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    Sorry for double post.
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    (Original post by Mus1995)
    Zwitterions are the dipolar ionic form of amino acids. They occur at the isoelectric point of the specified amino acid. At the isoelectric point (pH the Zwitterion occurs) you need to consider the amine and carboxyl group attached to the same carbon. The carboxyl group can act as an acid and donate a proton (H+ from O(delta-) - H(delta+) to the base amine group NH2. The Nitrogen has a lone pair of electrons so it can accept a proton to form a new covalent bond. (Acting as a base) Overall a Zwitterion has no charge as the single positive and single negative charge present in the molecule cancel out.

    So you end up with NH3+ and COO-. The positive charge on NH3 can also be written above the N.

    Now you have your Zwitterion you can move on to what happens at pH's above and below the isoelectric point. In questions there may be more than one carboxyl/amine group. These will exist in the R group, correct? As an a-amino acid is R - CH(NH2)COOH. So in the R group you may have HOOC- CH2NH2 -.

    Now that you understand that for the Zwitterion at the isoelectric point you only consider the carboxyl and amine group from the main part of the amino acid and not the R group, lets see what happens when we increase the pH to above the isoelectric point. This adds OH- (ie alkaline conditions) What this does is remove H+. So take ALL carboxyl groups (including the ones in R) and remove H+ from COOH to get COO- on all of them. You also remove the H+ from the NH3+ you had at the isoelectric point. This results in NH2 and COO- across the board.

    At a pH below the isoelectric point you introduce acidic conditions, so add H+ across all groups including R. Amine groups accept the protons and form NH3+. Carboxyl groups in R already have -OH. But the carboxyl group from the Zwitterion is COO- so can accept a proton. Forming COOH and NH3+ across the board.

    TLDR; pH below IP? Add H+. pH above IP? Remove H+.

    Different IP's (Isoelectric points) occur due to different R groups. This affects the amount of VDW forces and the polarity of the molecule. As a longer molecule has more electrons so more VDW. However it is less polar (as the polar part is COOH) so it's hydrogen bonds are weaker. These factors affect the pH.



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    I see! Thank you.

    In conclusion Isoelectric point is almost like a Base, where it sits comfortably as a Zwitterion. This is determined by the R group.

    Then whether you go above or below means excess H+ or less OH-

    Not to sure about the Van der Walls stuff though.

    Just working my way through all these topic booklets. Only of the Second one, but surprisingly the mistakes I'm making are from stuff outside the syllabus or AS Stuff. Surprised I've remembered so much.

    My style of learning has changed dramatically. I'm no longer reading the book before I do questions, which has turned Chem 4 into Maths.

    Remaining ideally I need to do around 6 of these today! Then move onto Chem 5 and Phys 5 revision.

    Amines (Done)
    Amino Acids (Done)
    Carboxlyic Acids & Esters
    Spectroscopy
    Arenes
    Synthesis
    Polyesters & Polyamides
    Carbonyl Compounds
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    Can someone please explain why to show Cis-Trans Stereoisomerism the C=C Carbon-Carbon Double bond CANNOT have two of the same groups attached to one of the Carbons.

    I do not understand this.

    Is there a difference between E-Z and Cis Trans.
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    (Original post by Better)
    Can someone please explain why to show Cis-Trans Stereoisomerism the C=C Carbon-Carbon Double bond CANNOT have two of the same groups attached to one of the Carbons.

    I do not understand this.

    Is there a difference between E-Z and Cis Trans.
    EZ occurs when both Carbons have one of the same atoms.

    Eg:

    H-C=C-H

    Then you can have any other groups attached to each Carbon and it will show EZ isomerism on the basis of E (means Engagen which is Against) so the Hydrogens are on opposite sides. Like Trans isomerism.

    Or it can be Z (ze zame side is how I remember it ie the same side) so this is where the Hydrogens are adjacent each other ie both are at the top. Like Cis isomerism.

    Replace Hydrogen with any atom/molecule. As long as they are the same it will show EZ.

    Cis Trans occurs when all 4 groups on C=C are DISTINCT. That's about the only difference really. Hope this helps.


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    (Original post by Mus1995)
    EZ occurs when both Carbons have one of the same atoms.

    Eg:

    H-C=C-H

    Then you can have any other groups attached to each Carbon and it will show EZ isomerism on the basis of E (means Engagen which is Against) so the Hydrogens are on opposite sides. Like Trans isomerism.

    Or it can be Z (ze zame side is how I remember it ie the same side) so this is where the Hydrogens are adjacent each other ie both are at the top. Like Cis isomerism.

    Replace Hydrogen with any atom/molecule. As long as they are the same it will show EZ.

    Cis Trans occurs when all 4 groups on C=C are DISTINCT. That's about the only difference really. Hope this helps.


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    Your Chemical knowledge is brilliant! I hope I can get to your level by the time Chem 4 comes around.

    Unless your a Teacher of course Then err ... that would take a while
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    (Original post by Better)
    I see! Thank you.

    In conclusion Isoelectric point is almost like a Base, where it sits comfortably as a Zwitterion. This is determined by the R group.

    Then whether you go above or below means excess H+ or less OH-

    Not to sure about the Van der Walls stuff though.

    Just working my way through all these topic booklets. Only of the Second one, but surprisingly the mistakes I'm making are from stuff outside the syllabus or AS Stuff. Surprised I've remembered so much.

    My style of learning has changed dramatically. I'm no longer reading the book before I do questions, which has turned Chem 4 into Maths.

    Remaining ideally I need to do around 6 of these today! Then move onto Chem 5 and Phys 5 revision.

    Amines (Done)
    Amino Acids (Done)
    Carboxlyic Acids & Esters
    Spectroscopy
    Arenes
    Synthesis
    Polyesters & Polyamides
    Carbonyl Compounds
    Yeah. By base do you mean a foundation from which you can do stuff with it? It is not literally a base (proton acceptor)

    Going above or below adds or removes H+ from the complete structure (including R groups)

    Van der Walls relies on number of electrons. If R is a larger molecule there are more electrons so more VDW forces. Also because this makes the whole amino acid larger the polar part of the molecule (the carboxyl group) has less effect overall. This carboxyl group forms hydrogen bonds.

    I've done the exam quest booklets I think they are different. Could you send me the topic booklets and ill send you the exam quest? I need more questions to do so. exams quest is just relevant past paper questions from the old spec. Covers all the topics.

    You still should have read through the book and learnt everything. You need to fully understand the topics in order to apply them. But yeah the knowledge required is less than F325 but more precise and tedious.

    Good luck with your revision. and exams.


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    (Original post by Better)
    Your Chemical knowledge is brilliant! I hope I can get to your level by the time Chem 4 comes around.

    Unless your a Teacher of course Then err ... that would take a while
    Thank you. just keep asking me stuff if you need to. It's good for me to iterate my understanding too.

    Nah I am a student in year 13. First time doing these exams man. Uni in October. :P


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    (Original post by Mus1995)
    Yeah. By base do you mean a foundation from which you can do stuff with it? It is not literally a base (proton acceptor)

    Going above or below adds or removes H+ from the complete structure (including R groups)

    Van der Walls relies on number of electrons. If R is a larger molecule there are more electrons so more VDW forces. Also because this makes the whole amino acid larger the polar part of the molecule (the carboxyl group) has less effect overall. This carboxyl group forms hydrogen bonds.

    I've done the exam quest booklets I think they are different. Could you send me the topic booklets and ill send you the exam quest? I need more questions to do so. exams quest is just relevant past paper questions from the old spec. Covers all the topics.

    You still should have read through the book and learnt everything. You need to fully understand the topics in order to apply them. But yeah the knowledge required is less than F325 but more precise and tedious.

    Good luck with your revision. and exams.


    Posted from TSR Mobile
    Courtesy of Master Yi, just download the whole Zip.

    https://mega.co.nz/#F!VRNSXQIS!X7ocggad45hcTZ18TYJzYA

    Do you think the Exam Quest are worth doing then?

    Well yes, it seems small things catch me out. I.e. some of the legacy and real past papers have different Temperatures of Reactions etc etc.

    So I'm finding it difficult to allocate the correct Temperatures and Conditions to the correct reactions.

    Yes I am trying to go for an A* in Chemistry (YOLO), so need over 90% in Chem 5 and Chem 4 raw marks wise due to my ISA Result...

    My Teacher said he thinks if the Boundaries are around 90% for a Perfect UMS Score in Chem 5 then he thinks I can do it.

    But Chem 4 I'm re-doing got 49/60..... But come at me Chemistry.

    ANY HELP would be great though.
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    (Original post by Better)
    Courtesy of Master Yi, just download the whole Zip.

    https://mega.co.nz/#F!VRNSXQIS!X7ocggad45hcTZ18TYJzYA

    Do you think the Exam Quest are worth doing then?

    Well yes, it seems small things catch me out. I.e. some of the legacy and real past papers have different Temperatures of Reactions etc etc.

    So I'm finding it difficult to allocate the correct Temperatures and Conditions to the correct reactions.

    Yes I am trying to go for an A* in Chemistry (YOLO), so need over 90% in Chem 5 and Chem 4 raw marks wise due to my ISA Result...

    My Teacher said he thinks if the Boundaries are around 90% for a Perfect UMS Score in Chem 5 then he thinks I can do it.

    But Chem 4 I'm re-doing got 49/60..... But come at me Chemistry.

    ANY HELP would be great though.
    Thanks man. Exams Quest are worth doing ill send you them soon.

    The only temperatures we need to know are 50 degrees C for nitration of benzene and <10 degrees C for diatoziation and coupling reactions. Other conditions include hot aqueous acid/base under reflux for hydrolysis etc.

    Same. I got 137/150 in F325 in January. 36/40 Raw in F326 should get me 48/60 UMS. So I need 85/90 UMS in this for my A*. Basically full raw marks.


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    (Original post by Mus1995)
    EZ occurs when both Carbons have one of the same atoms.

    Eg:

    H-C=C-H

    Then you can have any other groups attached to each Carbon and it will show EZ isomerism on the basis of E (means Engagen which is Against) so the Hydrogens are on opposite sides. Like Trans isomerism.

    Or it can be Z (ze zame side is how I remember it ie the same side) so this is where the Hydrogens are adjacent each other ie both are at the top. Like Cis isomerism.

    Replace Hydrogen with any atom/molecule. As long as they are the same it will show EZ.

    Cis Trans occurs when all 4 groups on C=C are DISTINCT. That's about the only difference really. Hope this helps.


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    Its not a big deal and we won't be tested but you got it the other way round, cis/trans is actually when you have 2 of the same group on each carbon. E/Z is when you have 4 different groups and then you assign them by priority.


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    (Original post by D4rth)
    Its not a big deal and we won't be tested but you got it the other way round, cis/trans is actually when you have 2 of the same group on each carbon. E/Z is when you have 4 different groups and then you assign them by priority.


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    Sorry, you are right. Here is the page explaining it better than I did on chemguide: http://www.chemguide.co.uk/basicorg/isomerism/ez.html


    (Original post by Better)

    Do you think the Exam Quest are worth doing then?
    Download Exams Quest booklets here: http://speedy.sh/fAA6k/Exams-Quest.zip
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    Hey guys here are all the F324 past papers from January 2010 to January 2013, including mark schemes. Grade boundaries can be found online, enjoy! https://mega.co.nz/#!3dsFgShT!ddcKyD...9yvPMW9dIyVk4Q
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    (Original post by Mus1995)
    Hey guys here are all the F324 past papers from January 2010 to January 2013, including mark schemes. Grade boundaries can be found online, enjoy! https://mega.co.nz/#!3dsFgShT!ddcKyD...9yvPMW9dIyVk4Q
    Thanks, but the link doesn't work? Or is my computer just being weird?
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    (Original post by Lilmzbest)
    Thanks, but the link doesn't work? Or is my computer just being weird?
    It has worked for my computer just
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    (Original post by Lilmzbest)
    Thanks, but the link doesn't work? Or is my computer just being weird?
    You should use a good browser like Chrome to make sure it works. Click to agree to the license agreement and it should let you download it.

    -----------------------------------------------------------------------

    Hey guys I need help with a question on F324 January 2010. Question 5(d)(i).

    Basically you have Aspirin and Paracetamol, shown below:

    Name:  2.png
Views: 250
Size:  6.7 KB Name:  Paracetamol.png
Views: 468
Size:  9.5 KB

    It wants you to identify a reagent that will react with both. I opted for hydrolyzing both compounds with hot NaOH(aq). My answer is shown below.

    Name:  IMG_1873.jpg
Views: 1119
Size:  501.6 KB

    The mark scheme chooses to do something else, so hydrolysis is allowed in the extras bit, here: Name:  1.png
Views: 172
Size:  7.8 KB

    However if you read it, they want all the groups to change to COO-Na+ and O-Na+.

    Could someone explain how they have done it this way? This answer goes against my understanding of hydrolysis. My understanding is that with basic hydrolysis of esters a carboxylate salt and alcohol form. With basic hydrolysis of a protein/polypeptide the amine and carboxylate salt from. I'll read the book again to make sure.
    Attached Images
     
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    (Original post by Mus1995)
    You should use a good browser like Chrome to make sure it works. Click to agree to the license agreement and it should let you download it.

    -----------------------------------------------------------------------

    Hey guys I need help with a question on F324 January 2010. Question 5(d)(i).

    Basically you have Aspirin and Paracetamol, shown below:

    Name:  2.png
Views: 250
Size:  6.7 KB Name:  Paracetamol.png
Views: 468
Size:  9.5 KB

    It wants you to identify a reagent that will react with both. I opted for hydrolyzing both compounds with hot NaOH(aq). My answer is shown below.

    Name:  IMG_1873.jpg
Views: 1119
Size:  501.6 KB

    The mark scheme chooses to do something else, so hydrolysis is allowed in the extras bit, here: Name:  1.png
Views: 172
Size:  7.8 KB

    However if you read it, they want all the groups to change to COO-Na+ and O-Na+.

    Could someone explain how they have done it this way? This answer goes against my understanding of hydrolysis. My understanding is that with basic hydrolysis of esters a carboxylate salt and alcohol form. With basic hydrolysis of a protein/polypeptide the amine and carboxylate salt from. I'll read the book again to make sure.
    I don't see what you're asking... you have drawn it right.....
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    (Original post by master y)
    I don't see what you're asking... you have drawn it right.....
    I had a picture of it but I uploaded the wrong one. Read the image showing the what the mark scheme said VERY carefully. This is what it wants:

    Name:  ImageUploadedByStudent Room1370815798.398812.jpg
Views: 317
Size:  150.9 KB

    Here I have uploaded the correct one. Do you understand what they did? I understand how that can happen but hydrolysis is only concerned with breaking up the molecules. This confuses me.


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    (Original post by Mus1995)
    I had a picture of it but I uploaded the wrong one. Read the image showing the what the mark scheme said VERY carefully. This is what it wants:

    Name:  ImageUploadedByStudent Room1370815798.398812.jpg
Views: 317
Size:  150.9 KB

    Here I have uploaded the correct one. Do you understand what they did? I understand how that can happen but hydrolysis is only concerned with breaking up the molecules. This confuses me.


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    Heading to sleep now...bit late.

    But does anyone please have a Revision sheet of all the reactions and conditions??
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    (Original post by Lysipud)
    Does anyone have the mark scheme for January 2013 please?? Just finished the paper and can't blooming mark it!
    Has anyone got a copy of January 2013 paper or markscheme????
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    (Original post by Better)
    Has anyone got a copy of January 2013 paper or markscheme????
    I can put it on tonight if you want?


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