1994 Al Chemistry Paper I Marking Scheme

1994 A-level chemistry paper I marking scheme -

-

2-

1.(a) (i) O (g) + e à O (g) [1m] (ii) Addition of an e to the O(g) atom is exothermic attraction between the nucleus and the incoming e outweighs the repulsion between e in O atom and incoming e . [1m] (if, attraction between the nucleus and the incoming e 1/2m) After addition of an e-, there is strong repulsion between the O (g) ion and the incoming e . [1m] (if, the size of O expands, hence the attraction of another e is weakened 1/2m) (iii) Screening effect of the stable electronic configuration of inert gases make the addition of an extra e an unfavourable process [1m] ∴inert gases have +ve first E.A. (if, addition of an e- destroys the extra stability of the electronic configuration of the inert gases 1/2m) (b) (i) No. of atom A per unit-cell = 8 x 1/8 = 1 No. of atom B per unit-cell = 12 x 1/4 = 3 Therefore Empirical formula of the compound is AB3 [1m] (ii) Coordination number of A = 6 [1/2m] Coordination number of B = 2 [1/2m] (c) (i)

F Drawing [1m] Triangular planar [1/2m] Zero dipole moment [1/2m]

B F

F (ii)

F F

Cl

Drawing [1m] T-shaped [1/2m] Non-zero dipole moment [1/2m]

F (0m if shape of ClF3 is described as triangular planar.) i.e.

.. F

Cl ..

(d) Ti

n+

F

F

-

+ ne à Ti No. of moles of Ti liberated = 5.60 / 47.90 = 0.1169 [1m] No. of moles of e- passed = 5.00 x 2.50 x 60 x 60 / 96500 ∴n = 4.663 x 10-1 / 1.167 x 10-1 = 3.989 = 4 [1m] -

-

+

(e) (i) BrO3 (aq) + 5Br (aq) + 6H (aq) à 3Br2(aq) + 3H2O(l) [1.5m] 2(ii) 2MnO4 (aq) + 3SO2(g) + 4OH (aq) à 2MnO2(s) + 3SO4 (aq) + 2H2O(l) [1/2m for completing the equation, 1m for balancing the equation] )(No penalty on state symbols, max. 1m for multiples of the correct equation.) 2-

(f) (i) HPO4 (aq) + H2O(l) (ii) At pH 10,

-

-

H2PO4 (aq) + OH (aq) [1m]

1994-AL-CHEM P 1 - 1

-

-4

-3

[OH (aq)] = 10 mol dm [1/2m] 2-1 -3 [HPO4 (aq)] = 10 mol dm +

3

2-

-

[Ag (aq)] [HPO4 (aq)][OH (aq)] -22 = 2.84 x 10 or Kc [1/2m] 3 -17 ∴ [Ag+(aq)] = 2.84 x 10 + -6 -3 [Ag (aq)] = 3.05 x 10 mol dm [1m] +

1 mole of Ag3PO4 produces 3 moles of Ag (aq) ions. -6 -3 ∴ solubility of Ag3PO4 = 1.017 x 10 mol dm [1m] 23 (Full mark should be awarded if the solubility x is solved by Kc=(3x) [HPO4 ][OH ] 2. (a)(i) Redox: one species is oxidized and another is reduced. [1m] Disproportionation: single species is simultaneously oxidized and reduced. [1m] (ii) 2KOH(aq) + Cl2(g) à KCl(aq) + KOCl(aq) + H2O(l) [1m] or 6KOH(aq) + 3Cl2(g) à 5KCl(aq) + KClO3(aq) + H2O(l) or 2OH (aq) + Cl2(g) à Cl (aq) + OCl (aq) + H2O(l) or 6OH (aq) + 3Cl2(g) à 5Cl (aq) + ClO3 (aq) + 3H2O(l) (Conditions are not necessary, the equation must be balanced.) 2+ + + (b) (i) Ni higher charge density / more electronegative than K / more polarizing than K [1m] (Or low-lying vacant d orbital, NOT accept effective nuclear charge argument) ∴ greater ability to form covalent bond / dative bond with ligand [1m] (ii) one example, not name [1m] (Correct charge; accept coordination numbers 4/6. Accept en etc.) (c) (i) a proton donor [1m] + (ii) HNO3 + H2O à (or ) H3O + NO3 [1m] + HNO3 + HF à (or ) H2NO3 + F [1m] (iii) HClO < HClO2 < HClO3 < HClO4 [2m] (1m for 3 formulas, 1m for order of acidity) (iv) HF is extensively hydrogen-bonded in water + (H-F)n + H2O(l) H3O (aq) + F (aq) + (H-F)n-1 [1m] The equilibrium lying to LHS. The Cl ion, having a large size, is highly polarizable, it is stable in water. Hence the equilibrium + HCl(aq) + H2O(l) H3O (aq) + Cl (aq) lies to the right, so HCl is a strong acid. or HX bond strength greater in H-F than H-Cl, H-F ionize less easily than H-Cl in water (1m), this outweighs the hydration energy from F to Cl . (1m) (d) (i) H atom is situated between 2 small / electronegative atoms [1m] One of these has a lone pair of electrons [1m] or bond energy in range 2 - 10 kJ mol-1 (accept weak, or up to 50) (ii) One example, must show X-H ... Y or X ... H ... X [1m] (Accept bond between 2 different species, and δ+, δ- instead of dots. If lone pair is shown, but in incorrect location 1/2m only) (iii)(I) Boiling points expected to increase with number of electrons in the molecule (CH4 à SiH4) due to increasing van der Waal's force [1m] (large surface area not enough) (II) Boiling point of NH3 higher than expected (i.e. > PH3) due to increased intermolecular attraction (hydrogen bonding) [1m] (e) Cs, having a lower I.E. / a larger size, the e- in the outermost shell can be ionized easily by absorption of visible light. Therefore it is more suitable to be used in making photo-electric cell. [1m] (Not accept argument based on the effective nuclear charge.) (f) In the periodic table, the elements are arranged in order of atomic number, but not in order of atomic mass. Argon having no electron in the 4th shell is placed in group I. [1m] (1 more proton 1/2m, Periodic table arranged in order of ascending atomic number 1/2m) 3. (a)(i) Add dil.(aq) HCl and (diethyl) ether to (C + D) [1m] Separate the layers (using a separating funnel) [1/2m] In aqueous HCl layer - D [1m] In ether layer - C[1/2m] (In place of HCl can use H2SO4. In place of ether can use CHCl3, CH2Cl2. If D forms salt with HCl, soluble in H2O, C does not 2m 1994-AL-CHEM P 1 - 2

If D may be recovered by addition of alkali (extracting with ether, drying and evaporation) - a BONUS 1/2m) (ii)

E: [1m]

F,G: [1m]

[1m]

CH3CH2CH=CH2

CH3

CH3

or but-1-ene

C=C

or

H

or H

CH3

or trans-2-butene H

2. Zn, H3O+

1.O3

C=C H

or cis-2-butene CH3CH2CH=CH2

H

CH3

CH3CH2CHO + CH2O or [1/2m]

[1/2m]

C=O H

(iii)

HNO2 C

No reaction [1/2m] HNO2

D

OR

CH3CH2CH2OH + N2

CH3CH2CH2N2+ (Unstable)

CH3CH=CH2

N2 + CH 3CH2CH2+

(If C is ignored - no mark for C. If "only D reacts" award 1/2m for C.

If D

CH3CH2CH2Cl examples of products

+

N2

+

If for D, CH3CH2CH2N

CH3CH2CH2OH etc.

N

or

award only 1m Cl

or

alone 1/2m each, max. 1m)

(iv) In the case of D colourless [1/2m] gas bubbles [1/2m] will be seen or N2 gas evolved with D. (If "look for gas bubbles" with no mention of D or C 1/2m) (b) (i)

CH3CH-CH3

or

Br

Br or isopropyl bromide [1m] or 2-bromopropane (If CH3CH2Br 0m) (ii) Mechanism: δ+H-Brδ−

CH3CH=CH2

+

CH3CHCH3 [1/2m]

Br

CH3CHCH3 Br

[1/2m] (If electrophilic additon only 1/2m) Minor product is CH3CH2CH2Br [1m] 1994-AL-CHEM P 1 - 3

+

It is a minor product because its intermediate (CH3CH2CH2 ) is less stable than the secondary carboncation (CH3CHCH3) [1/2m] OR The carboncation formed exists as an equilibrium mixture + +

CH3CHCH3 (more stable) The secondary carboncation (

CH3CH2CH2 (less stable) +

) is more stable than the primary carboncation

+ ( ) because the two electron releasing methyl groups disperse the charge more and so stabilize the +ve secondary ion more effectively. [1/2m] Bonus the electron release may be considered to be due to the inductive effect and the hyperconjugative effect. (1/2m) ("The more stable ion will produce the major product" This should be stated or implied as in above.) (c) (i) Chromatography or thin layer chromatography Paper chromatography: a small spot of solution of protein hydrolysate is placed near the bottom of a sheet of chromatography paper. In the same horizontal line is placed spots of all the likely known amino acids. After drying the paper is placed in a tank with a layer of suitable solvent below the line of spots. [Method 1m] After the solvent has reached near the top of the paper it is removed from the tank, dried and sprayed with ninhydrin (or stained) [1/2m] OR use of diagram to explain the method. (There are many ways of answering "method".) The amino acids in the mixture are identified from their Rf values when compared with that of the known amino acids. [1m] Rf is relative distance travelled [1/2m] (ii)

NH3+ | CH3 - C - CO2- or R-CH(NH3+)CO2- [1m] (If not an α-amino acid 1/2m) NH 2 | (If just RNH3+ or RCO2-, or R - CH - CO2H 0m) +

(iii) This is the H ion concentration [1/2m] of solution in which a particular amino acid [1/2m] of solution in which a particular amino acid [1/2m] does not migrate [1/2m] under the influence of an electric field. [1/2m] OR pH at which no ion migration occurs OR pH at which cationic form and anionic form of an amino acid are in equal concentration. 4.(a) Addition of Na2CO3(aq) [or NaHCO3(aq)] to CH3COOH(aq) gives CO2(g) / effervescence [1m] Addition of Na2CO3(aq) [or NaHCO3(aq)] to phenol does not give CO2(g) / effervescence [1m] (Correct reagent, but result incorrect, 1/2m only. No need to use lime water. Accept also reactions with insoluble basic oxides, or magnesium.) (b) Clean test tube [1/2m] to AgNO3(aq) [1/2m] add NH3(aq) (excess) [1/2m] in test tube until initial precipitate dissolves. + (If Ag(NH3)2 or ammoniacal silver nitrate, total 1/2m only, Tollens' reagent 0 m) Add a few drops of aldehyde [1/2m] Place tube in a beaker of warm water (or warm water bath) [1/2m] (Direct - gentle heating or heating 0m) An explosion may occur [1/2m] (c)(i) Carcinogenic / toxic [3m, deduct 1m for each incorrect (ii) Oxidizing answer, down to zero] (iii) Corrosive (iv) Flammable st (Accept 1 answer written down, if several answers.) 1994-AL-CHEM P 1 - 4

(d) Main products Reaction method Expected observation(s) Warm/reflux with conc. Miscible, fruity odour CH3COOC2H5(l) H2SO4 2+ Add acid dropwise at room Green / blue solution Cu [1/2m] temperature [1/2m] brown fumes [1/2m] NO2 [1/2m] or Cu dissolves [1/2m] CH3CHBr2(l) and 4M Gently heat mixture in a Pungent odour [1m] / CH3CHO(aq) NaOH test tube miscible CuSO4(aq) and 2NH3 Add NH3(aq) dropwise Pale blue precipitate, deep Cu(OH)2(s) 2+ [1m] (slowly) blue solution [Cu(NH3)4] (aq) Pb(NO3)2(aq) and 2M HCl Add acid dropwise at room White ppt [1m] milky PbCl2 [1m] temperature [1/2m]m / cloudy [1/2m] / turbid [1/2m] (Each box total = 1m, state symbol not necessary. Deduct 1/2m for mistake(s) in same box) Substance CH3COOH(l) and C2H5OH(l) Cu(s) and conc HNO3

2-

+

(e)(i) S2O3 (aq) + 2H (aq) à H2O(l) + SO2(g) + S(s) [1m] or Na2S2O3 + 2HCl à 2NaCl + S + SO2 + H2O 2(ii) Make [S2O3 ] solutions of known molarities and place equal volumes of these solutions in conical flasks. [1m] Measure temperature of solutions/set thermostat at 298 K. [1m] Add a fixed volume of acid to Na2S2O3 (using measuring cylinder), start stop-clock [1m] Note time, t, when a black "X" marked on a cardboard becomes invisible when lookng through the flask. [1m] Points are: 2- solutions of different molarities of S2O3 - equal volumes of these solutions - flasks - 298 K - add fixed volume of acid - start stop clock - note time - black X disappearts [1/2m for each point] -1 2-3 (iii) (1/t) / s and [S2O3 (aq)] / mole dm [1m] concentration (Accept log both sides) 5.

Chemical Knowledge (10 marks) Core marks (7) Discussion on the rate in the absence of an Fe surface Probability of a simultaneous collision of (4 or gaseous) molecules in the gas phase is extremely small. (1) Breaking of the strong N ≡ N bond imposes high activation energy (Ea) on the process. (1) Collision of molecules having high velocities should, in principle, provide the necessary Ea. (1) According to the (Boltzmann) distribution at moderate temperatures the number of such highvelocity molecules is (very) small. (1) (Looking for the graph, good organization of points) Discussion of the rate in the presence of an Fe surface

OR

The N ≡ N bond is significantly weakened in the Fe surface, and therefore providing a different reaction path with smaller Ea. Gaseous molecules covalent bond weakened. (1) All the gases involved are only weakly adsorbed on the Fe surface. Thus N2 and H2 1994-AL-CHEM P 1 - 5

molecules are quite mobile on the Fe surface, (and may encounter each other on this 2dimensional plane or higher concentration of reactants on the surface, therefore surface becomes better meeting place) (1) Instead of a 4-body collision in a 3-dimensional space in the gas phase, the presence of the Fe surface requires only that the adsorbed species be higher than the former event. OR 3-dimensional collision à 2-dimensional collision à higher frequency collision. (1) (7) Optional Mark (3; any 3 of the following) As a result of weak interaction of the product with the surface, NH2 desorbs easily. (1) Fe has (numerous) 3-d electrons and many vacant 3-d orbitals, and is therefore capable of temporarily donating or accepting electrons from adsorbed species, making it (one of the best catalyst in heterogeneous catalysis.) OR Variable oxidation state (1) (Steric effect) is more important in the gas phase: the (4) colliding molecules have to be in the correct orientations to yield the product. (1) The gas phase reaction may be speeded up by raising the temperature, but at high temperatures decomposition of NH3 is favoured, thus lowered the yield. (1) Specifically, N2 dissociates into (weakly adsorbed/ absorbed) N atoms at around (500 °C )

and H2 dissociates at temperatures as low as (-196 °C ) as weakly adsorbed H atoms. These atoms are highly reactive, and they form NH3 readily. (1) Breaking of the strong ( N ≡ N triple bond or resist breaking)

(1) (3)

(Looking for the adsorbed model, good organization of points) The following diagrams are expected: Diagram for Boltzmann distribution, change of reaction path in the presence of the catalyst, (pictorial illustration of gas phase collision and formation of ammonia on the Fe surface.) Organization ( 6 marks )(1/2 mark awarded) NOTE: The marks should be related to chemical knowledge General guidelines for Organization: Mark for chemical knowledge Maximum for organization 10 - 9 6 9-7 5 7-5 4 5-4 3 3-2 2 2-1 1 0 0 (i) The essay should be clearly ORGANIZED, with suitable DIVISION, PARAGRAPHS AND SUBHEADINGS. [2m] These should be clear to the reader. [2m] (ii) Terms must be clearly defined. [1m] (iii) The essay should be LOGICALLY organized. It must not be a list of facts. [2m] (iv) No irrelevant / wrong material. [1m] (v) No error in labels of diagrams, spelling etc. [1m] Presentation ( 4 marks ) This mark is awarded for the ability to PRESENT the organized Chemical Knowledge in a suitable, meaningful and readable form. NOTE: Marks awarded should be related to Chemical Knowledge. Marks for chemical knowledge Max. for presentation 10 ’ 8 4 7’ 6 3 5’ 4 2 1994-AL-CHEM P 1 - 6

<3 1 The followings are looked for: EQUATIONS, DIAGRAMS AND EXAMPLES. [1 ꙷ 2m] ENGLISH This mark is for the ability to express clearly in English [2 ꙷ 3 m] 6.

Chemical knowledge (10 marks) (Note: Emphasis on chemistry , e.g. preparation, reactions; not physical properties.) Core Area A. Composition (formulae), (natural abundances), (uses) [1m] B. Bonding in chlorides, structures, (relative stabilities), (states) [2m] C. Preparation, relation to chemical behaviour and bonding [3m] D. Hydrolysis (mechanisms), (reactions with other species) [4m] (Area in brackets: may be included to score up to 1m towards the area total) A more detailed break down of the marks for each of the core areas: Area A (Max. 1m) - Composition: Must give 1 formula for each element NaCl MgCl2 AlCl3 SiCl4 PCl3(l) S2Cl2(l) Cl2 [1m] (or PCl5(s)) (SCl2 or SCl4) (One formula incorrect or mising, only 1/2m) (For each chloride, if giving natural abundance / use è 1/2m; e.g. if the natural abundance / uses of NaCl & Cl2 are discussed è 1m) Area B (Max. 2m) - State: NaCl MgCl2

AlCl3

SiCl4

PCl3(l)

S2Cl2(l) Cl2 (or PCl5(s)) (SCl2 or SCl4) (---------- solid -------------------) (---------------- liquid*---------------------) gas [1m] * state must be matched with the formula or 2 examples of trend in states, melting points - Structure/bonding (transformation from giant ionic to discrete covalent molecules) [1m] (- amplifications of structures / bonding 2 x 1/2m = 1m) - drawing of outer e- diagram / structure for NaCl & Cl2. 2 x 1/2m [1m]

Area C (Max. 3m) (1/2m for general method + 1/2m for equation, up to 3m. Equation need not be balanced or complete) - Covlanet chlorides: from elements by direct reaction with Cl2 e.g. Si(s) + 2Cl2(g) à SiCl4 P4(s) à PCl3(l) à PCl5(s) 2S(s) + Cl2(g) à S2Cl2(l) etc. (or halogen exchange) [1m] - Ionic chlorides: by reaction of HCl(aq) with oxides, carbonates, hydroxides e.g. Na2CO3(s) + 2HCl(aq) à 2NaCl(aq) + H2O(l) + CO2(g) AlCl3: 2Al(s) + 6HCl(g) à 2AlC3(s) + H2(g) [1m] - Chlorine: HCl (conc) on oxidation by strong oxidizing agents (KMnO4 or MnO2, NOT K2Cr2O7) gives Cl2(g) e.g. MnO2(s) + 4HCl(aq) à MnCl2(aq) + Cl2(g) + 2H2O(l) 2KMnO4(s) + 16HCl(aq) à 2MnCl2(aq) + 5Cl2(g) + 2KCl(aq) + 8H2O(l) or action of dil. acids on bleaching power or 2NaCl + MnO2 + 2H2SO4 à 2NaHSO4 + 2H2O + Cl2 [1m] Accept electrolysis of brine Area D (Max. 4m) (Name + arrow equation for each hydrolysis = 1m; or full equation. Reaction with OH- accepted for AlCl3, MgCl2 or covalent chlorides.) - Ionic chlorides form solvated ions in water which do not hydrolyse: NaCl(s) + aq --> Na+(aq) + Cl-(aq) With increasing polarization of cation undergoes slight hydrolysis: MgCl2(s) + 2H2O(l) Mg(OH)2(aq) + 2HCl(aq) 1994-AL-CHEM P 1 - 7

Reversible hydrolysis of highly polarizing cation: AlCl3(s) + 6H2O(l) [Al(H2O)6]3+(aq) + 3Cl-(aq) then [Al(H2O)6]3+(aq) + H2O(l) H3O+(aq) + [Al(H2O)5(OH)]2+ à ... [1m for statement, equation not necessary, up to 2m] - For covalent chlorides SCl2, SiCl4, PCl3, PCl5, (XCln), the hydrolysis proceeds by nucleophilic attack by a lone pair of e on O in H2O: upon X, which if less electronegative than Cl. e.g. PCl3(l) + 3H2O(l) à P(OH)3(aq) + 3HCl(aq) 2S2Cl2(l) + 2H2O(l) à 3S(s) + SO2(aq) + 4HCl(aq) - Hydrolysis of chlorine Cl2(g) + H2O(l) HCl(aq) + HOCl(aq) [1m for each example & equation, up to 2m] - Trend: Pure ionic chloride - neutral / not hydrolysed; Covalently bonded - acidic / hydrolysed [1m] - Mechanisms of hydrolysis for one example [1m] - Reaction of the chlorides IF THEY ARE OF COMPARATIVE NATURE [1m each for 2 comparative chlorides, e.g. PCl3 + PCl5] Organization ( 6 marks )(1/2 mark awarded) NOTE: The marks should be related to chemical knowledge General guidelines for Organization: Mark for chemical knowledge Maximum for organization 10 - 9 6 9-7 5 7-5 4 5-4 3 3-2 2 2-1 1 0 0 (vi) The essay should be clearly ORGANIZED, with suitable DIVISION, PARAGRAPHS AND SUBHEADINGS. [2m] These should be clear to the reader. [2m] (vii) Terms must be clearly defined. (not relevant here) [0m] (viii) The essay should be LOGICALLY organized. It must not be a list of facts. [2m] (ix) No irrelevant / wrong material. [1m] (2 errors = -1) (x) No error in labels of diagrams, spelling etc. [1m] Presentation ( 4 marks ) This mark is awarded for the ability to PRESENT the organized Chemical Knowledge in a suitable, meaningful and readable form. NOTE: Marks awarded should be related to Chemical Knowledge. Marks for chemical knowledge Max. for presentation 10 ’ 8 4 7’ 6 3 5’ 4 2 <3 1 The followings are looked for: EQUATIONS, DIAGRAMS AND EXAMPLES. [1 ꙷ 2m] ENGLISH This mark is for the ability to express clearly in English [2 ꙷ 3 m] 7.

Chemical Knowledge (10 marks) Unique properties of benzene ring

(3)

the benzene ring with 3 π bonds is electron rich. The usual reactions are not electrophilic addition (like alkenes) because of the unusual stability of the ring- seen in the difference between calculated and measured heats of hydrogenation and combustion which is the -1 resonance energy (approx. 154 KJ mol ) 1994-AL-CHEM P 1 - 8

(Definition and formulae to explain resonance using correct arrows are expected.) Electrophilic substitution reactions being the common reactions. Examples: with electrophiles e.g. nitration, bromination, sulphonation. This part should include Unique chemical properties: Reaction expected of C=C - Electrophilic Addition Reaction Found for C6H6 - examples (some detail req.) - Ar Electrophilic substitution

(1/2) (1)

Explanation - resonance Evidence (Energy: Difference between experimental and theoretical, bond length, heat of hydrogenation, heat of combustion) (1/2) Effective of benzene ring on Reaction o Functional groups

max 4

Some answers may refer to the benzene ring as a SINK for electrons. The following examples are due to the interaction of lose pairs of electrons on a hetero-atom with the benzene ring. The ring appears to the attract electrons: Example: (max 11/2 mark for each example) Ph-NH2: less basic than NH2 or RNH2 (1/2) due to interaction of lone pair with ring. Resonance structures:

NH2

-

NH2+

...

Ph-OH:

acidic (1/2) due to stability of Ph-O- ion (due to resonance; explain (1/2)), ROH is not acidic (1/2).

Ph-Cl:

The Cl is very unreactive compared to HCl and won…t react with AgNO3 (due to stronger C-Cl bond - by lone pair interaction).

Other examples indicate the opposite: +

The unusual stability of the Phenyldiazoniun ion Ph − N ≡ N (1/2) compared with unstable alkyl type. These results in a coupling reaction (1/2) - only observed with aryl case: Accept other possible examples. [This part of the question requires more ability as the details required are not stated specifically like the other parts of the Q䀔 䀔 .hence 4 marks] Source: from crude oil (1/2) following by refining (distillation (1/2)). OR destructive distillation of coal (1/2). Synthetic route of amino benzene C6H6 conc.H2SO4/ conc.HNO3 (1/2)

PhNO2 (1/2) Sn/HCl (1/2)

PhNH2

Remaining (1/2) marks given to more detailed answer to any of the above 4 sections (1/2). __________ (10) Chemistry of benzene derivatives Phenol- substitution Nitrobenzene- substitution and others

(21/2 marks) (1) max (1) max

Organization ( 6 marks )(1/2 mark awarded) 1994-AL-CHEM P 1 - 9

NOTE: The marks should be related to chemical knowledge General guidelines for Organization: Mark for chemical knowledge Maximum for organization 10 - 9 6 9-7 5 7-5 4 5-4 3 3-2 2 2-1 1 0 0 (xi) The essay should be clearly ORGANIZED, with suitable DIVISION, PARAGRAPHS AND SUBHEADINGS. [2m] These should be clear to the reader. [2m] (xii) Terms must be clearly defined. [1m] (xiii) The essay should be LOGICALLY organized. It must not be a list of facts. [2m] (xiv) No irrelevant / wrong material. [1m] (xv) No error in labels of diagrams, spelling etc. [1m] Presentation ( 4 marks ) This mark is awarded for the ability to PRESENT the organized Chemical Knowledge in a suitable, meaningful and readable form. NOTE: Marks awarded should be related to Chemical Knowledge. Marks for chemical knowledge Max. for presentation 10 ’ 8 4 7’ 6 3 5’ 4 2 <3 1 The followings are looked for: EQUATIONS, DIAGRAMS AND EXAMPLES. [1 ꙷ 2m] ENGLISH This mark is for the ability to express clearly in English [2 ꙷ 3 m]

1994-AL-CHEM P 1 - 10