Aqa chem 4/ chem 5 june 2016 thread

you know the polypeptide q with the zig zag thing? how did u guys do that? did u leave trailing bonds as a repeating unit or draw a dipeptide?

trailing as it asked for a section of it

18:30- Updated- Version 2

18:12 Attempting version 1 of the unoffical mark scheme, will keep quoting this for others to see, may even start a thread. Please contribute i will update frequently before i start studying for my bio exam day after tomorrow heh rip

Misc: tell me where these go!!!

Equation representing ethanoic acid as a base with nitric acid:
CH3COOH + HNO3 -> CH3CO+NO3- + H2O

Identify what reagents are needed to distinguish between the two chlorine molecules, incl. observation. (Acyl chloride vs haloalkane (?))
Reagent: water/AgNO3 (?)/named carbonate
Observation: HCl fumes/White ppt./Effervescence -for the acyl chloride.

Which Nitrogen acts as a stronger base a vs. b (where a is attached to the benzene, and b is a tertiary amine) and why?
Nitrogen b due to the positive inductive effect of the carbons on the nitrogen, therefore making the lone pairs more available. Consequently nitrogen a is joined to a benzene so the lone pair delocalises into the benzene ring.

Order of reactions:
D 1
E 2

What is a racemic mixture?
Mixture containing equal quantities of each enantiomer.

How to distinguish between the two:
Expose to plane polarised light, rotates in opposite directions

Chiral Carbon relationship:
They are both mirror images of each other/enantiomers.

4.
Electrophile structure: CH3C(+)O

Reaction mechanism:
Arrow from benzene ring to C+ in CH3C(+)O, then arrow from hydrogen attached to the same carbon as the CH3CO back into the incomplete benzene ring (from carbon 1-4 i believe).

5. Can't remember exact questions, let me know i'll update ! =)
Notes:
Zwitterions have R-N(+)H3 and a COO-
Hydrogen bond between two amino acids: presumably show any partial bond from one hydrogen on one amino acid to either the nitrogen or oxygen on the other.
Dipeptides- essentially amides formed from 2 amino acids.

Advantage of using the polyester suture rather than the polyalkene?
the ester bond in polyester can hydrolyse whereas polyalkene C-C, C-H bonds are too strong thus cannot. Therefore the former can dissolve naturally whereas the former would require manual removal.

7. Conc. Of propanone increases by 100, What is the new rate equation and explain pls:
rate = k[H+]Due to the large excess of propanone, it is no longer affecting the rate as only the H+ concentration limits the speed at which the reaction proceeds.

Why is the initial rate of the reaction used to determine the order of the reactants rather than at any other point during the reaction? Or something
Initial rate takes into account the initial concentration of the reactants which is more accurate since, as the reaction proceeds the concentrations of the different species change. (?)

How do you calculate the initial rate of the reaction from a graph of concentration against time?
Calculate the gradient of the tangent to the slope. (?)

8. Organic synthesis to produce the branched primary amine:
Structure: Same as previous however Br is substituted with CN
Step 3: KCN w/ ethanol (?)
Step 4: H2/Ni, LiAlH4

Question 9 Notes (I don't even need to say the question, everyone knows this question by the number... eek)
Potassium dichromate turns green, either a primary or secondary alcohol, or aldehyde
O-H absorption in the Mass spec
O-H in NMR spectrum, singlet obvs
CH3-O present in NMR spectrum, singlet
RCH2 in NMR spectrum, triplet ?
R(CH3)2 in NMR spectrum, doublet ? uh pls halp don't remember values

Why is the initial rate of the reaction used to determine the order of the reactants rather than at any other point during the reaction?

I swear this question was 'why was initial concentration used to calculate the initial rate of reaction'
But i think its because the concentration of reactants decreases as the reaction progresses so using initial conc. Is more accurate

How do you calculate the initial rate of the reaction from a graph of concentration against time?
The gradient of the line when t=0

8. Organic synthesis to produce the branched primary amine:Structure: Same as previous however Br is substituted with CNStep 3: KCN w/ ethanol and also refluxStep 4: H2/Ni; with high pressure or LiAlH4 with dilute h2so4

you know the polypeptide q with the zig zag thing? how did u guys do that? did u leave trailing bonds as a repeating unit or draw a dipeptide?

Hold on, shouldn't be CH3COOH + HNO3 > CH3COOH2+ + NO3-

To act as a base it must accept a proton, so it accepts a proton from the HNO3 to become a conjugate acid.

I've seen a similar principle before:

Identify the conjugate acid/base pair:
a) CH₃COOH(aq)+ HClO₄(aq) == CH₃COOH₂⁺(aq) + ClO₄^-(aq)
(Taken from http://www.a-levelchemistry.co.uk/AQA%20Chemistry/AQA%20A2%20Chemistry/Unit%204/4.3%20Acids%20and%20Bases/4.3%20Exercise%201%20-%20%20Bronsted-Lowry%20theory.doc)

I did it as a dipeptide, not sure if this is right though!

Hold on, shouldn't be CH3COOH + HNO3 > CH3COOH2+ + NO3-

To act as a base it must accept a proton, so it accepts a proton from the HNO3 to become a conjugate acid.

I've seen a similar principle before:

Identify the conjugate acid/base pair:
a) CH₃COOH(aq)+ HClO₄(aq) == CH₃COOH₂⁺(aq) + ClO₄^-(aq)
(Taken from http://www.a-levelchemistry.co.uk/AQA%20Chemistry/AQA%20A2%20Chemistry/Unit%204/4.3%20Acids%20and%20Bases/4.3%20Exercise%201%20-%20%20Bronsted-Lowry%20theory.doc)

Did it not ask for it as a dipeptide?


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For initial rate I said that as the reaction progresses, the concentration of reactants decreases
Hence initial rate is when time = 0 where the initial concentration of reactants is known so you can find the initial rate at this time

Initial rate is calculated using the initial rate method;
Draw a tangent to the curve when time = 0
Gradient at this point = initial rate for that reactant

yeah i think it did

I said at the start - the rate of reaction is the fastest - over time- the concentration of the reactants will decrease so the change will be small? Got it wrong phahah

18:30- Updated- Version 2

18:12 Attempting version 1 of the unoffical mark scheme, will keep quoting this for others to see, may even start a thread. Please contribute i will update frequently before i start studying for my bio exam day after tomorrow heh rip

Misc: tell me where these go!!!

Equation representing ethanoic acid as a base with nitric acid:
CH3COOH + HNO3 -> CH3CO+NO3- + H2O

Identify what reagents are needed to distinguish between the two chlorine molecules, incl. observation. (Acyl chloride vs haloalkane (?))
Reagent: water/AgNO3 (?)/named carbonate
Observation: HCl fumes/White ppt./Effervescence -for the acyl chloride.

Which Nitrogen acts as a stronger base a vs. b (where a is attached to the benzene, and b is a tertiary amine) and why?
Nitrogen b due to the positive inductive effect of the carbons on the nitrogen, therefore making the lone pairs more available. Consequently nitrogen a is joined to a benzene so the lone pair delocalises into the benzene ring.

Order of reactions:
D 1
E 2

What is a racemic mixture?
Mixture containing equal quantities of each enantiomer.

How to distinguish between the two:
Expose to plane polarised light, rotates in opposite directions

Chiral Carbon relationship:
They are both mirror images of each other/enantiomers.

4.
Electrophile structure: CH3C(+)O

Reaction mechanism:
Arrow from benzene ring to C+ in CH3C(+)O, then arrow from hydrogen attached to the same carbon as the CH3CO back into the incomplete benzene ring (from carbon 1-4 i believe).

5. Can't remember exact questions, let me know i'll update ! =)
Notes:
Zwitterions have R-N(+)H3 and a COO-
Hydrogen bond between two amino acids: presumably show any partial bond from one hydrogen on one amino acid to either the nitrogen or oxygen on the other.
Dipeptides- essentially amides formed from 2 amino acids.

Advantage of using the polyester suture rather than the polyalkene?
the ester bond in polyester can hydrolyse whereas polyalkene C-C, C-H bonds are too strong thus cannot. Therefore the former can dissolve naturally whereas the former would require manual removal.

7. Conc. Of propanone increases by 100, What is the new rate equation and explain pls:
rate = k[H+]Due to the large excess of propanone, it is no longer affecting the rate as only the H+ concentration limits the speed at which the reaction proceeds.

Why is the initial rate of the reaction used to determine the order of the reactants rather than at any other point during the reaction? Or something
Initial rate takes into account the initial concentration of the reactants which is more accurate since, as the reaction proceeds the concentrations of the different species change. (?)

How do you calculate the initial rate of the reaction from a graph of concentration against time?
Calculate the gradient of the tangent to the slope. (?)

8. Organic synthesis to produce the branched primary amine:
Structure: Same as previous however Br is substituted with CN
Step 3: KCN w/ ethanol (?)
Step 4: H2/Ni, LiAlH4

Question 9 Notes (I don't even need to say the question, everyone knows this question by the number... eek)
Potassium dichromate turns green, either a primary or secondary alcohol, or aldehyde
O-H absorption in the Mass spec
O-H in NMR spectrum, singlet obvs
CH3-O present in NMR spectrum, singlet
RCH2 in NMR spectrum, triplet ?
R(CH3)2 in NMR spectrum, doublet ? uh pls halp don't remember values

Keep doubting myself even over the seemingly easy questions, this is too much stress 😂


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Hi thank you for doing this! if possible could you add in the marks for the questions so i can estimate how badly i did.. also i dont remember a question about how to distinguish between enantiomers?? Did i miss this??

Wait did they ask us how to distinguish between the enantiomers because I didn't see that?Posted from TSR Mobile