VCE Chemistry Question Thread

[katiesaliba]

Is this correct: more protons then more energy released when an excited electron returns to its ground state

[lzxnl]

Is this correct: more protons then more energy released when an excited electron returns to its ground state

What's this for? It reminds me suspiciously of photosynthesis which isn't exactly chemistry.

[hobbitle]

Is this correct: more protons then more energy released when an excited electron returns to its ground state

Does this sentence even make sense?  I can't figure out what she's asking.

[lzxnl]

Does this sentence even make sense?  I can't figure out what she's asking.

Me neither. Only sounds like photosynthesis because I hear "excited electrons", "more protons" and "energy released" in the same sentence.

[thushan]

Is this correct: more protons then more energy released when an excited electron returns to its ground state

I think what Katie's asking is whether if the nucleus of an atom has more protons, then the energy difference of an electron in the ground state and in the excited state is greater.

To be honest, I don't actually know the answer to that conclusively. All I know is that a higher nuclear charge will tend to pull all the electron shells towards the nucleus (due to the attractive force), but I'm not sure whether as a result the electron shells will be closer to one another or further away. My educated guess is that the electron shells become closer to one another, which tends to decrease the difference between energy levels. On the flip side, the electron shells will both be closer to the nucleus, which may tend to increase the difference between energy levels of the valence shell and unoccupied shells. I don't know which effect is predominant.

On another note - lzxnl - I know you probably didn't mean it, but what you said came across to me as a little derisive and offensive. Just letting you know. Katie has every right to ask questions here without being derided.

[Snorlax]

What exactly is the chemical shift in NMR?
In a compound, how would I know where to put each peak (whether C-13/H1 NMR) along the horizontal axis with the chemical shift(ppm) on it?
I heard it was something to do with electronegativity or polarity of the different chemical environments of the compound..

help would be appreciated!

Thanks!

[Rishi97]

How would I change 1,4-dichlorobutane to an alcohol? What would I add?

[Rishi97]

What effect does having a COOH group have on the physical and chemical properties of carbon compounds.
The only one I know it that it increases solubility. 

[nhmn0301]

How would I change 1,4-dichlorobutane to an alcohol? What would I add?

You double the amount of NaOH that you normally because you have 2 Cl- there, hence, in the end, you have butane -1,4- diol, which has 2 OH- group on it.

What effect does having a COOH group have on the physical and chemical properties of carbon compounds.
The only one I know it that it increases solubility. 

Physical: you certainly increase boiling points, melting points, decrease volatility, increase solubility (as you increase the amount of both dispersion forces and polar bonds)
Chemical: it's an acid as the name suggests

[Jawnle]

You double the amount of NaOH that you normally because you have 2 Cl- there, hence, in the end, you have butane -1,4- diol, which has 2 OH- group on it.
Physical: you certainly increase boiling points, melting points, decrease volatility, increase solubility (as you increase the amount of both dispersion forces and polar bonds)
Chemical: it's an acid as the name suggests

I'm pre sure density increases aswell because the forces between molecules increase due to multiple hydrogen bonding/ increased dispersion forces, and this makes the molecules draw more closely to one another.

[nhmn0301]

I'm pre sure density increases aswell because the forces between molecules increase due to multiple hydrogen bonding/ increased dispersion forces, and this makes the molecules draw more closely to one another.

Yeah, thanks for adding !

[Blondie21]

What exactly is the chemical shift in NMR?
In a compound, how would I know where to put each peak (whether C-13/H1 NMR) along the horizontal axis with the chemical shift(ppm) on it?
I heard it was something to do with electronegativity or polarity of the different chemical environments of the compound..

help would be appreciated!

Thanks!

Mmm well you have to have a pretty good understanding of the background information of NMR. However, I have never come across a questions which asks to literally place a peak onto an NMR spectrum! The questions you will normally recieve would have something to do with identifying what the molecule is.

You are right when you say it has something to do with electronegativity. BUT YOU DO NOT NEED TO KNOW THIS. THIS IS ONLY FOR YOUR UNDERSTANDING. From what I gather, we won't be asked to describe this background info at all.

The reason for the different chemical shifts depends on the 'shielding' of a nucleus and how 'exposed' it is. The energy from the radio waves cause the 'spinning' of electrons around each nucleus from the applied magnetic field. THe amount of nuclear shielding depends on other atoms surrounding the nucleus.

The chemical shift is basically the difference in energy needed to change the spin state compared to TMS.

Sooo back to electronegativity.. the more electronegative an atom is, the greater pull it will have from the other atoms .. decreasing the shielding.. leaving it more exposed and .:. allowing it to have a greater chemical shift

Like the hydrogen in -CH3- will absorb at a different rate than the hydrogen in -CH2- because of the different electronegiativity and thus the 'shielding'

CH2     CH3      TMS

That is normally the order ^^^^ (LMAO worst NMR ever). As you can see, the CH2 requires more energy to 'spin' because it is more 'exposed' as the electronegativity is greater

We add TMS as the reference sample because all the protons are in the same chemical enviro and will need the smallest chemical shift becuase it is the least 'exposed' ... because TMS is surrounded by CH3



Would love it if someone could please read over that and check my understanding. Thanks

[Yacoubb]

What effect does having a COOH group have on the physical and chemical properties of carbon compounds.
The only one I know it that it increases solubility. 

The presence of a carboxyl (COOH) group in a compound gives it the ability to form hydrogen inter-particle bonds with water molecules. Thus, compounds with a carboxyl group will have increased solubility in water. With that, increases the melting and boiling point of the compound. The reason is because more energy is required to disturb the stronger hydrogen bonds that exist between the molecules of water and the carboxylic acid molecules, and thus, the temperature at which the compound boils/is melted increases. Also, decreased volatility. Because the hydrogen inter-particle bonds require more energy to disrupt, the compound cannot turn to a gaseous state as easily. Hence, the decreased volatility.

Chemically, it is an acid, and come all the chemical properties of acids with that, including pH<7, it being a proton donor, etc.

[Jawnle]

Hey guys, just want some opinions on whether it'd be better to go to the TSFX Chem Unit 3 revision and extension lecture, or the Unit 4 head start?

[Yacoubb]

Hey guys, just want some opinions on whether it'd be better to go to the TSFX Chem Unit 3 revision and extension lecture, or the Unit 4 head start?

If you can, both! I think U3 revision is excellent because you can consolidate everything + add any information to your knowledge bank that'll assist you for the exam. Unit 4 headstart is exactly as it sounds - it is essentially a head start to U4 and gives you a general outlook of the entire unit 4 chem course before you actually start it. I'd also go to Exam revision lectures at the end of the year. Any loose ends of your knowledge can be tied up and you'll be set for the exam.

If, however, you must choose, I'd go U3 revision and then U4 revision toward the end of the year.