Nitrogen Compounds. Mark Scheme 4. Level. International A Level Subject. Chemistry Exam Board. CIE Topic. Sub-Topic Paper Type.

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Nitrogen Compounds

Mark Scheme 4

Level International A Level

Subject Chemistry

Exam Board CIE

Topic Sub-Topic

Paper Type Theory

Booklet Mark Scheme 4

Time Allowed:

Score:

77 minutes /64

Percentage: /100

Nitrogen Compounds

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1 (a) (i) E is CH₃CH(NH₂)CNCN (ii) C₆H₅CH₂CHOHO

[2]

(b) (i) a polymer/polypeptide of amino acids, (joined by peptide bonds)

(allow ‘chain of amino acids’ but not ‘sequence’: the idea of ‘many’ has to be conveyed) [1]

(ii)

HN

NH O

O

[1]

peptide bond shown in full (C=O) in an ala-ala fragment in a chain two repeat units

Allow peptide bond shown in full (C=O) in a dipeptide ala-ala for 1 mark

H₂N

NH O

O OH

[3]

(c) (i) HCl or H2SO₄ or NaOH or H⁺ or OH^– reagents [1]

+ heat and ₂O/aq (allow H₃O⁺).

If T is quoted, 80 ^oC < T < 120 ^oC. NOT warm. conditions [1]

(ii)

NH₂ CO₂H

and

CO2H H2N

HO₂C

(if a structural formula, it must have all H atoms) allow protonated or deprotonated

versions [1] + [1]

[max 3]

Dr. Asher Rana www.chemistryonlinetuition.com asherrana@chemistryonlinetuition.com

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(d) (i) NH₃⁺–CH(CH₃)–CO₂^– [1]

(ii)

ompound zw

compound

H₂N CO₂H H₃N CO₂

OH NHCH3

O NH2CH3

HO SO₂ NH2 O SO₂

NH₃

[3]

[4]

(e) (i) A buffer is a solution whose pH stays fairly constant or which maintains roughly the [1]

same pH or which resists/minimises changes in pH

when small/moderate amounts of acid/H⁺ or alkali/OH^– are added [1]

[1 (ii) NH₂CH(CH₃)CO₂H + H(Cl) →⁺NH₃CH(CH₃)CO₂H (+ Cl ^–)

(iii) blood contain HCO₃^– (or in an equation) [1]

which absorbs H⁺ or equn or absorbs OH^– or equn

H⁺ + HCO₃^–→ H2CO₃ (H₂O + CO₂)

OH^– + HCO₃^–→ CO32– + H₂O [1]

(iv) [CH₃CO₂Na] = 0.05 [CH₃CO₂H] = 0.075 [1]

pH = 4.76 + log (0.05/0.075) = 4.58 or 4.6 [1]

[7]

[Total: 19]

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(1)

(1 [2]

(1)

(1) [2]

[1]

N ( (1) (1) [3]

2 (a hydrogen bonding

diag: NH₂CH₂CH₂OH---OHCH₂CH₂NH₂ or NH2CH₂CH₂OH---NH₂CH₂CH₂OH (i.e. H-bond from OH group to either OH or NH₂)

(b) propylamine is more basic than phenylamine

because lone pair on N is delocalised over ring in phenylamine (so less available for protonation)

or the propyl group is electron-donating, so the lone pair is more available

(c) HOCH₂CH₂NH₂ + H⁺ → HOCH2CH₂NH₃⁺

or HOCH2CH₂NH₂ + HCl → HOCH2CH₂NH₃⁺Cl^– or HOCH2CH₂NH₂ + H₂O → HOCH2CH₂NH₃⁺OH^– (reaction with any acceptable Bronsted acid accepted)

(d)d) ( X is CH₃CH₂CN

(ii) step 1 is KCN in ethanol, heat [HCN negates]

step 2 is H₂+Ni / Pt or LiAlH₄ or Na in ethanol [NOT NaBH₄ or Sn/HCl]

(e) ethanolamine:

or or

effervescence / bubbles produced colour turns from orange to green purple colour disappears

or Na

Cr₂O₇^2–/ H⁺ MnO₄^–/ H⁺

PCl3 / PCl5 / SOCl2 (1) steamyfumes (1)

phenylamine:

Br₂(aq) decolourises / white ppt formed

or HNO2 / H⁺ at T<10^oC, then phenol in NaOH (1) coloured dye formed (1) [4]

[Total: 12]

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3

(2) [2]

(a) The amino acid is uncharged / neutral / a zwitterion or charges balance / are equal (NOT “is non-polar”)

It is equally attracted by the anode / + and the cathode / – or attracted by neither The pH of the buffer is at the isoelectric point/IEP of the amino acid any two

(b) (at pH 10), H₂NCH₂CO₂^–or NH2CH₂COO^– (1) [1]

(c)

amino acid relative size charge

A small(est) (1) ––v

B large(st) (3) ––v

C middle (2) ++v

(numbers are OK to show relative sizes)

Mark each row (3) [3]

(2) (1) (d) (i) lys – val – ser – ala – gly – ala – gly – asp

(ii) gly – ala – gly

(iii) aspartic acid (or lysine) (1) [4]

[Total: 10]

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4 (a (i) Disulfide bond / group / bridge (1) (ii) The tertiary structure (1)

(iii) The substrate will no longer bond to / fit into the active site (1)

or shape of active site is changed [3]

(b) (i) Acid-base / proton donor / neutralisation / salt formation (1)

(ii) The ability of the –CO2H group to form hydrogen bonds (1) and ionic interactions (1) The –CO2H/–CO2–

group is no longer able to interact with –NH2/–NH3+

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The Ag⁺ forms a strong bond with –COO^– (1) [5] max [4]

(c) (i) 8 but allow 4O2 if specified as molecules (1) (ii) Dative / co-ordinate (1)

(iii) Octahedral / 6 co-ordinate (1) [3]

[Total: 10]

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5 (a (i) I:

[1]

SOCl2 or PCl5 or HCl + ZnCl2 or PCl3 + heat or Cl2 + P + heat [NOT NaCl + H2SO₄]

(mention of aq negates mark)

II: NH₃ (ignore any conditions stated) [1]

(ii) nucleophilic substitution or S_N or S_N1or S_N2 [1 (iii) delocalisation of lone pair on Cl over benzene ring produces a stronger C-Cl bond [1]

[4]

(b)b) ( III: HNO₃ + H₂SO₄ [1]

[1 both conc., and at T < 60^oC

IV: Sn + conc HCl [NOT LiAlH4 or H₂ + Ni] [1]

[1]

(ii) III: electrophilic substitution

IV: reduction or redox [1]

[5]

(c) e.g. add bromine water or Br₂(aq) (a solvent is needed for the mark) [1]

or add UI solution

phenylamine decolorises the bromine or gives a white ppt., hexylamine does not [1]

or hexylamine turns UI blue, with phenylamine it stays green [2]

(d)

N N Cl N N

CH₃

CH₃ OH (allow + charge on either N)

(allow double or triple bond)