CBSE Guess > Papers > Important Questions > Class XI > 2013 > Chemistry By Mr. Sachin Prajapati

CBSE CLASS XI

Chemistry

1. Explain why 0-nitrophenol has a lower boiling point than p-nitrophenol?
2. Why alkali metals used in photoelectric cells?
3. Due to which compound, ozone depletion is caused in Antarctica?
4. Which of the element among B, Al, C and Si :-
   1. Has the highest first ionization enthalpy?
   2. Has the most negative electron gain enthalpy?
5. 1. Write the atomic number of the element present in the third period and seventeenth group of the periodic table.
   2. Out of the elements Cr (Z-24), Mg (Z=12), and Fe (Z=26), identify the element with five electrons in 3d sub shell.
6. Critical temperature of ammonia and carbon dioxide are 405.5 K and 304.10 K respectively. Which these gases will liquefy first when you start cooling from 500K to their critical temperature
7. An element ‘A’ belongs to group 2 of the periodic table. It shows anomalous behavior from the rest of the elements of its group. It shows a diagonal relationship with another element ‘B’. Chlorides of both ‘A’ and ‘B’ have bridged structure in vapour phase. Identify A and B and draw the structures of their respective chlorides.
8. Calculate the mass percent of different elements in sodium sulphate (Na₂SO₄).
9. Why does the rain water normally have a pH of about 5.6? When does it become acid rain?
10. The threshold frequency for the ejection of electron from a metal is 5 X 10¹⁴ s-1. Will the photon of radiation having energy 3.0 X 10^-19 J give photo electric effect or not?
11. A metal ‘X’ is present in chlorophyll. Identify the metal ‘X’. write the reaction of this metal with N₂.
12. An orbital has n=3. What are the possible values of l  and m l ?
13. Explain the hybridization of PCl₅ molecule. Why PCl₅ on decomposition gives PCl₃ and Cl₂ ?
14. Consider the chemical reaction:
    2SO₂ (g) + O2 (g) 2SO₃ (g) +189.4 KJ. Indicate the direction in which the equilibrium will shift when:-
    
    
    1. Temperature is increased.
    2. Pressure is increased.
    3. Concentration of SO₂ is increased.
15. Write the IUPAC names of the following compound:-
    
16. For the reaction NH₄Cl(s) → NH₃ (g)+ HCl(g)  at 25⁰C, enthalpy change ∇H =+177 kJmol^-1and entropy change ∇S = +285JK^-1mol^-1 .Calculate free energy change  ∇G at 25⁰ C and predict whether the reaction is spontaneous or not.
17. Explain giving reasons :-
    1. Boron does not form B³⁺ ions.
    2. B-Cl bond has a dipole moment but BCl₃ has zero dipole moment.
    3. Aluminium is used to make transmission cables.
    4. Alkali metals impart colour to the flame.
    5. Second ionization enthalpy of Na is higher than Mg.
18. Which of the two is bigger in size and why? Cl or Cl-
19. What is the conjugate base of HCO₃- and H₂O ?
20. Why are metallic hydrides used for storing hydrogen?
21. Name the two methods for estimation of nitrogen.
22. Yellow light emitted from a sodium lamp has a wavelength (.) of 580 nm. Calculate frequency (.) and wave number of the yellow light?
23. Calculate the oxidation number of Mn in K₂MnO₄ and N in HNO₃.
24. Compound ‘A’ with the molecular formula C₅H₈ reacts with hydrogen in the presence of Lindlar’s catalyst to form a compound ‘B’ with the molecular formula C₅H₁₀. ‘A’ on reacting with sodium in liquid ammonia forms a compound ‘C’ with same molecular formula as that of ‘B’. Identify A, B and C. Also write the chemical reactions involved.
25. Write the general electronic configuration of p-block and f-block elements.
26. Which of the following free radicals is most stable and why? CH₂CH₃<CH(CH₃)₂ <C(CH₃)₃
    
27. Write a short note on the following:-
    1. Wurtz reaction
    2. Friedel-crafts alkylation
28. Define the following terms:-
    1. Biological Oxygen Demand (BOD)
    2. Eutrofication.
29. Give reasons for the following:-
    1. [SiF6]2- is known whereas [SiCl₆]^2- is not known.
    2. Diamond is covalent, yet has high melting point.
    3. BF3 behaves as Lewis acid.
    4. F has lower electron gain enthalpy than Cl.
    5. Ionization enthalpy of N is higher than O.
    6. Falling liquid drops are spherical.
    7. Conc. HNO₃ can be stored in aluminium container.
30. Explain structure of Diborane.

Submitted By Mr. Sachin Prajapati
Email: [email protected]