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SECOND YEAR HIGHER SECONDARY MODEL EXAMINATION 2023 – ANSWER KEY
SUBJECT: CHEMISTRY Qn. Code: SY 225

Sub
Qn. Scor
Qns Answer Key/Value Points Total
No. e
.
Answer any 4 questions from 1 to 5. Each carries 1 score
1. Zero 1 1
2. Lanthanide contraction 1 1
3. Ethylenediaminetetraacetate ion (EDTA4–) 1 1
4. (d) Benzaldehyde 1 1
5. (a) Chloroform 1 1
Answer any 8 questions from 6 to 15. Each carries 2 scores
6. (i) Raoult’s law states that for a solution of volatile liquids, the partial vapour
pressure of each component in the solution is directly proportional to its mole 1
fraction in solution.
2
OR, the mathematical expression p1 = p10χ1 and p2 = p20χ2
(ii) A solution of n-hexane and n-heptane OR, bromoethane and chloroethane OR, 1
benzene and toluene.
7. Two solutions having same osmotic pressure at a given temperature are called
1
isotonic solutions.
2
E.g. The fluid inside our blood cells are isotonic with 0.9% (mass/volume) sodium
1
chloride solution.
8. Anode reaction: Zn(s) → Zn2+(aq) + 2 e- ½
Cathode reaction: Cu2+(aq) + 2 e- → Cu(s) ½ 2
Net reaction: Zn(s) + Cu2+(aq) → Zn2+ (aq) + Cu(s) 1
9. For a first order reaction, k= 2.303 log [R]0
1
t [R]
-3 -1
Here k = 1.15 x 10 s , [R]0 = 5g and [R] = 3g
So, t = 2.303 log [R]0
1 2
k [R]
= 2.303 x log(5/3)
1.15 x 10-3
= 440.5 s
10. K3[Fe(CN)6] – Potassiumhexacyanidoferrate (III) 1
2
[Ni(CO)4] – Tetracarbonylnickel(0) 1
11. Chloroform is stored in closed dark coloured bottles filled up to the neck in order to
prevent its oxidation to the poisonous gas; carbonyl chloride (COCl2) or phosgene.
2 2
OR, the equation: 2CHCl3 + O2 light 2COCl2 + HCl

12. Phenols are acidic, due to the following reasons:
(i) Due to the greater electronegativity of sp2 hybridized carbon atom to which 1 2
-OH group is attached.


+2 CHEMISTRY MODEL EXAM ANSWER KEY PREPARED BY ANIL KUMAR K L, APHSS ADICHANALLOOR, KOLLAM 1

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(ii) The greater stability of phenoxide ion compared to phenol. 1
Due to these reasons, phenols readily lose H+ ions and hence are more acidic.
13. The reaction of an aromatic primary amine with nitrous acid [NaNO2 and HCl] at 273
to 278 K to form an aromatic diazonium salt is called diazotization.
Or, the equation:

2 2




14. This is because of the presence of partially filled d orbitals in transition elements.
When an electron from a lower energy d orbital is exited to higher d level, it absorbs
energy and this energy is equal to the energy of certain colours in the visible region. 2 2
So the colour observed is the complementary colour of the light absorbed.
OR, The colour is due to d-d transition of electrons.
15. DNA RNA
1. Double stranded Single stranded
2. The pentose sugar is 2-deoxy The pentose sugar is ribose
ribose
2 2
3. Nitrogen bases present are Instead of Thymine, Uracil is present
Adenine, Guanine, Cytosine
and Thymine.
[Only 2 differences required]
Answer any 8 questions from 16 to 26. Each carries 3 scores
16. (i) (c) Lead Storage battery 1
(ii) Fuel cells are galvanic cells which convert the energy of combustion of fuels (like 1
hydrogen, methane, methanol, etc) directly into electrical energy. 3
(iii) 2H2(g) + O2(g) ⎯→ 2 H2O(l ) 1
17. (i) The Arrhenius equation is k = A.e-Ea/RT 1
(ii) Activation energy is the minimum amount of kinetic energy required for the reactant
molecules for effective collision. 1
Or, It is the energy required for the reactant molecules to form activated complex in 3
a chemical reaction.
(iii) k = [R]0 – [R]
t 1
18. (i) These are reactions which appear to follow higher order but actually follow first 1
order kinetics.
3
(ii) 3 1
(iii) 5/2 OR, 2½ 1
19. (i) Potassium permanganate is commercially prepared from MnO2. The preparation
involves two steps.
3
Step 1: Conversion of MnO2 to potassium manganate (K2MnO4) by fusing with KOH in
presence of air.


+2 CHEMISTRY MODEL EXAM ANSWER KEY PREPARED BY ANIL KUMAR K L, APHSS ADICHANALLOOR, KOLLAM 2