Unit 3 Questions MEGATHREAD :)

[ulbasour]

Question:

I was UNder the impression GC and HPLC can be used for QUANTITATIVE analaysis by determine relative peak areas, hence allowing you do determine % concentration

On an exam i did the answer said to use a calibration curve, and use standard solutions etc, for the samples Rt, under analysis

Can anyone clear this up?

[david10d]

Question:

I was UNder the impression GC and HPLC can be used for QUANTITATIVE analaysis by determine relative peak areas, hence allowing you do determine % concentration

On an exam i did the answer said to use a calibration curve, and use standard solutions etc, for the samples Rt, under analysis

Can anyone clear this up?

Yep, correct.

You just plot a calibration curve with standards and then compare with your solution.

[Water]

When describing HNMR.



Is it possible to say that HNMR allows the identification of the basic backbone of an organic compound?

And can Infrared POSSIBLY be used for quantitative analysis.

On your first question, it isn't the best method without supplementary information from MS or IR.

And i don't think so for IR

I was asking if my definition for it was apprioriate? lol ):

[ulbasour]

When describing HNMR.



Is it possible to say that HNMR allows the identification of the basic backbone of an organic compound?

And can Infrared POSSIBLY be used for quantitative analysis.

On your first question, it isn't the best method without supplementary information from MS or IR.

And i don't think so for IR

I was asking if my definition for it was apprioriate? lol ):

Ah my bad... Probably would say "HNMR is used in identifying Hydrogen environments in a compound."

[ulbasour]

Question:

I was UNder the impression GC and HPLC can be used for QUANTITATIVE analaysis by determine relative peak areas, hence allowing you do determine % concentration

On an exam i did the answer said to use a calibration curve, and use standard solutions etc, for the samples Rt, under analysis

Can anyone clear this up?

Yep, correct.

You just plot a calibration curve with standards and then compare with your solution.

But why doesn't the peak area suffice?

[chemkid_23]

what would a 70% on vcaa 2009 have gotten me?

[luken93]

what would a 70% on vcaa 2009 have gotten me?

http://www.vcaa.vic.edu.au/vce/statistics/2009/section3/vce_chemistry_ga09.pdf

[mickeymouse]

do hydrogen bonds exist between alcohol molecules so there are no dispersion forces?

[luken93]

do hydrogen bonds exist between alcohol molecules so there are no dispersion forces?

Nah, there are dispersion forces as well, but they're nothing in comparison to hydrogen bonding.
Take a look at the boiling point of Ethane vs Ethanol for proof.

[azure]

Question regarding KBT exam question 2d)
Does erucic acid (C66 H126 O6) have any carbon-carbon double bonds? If so, how many?
Working out the no. of double bonds with DBE = 66 - 126/2 + 1 = 4
Therefore there are 3 C=C double bonds and one C=O double bond.

However, the answers work with the empirical formula of euric acid.
Working with DBE again but with the empirical formula would give 2 --> One C=C double bond and one C=O double bond?...

Question is... to work out the number of double bonds, do we use the empirical formula or the molecular formula? Because they'll give different answers....

Edit: Oops, forgot that there are 6 oxygens in the molecular formula of erucic acid.. does that mean there are 3 C=O? Hence one C=C double bond?

If so, that works out right.... hm.

[homosapiens]

About using IR for quantitative analysis, if there are two C=O bonds, will the transmittance be double? Or do we not have to know this...

[chemkid_23]

how do u read the grade distributions???

[luken93]

how do u read the grade distributions???

First page is the Unit 3 Exam
Second page is your SACs
Third page is Unit 4 Exam.

The distributions represent how many marks were needed to attain a particular grade, ie 57/73 was needed for an A+ in 2009.
Exams are marked twice, hence why they are out of 146.

[chemkid_23]

LOL ok thanks for that
i was wondering why it was out of 146

[RobM8]

Question regarding KBT exam question 2d)
Does erucic acid (C66 H126 O6) have any carbon-carbon double bonds? If so, how many?
Working out the no. of double bonds with DBE = 66 - 126/2 + 1 = 4
Therefore there are 3 C=C double bonds and one C=O double bond.

However, the answers work with the empirical formula of euric acid.
Working with DBE again but with the empirical formula would give 2 --> One C=C double bond and one C=O double bond?...

Question is... to work out the number of double bonds, do we use the empirical formula or the molecular formula? Because they'll give different answers....

Edit: Oops, forgot that there are 6 oxygens in the molecular formula of erucic acid.. does that mean there are 3 C=O? Hence one C=C double bond?

If so, that works out right.... hm.

C66 H126 O6 is three euric acid molecules --> one euric acid molecule is then C22 H42 O2 which is the same as C21H41COOH
using CnH2n+1COOH --> there is one C=C bond in euric acid.
I wouldn't use DBE in this case as it needs an extra step to get rid of any C=O bonds you have calculated which you can forget to remove.