Archive for March, 2011

Selected Questions for Class XI Chemistry

  1. State Aufbau Principle
  2. State Hund’s Rule
  3. State Pauli’s Exclusion principle
  4. State Heisenberg’s uncertainty principle.
  5. What are the Limitations of Thomson Model of atom?
  6. What are the Limitations of Rutherford Model of atom?
  7. What are the Limitations of Bohr Model of atom?
  8. State Pauli’s Exclusion principle
  9. State Modern periodic law.
  10. Explain sp, sp2 and sp3 hybridisation
  11. State Boyle’s law, Charle’s law, Avogadro’s lawand   Gaylussac’s law
  12. Explain the empirical derivation of gas equation
  13. Explain the concept of entropy
  14. State Hess’ law of constant heat summation
  15. Show that chemical equilibrium is synamic in nature
  16. State and explain Le Chatlier’s principle
  17. Why hydrogen is sjhown saparately in the periodic table?

More will be posted soon. You can also add more questions as comments.

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Be the first to comment - What do you think?  Posted by admin - March 19, 2011 at 9:38 pm

Categories: CBSE Chemistry, Question bank   Tags:

Defects of a Simple Voltaic cell

voltaic-cell

A simple voltaic cell has two major defects. They are

  1. Local action and
  2. Polarisation

 

  1. Local Action : This is caused by the impurities present in zinc rod. When the zinc rod isimmersed in acid, the zinc atoms and the impurity atoms form a large number of local cells and the zinc rod gets consumed even when the cell is not in use. This defect can be avoided by using amalgamated zinc rods. Mercury dissolves zinc and allows only zinc atoms to come into contact with acid and thus avoids formation of local cells.
  2. Polarisation: The hydrogen ions reaching the negative electrode get accumulated preventing further neutralization of hydrogen ions. This results in decrease of emf of the cell and produces a back emf. This can be eliminated by :

(i) Mechanical method. In this method, the hydrogen layer from the positive electrode is removed, using a brush. But this method is not so satisfactory.

(ii) Electrochemical method. In this method, a liquid called depolariser is used. The hydrogen ions react with this and some other gas is produced which does not – cause polarisation.

(iii) Chemical method. In this method, hydrogen is converted to water with an oxidising agent like manganese dioxide, potassium dichromate etc.

1 comment - What do you think?  Posted by admin - March 15, 2011 at 9:32 am

Categories: General   Tags:

Chemistry Ebooks for easy revision for Class XI CBSE

  • NCERT Chemistry Textbook for Class XI Unit-1 (102498-14523-NCERT-Chemistry-Textbook-for-Class-XI-Unit-1.pdf)
  • NCERT Chemistry Textbook for Class XI Unit-2 (102498-14523-NCERT-Chemistry-Textbook-for-Class-XI-Unit-2.pdf)
  • NCERT Chemistry Textbook for Class XI Unit-3 (102498-14524-NCERT-Chemistry-Textbook-for-Class-XI-Unit-3.pdf)
  • NCERT Chemistry Textbook for Class XI Unit-4 (102498-14525-NCERT-Chemistry-Textbook-for-Class-XI-Unit-4.pdf)
  • NCERT Chemistry Textbook for Class XI Unit-5 (102498-14525-NCERT-Chemistry-Textbook-for-Class-XI-Unit-5.pdf)
  • NCERT Chemistry Textbook for Class XI Unit-6 (102498-14526-NCERT-Chemistry-Textbook-for-Class-XI-Unit-6.pdf)
  • NCERT Chemistry Textbook for Class XI Unit-7 (102498-14527-NCERT-Chemistry-Textbook-for-Class-XI-Unit-7.pdf)
  • NCERT Chemistry Textbook for Class XI Appenxix. (102498-14527-NCERT-Chemistry-Textbook-for-Class-XI-Appenxix.pdf)
  • NCERT Chemistry Textbook for Class XI Answers (102498-14527-NCERT-Chemistry-Textbook-for-Class-XI-Answers.pdf)
  • Be the first to comment - What do you think?  Posted by admin - March 9, 2011 at 8:32 pm

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    Sample Paper for Class XI Chemistry

    http://www.kvsrobhopal.org.in/XI/XI-CHEM.pdf

     

    1 comment - What do you think?  Posted by admin - at 8:31 pm

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    Valence Bond Theory:

    • A discussion of valence bond theory is based on the knowledge of atomic orbitals, electronic configuration of elements, overlap criteria of atomic orbitals and principles of variation and superposition. • Orbital Overlap Concept of Covalent Bond: When two atoms approach each other, partial merger of two bonding orbitals, known as overlapping of the orbitals occurs.  • Depending upon the type of overlapping, the covalent bonds  may be divided as sigma (σ) bond and Pi ( π ) bond. • Sigma (σ) bond: This type of covalent bond is formed by the end to end (hand on) overlapping of bonding orbitals along the inter-nuclear axis. The overlap is known as head on overlap or axial overlap. The sigma bond is formed by any one of the following types of combinations of atomic orbitals. Sigma (σ) bond can be formed by  s – s overlapping, s – poverlapping, p – p Overlapping etc. • Pi ( π ) Bond: This type of covalent bond is formed by the sidewise overlap of the half- filled atomic orbitals of bonding atoms.  Such an overlap is known as sidewise or lateral overlap.

    Be the first to comment - What do you think?  Posted by admin - at 8:28 pm

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