Solved Board Paper For ICSE Class 12 Chemistry

(a)

1. Unit cell

2. Bent, Tetrahedral
3. Positive
4. Adipic acid, hexamethylenediamine

(b)

(i) (3)

Explanation:

(ii) (2)

Explanation: The value of the equilibrium constant for a reaction always depends only upon the temperature of the reaction and is independent of the concentrations of the reactants with which we start or the direction from which the equilibrium is approached.

(iii) (2)

Explanation:

Number of optical isomers = 2ⁿ, where n is the number of asymmetric carbon atoms.

∴ Number of optical isomers = 2² = 4

(iv) (1)

Explanation: Lower the pK_a value, stronger is the acid.

(c)

(i) – (c), (ii) – (a), (iii) – (d), (iv) – (b)

(d)

(i) A peeled egg swells when placed in water due to endosmosis. It happens because the solution inside the egg is the concentrated one. However, it shrinks when it is placed in the concentrated NaCl solution due the process of exo-osmosis.

(ii) The Le-Chatelier’s principle can be used to predict the favourable conditions for the maximum yield in many industrial processes such as the manufacture of NH₃ by the Haber’s process and the manufacture of H₂SO₄ by the contact’s process.

(iii) When a few drops of acid or alkali are added to CH₃COONH₄, it acts as a buffer. Hence, there is no change in the pH on adding a small amount of the acid or base.

(iv) The reduction reaction involved is:

Cu²⁺ + 2e^– → Cu

∴ the charge required for the reduction of one mole of Cu²⁺ to Cu = 2F = 2 x 96500C = 193000 C.

A homogenous catalyst enters into chemical combination with one or more reactants forming an intermediate compound. This intermediate compound then combines with one of the reactants to form the product and regenerate the catalyst.

In case of heterogeneous catalysis, the gaseous reactants first get chemisorbed on the surface of the catalyst after getting diffused towards the catalyst. The reactants formed the products, which get absorbed on the catalyst’s surface and finally desorbed.

(a) Antiseptics are the chemicals used to prevent the growth of microorganisms or to kill them but these are not harmful to animal tissues. Examples, Furacin and Soframycin

Disinfectants are the chemicals which are used to kill microorganisms but these are harmful to the animal tissues. Examples, phenol and chlorine

(b) Detergents contains calcium and magnesium salts of sulphonic acids which are soluble even in hard water but soaps are not soluble in hard water.

(a) When ethyl alcohol is made unfit for drinking purposes by adding poisonous and nauseating materials like methanol or pyridine etc. the process is called denaturing and the spirit formed is called denatured spirit.
(b) Butanol-1 < Secondary butyl alcohol < Tertiary butyl alcohol

(a) 1,3-Butadiene and styrene

(b) Hexamethylenediamine and adipic acid

In alcohols, O-atom contains 2 lone pairs of electrons. So, they act as weak bases and they are replaced to get a substitution product. While in phenols, phenoxide ion is resonance stabilized and phenol releases H+ ions. Hence substitution reaction is not possible.

1. The two reasons can be:

1. Electron capture by the particles from the air and during electro dispersion in Bredig’s arc method.
2. Dissociation of molecules followed by aggregation of ions as in the case of soaps.

2. Brownian movement is caused by the striking of the colloidal particles by the molecules of dispersion medium due to their kinetic energy.

3. Higher is the critical temperature of a gas, the more easily it will be liquefied and more readily it will be adsorbed on the solid surface.

(a)

1. [Pt(NH₃)₂Cl₂]

2. [Co (en)₂Cl₂]

(b)

1. [Co(SO₄)(NH₃)₅]NO₃

2. [Co(NH₃)₅(ONO)]Cl₂

1. Electronic configuration of Mn²⁺ is 3d⁵ which is half filled and hence stable. So third ionization enthalpy is very high so third electron cannot be lost easily. In case of Fe²⁺ electronic configuration is 3d⁶. So it can lose one electron easily to give the stable configuration 3d⁵.
2. As atomic number increase the nuclear charge increases but the addition of electron in d-subshell increases the screening effect which counter balances the effect of increased nuclear charge.
3. +2, +3, and +4

(i) Ammonia < Triethylamine < Ethylamine

(ii) Aniline < p-nitroaniline < p-toludine

2. Electronegativity of nitrogen atom is less than that of oxygen atom. Therefore, hydrogen bonds formed in amines are weaker as compared to those formed in alcohols and carboxylic acids. Therefore, boiling point of amines is lower than those of the alcohols and carboxylic acids of comparable molecular masses.

(i) It is known as oil of vitriol due to its oily appearance and the fact that it was obtained by the distillation of green vitriol (FeSO₄.7H₂O).

(ii)

On passing excess of SO₂ gas through lime water, its milkiness disappears due to the formation of calcium bisulphate, which is soluble.

(ii)

1. Due to the small size of the oxygen, it forms a strong pi-bond with another oxygen atom by the sidewise overlap of the two partially filled p-orbitals. Thus, the oxygen satisfies its divalency by forming a double bond with another oxygen atom. As the atomicity of the oxygen is two, it is a small molecule and Van der Waal’s forces in it are small. Hence, it is a gas. On the other hand, sulphur occurs as S₈. This is because of its inability to form multiple bonds due to its larger size. Due to the higher atomicity, Van der Waal’s forces in sulphur are stronger. Hence, sulphur is solid.
2. The sum of the four ionisation enthalpies for nickel is much higher than the sum of the four ionisation enthalpies of platinum, i.e., the energy required to remove four electrons from platinum is much less than the energy required for removing four electrons from nickel.

(ii)

(1)The carbylamine reaction is used to distinguish between 1º amines and 2º or 3º amines. Both 1º aliphatic and aromatic amines give this reaction. They form foul smelling isocyanide on reaction with chloroform and alc. KOH.

(2) Electron donors are bases. The methyl group is electron donor. Methyl amine, due to presence of electron donor methyl group, has higher electron density and is stronger base as compared to ammonia.