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G.C.E. (A. L.) Support seminar - 2014 Chemistry - Paper I Answer Guide
QuestionNumber
Answer QuestionNumber
Answer
(1) 3 (26) 2
(2) 5 (27) 5
(3) 1 (28) 4
(4) 1 (29) 2
(5) 3 (30) 3
(6) 3 (31) 5
(7) 4 (32) 3
(8) 5 (33) 2
(9) 1 (34) 5
(10) 5 (35) 2
(11) 3 (36) 3
(12) 3 (37) 5
(13) 2 (38) 1
(14) 3 (39) 1
(15) 4 (40) 2
(16) 4 (41) 2
(17) 3 (42) 5
(18) 2 (43) 1
(19) 5 (44) 4
(20) 1 (45) 5
(21) 2 (46) 3
(22) 4 (47) 4
(23) 2 (48) 1
(24) 5 (49) 4
(25) 1 (50) 2
[see page 2
[see page 3
1. (a) (i) He < O < Cl < Mg
(ii) Li
(iii) chlorine
(iv) CH4 < CO < CO2
(v) NO2
+ < NO2
− < NO3
−
(4×5 = 20 marks)
(b) (i) (+) (+)
(−)
COa Ob
Oc ≡ N (10 marks)
(ii) (+) (+)
(−)
CO ≡O
O N
(+) (+) CO ≡
O
O N
(−)
(1) (2)
As the charge distribution is equal, stabilities are similar to each other. But, stability decreases due to the presence of minus charges on more electronegative N
and O atoms.
(5×3 = 15 marks)
(iii) CO/ Carbon monoxide (02 marks)
(c) Atom Hybridization Electron geometry around the atom
Oa SP3Tetrahedral
Na SP2Trigonal planar
C SP Linear
(3×6 = 18 marks)
(d) (i) Electron configuration
Zn − 4s2 3d10 Co − 4s2 3d7
Configuration of Zn is relatively more stable. Less tendency for the de-localization of
electrons. Strength of the metallic bond is low.
(2×5 = 10 marks)
(ii) C
O
OHCH3 has intermolecularH bonds. But C
O
HCH3 has only permanent
dipole-permanent dipole attractions, which is relatively less stronger. (3×3 = 9 marks)
(Total marks92)
G.C.E. (A.L.) Support seminar - 2014 Chemistry - Paper II Answer Guide
6. (a) (i) i. Substances which are completely dissociated into ions in the aqueous solution. or
Substances in which ions exist in its solid, liquid and in the aqueous solution.
ii. Ion concentration is very high in the saturated solutions of such compounds. There are attractive forces between the ions. (Ions are not independent on each other).
- 8 -
(ii) Ú First, Ag2CrO4(s) dissociates. Ú At a particular instance, the rate of the forward and backward reactions becomes equal to each other.
Ag2CrO4(s) 2Ag+(aq) + CrO4 (aq) −2 ^01)
Ú From that instant, concentration of ions remain constant, the ionic product,
2−[Ag+(aq)]2 [CrO4- (aq)] is equal to KSP of the compound at the given temperature.
When NH3 is added,
Ú As the equilibrium,Ag+(aq)+2NH3(aq) [Ag(NH3)2]
+(aq)
(2) reaches,
Ag+ ion concentration decreases. There, according to Le Chatterlier's principle,
as the reaction (1) above, gets shifted towards the products, [CrO42−(aq)] increases.
III. ∆G° = ∆H°− ∆S°T = 299 kJ mol−1 − 224 JK−1 mol−1 × 298 K
= 299 kJ mol−1 − 66.752 kJmol−1
= (299 − 66.752)kkJmol−1
= 232.248 kJmol−1 (12)
(ii) (+) ve value obtained for ∆G°. The reaction given, is not spontaneous. According
to that, X should act as the oxidizing agent and Y should act as the reducing agent. Therefore, Y is above X in the electro-chemical series. (10)
(iii) I. Anode - Y Cathode − X II. Anode Y(s) Y2+
(aq) + 2e III. Cathode X2+
(aq) + 2e X(s) IV. Y(s) Y2+(aq, 1moldm−3) X2+(aq, 1moldm−3) / X(s) ^14marks&
6b - (60 marks)
7' (a) (i)
C ≡ C − H C ≡ C − NNa+
+ 2Na 22 + H2 (10)
(ii) C ≡ C − NNa+
+ CH3 C H O
CH3 C C ≡ CO− NNa+
H
(iii) C ≡ C − HH
C ≡ C− NNa+
Hg2+
Na
dil. H2SO4
CO
CH3
CH3 C CC ≡ O− NNa+
CH3 C CC ≡ OH
CH3 C CC ≡ Br
CH3 C CC Br
H2O
PBr3
Br2 / CCl4 Br
Br Br
Br
(5 × 11 = 55) marks
7a - (75 marks)
[see page 10
(vi) i. W;afm%arlhla Ndú; ls¯fï jdish
l=ula o @
ii. W;afm%arlhla m%;sl%shdj
- 10 -
[see page 11
(b) (i) a, h and f (10)
(ii) a - acid base h - acid base f - nucleophylic substitution (15) ^25marks&
7b - (25 marks)
(c) (i)
CUCNKCN
0 - 5 °C A
NH2 NN2Cl
OH COOHOOH
CNNaNO2(i)
dil. H2SO4
(ii) dil. HCl
Room temperature
conc.HH2SO4
O
O
C
B
(9 × 4 = 36) marks
(ii)
+
+ NaCl
+ dil. HCl
+ dil.HCl
NaOH(aq)NN
H O
CC O− NNa+
O
C O− NNa+
O
NH2
NH2
he resultant solution is treated with dil.HCl solution.
The resultant white precipitate is filtered and separated. It is benzoic acid. (14)
Alternative answer :
NH3
+Cl
−
(aq)
COOH
dil. HCl
The resultant white precipitate is filtered and separated. It is benzoic acid.
N
H O
C
NH3
+Cl
−
(aq) COOH
+
The compound given below is heated with aqueous NaOH.
7c - ^50marks&
8' (a) (i) Presence of PbI2 is confirmed as the dark yellow precipitate is dissolved in water when heated and precipitated back when cooled. As the pink compound dissolves in a acid, it is a basic compound. The species which forms blue with conc.HCl, is Co2+.
∴ Contain PbI2 and Co(OH)2 . (2 × 8) + (4 + 4) = 24 marks
(ii) [CoCl4]2−
Tetrachlorocobaltate(II) ion (3 × 2 = 6) marks
8a - 30 marks (b) (1) The white precipitate of lead, which turns black when heated, is PbS2O3 . (3 × 3 = 9) marks (2) ÷ Filtrate Y contains a reducing agent. ÷ That reducing agent is removed with Ca2+ ions by forming a precipitate. ÷ This precipitate should be CaC2O4 . (3 × 3 = 9) marks
(3) There are Ca2+ ions remain in the filtrate Z. As a precipitate was formed on heating, HCO3 ions have dissociated to CO3
2− ions. CaCO3 precipitates.
(3 × 3 = 9) marks
(4) Possible to be NO3
−
or NO2
− . As an oxidation is not possible in the filtrate Z, it can not be NO2
− . (2 × 4 = 8) marks
∴ Four anions are,
C2O4
2−,S2O3
2− , HCO3 −
and NO3
−
. (4 × 4 = 16) marks
8b - ^50maximummarks& (c) (A) Determination of the concentration of Cl
−
AgCl mol = Ag+ mol
= 0.002mol Concentration of Cl
− = 0.08moldm−3
= 0.287g
143.5gmol−1
^7marks&
(B) 2Fe3+ + 3H2S 2FeS + S(4)+ 6H+
4Fes + 7O2 2Fe2O3 + 4SO2(4) (01)S + O2 SO2
H2O + 5SO2 + 2MnO4 5S2O4 +
2Mn2+(4)+ 4H+
6H+ + 5C2O4 + 2MnO4 10CO2 +
2Mn2+(4)+ 8H2O
C2O4 mol = 0.12 × 25 1000
= 3 × 10−3mol
moles MnO4 remain = 3 × 10−3 × 2
5 = 1.2 × 10−3mol
MnO4 moles reacted with SO2 = 0.048 × 50 1000
− 1.2 × 10−3
= 1.2 × 10−3mol
− −
2−
2−
−
−
(4) ^3 × 5 = 15marks&
Fe3+ mol = Fes mol = SO2 mol = 1.2 × 10−3mol × 5
2× 2
3 Fe3+ concentration =
2 × 10−3
× 1000 25
= 0.08 mol dm−3 (3 × 8 = 24 marks)
- 11 -
[see page 12
(C)Determination of the concentration of H+ :
NaOH mol = overall H+ mol in the filtrate (B)
= 0.6
× 201000
= 12 × 10−3mol
H+ mol from H2S = 3 × Fe3+ mol
= 3 × 2 × 10−3mol = 6 × 10−3mol
H+ mol in the initial solution = (12 × 10−3
− 6 × 10−3
)
= 6 × 10−3mol concentration of H
+ in the =
6 × 10−3
× 1000
25initial solution
= 0.24 moldm−3
(3 × 8 = 24) marks
9' (a) (i) (i) Ca(PO4)/ Ca(PO4)2 CaX2 (05) (ii) As its water solubility is low. (05)
(iii) 3Ca3(PO4)2 CaX2 + 14HNO3 3Ca(H2 PO4)2 + 7Ca(NO3)2 + 2HX (10) (iv) Due to high water solubility, can be applied for short term crops, too. Those ions are
easily absorbed by the roots of plants. (05)
(v) Petroliem
air
water
Superphosphate
Y
XH2(g)
P = 250 atmT = 450°Ccatalyst Fe
NH3(g)
N2(g) fractional distillation
P = 1 - 9 atmT = 850 - 1225°Cpt/ Rd catalyst
NO(g)
NO2(g)
HNO3 (aq)
Apatite
partial
electrolysis
- 12 -
[see page 13
(I) A - H2((g) B - N2(g) C - NH3(g) D - NO(g) E - NO(g) F - Apatite (6 × 4 = 24) marks
(II) P - Fractional distillation
Q - Electrolysis
R - Partial acidulation (3 × 3 = 09) marks
(III) X - 250 atm, 450°C, Fe - catalyst Y - 850°C - 1225°C ,1 - 9 atm, Catalyst Platinum / Rhodium (6 × 2 = 12) marks
9a - ^70marks&
(b) (i) Anode - Titanium
Cathode - Nickel (3 × 2 = 06) marks
(ii) 2Cl(aq)
−
Cl2 (g) + 2e
( At the anode ) (04)
2H2O (l) + 2e
−2OH(aq) + H2 (g) (At the cathode) (04)
(iii) As charge removes at the anode and charge is supplied at the cathode / By moving Na+ ions from anode to cathodic compartment. (04)
(iv) As anions are not exchanged through the membrane, it is prevented the moving of OH−
ions, by that prevents the collision with Cl2. (04)
(v) For the absorption of CO2 and other acidic gases ; production of soap, paper, dyes ; refining of water ; removing heavy metals ; removing the acidity of water. (4×2 = 08)
9b - ^30marks&
(c) (i) In the photosynthesis, breaking of water molecules by sunlight (photo-lysis) (3×2= 06) (ii) NH4 , NO2 , NO3
+ − − (3×2= 06)
(iii) Acceptable answers such as, Ú Bringing down the human health Ú Growth retarding in plants
Ú Destroying the structures made of marble and metals.
Ú Weathering of rocks. Ú Weather changing etc.
(3×4= 12) (iv) 1. Acids such as sulphuric, nitric etc. dissolve the the substance of alumino-silicates
in the soil, and release Al3+ ions into water. This disturbs the function of the gills in fish.
2. Acidic rain water which flows through soil, removes nutrients and releases Al3+ ions. Therefore instead of the essential nutrients such as Ca2+ and Mg2+ , plants absorb Al3+ ions. (4×2= 08)
(ii) I Amount of A consumed = 0.2 mol (02) Amount of B formed = 0.2 mol (02) ∴ n = 2 (02) As, 0.2 mol of A is consumed, when 0.2 mol of B is formed. (02)