed it was 1 mole of each substance because the way I saw it, if there was 2 moles of 2-butanone, two molecules would've been drawn out rather than just 1, or something would've been stated in the problem that would indicate that there is more than 1 mole of each substance. Since all of the substances only had one molecule shown, I assumed everything was balanced.

Giselle Granda 3F
Posts: 116
Joined: Wed Sep 30, 2020 10:00 pm

Re: Sapling Q #10-Balancing

Hello, I believe that we would assume it is balanced in this particular problem because we do not yet know the molecular or empirical formula of 2-butanone. Since we are trying to determine the subscripts first, we would have to assume the stoichiometric coefficients are 1 (since there is no way to balance it yet) and then we would have to determine the amount of moles of carbon, hydrogen, and oxygen there is from the products. Only then can we determine the empirical formula, and as a result, the molecular formula.

Gian Boco 2G
Posts: 96
Joined: Wed Sep 30, 2020 9:36 pm

Re: Sapling Q #10-Balancing

I initially thought that the number before the organic compound was the number of moles but I realized that that was part of the name hahaha. Because I don't see how we can be expected to be familiar with these compounds and balance the equation, I think we should be safe to assume that they are all 1:1 mole ratios. From there, I just google searched the molar mass of the relevant compounds so that I can properly work out the problem.