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Unit 4- June 2004 Markscheme

Q1

(a) (i) 2P + 3Cl2

2PCl3

(2)

Species (1)

Balancing (1)

OR an equation starting from P4

PCl3 + C12 PCl5(1)

OR

2P + 5Cl2 2PCl5(1) 3

(ii) PCl3 + 3H2O H3PO3 + 3HCl (2)

Species (1)

Balancing (1)

PCl5 + 4H2O H3PO4 + 5HCl (2)

Species (1)Balancing (1) 4

(b) (Polarity of PCl bond makes) P+/chlorine has higher electronegativity

than P (1)

P is attacked by lone pair on water/nucleophilic attack by water(1) 2[9]

Q2

(a) (i) pH = log(10) [H3O+] (1)

OR [H+] instead of[H3O

+] applied throughout 1

(ii) [H3O+] greater than 1 (mol dm

3) 1

(b) (i) Ka. =[HA]

][A]O[H

3+

(1)

[H3O+] = 1.14 10

3mol dm

3(1)

pH = 2.9(4) (1) 3

(ii) Start at the same pH as in (i) (1)Graph showing vertical at 25 cm

3(1)

vertical section 35 units in length with midpoint around pH 8 (1)

general shape correct including buffer zone and final pH not > 13

(1) 4

(iii) pH = pKa 1

[10]

Q3

(a) (i) It is non-superimposable on mirror image/ it has a single

asymmetric

carbon atom 1

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(ii) rotates the plane (of polarisation) (1)

of (plane) polarised (monochromatic) light (1)

OR

Use a polarimeter(1)

rotates the plane (of polarisation) of the light (1) 2

(iii) product is an equimolar mixture/racemic mixture (1)

so rotations cancel (1) 2

(b) NH3+Cl

on the amino group (1)

COO

Na+

on the carboxyl group (1) 2

(c) Zwifterions structure (1)

There is ionic attraction between adjacent zwitterions (1) 2

(d) (i) (polymer formed by) elimination/ removal of a small molecule/

water

(between two monomers) 1

(ii) any CIOC***COCl (1) and H2N*CH2*NH2(1) 2

(iii) structure consequential on answer to (ii) showing amide link(1)and extension of the chain (1) 2

(iv)

N C C N C C N C C

H C H O C H O H C H O

H H H H

3 3 3

CONH drawn out (1)

Show 3 units (1) 2[16]

Q4

(a) Pressure exerted by the gas if it alone occupied the same volume at the

same temperature/mole fraction total pressure 1

(b) (i) Kp = 222

)NO(

)O()N(

p

pp1

(ii) Correct number of moles (1)

Correct mole fractions (1)

Correct partial pressures (1)

2.45 103(1) ACCEPT 24 SF 4

(c) Kp increases (1)

Equilibrium moves to r.h.s. (1)

which is the exothermic direction (1) 3

(d) (i) Kp= p (Ni(CO)4) /p(CO)4

1

(ii) High partial pressure with some reason (1)

so the pressure Ni(CO)4 increases to keep Kp constant. (1) 2[12]

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Q5

(a) (i) Energy released/ exothermic/ H negative (1)

when one mole of lattice/crystal solid is formed (1)

from its gaseous ions (1) 3

(ii) BornHaber cycle (2)

1 mark for cycle showing all balanced species

1 mark for all state symbols correct

Calculation marks (3)

1 mark for 2x EA of Cl

1 mark for 2x Hat of Cl used

1 mark for working plus answer = +123 kJ mol1

5

(b) Radius of Mg2+

is smaller than that of Mg+(1)

And it has a higher charge (1) 2

(c) Fluoride ion small and not polarisable (1)

larger I ion easily polarised (1)

so (considerable) covalence in MgI2(1). 3

(d) Ba2+

is larger than Mg2+

(1)

so enthalpy of hydration is less exothermic/negative (1)

so enthalpy of solution of BaSO4 is more positive (1).

OR

Sulphate ion is large and so lattice enthalpy is fairly constant (1)

Therefore solubility depends on the hydration enthalpy of the cations (1)

The larger the cation size, the less exothermic the enthalpy of hydration

(1) 3[16]

Q6

(a) Mg (1)

dry ether/ethoxyethane (1) 2

(b) (i) (dilute) hydrochloric acid /other named acid/water(1) 1

(ii) (CH3)2CHCH2CH2OH 1

(c) (i) acidic 1

(ii) (CH3)2CHCH2COOH 1

(d) (i) ester 1

(ii) (CH3)2CHCH2COOCH2CH2CH(CH3)2 1

(iii) (conc) sulphuric acid/phosphoric/hydrochloric 1

(e) (i) acidic hydrolysis gives an equilibrium mixture/is reversible (1)

but with alkali it is complete/is not reversible (1) 2

(ii) Acidification/add acid named or otherwise 1[12]