## Sapling Question #10

Xinying Wang_3C
Posts: 105
Joined: Wed Sep 30, 2020 9:39 pm

### Sapling Question #10

Hi, I know there are a lot of topics about #10 already, but I still don't know how to find the moles of 3-methyl-3-hexanone.

I understand the mass of 2-butanone can be calculated using 0.40mL and 0.81g/mL, and the number of mole of 2-butanone can be calculated by dividing 72.1g/mol, but how to find moles of 3-methyl-3-hexanone?

The original question:
"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. A reaction was performed in which 0.40 mL of 2‑butanone was reacted with an excess of propyl magnesiumbromide to make 0.45 g of 3‑methyl‑3‑hexanol. Calculate the theoretical yield and percent yield for this reaction."

Selena Quispe 2I
Posts: 129
Joined: Wed Sep 30, 2020 10:01 pm
Been upvoted: 3 times

### Re: Sapling Question #10

Hi! So you are correct!! In order to find the mass of 2-butanone you must multiply the density by 0.40mL and then to find the moles you must divide it by 72.1g. Because 2-butanone is your limiting reactant the number of moles for 3-methyl-3-hexanol will be the same number of moles you got for 2-butanone (The limiting reactant determines how much product is formed). Hope this helps!!

Audrey Han 3L
Posts: 101
Joined: Wed Sep 30, 2020 9:38 pm

### Re: Sapling Question #10

The ratio of moles from 2-butanone to 3-methyl-3-hexanol is 1 to 1 in the chemical equation given,
so it would be 1 mol 3-methyl-3-hexanol/1 mol 2-butanone.

Emma Ide 2E
Posts: 50
Joined: Wed Sep 30, 2020 9:39 pm

### Re: Sapling Question #10

I ended up with the same answer but never got 72.1 g/mol for 2 butanone and am not sure where everyone is getting that calculation? Is that just from getting the molecular formula and then determining the molar mass?

Posts: 53
Joined: Wed Sep 30, 2020 9:33 pm

### Re: Sapling Question #10

Emma Ide 2E wrote:I ended up with the same answer but never got 72.1 g/mol for 2 butanone and am not sure where everyone is getting that calculation? Is that just from getting the molecular formula and then determining the molar mass?

I actually just googled the molar mass of butanone :') I'm not sure if we were supposed to manually calculate it ourselves.

Angelica Soriano 3L
Posts: 102
Joined: Wed Sep 30, 2020 9:50 pm
Been upvoted: 1 time

### Re: Sapling Question #10

Emma Ide 2E wrote:I ended up with the same answer but never got 72.1 g/mol for 2 butanone and am not sure where everyone is getting that calculation? Is that just from getting the molecular formula and then determining the molar mass?

I actually just googled the molar mass of butanone :') I'm not sure if we were supposed to manually calculate it ourselves.

I googled it too!! Do you know if we have to be able to look at the structure of a molecule to find the molar mass in the future?

Posts: 53
Joined: Wed Sep 30, 2020 9:33 pm

### Re: Sapling Question #10

AngelicaSoriano_1F wrote:
Emma Ide 2E wrote:I ended up with the same answer but never got 72.1 g/mol for 2 butanone and am not sure where everyone is getting that calculation? Is that just from getting the molecular formula and then determining the molar mass?

I actually just googled the molar mass of butanone :') I'm not sure if we were supposed to manually calculate it ourselves.

I googled it too!! Do you know if we have to be able to look at the structure of a molecule to find the molar mass in the future?

Hopefully not; I hope that they'll just give us the molar mass or at least the molecular formula so we can calculate it ourselves-- I hope we don't have to find it by looking at the structure of the molecule.

haley f
Posts: 103
Joined: Wed Sep 30, 2020 9:49 pm

### Re: Sapling Question #10

This was all super helpful, thank you so much!

Kyla Roche 2K
Posts: 104
Joined: Wed Sep 30, 2020 9:59 pm

### Re: Sapling Question #10

Yes, I recall hearing that we will be given the molecular formula or the molar mass for problems like these!

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

### Re: Sapling Question #10

I googled the molar masses as well hahaha! I think it's clear that having prior understanding of what these organic compounds are is unrealistic for us to already know. It's safe to assume that for future tests or quizzes, we are most likely to be given these molar masses as well other information we wouldn't expect to already know or memorize such as constants, etc.