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ISC Class 12 Chemistry Solved Question Paper 2007

Short Answer Type

11.

Correct the following statements:

Chloroacetic acid is more acidic than acetic acid because of the - M effect.

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12.

Correct the following statements:

When acetone is treated with bleaching powder, acetaldehyde is obtained.

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13. The molecular weights of sodium chloride and glucose are determined by the Depression of freezing point method. Compared to their theoretical molecular weights, what will be their observed molecular weights when determined by the above method ? Justify your answer.

The observed molecular weight of NaCl will be half of the normal value because the number of particles gets doubled due to dissociation of ions as follows :

NaCl → Na⁺ + Cl^-

The increase in a number of particles of solute due to dissociation leads to an increase in the magnitude of colligative property and therefore a lower value of molecular weight is obtained.

The observed molecular weight of glucose will be same as the theoretical molecular weight because glucose does not undergo association or dissociation when dissolved in a solvent.

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14. An aqueous solution containing 1.70 g of cane sugar in 100 ml water begins to freeze at – 0.093°C. The cryoscopic constant (molal depression constant) of water is 1.86 K Kg mole^{– 1}. Calculate the molecular weight of cane sugar.

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15. A decinormal solution of sodium chloride exerts an osmotic pressure of 4.82 atmosphere at 27°C. Calculate the degree of dissociation of sodium chloride.

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16. The half life of a radioactive isotope is 10 hours. How many atoms of this isotope will be left after 4 hours if initially 1 gm mole of the radioactive isotope was taken ?

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17. ₉₀Th²³⁴ emits 7alpha particles and 6 beta particles. What will be the atomic number and mass number of the resulting atom.

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18. What is the function of the moderator and the control rod in nuclear reactor ?

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19. The melting point of pure silver and pure lead is 961°C and 327°C respectively. A molten mixture of the two metals on cooling at a constant temperature forms a eutectic mixture with a composition of approximately 5% silver and 95% lead at 305°C. Draw a schematic phase diagram for the silver-lead system. Label all the parts of the diagram. Indicate the number of components, phases and degrees of freedom present at the eutectic point.

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20. An aqueous solution of an organic compound contains 10 g of solute per litre. When 1 litre of this solution is treated with 100 ml of ether, 6 g of the organic solute is extracted. How much of the solute will be extracted from the aqueous solution by adding further 100 ml of ether ? (Assume that the molecular state of the solute is the same in ether and water.)

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