Blakhitman's chem questions thread!

[Blakhitman]

lol thanks, I already googled it...

but I don't see the connection the person places between lawn food and the uses of the elements in the human body...unless you're gonna eat the stuff...

This all reminds me of dreadful biology!

[Blakhitman]

nevermind...Solved...

[Blakhitman]

How can 13C NMR be used to distinguish between 2-butanone and butanal?

it can't right? you need to use 1 H NMR to distinguish between the isomers??

[Mao]

This is not completely straight forward. But first thing first, there is only one isomer of butanone, so the 2- is redundant.

C-C(=O)-C-C
1  2       3  4

C2 will be most downfield, C1 and C3 will be closer together, and C4 will be most upfield. Spectrum would look like

      |                    |  |       |


O=C-C-C-C
    1  2  3 4
C1 will be most downfield, C2 will be further up, C3 and C4 will be fairly close and most upfield. Spectrum will look like:

      |                    |         |  |

[Note, downfield = high chemical shift, upfield = low chemical shift]

[Blakhitman]

Thanks a lot Mao!

I thought it might have something to do with that.

[Blakhitman]

The Hydrogen environment on the CH3 on the methyl part of methyl propanoate will produce a singlet right?

If asked about the number of splits due to it would you say 1? or 0?

[Mao]

The Hydrogen environment on the CH3 on the methyl part of methyl propanoate will produce a singlet right?

If asked about the number of splits due to it would you say 1? or 0?

It wouldn't hurt to say 'no splitting, produces a singlet'

[Blakhitman]

K thanks.

[Blakhitman]

Butane is used as the fuel in cigarette lighters.

2C4H10 + 13O2----> 8CO2 + 10H20 delta H= -5772 kJ/mol

Calculate the amount of energy produced when 50g of butane reacts with 100L of Oxygen at SLC.

I'm guessing Oxygen has to be excess??

[m@tty]

Hence, as mole ratio is 2:13 oxygen is the limiting reactant.

Where E=energy produced, using the fact that the ratio of moles reacting equals the ratio of energy involved.

Therefore (2 significant figures)

Hope this is right, going purely off logic as I haven't actually seen a question like this done. (sorry if it is wrong)

[Blakhitman]

That's exactly what I did and got.

I was just worried that for the complete combustion to occur Oxygen had to be in excess, but I suppose it doesn't?

Thank you so much m@tty!!

[m@tty]

I'm unsure, actually. Because in short supply of oxygen don't combustion reactions give off carbon monoxide and eventually plain carbon? But that couldn't be expected for this question, I think, as you would need more equations. =S

[Blakhitman]

That's what I was thinking.

I guess someone can clarify tomorrow...I hope.

But for the time-being I'm gonna assume we're correct .

[fady_22]

That's what I was thinking.

I guess someone can clarify tomorrow...I hope.

But for the time-being I'm gonna assume we're correct .

Using the equation given, it is assumed that they butane undergoes complete combustion. Therefore, your answers are correct.

Realistically, incomplete combustion will occur (as there isn't enough oxygen for complete combustion), but the assumption that should be made from the reaction is that it is complete.

[Blakhitman]

That's what I was thinking.

I guess someone can clarify tomorrow...I hope.

But for the time-being I'm gonna assume we're correct .

Using the equation given, it is assumed that they butane undergoes complete combustion. Therefore, your answers are correct.

Realistically, incomplete combustion will occur (as there isn't enough oxygen for complete combustion), but the assumption that should be made from the reaction is that it is complete.

Ahh ok, sweet thank you!