| (a) | (i) | (63.8/66.6x 31.97 ) + (2.8/66.6 x 33.97) = 32.33 |
| (ii) | FeS2
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| (b) |  |
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| (c) | (i) | First IE is the energy required to remove 1 mole of electrons from 1 mole of gaseous S atoms to form 1 mole of S+ ions.
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| (ii) | Across the period, nuclear charge increase, shielding effect remains relatively constant, first IE increases due to increase nuclear attraction. Sulfur has a pair of e in 3p orbital which results in inter-electronic repulsion. |
| (d) | (i) | 
C has 2 sp hybrid orbitals to form sigma bonds w each S and 2 unhybridised p orbitals to form pi bonds w each S respectively. |
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| (ii) |  |
| 2 | (a) | (i) | Down the group, quantum shells increases, ionic radius increases.
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| (ii) | Cs has larger ionic radius, can accommodate more anions around it.
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| (b) | Factors: charge and ionic radius Charge has greater effect as it is multiplication compared to addition (for radius) |
| (c) | (i) |  |
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| (ii) | Energy released on forming ion dipole interactions between Na+/Cl– w water is sufficient to compensate for energy required to break ionic bonds in NaCl.
In hexane, no ion-dipole interactions are possible / no favourable interactions.
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| (d) | (i) | NH4Cl(s) -> NH4+ (aq) + Cl–(aq) | |
| (ii) |  |
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| (iii) | 
207K is below freezing point of water. Water would exist as ice, unable to have any solvation. |
| 3 | (a) | H-F BE = 562 (stronger, less likely to dissociate, so weaker acid) H-Cl BE = 431 |
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| (b) | 
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| (c) | (i) | F– / HF buffering system
HF + OH– -> F– + H2O
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| (ii) | Cl– is a neutral salt. It is unable to resist a change in pH when a small amt of strong acid/base is added.
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| (iii) | nH+ = 50/1000 x 0.1 x 2 = 0.01 mol
nF– in 200 cm3 = 100/1000 x 1.78 = 0.178 mol nF– in 75 cm3 = 0.178 / 200 x 75 = 0.06675
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| (d) | (i) | Smaller pKa, stronger acid, larger extent of dissociation. CCl3COOH has larger extent of dissociation than CH3COOH. | |
| (ii) | 0.50 (any value smaller than 0.66). F is more electronegative than Cl, so it will stabilise CF3COO– more than CCl3COO–. CF3COOH is more acidic than CCl3COOH. | ||
| (e) | (i) | CaF2 ⇌ Ca2+ + 2F– —– (1)
Ksp = [Ca2+] [F– ]2 = (x)(2x)2 = 4x3 X = 2.14 x 10-4 [F– ] = 2x = 4.27 x 10-4
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| (ii) | H+ + F– ⇌ HF —– (2)
In acidic soln, [H+] increase, eqm (2) shifts right, [F–] decreases, eqm (1) shifts right, hence CaF2 becomes more soluble. |
| 4 | (a) | All bonds are saturated. C-F bond is also quite strong so unable to perform nucleophilic subn rxn.
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| (b) | Ozone layer depletion due to CFC.
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| (c) | High temp. Low pressure.
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| (d) | (i) | Covalent bond breaks where each atom obtains 1 e.
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| (ii) | A: initiation B: propagation C: propagation D: termination |
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| (iii) | Free radical addition | ||
| (iv) |  |
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| (v) | ∆H = 150 + 12(610-350) [pi bond only] – 2(360) – 11(350) = -1300 kJ mol-1
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| (vi) | P is the major species. Radical can be stabilised via delocalisation into the benzene ring. |
| 5 | (a) | Reducing agent. Reduces Fe3+ -> Fe2+
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| (b) | Dative bond from lone pair of O to Fe2+ | ||
| (c) | To deprotonate HSCH2COOH
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| (d) | HSCH2COOH + NH3 -> NH4+ + HSCH2COO–
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| (e) | (i) | HSCH2COOH has stronger id-id interactions due to larger e cloud size, more e to be polarised.
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| (ii) | HOCH2COOH has stronger pd interactions because O is more electronegative than S in HSCH2COOH.
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| (f) | 
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| (g) |  |