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Chemistry > Paper 4 Corrections > Flashcards

Paper 4 Corrections Flashcards

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1
Q

9701/42/M/J/23:
Explain why phenol is brominated much more easily than benzene is brominated. (3)

A
  • lone pair on O atom is delocalised into the ring
  • greater pi-electron density around the ring
  • polarises electrophiles more easily
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2
Q

9701/43/O/N/23:
CH3CH2COOH, CH3CCl2COOH, & H2SO4 are all acidic.
Suggest the trend in the relative acid strength of these three compounds.
Explain your answer.

A
  • (From strongest to weakest acid) H2SO4 > CH3CCl2COOH > CH3CH2COOH

Any 4:
- H2SO4 is fully dissociated / strong acid
- CH3CH2COOH / CH3CCl2COOH are partly dissociated / weak acids
- Cl is electron-withdrawing / electronegative
- alkyl group in CH3CH2COOH is electron-donating
- stabilises / destabilises anion OR weakens / strengthens O-H bond (linked correctly)
- correct ref. to donation of H+

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3
Q

Define partition coefficient, Kpc.

A

Ratio of the concentrations (of a solute between) 2 solvents (at equilibrium).

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4
Q

Explain why transition elements behave as catalysts. (2)

A
  • more than 1 (stable) oxidation state
  • empty d-orbitals can form dative bonds with ligands
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5
Q

9701/43/O/N/23 Q5div:
Suggest why a solution of Cu2+ is coloured but solid CuI is white.

A
  • Cu2+ is d^9 / orbitals not full AND Cu+ is d^10 / orbitals full
  • d-orbital electron promotion not possible
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6
Q

9701/42/O/N/23 Q4f:
A solution of [Cu(EDTA)]2- ions is pale blue while a solution of [Cu(NH3)4(H2O)2]2+ ions is deep blue.
Explain this difference in colour.

A
  • different energy gap between d-orbitals
  • absorption of different wavelengths
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7
Q

9701/42/O/N/23 Q6aii:
Define transition element complex.

A
  • Metal atom or ion bonded to one or more ligands.
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8
Q

9701/42/O/N/23 Q6aiii:
Explain why transition elements form complexes.

A
  • Has vacant d-orbitals which are energetically accessible.
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9
Q

9701/42/O/N/23 Q8bii:
Name the substance responsible for the peak at ppm = 0.0.

A

TMS / tetramethylsilane

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10
Q

9701/42/O/N/23 Q8cii:
Suggest suitable substances or types of substances, that could be used as the mobile & stationary phases.

A
  • mobile phase: an unreactive gas
  • stationary phase: a non-polar liquid
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11
Q

9701/42/O/N/23 Q8ciii:
Describe how the percentage composition of the mixture can be determined from the gas/liquid chromatogram.

A

Area of peak divided by total area of all peaks x 100%

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12
Q

9701/42/O/N/23 Q9a:
State the reactants & conditions for 2 different types of reactions that both produce diethylamine, CH3CH2NHCH2CH3.

A
  • Reaction 1: CH3CH2Cl + CH3CH2NH2, heat under pressure in alcoholic solution
  • Reaction 2: CH3CONHC2H5, CH3CH2NH2, LiAlH4
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13
Q

Chlorobenzene & phenol both show a lack of reactivity towards reactants that cause the breaking of the C-X bond (X=Cl or OH). Explain why. (9701/43/o/n/18 Q7a)

A
  • C-X bond is stronger (in chlorobenzene / phenol)
  • lone pair on Cl / OH
  • overlap / delocalise with pi-electron cloud AND electrons (of the Cl / O)
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14
Q

9701/42/F/M/23 Q1aiv:
Explain why the lattice energy of ZnO is more exothermic than that of ZnS.

A
  • O2- has smaller ionic radius that S2-
  • greater attraction between Zn2+ & O2-
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15
Q

9701/42/F/M/23 Q2d:
Describe the mode of action of a heterogeneous catalyst. (3)

A
  • reactants adsorb (to surface of catalyst)
  • bonds (in reactant) weaken
  • (reaction occurs & the) products are desorbed
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16
Q

9701/42/F/M/23 Q3a:
Define transition element.

A

A d-block element that forms 1 or more stable ions with incomplete filled d-orbitals.

17
Q

9701/42/F/M/23 Q3bii:
Explain why transition elements have variable oxidation states.

A

The d & s orbitals are similar in energy (level).

18
Q

9701/42/F/M/23 Q4b (adapted):
What determines the relative basicities of ammonia, ethylamine & phenylamine? (1)

A

Ability of base to accept a proton

19
Q

9701/42/F/M/23 Q4dii:
State the reagents used to convert phenylamine to benzenediazonium chloride.

A

NaNO2 + dilute HCl

20
Q

9701/42/F/M/23 Q4fiv:
When CH3NH2 (aq) is added to Cd2+ (aq), a mixture of [Cd(CH3NH2)4]2+ (aq) & [Cd(OH)4]2- forms.

Suggest how [Cd(OH)4]2- is formed. (1)

A

CH3NH2 is basic so reacts with water to produce OH- that reacts with Cd2+.

21
Q

9701/42/F/M/23 Q5a:
Describe & explain the shape of benzene, include:
- the bond angle between carbon atoms
- the hybridisation of the carbon atoms
- how orbital overlap forms sigma & pi bonds between the carbon atoms. (5)

A
  • bond angle = 120° AND shape is trigonal planar
  • (carbons are) sp2 hybridised
  • contains delocalised electrons in the pi bonds / system
  • (sp2 orbitals) overlap head-on to form sigma bonds
  • a p-orbital (from each carbon atom) overlaps sideways (with each other above & below the ring) forming pi bonds
22
Q

9701/42/F/M/23 Q5ei:
Define enantiomers.

A
  • rotates the plane of polarised light in the opposite direction
  • molecules that are non-superimposable mirror images
23
Q

9701/42/F/M/23 Q5eii:
Suggest one disadvantage of producing 2 enantiomers in this synthesis.

A
  • need to separate the optical isomers to form the pure active isomer
  • OR reduced / different biological activity of ‘other’ enantiomer
  • OR lower yield of biologically active molecule / desired molecule
24
Q

9701/42/F/M/23 Q5eiii:
Suggest a method of adapting the synthesis to produce a single enantiomer.

A
  • Chiral catalyst
  • OR use of an enzyme
25
Q

9701/43/O/N/22 Q1di:
Define enthalpy change of atomisation.

A

Enthalpy change when 1 mole of gaseous atoms formed from the element (in its standard state at 298K).

26
Q

9701/43/O/N/22 Q1dii:
Define first electron affinity.

A

Enthalpy change when 1 mole of gaseous atoms gains 1 mole of electrons.

27
Q

9701/43/O/N/22 Q1ei:
Explain what is meant by entropy, S.

A

Number of possible arrangements of particles & energy in a system.

28
Q

9701/43/O/N/22 Q2aiii:
Iodide ions react with peroxydisulfate ions.
2I- + S2O82- –> I2 + 2SO42-
This reaction is slow, but it is catalysed by Fe2+ ions.

Suggest why the alternative route in the presence of Fe2+ ions has a lower activation energy than the route in the absence of a catalyst.

A

Reactants are both anions AND so they repel each other.

29
Q

9701/43/O/N/22 Q3aiii:
Equal volumes of 1.0 mol dm-3 Sn2+ (aq) & 1.0 mol dm-3 Cl- (aq) are mixed.
Use relevant E° values to explain whether a reaction occurs between these 2 ions.

A
  • no (reaction) AND both E° values (Sn2+/Sn) -0.14 V & Cl2/Cl- +1.36 V
  • E°cell is negative OR E° of Sn4+/Sn2+ is more negative than E° Cl2/Cl-
30
Q

9701/43/O/N/22 Q5bi:
(Transition Metals) Explain why 2 solutions are coloured, & why the colours are different. (4)

A
  • d-orbitals or different energy / d-d splitting occurs
  • electron(s) promoted / excited
  • wavelength of visible light absorbed AND complementary colour seen
  • different energy gap OR different frequency of light is absorbed
31
Q

9701/43/O/N/22 Q5c:
Iron(II) carbonate, FeCO3, & nickel(II) carbonate, NiCO3, both decompose when heated. FeCO3 decomposes at a lower temperature than NiCO3.
Suggest a possible reason for this difference. Explain your answer. (2)

A
  • Fe2+ has a smaller radius OR Fe2+ has a greater charge density
  • polarises CO3^2- more
32
Q

9701/43/O/N/22 Q7di:
Explain what is meant by isoelectric point. (1)

A
  • pH where the species is electrically neutral
  • pH where the species is a zwitterion is a dominant form
33
Q

9701/43/O/N/22 Q8ci:
Chlorobenzene & chloroethane have different reactivities in nucleophilic substitution reactions.
Identify a suitable reagent to illustrate this difference in reactivity.
The reagent chosen should give visibly different results with chlorobenzene & chloroethane. (1)

9701/43/O/N/22 Q8cii:
Write equations to describe any reactions that occur. (1)

A

(i) AgNO3

(ii) C2H5Cl + H2O –> C2H5OH + HCl / C2H5Cl + NaOH –> C2H5OH + NaCl
AND Ag+ + Cl- –> AgCl

AND NO equation shown for C6H5Cl

34
Q
A

Chemistry (13 decks)

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