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NIOS Sample Question Paper Chemistry Class – XII (2010)

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Sample Question Paper

Chemistry

Class – XII

Time : 3 hrs.                                                                            Maximum Marks : 80

Note : (i) All questions in Section A are compulsory
          (ii) Attempt only one out of three options in Section B, i.e., attempt either Part I or Part II or Part III in Section B.
         (iii) marks for each question are indicated against it.
         (iv) Use log tables if necessary.

Section A

1. What are the SI units of mass?                       1

Hint: Kilogram kg

2. How may moles of hydrogen gas are there in 11.2 liters of hydrogen gas at STP?                 1

Hint: 0.5 mol

3. Name a lyophilic colloid.                    1

Hint: Gum, gelatin or starch (any one) or any other suitable example.

4. What do the molecular solids have low melting points?                    1

5. Define enthalpy of formation.                                                 1

6. Why is lithium most difficult to be reduced?                           1

Hint: Because the reduction potential of lithium is minimum or its oxidation potential is maximum.

7. Define an isolated system.                                                      1

8. What is Le Chatelier's principle.                                              1

9. Name the components of Bordeaux mixture.                         1

Hint: CuSO4 (aq) + CaO

10. State two characteristic properties of transition elements which are different from group I elements.              1

11. Give the structural formula of the product obtained on mono bromination of phenol.                    1

12. Derive the SI units for the following quantities                   2
                i) Force
               ii) Pressure

Hint: (i) Force = mass x acceleration = kg.ms-2 or N

          (ii) Pressure = Force/Area = N/m2 = Nm-2 or kg m-1-s-2

13. 10 g of a non-volatile solute in 100g of benzene raises its bioling point by 1 K.

What is the molecular mass of the solute? Kf for benzene = 2.53 K g-1mol-1 . 2

14. Glucose is formed according to the following reaction :

                    6CO2 (g) + 6 H2O (1) → C6H12O6 (s) + 6O2 (g)

absorbing 2840 kJ of heat. How much energy will be given out by combustion of 1.08g of glucose?                     2

Hint: Correct value for enthalpy of combustion of glucose by reversing the reaction = -2840 KJ

          No. of moles of glucose = 1.08/180

          Now the heat evolved by the combustion of 1 mol (180g) of glucose = 2840 kJ

          By the combustion of 1.08g of glucose the energy given out = 2840 kJ x 1.08g/180g = 17.04 kJ

15. State Heisenberg's principle of uncertainty and give its mathematical relationship.                                       2

16. The solubility of calcium sulphate in water is 4.9x10-3M at 250C. Calculate the value of Ksp for CaSO4 at this temperature

               Given : CaSO4 (s) ↔ Ca2+ (aq) + SO42-(aq)                                                   2

Hint: For the reaction Ksp = [Ca2+- ] [SO42-].

         From the equation we see that when 4.9x10-3 mol of CaSO4 dissolves

         to makes IL of a saturated solution, the reacting ionic concentration are

          [Ca2+-]= 4.9 x 10-3 M or 4.9 x 10-3 mol L-1

          [SO42-] = 4.9 x 10-3 M or 4.9 x 10-3 mol L-1

          Ksp = [Ca2+] [SO42- ]= (4.9 x 10-3 mol L-1) x (4.9 x 10-3 mol L-1) = 2.4 x 10-5 mol2 L-2

17. Explain the variation of ionization energy down the group in a periodic table. State the relationship of ionization energy of an atom with its reactivity.                 2

Hint: Ionization energy decreases down the group because outermost electrons are weakly held.
         Lesser ionization energy, more reactivity.

18. Paramagnetism of a substance can be calculated in terms of magnetic moment in Bohr Magneton (BM) by using the expression :

                         μ = [n (n+2)]1/2

The atomic number of chromium is 24. In which oxidation state the magnetic moment of its (Chromium) ion will be maximum and in which it will be zero? (n is the number of unpaired electrons).                                         2

Hint: Magnetic moment will be maximum in Cr2+

          Magnetic moment will be zero in Cr6+

19. Write briefly about "Aldol condensation' and give an example.                                2

Hint: Aldol condensation is the condensation of aldehydes and/or ketones possessing at least one H-atom attached to a-carbon atom in the presence of an alkali.

            2CH3CHO → CH3CHOH.CH2 CHO → CH3CH = CHCHO + H2O

20. Differentiate between a gangue and slag. Give an example of a metallurgical step where stag, flux and gangue are involved simultaneously.          2

Hint: Slag is a fusible substance formed by the reaction of flux with the impurity (gangue).

           CaCO3 + FeSiO3 → CaSiO3 + CO2 + FeO

21. Define the term isomerism. Give one example of each of the two types of isomerism.                       2

22. Normally each shell of an atom can accommodate a maximum of 2n2 number of electrons. Let us suppose the rule changes to 2n3. What shall be the configuration of element number 11 and what type of element it shall be as per allotment of its sub shell?                                 2

Hint: 1s2 2s2 2p6 2d1

23. Given the reaction :

                  XeF4 (g) + F (g) → XeF6 (g)

Predict the change in hybridization and consequent, final shape of the molecule followed in the above reaction.                                 2

24. Write a chemical equation showing the oxidation of hydrogen sulphide with the help of acidified potassium dichromate.               2

Hint: K2Cr2O7 + H2SO4 + H2S → K2 SO4 + Cr2(SO4)3 + H2O + SO2

25. State the following laws and give the mathematical expression for each law :

                 (i) Boyle’s law

                 (ii) Charles’ law

                 (iii) Dalton’s law of partial pressures.                                 3

26. State the modern periodic law. Write the special names given to elements of group 1,2, 17 and 18.                    3

Hint: Group 1 = alkali                      Group 2 = alkaline
           Group 17 = halogens              Group 18 = noble gases

27. (i) What is diazotization? Explain giving an example

      (ii) Describe the preparation of sulphanilic acid form aniline. Write its witter ionic structure.          3

28. Molar mass of NaCl is 58.5g mol-1. Calculate the number of moles of Na Na+ ions and Cl- ions and also their masses in 11.7g of NaCl.                     3

29. A galvanic cell consists of metallic Zn plate immersed in 0.1 M Zn (NO3)2 solution and metallic plate of lead in 0.02 M Pb (NO3) solution. Given

                  E0Zn2+ → Zn = -0.76 V, E0Pb2+ → Pb=-0.13 V

                a) Write the half-cell reactions

                b) Write the overall reaction of the cell

                c) Calculate the e.m.f. of the cell                                       3

30. Write one reaction each for the preparation of the following. Also write one use of each product.

(i) Bleaching power

(ii) Caustic soda

(iii) Quick lime                                             3

31. (i) Which of the following acid is more acidic? Explain giving reasons.

                           CH3 COOH and Cl-CH2COOH

(ii) Explain why is the boiling point of an acid greater than the corresponding halo alkane.                                4

32. (i) What do you understand by entropy? In what way is the total entropy change related to spontaneity of a system and to a system in equilibrium.

     (ii) Entropy change from liquid water to steam at 373K is 109J mol-1 K-1. What is the enthalpy change for the transition of liquid water to steam at 373K .           4

33. Valence shell electron pair repulsion theory can be used to predict the shapes of molecules. Using this theory :

            (i) explain the shapes acquired by BF3 and CH4

            (ii) explain why HOH bond angle in H2O is slightly less than the tetrahedral angle 109.5.                             4

Hint: (i) BF3 – triangular + explanation

CH4 – tetrahedral + explanation

(ii) The oxygen atom in H2O has two bond pairs and two lone pairs. Therefore, two of the four vertices of a tetrahedron are occupies by lone pairs. Because of the lone pair bond pair repulsion, the bond angle in H2O is slightly less than 109.50.

Section B
PART I : (Agricultural Chemistry)

1. Define composting.                                    1

Hint: Composting is a biological process in which micro organisms decompose organic matter in the presence/absence of oxygen, and lower the carbon nitrogen ratios of refuse.

2. List two points of differences between micro nutrients and macro nutrients.                1

3. What can be done to overcome the dangerous effects of modern agriculture?                1

Hint: Cheapest and permanent solution to overcome the dangerous effects of modern agriculture is to do sustainable farming or organic farming or natural farming.

4. Why do we need biological nitrogen fixation?                                                                   2

Hint: In our country there is a big gap between consumption and production of nitrogenous fertilizers. Hence we have a import fertilizers. Under such circumstances the biological nitrogen fixation provides the answer to meet the nitrogen requirement of leguminous and pulse crops.

5. Define soil. List four major soil groups of India.                                                                2

Hint: Four major soil groups of India are : Alluvial soil, black soil, red soil and laterite soil.

6. Give the classification of pesticides based on target organisms.                                      3

PART II : (Bio Chemistry)

1. Give two examples of polysaccharides.                                        1

Hint: Starch, cellulose and glycogen (any two)

2. Write two properties which are common to chemical catalysts and enzymes.                1

Hint: Any two properties like both are not consumed during course of reaction, they do not cause reaction to take place or any other property.

3. List two differences between enzymes and catalysts.                  1

Hint: Any two differences like enzymes exhibit high specificity where as catalyst are more general and can act on various similar substrate, the rate of an enzymatic reaction is proportional to the amount of enzyme where as this is not so with catalyst or any other difference.

4. Define lipids. List 3 different types of lipids.                                2

Hint: Three different types of lipids are : simple lipids, compound lipids and derived lipids.

5. Why are fats a better source of energy than glucose?                    2

Hint: Because the energy released by the oxidation of one molecule of fatty acid is far more higher (at least twice) than that released by oxidation of glucose.

6. List 3 functions of DNA.                                                                 3

PART III : (Environmental Chemistry)

1. Define water pollution.                         1

Hint: Water pollution is any physical, chemical or biological change in a water body that has an undesirable effect on living organisms.

2. Why is chlorination not the most desirable method of disinfecting polluted water?                    1

Hint: Because chlorine reacts with organic matter to produce highly toxic chlorinated hydrocarbon which can cause cancer.

3. What are the effects of detergents on fresh water bodies?                                                         1

Hint: Detergents contain phosphates with promote algal growth in a water body leading to eutophiction.

4. What are anthropogenic pollutants?. Give two examples each of primary and secondary pollutants.               2

Hint: Pollutants added to the environment through human activities are termed anthropogenic pollutants

Examples of primary pollutants : CO2, CO from burning of fuel; SO2 and oxides of nitrogen from vehicular combustion and thermal power station (any two)

Examples of secondary pollutants : SO3, H2SO4,NO2 (any two)

5. Why is it impossible for a nuclear reactor to blow up like a bomb? Explain.                                  2

Hint: The nuclear fuel that is used in a reactor contains a low concentration of fissionable U-235 (only 3%). Since the critical mass required for a self sustaining fission reaction is not available, the probability of nuclei hitting fissionable nuclei is low. Thus the reaction continues in a slow fashion. Also coolants are used to slow down the reaction.

6. How is global warming caused? List four consequences of green house effect.                            3

Hint: If proportion of green house gases increase in the atmosphere, heat trapped by them will raise the temperature of the earth causing global warming. 1 mark
Consequences of green hose effect :
1. Rise in sea level
2. Drought
3. Reduced plant growth
4. Encourage growth of pests
5. Water shortage.

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