/sci/ - Science & Math

[Anonymous No.1692419]

Halp

I am in organic chem and had my first lab class yesterday, I am doing the assigned questions on our first real lab that must be done in order to actually do it. I have answered most of the questions sufficently, its about TLC plates. I took AP chem in HS but it never prepared me for this, I am totally baffled, dont know how to use any of these machines and really overwhelmed since all of these people aparently did.

But my question is "Arrange the following in order of increasing Rf by TLC: octane, ethanoic acid, dichloromethane, hexanol."

I think its octane, hexanol, and then ethanoic acid. But I dont know where dicholoromethane goes or even why it goes whereever. halp please : (

also I never realized how tough this class would be, I only have it monday nights and then lab wendsdays and we dont even have class next week because my teacher will be in europe or something.

[Anonymous No.1692443]

Polar compounds move the shortest (low Rf.).
So arrange it from the most polar to least polar.

[Anonymous No.1692448]

>>1692419
Unlike in high school, when you're missing classes, it's not fun, nor beneficial. The days when you can say "YAY! NO CLASSES! THE SUB ISN'T GOING TO DO SHIT" is over, now all you can say is "shit, I better self teach myself, or else I'll fall behind".

Also, AP classes are worthless. I left them when I realized that we're doing the exact same things as the regular classes, but with more practice questions. Instead of doing odds only, we do both odds and even. Also, the credits doesn't transfer over. I mean, even if it did, I wouldn't skip a year. But still.

[Anonymous No.1692473]

>>1692448
I dont see what that has to do with my thread at all other than you ranting about AP classes.

I enjoy this class and I want to be here, I want to pass.

>>1692443
lol I'm not stupid, I know what the objective of the question is. My issue is that I know that octane will be least and ethanoic acid will be most and that hexanol is in between them, but I dont know where the dicholoromethane goes.

[Anonymous No.1692489]

ethanoic acid, hexanol, dcm, octane.

ethanoic acid contains COOH group which is most polar.
hexanol contains OH group which is polar.
octane must be least polar.
DCM should be inbetween OH and octane because it is not that non-polar but it contains halogen group to start with.

[Anonymous No.1692506]

Polarity Pattern:
Carboxylic acids > alcohols > amines > ketones/aldehydes > esters > ethers >
halocarbons > arenes > alkanes

• Adding additional nonpolar hydrocarbon to a given molecule moves it in the non-polar
direction (tiebreaker). For example, C4H9OH will be more polar than C7H15OH.

• Key: More polar sample -> moves less. Less polar sample -> moves farther.

[Anonymous No.1692511]

>>1692489
>octane
>polar
DCM is more polar than hexanol, ethanoic, DCM, hexanol, octane

[Anonymous No.1692523]

>>1692506
>>1692489
oh. I thought that more polar goes further.. Our book says that a less polar solvent will cause less movement of the solute across the TLC plate. But I dont think that has anything to do with this... It doesnt say what the solvent is.

alright, I thought that the halogens would make it a bit polar. There is a chart we are supposed to be referencing to this, but it only says alkenes for least polar and doesnt say alkanes anywhere so I was more confused >_>

>Carboxylic acids > alcohols > amines > ketones/aldehydes > esters > ethers >
halocarbons > arenes > alkanes

which catagory does DCM go under?

[Anonymous No.1692535]

>>1692523
Halogens will make a substance pretty damn polar, fluorine is the most electronegative atom and will hog most of the electrons in a bond. The basic trend is everything to the left and below fluorine is less electronegative the further away it is. Chlorine being directly bellow fluorine and the tetrahedral structure of methane means a lot of the electron density of that molecule is located on the chlorine side of the molecule and being only a methane it doesn't have the non-polar effect of larger carbon chains like hexane etc.

[Anonymous No.1692561]

>>1692523
Technically it's a alkane, although it doesn't fit into any of those categories listed. It's just one of those things you have to judge, although DCM is a pretty simple example because of the structure and the fact they used chlorine in it.

[Anonymous No.1692575]

>took ap chem in high school
>in o chem now

whoa do they let you skip all of G chem because you passed an ap test?

[Anonymous No.1692598]

>>1692575
well I took AP chem as a junior and now I am a senior and I am dual enrolling in night classes.

I really love chemistry, this is what I want to do, I find it extremely fascinating but feel VERY unprepared when compared with the rest of the students.

In org chem lecture I feel like one of the smartest people and I am good at teaching myself, but in lab there are different people from the morning classes as well and I feel very bad compared to them. We all get these tools and kits and shit and I dont even know how to use a hood, I never have. or gas chromotographer?

But thanks all very much for the help, I need it! lol.

[Anonymous No.1692608]

fuck I need to go study, not waste my time on 4ch, should have left like an hour ago lol

going to go study, thanks

[Anonymous No.1692619]

>>1692598

I'm just kinda surprised, that's all. I took college O chem as a senior in HS too but I also took G chem as a junior because around here you can take college courses for hs credit the last two years of high school. I never took ap chem but I just can't imagine any high school class preparing you for O chem. I give you props for not dropping the class after the first lecture lol.

[Anonymous No.1692632]

wait quick question

how can i even begin to organize them by Rf value when it doesnt tell me if the solvent is polar or mostly nonpolar ??? : /

[Anonymous No.1692636]

>>1692473
if you want to know polarity check the 'dipole moment' of the compound. i think it's on most wikipedia pages. that will tell you how polar it is. problem solved.