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ISC Class 12 Chemistry Solved Question Paper 2005

Short Answer Type

11.

Correct the following statements :

Graphite has a two-dimensional sheet-like structure in which each carbon atom is sp³ hybridized.

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12.

Correct the following statements :

For water-system, the number of phases that can exist in equilibrium is two.

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13. Calculate the mole fraction of water in a sodium hydroxide solution which has 80 g of NaOH and 54 g of H₂O. [Relative atomic masses : Na = 23, O = 16, H = 1].

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14. The bond angles in CH₄ (109.5°), NH₃ (107°) and H₂O (104.5°) are different although these molecules have the same hybridization, sp³. Give a suitable reason for this.

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15.

Radium has a half-life of 1580 years. How long would it take for each of the samples of radium given below to disintegrate ?

(i) 20% of a 5 g sample.

(ii) 20% of a 50 g sample.

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16. State the main characteristics of an ionic and a network type of crystal citing a suitable example for each.

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17.
For the cell

Zn | Zn²⁺ (a = 1) | | Cu²⁺ (a = 1) | Cu

Given that E_Zn . Zn²⁺ = +0.761 volt; E_cu²⁺, Cu = +0.339 volt

(i) Write the cell reaction

(ii) Calculate the emf and free energy change at 298 K involved in the cell. [Faraday’s constant F = 96500 coulomb equivalent^{– 1}].

$Zn space rightwards arrow Zn to the power of 2 plus end exponent space plus 2 straight e to the power of minus Cu to the power of 2 plus end exponent space plus 2 straight e to the power of minus rightwards arrow space Cu Zn space plus Cu to the power of 2 plus end exponent space rightwards arrow space Zn to the power of 2 plus end exponent space plus Cu straight E subscript cell superscript 0 space equals space straight E subscript cathode superscript 0 space plus straight E subscript anode superscript 0 space equals space 0.339 space plus.761 space equals space 1.100 space volt ii right parenthesis space For space energy space change space increment space straight G space equals negative nFE subscript cell superscript 0 equals space minus left parenthesis 2 space mol right parenthesis space straight x space 96500 space straight C space mol to the power of negative 1 end exponent right parenthesis space straight x space 1.10 space volt equals negative 212300 space straight J equals negative 212.3 KJ$