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Monday, 11 January 2016

CHEMISTRY (Theory) Class – XI sample paper

                        CHEMISTRY (Theory)
                   Class – XI
Time allowed: 3 hours                                                Maximum Marks: 70
General Instructions:
a) All the questions are compulsory.
b) There are 26 questions in total.
c) Questions 1 to 5 are very short answer type questions and carry one mark each.
d) Questions 6 to 10 carry two marks each.
e) Questions 11 to 22 carry three marks each.
f) Questions 23 is value based question carrying four marks.
g) Questions 24 to 26 carry five marks each.
h) There is no overall choice. However, an internal choice has been provided in one question of  two marks, one question of three marks and all three questions in five marks each. You have to attempt only one of the choices in such questions.
i) Use of calculators is not permitted. However, you may use log tables if necessary

 1. Which of these contain the largest number of atoms – 
   1.0 g Li(s) and 1g Na(s)?

2. Predict the shape of the PH3 molecule according to VSEPR theory.

3. Give reason: “Metallic hydrides are used for storing hydrogen”.

4. If a metal is higher than a particular metal in electro chemical series, will it be stronger reducing agent or weaker reducing agent? Why?

5. If the critical temperature for carbon dioxide and methane are 31.10C and – 81.90C respectively, then which of these has strong inter molecular forces? Give reason.

6. Given the electrode reduction potentials of four metallic elements A, B, C and D = + 0.79, - 0.74, 1.08 and – 0.31 V. Arrange these in order of decreasing electro positive character and support you answer.

7. Give any three factors favourable for the formation of ionic bond.

8. Convert:
a) Carbon to benzene.
b) Calcium carbide to oxalic acid.
9. How would you calculate the pH of 0.001 M NaOH?
              Or
Ramesh forgot to add the reaction mixture to the round bottomed flask at 27oC but instead he placed the flask on the flame. But after sometime, he realized his mistake and used pyrometer and found the temperature of the flask which was 477oC. What fraction of air would have been expelled out?

10. State the difference between classical smog and photo chemical smog.

11. Explain:
i. Boron is unable to form BF63- ion.
ii. [SiF6]2- is known whereas [SiCl6]2- not known.
iii. Conc. HNO3 can be stored in aluminium container.

12. Identify the species undergoing oxidation and reduction in the reactions given below.
i) H2S (g) + Cl2 (g) → 2 HCl (g) + S (s)
ii) 3Fe3O4 (s) + 8 Al (s) → 9 Fe (s) + 4Al2O3 (s)
iii) 2 Na (s) + H2 (g) → 2 NaH (s)

13. What are the conclusions made by Rutherford w.r.t the structure of atom?

14. Define the following terms:
i. Functional groups
ii. Homologous series
                Or
Predict about the formation of M3+ ion in solution and compare the electro positive character of the two metals given. The standard electrode potential values, Eq for Al3+/Al are –1.66 V and that of
Tl3+/Tl is +1.26 V.

15. Give reasons:
a) HCl is predominantly covalent in gaseous state.
b) KHF2 exists while KHCl2 does not.
c) Sigma bond is stronger than the pi bond.
d) NaCl gives white precipitate with silver nitrate solution.
  
16.i. Which of the two is more stable + 2 H or 2 H- and why?
ii. All bonds in PCl5 are not equal. Explain.
iii. Which of the two is more ionic - NaCl or NaI and why?

17. Explain the following terms with an example each: i) Open system
ii) Isolated system
iii) Closed system

18. Draw the structure of the following IUPAC compounds:
a) 2,8-Dimethyl-3, 6-decadiene
b) 4-Ethyl-2,6-dimethyl-dec-4-ene
c) 1,3,5,7 Octatetraene
d) 4-Nitroso-N-dimethylbenzenamine
e) Benzene 1,4-dicarboxylic acid
f) 1-Phenylpropanone

19.
i) Calculate the percentage of C and H in 0.2475 g of an organic compound gave on combustion 0.4950 g of carbon dioxide and 0.2025 g of water.
ii) What will happen during Lassaigne's test for nitrogen if the compound also contains
sulphur?

20. If water vapour is assumed to be a perfect gas, molar enthalpy change for vapourisation of 1 mol of water at 1bar and 100°C is 41kJ mol–1. Calculate the internal energy change, when
i) 1 mol of water is vaporised at 1 bar pressure and 100°C
ii) 1 mol of water is converted into ice.

21. Define:
i. Lattice enthalpy
ii. Bond length
iii. Bond angle.

 22.
i. Name the class of hydrides to which H2O and NaH belong.
ii. What do you understand by the term hydride gap?
iii. What do you mean by 15 volume H2O2 solution?

23. Ram uses urea and DAP for his crops whereas Shyam uses compost. Ammonia is prepared by Haber’s process. It is used for making fertilizers. If it is used in excess, it is harmful for crops.
a) What is DAP?
b) What can be done with waste products?
c) What is the use of avoiding excess of fertilizers?
d) Natural manure is preferred than synthetic fertilizers. Why?

24. Differentiate valence and oxidation number. [Any five points]

25. Explain the rules for calculating oxidation number.
Or
i) Write the chemical reactions when borax solution is acidified.
ii) Explain why BF3 exists whereas BH3 does not?
iii) SiO2 is solid but CO2 is a gas at room temperature.

26.
a) In which C-C bond of CH3CH2CH2Br, the inductive effect is expected to be least?
b) Which of the following compound shows geometrical isomerism?
i. Pent-1-ene
ii. Pent-2-ene
iii. 2-Methylbut-2-ene
c) What type of isomerism is present in the following pairs?
i) CH3 – CH2 – CH2 – OH and CH3 – CH (OH) – CH3
ii) CH3 – CH2 – CO – CH2 – CH3 and CH3 – CO – CH2 – CH2 – CH3

iii) CH3 – CH2 – OH and CH3 – O – CH3

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