Class XII Exam (board pattern) From First 5 chapters

Sulekha Rani.R,P.G.T Chemistry,KV NTPC Kayamkulam

(23 marks from first 5 chapters)

2008 questions

SET I

1. Atoms of element B form hcp lattice and those of element A occupy 2/3rd of tetrahedral voids. What is the formula of the compound formed by the elements A and B? (2m)

2. Explain the terms Schottky defect and F-centres. (2m)

Or

Explain paramagnetism and ferrimagnetism.

3. Define osmotic pressure and write the equation relating osmotic

pressure and molar mass (2m)

4. Why do KCl and acetic acid show abnormal molar mass? What do

we infer when Vant Hoff’s factor is unity. (2+1)

5. Write the cell notation for a cell having magnesium anode and copper cathode. Also calculate the emf of this cell where concentration of magnesium ions is 0.001 M and copper ions is 0.0001 M. The standard emf of Mg is -2.36 V and Cu is 0.34 V. (3m)

6. The conductivity of 0.20 M solution of KCl at 298K is

0.0248 S/cm. Calculate its molar conductivity. (2m)

7. a) Show that for a zero order reaction, half life is directly proportional to the initial concentration of the reactant, but in a first order reaction, the half life of the reaction is independent of the initial concentration of reactant. (3)

b) A first order reaction has a rate constant of 0.00115/s.How long will

5 g of this reactant take to reduce to 3 g? (2)

Or

a) The rate constants of a reaction at 500 K and 700 K are 0.02/s and 0.07/s respectively. Calculate activation energy.

(R=8.314 J/K/mol) (3)

b) A reaction is first order in A and second order in B.Write the rate law expression and how will the rate be affected if concentration of B is increased three times? (2)

8. What is Hardy-Schulze rule? (1m)

9. What is Kraft temperature? Distinguish between lyophilic and lyophobic colloides with an example each. ( 3m)

SET II

1. What is the number of atoms per unit cell in a body centered cubic structure ? (1m)

2. Calculate the density of silver which crystallizes in the face-centered cubic

structure. The distance between the nearest silver atoms in this structure is

287 pm.(Molar mass of Ag =107.87 g mol -1, NA =6.02 x 10 23 mol-1) (3)

OR

Analysis shows that nickel oxide has formula Ni 0.98O1.00. What fractions of the nickel exist as Ni2+ and Ni3+ ions? (3)

3. Two liquid A and B boils at 145°C and 190°C respectively. Which of them has a higher vapour pressure at 80°C. (1m)

4. State Henry’s law of solubility of a gas in a liquid.Give the significance of Henry’s law constant. (2m)

5. A 5% solution (by mass) of cane sugar in water has freezing point of 271K.

Calculate the freezing point of a 5% glucose in water if freezing point of pure water is 273.15K. (2m)

6. Define molar conductivity. Write the unit of molar conductivity. (1m)

7. How does molar conductivity vary with concentration for

i)weak electrolyte and for

ii) strong electrolyte. Give reason for these variation (2m)

8. Calculate the emf of the cell

Mg(s)/Mg2+(0.01M) // Cu2+(1 x10-3M)/ Cu(s)

Given :E° Cu2+/ Cu(s) =+ 0.34 V, E° Mg(s)/Mg2+ = -2.36 V. (2m)

9. What is meant by elementary reaction ? (1m)

10. What are pseudo unimolecular reaction ? Give an example.(2m)

11. A reaction is first order in A and second order in B :

i) Write differential rate equation.

ii) How is the rate affected on increasing the concentration of B three times? (2m)

12. Explain the following terms :

i) Hardy-schulze rule.

ii)Electrophoresis. (2m)

13. Explain what is observed when,

i)The path of the light becomes visible when it is passed through As2O3 sol in water.

ii)an electrolyte NaCl is added to ferric hydroxide sol. (2m)

2009 board XII chemistry --set 1

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6. 7. 8. 9. What is tyndall effect