Question Paper XII Chemistry Sept. 2011

CLASS - XII

TIME: 3 Hrs.                                 SUBJECT- Chemistry                               M.M.:-70

 

General Instructions:

1. All questions are compulsory.

2. Questions no. 1 to 8 are very short answer questions and carry 1 mark each.

3. Questions no. 9 to 18 are short answer questions and carry 2 marks each.

4. Questions no. 19 to 27 are also short answer questions and carry 3 marks each.

5. Questions no. 28 to 30 are long answer questions and carry 5 marks each.

6. Use log tables if necessary, use of calculators is not allowed.

Values of Logarithms: Log 4 = 0.6020

1. A compound is formed by two elements M and N. The element N forms ccp and atoms of M occupy 1/3^rd tetrahedral voids. What is the formula of the compound?

2. At the same temperature Hydrogen is more soluble in water than Helium. Which of the two has higher K_H value?

3. What is Faraday’s second law of electrolysis.

4. For a reaction, A + B → Products, the rate law is given by r = k[A]^1/2[B]². What is the order of the reaction?

5. What is chemisorption?

6. Between C and CO, which one is better reducing agent after 983K.

7. Why +5 state of Bi is less stable than +5 state of Sb?

8. What is co ordination entity?

9. (i) The reaction 2H₂(g) + O₂(g) → 2H₂O is thermodynamically feasible. How is it that a Mixture of H₂ and O₂

kept at room temperature has no tendency to form water?

(ii) Identify the reaction order if the unit of the rate constant is sec^-1.

10. State what are:  (i) Henry’s law?  (ii) Relative lowering of vapour pressure?

11. Calculate the freezing point of a one molar aqueous solution of KCl  [Density of the solution = 1.04 g/cc., K_f = 1.86 K kg mol^-1, At wt. of K = 39 and Cl = 35.5]

12. State: (a) One limitation of Ellingham diagram. (b) A chemical equation illustrating van-Arkel method.

13. Define the following terms (i) Ferromagnetism (ii) F center

14. What is semiconductor? Describe the two main types of semiconductors.

15. The specific conductance of 0.05 N solution of an electrolyte at 298 K is 0.02 Scm^-1. Calculate the equivalent

conductance.

16. Complete the following

Fe³⁺  +  SCN^- →  A  (Blood Red Colour) + F^-  →     B.   Find the spin magnetic moment of B

17. (i) Write the IUPAC name of the following Compound  NH₄[Cr(NH₃)₂(SCN)₄]

(ii) Write the formula of the following compound  - Dichloridobis(ethane-1,2-diamine)platinum(IV) nitrate

18. For the complex [Fe(en)₂Cl₂]Cl, identify (a) the number of geometrical isomers (b) whether there is an optical isomer. If yes draw structure

19. calculate the density of silver which crystallizes in fcc form. The distance between nearest metal atom is 287 pm ( molar mass of Ag = 107.87 gmol^-1; N_o = 6.022×10²³)

20. Determine the osmotic pressure of a solution prepared by dissolving 25 mg of K₂SO₄ in 2 litre of water at 25^oC, assuming that it is completely dissociated.

21. How will you classify the colloids on the basis of molecular size? Distinguish between multimolecular and macromolecular colloids with the help of example.

22. Explain the following terms (i) Tyndall effect (ii) Gold number (iii) Peptization

23. Write the chemical reactions which take place in different zones in blast furnace during the extraction of iron.

24. State why: (a) Bleaching of flowers by Cl₂ is permanent while that by SO₂ is temporary. (b) Enthalpy of dissociation of F₂ is much less than that for Cl₂. (c) Nitric oxide becomes brown when released in air.

25. Draw the structures and write basicity of: (i) Marshall’s acid (ii) Pyrophosphoric acid (iii) Sulphurous acid

26. Explain the followings (i) Variation of acidic strength of oxoacids of a particular halogen in different oxidation states. (ii) Reaction condition used to maximize the yield in Haber process.

27. (i) Write chemical reaction involving in preparation of KMnO₄ from pyrolusite. (ii) At 300 K H₂O is liquid while H₂S is gas. Why?

28. (a) State two consequences of lanthanide contraction.                                                                             2

(b) Account for the following:                                                                                                                                1×3

(i) Vanadium pentoxide acts as a catalyst?  (ii) In any transition series with increase in atomic number, the atomic radius does not change very much. (iii) f-Block elements are called inner-transition elements.

OR  

(a) Complete the following:

(i) Cr₂O₇^2- + 14H⁺ + 6e^- → ………….. + 7H₂O                                                                                                     1×2

(ii) CrO₄^2- + …………. →                   +    H₂O

(b) Account for the following:                                                                                                                                 1×3

(i) Size of trivalent cations in the lanthanoid series decreases with increasing atomic number.

(ii) Transition metal fluorides are ionic whereas chlorides and bromides are usually covalent.

(iii) Chemistry of lanthanoids is quite similar.

29. (a) Write down the reactions involved in the working of a H₂–O₂ fuel cell.                                             2

(b) A solution of Ni (NO₃)₂ is electrolysed between platinum electrodes using a current of 5.0 amperes for

20.0 minutes. What mass of Ni is deposited at the cathode? [At. Wt. Ni = 58.7]                                             3

OR

(a) (i) State Kohlrausch’s law.                                                                                                                                1×2

(ii) Why does an alkaline medium inhibit the rusting of iron?

(b) Calculate the equilibrium constant for the following reaction:                                                                      3

Zn(s) + Cu²⁺(aq) –→    Zn²⁺(aq) + Cu(s)

[ E⁰Zn²⁺/Zn = – 0.763 V and E⁰Cu²⁺/Cu = + 0.34 V ]

30. For a chemical reaction variation in concentration, ln[R] vs time(min) plot is shown below:

i) What is the order of the reaction?                                                                                                                    1×5

ii) What are units of rate constant k for the reaction?

iii) If initial concentration of the reactant is half of the original concentration how will t_1/2 change?

iv) Draw the plot of log[R_o]/[R] vs time(s).

v) What will be the plot of half life vs [R_o] of the reaction?

Or

i) What is the difference between order of reaction and molecularity?                                                          2

ii) The rate of reaction quadruples when the temperature changes from 293 K to 313 K. calculate the energy of activation of the reaction assuming that it does not change with temperature.                           3

Question Paper XII

                                                                             CLASS - XII
TIME: 3 Hrs.                                                    SUBJECT- Chemistry                                        M.M.:-70

General Instructions:
1. All questions are compulsory.
2. Questions no. 1 to 8 are very short answer questions and carry 1 mark each.
3. Questions no. 9 to 18 are short answer questions and carry 2 marks each.
4. Questions no. 19 to 27 are also short answer questions and carry 3 marks each.
5. Questions no. 28 to 30 are long answer questions and carry 5 marks each.
6. Use log tables if necessary, use of calculators is not allowed.
Values of Logarithms: Log 4 = 0.6020

1. A compound is formed by two elements M and N. The element N forms ccp and atoms of M occupy
   1/3rdtetrahedral voids. What is the formula of the compound?
2. At the same temperature Hydrogen is more soluble in water than Helium. Which of the two has
    higher KH value?
3. What is Faraday’s second law of electrolysis.
4. For a reaction, A + B ----- Products, the rate law is given by r = k[A]1/2[B]2. What is the
    order of the reaction?
5. What is chemisorption?
6. Between C and CO, which one is better reducing agent after 983K.
7. Why +5 state of Bi is less stable than +5 state of Sb?
8. What is co ordination entity?
9. (i) The reaction 2H2(g) + O2(g) → 2H2O is thermodynamically feasible. How is it that a
    Mixture of H2 and O2kept at room temperature has no tendency to form water?
    (ii) Identify the reaction order if the unit of the rate constant is sec-1.
10. State what are:
      (i) Henry’s law?
      (ii) Relative lowering of vapour pressure?
11. Calculate the freezing point of a one molar aqueous solution of KCl.
      [Density of the solution = 1.04 g/cc., Kf = 1.86 K kg mol-1, At wt. of K = 39 and Cl = 35.5]
12. State:
      (a) One limitation of Ellingham diagram.
      (b) A chemical equation illustrating van-Arkel method.
13. Define the following terms (i) Ferromagnetism (ii) F center
14. What is semiconductor? Describe the two main types of semiconductors.
15. The specific conductance of 0.05 N solution of an electrolyte at 298 K is 0.02 Scm-1. Calculate the  
      equivalent conductance.
16. pin magnetic moment of B
17. (i) Write the IUPAC name of the following Compound
NH4[Cr(NH3)2(SCN)4]
(ii) Write the formula of the following compound
Dichloridobis(ethane-1,2-diamine)platinum(IV) nitrate
18. For the complex [Fe(en)2Cl2]Cl, identify (a) the number of geometrical isomers (b) whether there is an optical
isomer. If yes draw structure

19. calculate the density of silver which crystallizes in fcc form. The distance between nearest metal atom is 287
pm ( molar mass of Ag = 107.87 gmol-1; No = 6.022×1023)
20. Determine the osmotic pressure of a solution prepared by dissolving 25 mg of K2SO4 in 2 litre of water at 25oC,
assuming that it is completely dissociated.
21. How will you classify the colloids on the basis of molecular size? Distinguish between multimolecular and
macromolecular colloids with the help of example.
22. Explain the following terms (i) Tyndall effect (ii) Gold number (iii) Peptization
23. Write the chemical reactions which take place in different zones in blast furnace during the extraction of iron.
24. State why:
(a) Bleaching of flowers by Cl2 is permanent while that by SO2 is temporary.
(b) Enthalpy of dissociation of F2 is much less than that for Cl2.
(c) Nitric oxide becomes brown when released in air.
25. Draw the structures and write basicity of:
(i) Marshall’s acid (ii) Pyrophosphoric acid (iii) Sulphurous acid
26. Explain the followings
(i) Variation of acidic strength of halogen acids of a particular halogen in different oxidation states.
(ii) Reaction condition used to maximize the yield in Haber process.
27. (i) Write chemical reaction involving in preparation of KMnO4 from pyrolusite.
(ii) At 300 K H2O is liquid while H2S is gas. Why?
28. (a) State two consequences of lanthanide contraction. 2
(b) Account for the following: 1×3
(i) Vanadium pentoxide acts as a catalyst?
(ii) In any transition series with increase in atomic number, the atomic radius does not change very much.
(iii) f-Block elements are called inner-transition elements.
OR
(a) Complete the following:
(i) Cr2O72- + 14H+ + 6e- → ………….. + 7H2O 2

(ii) CrO42- + …………. ……………. ………….. + 4OH-

(b) Account for the following: 1×3
(i) Size of trivalent cations in the lanthanoid series decreases with increasing atomic number.
(ii) Transition metal fluorides are ionic whereas chlorides and bromides are usually covalent.
(iii) Chemistry of lanthanoids is quite similar.

29. (a) Write down the reactions involved in the working of a H2–O2 fuel cell. 2
(b) A solution of Ni (NO3)2 is electrolysed between platinum electrodes using a current of 5.0 amperes for
20.0 minutes. What mass of Ni is deposited at the cathode? [At. Wt. Ni = 58.7] 3
OR
(a) (i) State Kohlrausch’s law. 1×2
(ii) Why does an alkaline medium inhibit the rusting of iron?
(b) Calculate the equilibrium constant for the following reaction: 3

Zn(s) + Cu2+(aq) Zn2+(aq) + Cu(s)

[ E0Zn2+/Zn = – 0.763 V and E0ZCu2+/Cu = + 0.34 V ]




30. For a chemical reaction variation in concentration, ln[R] vs time(min) plot is shown below:
i) What is the order of the reaction? 1×5

ii) What are units of rate constant k for the reaction?
iii) If initial concentration of the reactant is half of the original concentration how will t1/2 change?
iv) Draw the plot of log[Ro]/[R] vs time(s).
v) What will be the plot of half life vs [Ro] of the reaction?
Or
i) What is the difference between order of reaction and molecularity? 2
ii) The rate of reaction quadruples when the temperature changes from 293 K to 313 K. calculate the energy of
activation of the reaction assuming that it does not change with temperature. 3

Chemistry

Atomic Structure and Chemical bonding

De Broglie equation λ = h / mv or λ = h / p

Heisenberg`s Uncertainty Principle

Number of waves in nth orbit

h

Schrodinger wave equation

Energy of hydrogen atom E_n =

Angular momentum of the electron =

Spin angular momentum of electron =

Bond order = ------- N_b --- is no of electrons in bonding molecular orbital

N_a --- is no of electrons in antibonding molecular orbitals

Radius of n^th orbit of Hydrogen atom is = 5.29 nm

No. of orbitals in n^th shell = n²

No of electrons in n^th shell =2n²

The no of spectral lines when an electron jumps from n^th level to ground level (n=1)

=

No of spherical nodes in an orbital =

Type of Hybridization	Orbitals participating	Examples
		CH4 ,SiF4 ,OF2 ,H2O ,NH3, ,
sp3d		PCl5 ,,

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The Solid State

Bragg’s equation -----

Density formula gcm^-3

Radius ratio and Coordination number

Radius ratio	Structure	Coordination no	Example
0.155-0.225	Planar triangular	3	B2O3
0.225-0.414	Tetrahedral	4	ZnS, CuCl, CuBr, CuI, BaS, HgS
0.414-0.732	Octahedral	6	NaCl, MgO, NaBr, CaS , CaO
0.732-1.000	Cubic	8	CsCl, CsBr, TlBr, NH4Br

Relationship between the nearest neighbor distance and radius of atom and edge length (a)

Unit Cell	Distance bt Nearest neighbor (d)	Radius (r)
Simple Cubic
Face centered cubic
Body centered cubic

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Solution

Mass % of component A is =

Volume % of component A is =

Parts per million (ppm) =

(W_A is the mass solute & W_solution is the mass of total solution)

Molarity of a solution =

Molality of a solution =

Mole fraction of solute A is ( x_A) = Mole fraction of solvent B is (x_B) = ; ( x_A + x_B = 1)

Normality = =

(E_equivalent is the no. of gram equivalent of solute)

Molarity equation M₁V₁ = M₂ V₂ ;

Henary `s law m = K.p

Raoult`s law for binary solution of Volatile liquids

Raoults law for binary solution of Non Volatile liquids

Determination of molar masses of solute by using colligative properties

1. Relative lowering of vapour pressure

2. Elevation in boiling point

3.Depression in freezing point

4. Osmotic pressure

Abnormal molar masses and Van`t Hoff factor

Degree of dissociation (ά) = =

Degree of association (ά) = =

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Thermodynamics

First law of thermodynamic

Enthalpy change or ( for gaseous Rx )

Entropy and entropy change

Free energy change

- (for electric work)

Efficiency of fuel cell =

Standard free energy change

; K =

Third law of thermodynamics S =

Spontaneity and Temperature

Sign of Enthalpy	Sign of Entropy	Value of T	Spontaneity
+ve	+ve	high	Spontaneous
+ve	+ve	Low	Non Spontaneous
+ve	-ve	Low/high	Non Spontaneous
-ve	-ve	low	Spontaneous
-ve	-ve	high	Non Spontaneous
-ve	+ve	Low/high	Spontaneous

for isothermal process

for isobaric process

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Electrochemistry

Faraday`s first law of electrolysis W = ZQ or W = Zit

Faraday`s second law of electrolysis

=

Conductance = ; Conductivity =

Equivalent conductance = Λ_eq

Molar conductance = Λ_m =

Units of Molar conductance Ω^-1cm²mol^{-1 ;} Scm²mol^-1 ; Sm²mol^-1 (SI units)

Units of Equivalent conductance Ω^-1cm²gequ^-1 ; Scm²gequ^-1 ; Sm²gequ^-1

Kohlrausch`s law

for a hypothetical reaction Kohlrausch`s law becomes

Degree of dissociation

Dissociation constant of a weak electrolyte =

Solubility of a sparingly soluble salt =

Nernest equation =

Chemical Kinetics

Rate of reaction = (for a reaction A → P)

For a Rx. the unique reaction rate is

Law of mass action for is rate =

and rate law is rate = Where ά and β are the experimental

found exponent and there sum is known as order of reaction

Units of rate constant for different order reactions are

For zero order Rx -- Mol L^-1 S^-1

For 1^st order Rx. -- S^-1

For 2^nd order Rx. -- L Mol^-1 S^-1

Integrated rate equation for different order reactions

Zero order where [A_o] is the initial concentration and [A] is final concentration

1^st order or where is initial conc. and x is the amount consumed

Half life equation for different order reactions for zero order

For 1^st order Rx.

Amount left after n half lives where n is no. of half lives i.e.

Calculation of order of a reaction by half life method

n is the order of reaction

Arrhenius equation or

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Surface Chemistry

Freundlich adsorption isotherm

Langmuir adsorption isotherm

Type of colloidal system

S.No.	Dispersed Phase	Dispersion Medium	Name	Example
1	Solid	Solid	Solid Sol	Some coloured glasses, gemstone
2	Solid	Liquid	Sol	Some paints , cell fluids
3	Solid	Gas	Aerosol	Smoke , dust
4	Liquid	Solid	Gel	Cheese , butter , jellies
5	Liquid	Liquid	Emulsion	Milk , hair cream
6	Liquid	Gas	Aerosol	Fog , mist, cloud
7	Gas	Solid	Solid foam	Pumice stone , foam rubber
8	Gas	Liquid	Foam	Froth, whipped cream soap lather

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