Chemistry 3/4 2013 Thread

[brightsky]

draw 2-3-dibromobutane and you shall see. note the symmetry of the molecule. the spectrum suggests that there should be 4 different carbon environments. are there 4?

[Jaswinder]

draw 2-3-dibromobutane and you shall see. note the symmetry of the molecule. the spectrum suggests that there should be 4 different carbon environments. are there 4?

since its symmetrical would there only be 2 peaks or 1 peak? 

[Dismounted]

since its symmetrical would there only be 2 peaks or 1 peak? 

2,3-dibromobutane would have two peaks on C-13 NMR. One for the two middle carbons attached to a bromine, and one for the outside carbons with three hydrogens attached.

[Scooby]

Is it possible to use TLC for quantitative analysis?

How do we convert between wavelength and wavenumber?

Does an amino group necessarily have to be -NH₃? Is the principal functional group in a secondary or tertiary amine also considered an amino group?

Do we need to know how to work with titrations involving polyprotic acids?

Why is HPLC more suitable for analysing caffeine content in drinks than GLC (this has come up a surprising amount)? Since the M of caffeine is less than 300 g/mol, why isn't GLC more appropriate?

If we've got an Hg hollow cathode lamp in AAS, will elements other than Hg in the sample also absorb the light emitted to some extent?

Thanks

[clıppy]

Just a quick question to those who have done the 2013 STAV paper. Do you feel like it was a fair exam, how did you go? Or do I just need to really brush up on my skills?

[Jeggz]

I felt okay overall, but there were certainly a few questions which I should've been prepared for :\

[psyxwar]

How do we convert between wavelength and wavenumber?

Isn't wavenumber just 1/wavelength? o.o

[Jeggz]

Isn't wavenumber just 1/wavelength? o.o

Yeaaap.

[teletubbies_95]

Just a quick question to those who have done the 2013 STAV paper. Do you feel like it was a fair exam, how did you go? Or do I just need to really brush up on my skills?

We did that as our trial and the average was 50%

I thought it was not too bad , but it told us what we were bad at and for me it was calorimetry ( which i hate so much)

DAT weird organic chemistry question ...WTF.

[Jeggz]

We did that as our trial and the average was 50%

I thought it was not too bad , but it told us what we were bad at and for me it was calorimetry ( which i hate so much)

DAT weird organic chemistry question ...WTF.

Which organic question?

[neonperson]

Just a quick question to those who have done the 2013 STAV paper. Do you feel like it was a fair exam, how did you go? Or do I just need to really brush up on my skills?

I did it during the term 3 holidays as our mock and got 74/124. . .

but I feel like it was a fair paper though my teacher said it wasn't easy.

@teletubbies_95 - heh. we go to the same school.

[lolipopper]

hey guys, how is a 113/120 for the 2013 CSE paper. Im also rank 1 at school. Made some really stupid mistakes, but its all for the good.

[Dismounted]

Is it possible to use TLC for quantitative analysis?

You'll see certain textbooks/notes that say yes - by "scraping off" the dot of the sample. It's a bit far-fetched... But is a technique nonetheless. I would largely stick with qualitative "only" though.

Do we need to know how to work with titrations involving polyprotic acids?

Yes. It's exactly the same, except the neutralisation formula changes slightly with different mole ratios.

Why is HPLC more suitable for analysing caffeine content in drinks than GLC (this has come up a surprising amount)? Since the M of caffeine is less than 300 g/mol, why isn't GLC more appropriate?

Both techniques should be suitable, barring any other information given in the stimulus. However, HPLC could possibly give a higher resolution of data. Is there any specific question you can point us to?

If we've got an Hg hollow cathode lamp in AAS, will elements other than Hg in the sample also absorb the light emitted to some extent?

No, not at all. This is a case where's it's clear cut. For more detail, you'll have to study physics. But what you need to know is that each element has unique electron energy levels, and these differ between elements. It is this that gives rise to unique emitted/absorbed wavelengths.

[lzxnl]

Just a quick question to those who have done the 2013 STAV paper. Do you feel like it was a fair exam, how did you go? Or do I just need to really brush up on my skills?

My school did that exam as a mock exam too. I think it was a fair exam; I messed up several questions on that exam, which was quite annoying, and it was nice that there was that one question there (lol the organic) that made people think.

hey guys, how is a 113/120 for the 2013 CSE paper. Im also rank 1 at school. Made some really stupid mistakes, but its all for the good.

Don't make those silly mistakes and you'll be fine. You know how well you know your stuff better than we do

[Scooby]

Q8 from VCAA Exam 2 2008

Why does H₂PO₄^- move towards the anode?

And the hydrogen ions would migrate towards the cathode, right (since they're consumed there)?