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Aqa chem 4/ chem 5 june 2016 thread

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http://filestore.aqa.org.uk/subjects/AQA-CHEM4-W-QP-JUN10.PDF

4b anyone?!!
Original post by dnan
Very likely it comes up, not likely that it is over 5 marks worth on it.

Mobile phase, Stationary phase, what the solvent does, . How it distinguishes. Different types.


cud u answer the questions: what the solvent does
why is it used
How it distinguishes. Different types
http://filestore.aqa.org.uk/subjects/AQA-CHEM4-QP-JAN13.PDF question 2cii why do they not divide by the total volume here to make it concentration?????????

http://filestore.aqa.org.uk/subjects/AQA-CHEM4-W-MS-JAN13.PDF MS
Original post by nutcase13
Im not sure if this is the "official" rule but i've noticed that when it is singular you leave out the e, but when it is dioc/dione/diol you use the e


If its a vowel or two fuctional groups... leave the e.

If its anything else - remove the e.
Original post by ssamarai
http://filestore.aqa.org.uk/subjects/AQA-CHEM4-QP-JAN13.PDF question 2cii why do they not divide by the total volume here to make it concentration?????????

http://filestore.aqa.org.uk/subjects/AQA-CHEM4-W-MS-JAN13.PDF MS


You still get the same answer :smile:

if you add 5cm3 - thats 0.005. So adding that value to 1dm3 gives you 1.005- so your value doesnt change much :smile:
Original post by ssamarai
http://filestore.aqa.org.uk/subjects/AQA-CHEM4-QP-JAN13.PDF question 2cii why do they not divide by the total volume here to make it concentration?????????

http://filestore.aqa.org.uk/subjects/AQA-CHEM4-W-MS-JAN13.PDF MS


You can do that. Should give the same answer if you find the conc of each in the total volume. They didn't do it because it's just a longer calcuation.
Original post by ssamarai
http://filestore.aqa.org.uk/subjects/AQA-CHEM4-QP-JAN13.PDF question 2cii why do they not divide by the total volume here to make it concentration?????????

http://filestore.aqa.org.uk/subjects/AQA-CHEM4-W-MS-JAN13.PDF MS


I think a similar question was asked in the thread earlier, but you don't have to divide by the volume as V cancels in [HA]/[A-]. If you do calculate the concentration you should get the same answer as you would with using moles.
Original post by Signorina


The molecular formula of TCDD is C12H4O2Cl4Chlorine exists as two isotopes 35Cl (75%) and 37Cl (25%).Deduce the number of molecular ion peaks in the mass spectrum of TCDD andcalculate the m/z value of the most abundant molecular ion peak.

So we're looking at Cl which has two Isotopes 35,(75%) and 37 (25%)

So it Could be the Mr of C12H4O2 + 35 + 35 + 35+35
Or 37 + 37 + 37 +37
Or 37+37+35+35
Or 37+35+35+35
Or 35+37+37+37

Could be any combination of isotopes, 5 peaks formed
M/z of most abundant ion peak (35 is 75% abundant so) you would add Mr of C12H14O2 to (4X35) which gives you 320.0

Hope that helps!
Original post by ssamarai
http://filestore.aqa.org.uk/subjects/AQA-CHEM4-QP-JAN13.PDF question 2cii why do they not divide by the total volume here to make it concentration?????????

http://filestore.aqa.org.uk/subjects/AQA-CHEM4-W-MS-JAN13.PDF MS


When you get the final moles for the weak methanoic acid and its salt by adding/ minus from the moles of H+ added, you divide by the total volume which is 1.005 since 5cm3 is turned to dm3 and added to 1dm3 so just divide by one.
There are five different combinations of molecular ions as there are two different isotopes of chlorine which surround the benzene rings. You could have 4 Cl-35, 4 Cl-37, 2 Cl-35 and 2 Cl-37, 3 Cl-35 and 1 Cl-37, 3 Cl-37 and 1 Cl-35. So there will be five different molecular ion peaks. It sounds confusing but it helps if you draw it out! Hope this helps
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idk97
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I have a feeling theyre gonna throw in some annoying how science work questions that we dont expect
Original post by sockface
cud u answer the questions: what the solvent does
why is it used
How it distinguishes. Different types

The solvent is the mobile phase (e.g. of column, tlc and paper) A compound dissolves in it depending on it's solubility (solvent is often polar). This allows the compound to move through the column / up the paper/glass

Distinguishes: In TLC and Paper retention factor is calculated and compared to known factors, allowing compounds (esp. amino acids) to be identified,
In column the retention time (time to leave the column once inserted) is measured and compared to known values.

Gas Liquid Chromatography depends on each compounds adsorption to the carrier gas (N2) and so allows compounds to be separated and retention time is calculated. Retention times can often be similar in similar compounds so GLC machines are often paired with mass spec/ IR to allow further analytic techniques to occur.
I'm preparing myself for a chromatography question. Last years paper was so nice but they literally asked all the questions I wanted so doubt we'll see them. I hope they leave out the nmr spectra questions and just make us draw the compounds from the formula and little facts they give.
The specification only mentions column and GLC so do we not need to know paper and thin layer?
Original post by Mriffin
The solvent is the mobile phase (e.g. of column, tlc and paper) A compound dissolves in it depending on it's solubility (solvent is often polar). This allows the compound to move through the column / up the paper/glass

Distinguishes: In TLC and Paper retention factor is calculated and compared to known factors, allowing compounds (esp. amino acids) to be identified,
In column the retention time (time to leave the column once inserted) is measured and compared to known values.

Gas Liquid Chromatography depends on each compounds adsorption to the carrier gas (N2) and so allows compounds to be separated and retention time is calculated. Retention times can often be similar in similar compounds so GLC machines are often paired with mass spec/ IR to allow further analytic techniques to occur.

thnx
Original post by emma_1111
The specification only mentions column and GLC so do we not need to know paper and thin layer?


Yeah its not in the book either... I have some random notes about RF values though but if the spec explicitly states GLC and column and not the other two then I would assume that means we don't need to know it.
Ohhh... Gosh I'd never get that in the exam haha, good thing it's only few marks ! Thank u both!
Original post by katied98
There are five different combinations of molecular ions as there are two different isotopes of chlorine which surround the benzene rings. You could have 4 Cl-35, 4 Cl-37, 2 Cl-35 and 2 Cl-37, 3 Cl-35 and 1 Cl-37, 3 Cl-37 and 1 Cl-35. So there will be five different molecular ion peaks. It sounds confusing but it helps if you draw it out! Hope this helps


Original post by hopingmedicinae
The molecular formula of TCDD is C12H4O2Cl4Chlorine exists as two isotopes 35Cl (75%) and 37Cl (25%).Deduce the number of molecular ion peaks in the mass spectrum of TCDD andcalculate the m/z value of the most abundant molecular ion peak.

So we're looking at Cl which has two Isotopes 35,(75%) and 37 (25%)

So it Could be the Mr of C12H4O2 + 35 + 35 + 35+35
Or 37 + 37 + 37 +37
Or 37+37+35+35
Or 37+35+35+35
Or 35+37+37+37

Could be any combination of isotopes, 5 peaks formed
M/z of most abundant ion peak (35 is 75% abundant so) you would add Mr of C12H14O2 to (4X35) which gives you 320.0

Hope that helps!
Can someone explain 5ci. Why don't you produce a carboxylic acid?
Original post by Manexopi
I'm preparing myself for a chromatography question. Last years paper was so nice but they literally asked all the questions I wanted so doubt we'll see them. I hope they leave out the nmr spectra questions and just make us draw the compounds from the formula and little facts they give.


I agree, last year's paper was lovely - surprisingly, the grade boundary for 120 UMS was the lowest it's ever been (92/100).

nmr is ok if you take care and don't jump to conclusions in your explanations!
Original post by Super199
Can someone explain 5ci. Why don't you produce a carboxylic acid?


5ci from what?

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