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ISC Class 12 Chemistry Solved Question Paper 2010

Short Answer Type

11.
Answer the following questions:

Write the relationship between Gibb’s free energy, enthalpy, entropy and the temperature of a system. What is the equation known as?

G = H - TS Or
ΔG = ΔH - T.ΔS

This equation is known as Gibb’s Helmholtz equation.

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12.

Answer the following questions:

The elevation of boiling point produced by dilute equimolar solutions of three substances is in the order A> glucose>B. Suggest a reason for this observations.

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13. What is the mass of a non-volatile solute (molar mass 60) that need to be dissolved in 100 g of water in order to decrease the vapour pressure of water by 25%? What will be the molality of the solution?

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14. Show that the time required for the completion of 75% of a reaction of first order is twice the time required for the completion of 50% of the reaction.

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15.

Give reason for the following:

(i) The density of ice is less than that of water.

(ii) A solution of potassium carbonate turns red litmus paper blue while that of potassium sulphate has no effect on litmus.

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16. Draw the structure of sulphur hexafluoride molecule. State the hybridization of the central atom and the geometry of the molecule. How many sigma bonds are present in the molecule?

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17. Lead (II) sulphide has FCC crystal structure. The edge length of the unit cell of PbS crystal is 500 pm. What is its density? [Pb = 207.2 S = 32]

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18. i) Explain the purification of common salt by bubbling hydrogen chloride through the aqueous solution.

ii) Calculate the pH of a buffer solution containing 0.45 moles of NH₄OH and 0.75 moles of NH₄Cl. K_bfor NH₄OH is 1.8 x 10^-5.

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