# AS Organic Chem- AlkanesWatch

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#1
I've got a table to fill out on Alkanes, and I'm stumped on the Molecular Formula, and Empirical Formula. I think Molecular Formula is determined by CnH2n+2 but then what's the Empirical Formula?

I thought that the empirical formula was the simplest ratio of elements in a compound, so C2H6 (Ethane)would be CH3? But then what about the empirical formula for C3H8 (Propane)? Would that still remain C3H8?

Then the final column is 'Displayed formula', so is that basically this- and so on? This is the introductory work to our next module, so I just want to make sure I'm getting it all right and then I can learn it all, thanks
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6 years ago
#2
(Original post by Eskyy)
I've got a table to fill out on Alkanes, and I'm stumped on the Molecular Formula, and Empirical Formula. I think Molecular Formula is determined by CnH2n+2 but then what's the Empirical Formula?

I thought that the empirical formula was the simplest ratio of elements in a compound, so C2H6 (Ethane)would be CH3? But then what about the empirical formula for C3H8 (Propane)? Would that still remain C3H8?

Then the final column is 'Displayed formula', so is that basically this- and so on? This is the introductory work to our next module, so I just want to make sure I'm getting it all right and then I can learn it all, thanks

Yeah the empirical formula for C3H8 is C3H8 because you can't simplify it further

Yep that's the displayed formula 1
#3
(Original post by Secret.)
Yeah the empirical formula for C3H8 is C3H8 because you can't simplify it further

Yep that's the displayed formula Okay took me a little bit longer than I thought to write them all out, Decane was particularly annoying but they're all done. Phew.

Now there's just a question on the back-

'Describe how molectular size determines the boiling point of the hydrocarbons produced by fractional distillation of crude oil.'

I was going to launch into an answer about how the number of bonds in the molecule will determine the boiling point, something like more bonds require more energy to overcome?
0
6 years ago
#4
(Original post by Eskyy)
Okay took me a little bit longer than I thought to write them all out, Decane was particularly annoying but they're all done. Phew.

Now there's just a question on the back-

'Describe how molectular size determines the boiling point of the hydrocarbons produced by fractional distillation of crude oil.'

I was going to launch into an answer about how the number of bonds in the molecule will determine the boiling point, something like more bonds require more energy to overcome?

In simple terms yeah, you've probably come across the term Van der Waals forces?

The bigger the molecular size the more Van der Waals forces that are present so it would take more energy to break the bonds. Remember to link it to fractional distillation like the questions asks
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#5
(Original post by Secret.)
In simple terms yeah, you've probably come across the term Van der Waals forces?

The bigger the molecular size the more Van der Waals forces that are present so it would take more energy to break the bonds. Remember to link it to fractional distillation like the questions asks

'The more bonds a molecule has, the higher the van der Waals' forces, where propane will have a lower boiling point than butane; this difference in boiling point allows for fractional distillation to differentiate the different oil types, in crude oil, based on their respective boiling points.

I just want to make sure that I've got that right, I understand how fractional distillation works in crude oil, but I'm not sure if that's just an example, or the example that they're looking for in an answer
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6 years ago
#6
(Original post by Eskyy)

'The more bonds a molecule has, the higher the van der Waals' forces, where propane will have a lower boiling point than butane; this difference in boiling point allows for fractional distillation to differentiate the different oil types, in crude oil, based on their respective boiling points.

I just want to make sure that I've got that right, I understand how fractional distillation works in crude oil, but I'm not sure if that's just an example, or the example that they're looking for in an answer
Seems correct, although I'm not sure if they want you to say something about the fact that being higher in the fractional distillation column produces shorter chain hydrocarbons due to them being a smaller molecule therefore having weaker Van der Waals

I think the question is asking how molecular size (and therefore Van der Waals forces) results in different columns and different products from each of these columns
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#7
(Original post by Secret.)
Seems correct, although I'm not sure if they want you to say something about the fact that being higher in the fractional distillation column produces shorter chain hydrocarbons due to them being a smaller molecule therefore having weaker Van der Waals

I think the question is asking how molecular size (and therefore Van der Waals forces) results in different columns and different products from each of these columns
I've re-written it to fit the different columns and different condensation points on the fractional column, now there's about 7 questions to do from the textbook and I'm completely stuck on one and google isn't helping nor is the textbook so hopefully you can help.

'Hexane can be reformed to produce a six-membered cyclic compound. Using displayed formulae, write a balanced equation for this reaction.'

I'm not even sure how a balanced equation for reforming should look, I know that reforming is the reverse of cracking. So, in Octane for example, the cracking formula is

C8H18 ---> C4H10 + C4H8

So when it asked to put the equation for reforming of Octane, I put

C4H10 + C4H8 -----> C8H18?

I'm not sure if that's correct, but I think it must me something similar to that since reforming is short-chain to long-chain hydrocarbons, where they're rearranged to alter their properties?

Edit: I've been scouring google and I think that a 'six membered cyclic compound' is cyclohexane, so I wrote the balanced chemical equation for the reforming of Hexane (C6H14 --> C6H12 + H2), then did the displayed formula as this- 0
6 years ago
#8
(Original post by Eskyy)
I've re-written it to fit the different columns and different condensation points on the fractional column, now there's about 7 questions to do from the textbook and I'm completely stuck on one and google isn't helping nor is the textbook so hopefully you can help.

'Hexane can be reformed to produce a six-membered cyclic compound. Using displayed formulae, write a balanced equation for this reaction.'

I'm not even sure how a balanced equation for reforming should look, I know that reforming is the reverse of cracking. So, in Octane for example, the cracking formula is

C8H18 ---> C4H10 + C4H8

So when it asked to put the equation for reforming of Octane, I put

C4H10 + C4H8 -----> C8H18?

I'm not sure if that's correct, but I think it must me something similar to that since reforming is short-chain to long-chain hydrocarbons, where they're rearranged to alter their properties?

Edit: I've been scouring google and I think that a 'six membered cyclic compound' is cyclohexane, so I wrote the balanced chemical equation for the reforming of Hexane (C6H14 --> C6H12 + H2), then did the displayed formula as this- Yeah thats the ryt equation for reforming
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