Subject

Chemistry

Class

CBSE Class 12

Pre Boards

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Sample Papers

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 Multiple Choice QuestionsShort Answer Type

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1.

What are n-types semiconductors?


The semiconductor whose increased conductivity is a result of negatively-charged electrons is called an n-type semiconductor. These are generated when the crystal of a group 14 element such as Si or Ge is doped with a group 15 element such as P or As.

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2.

Define ‘peptization’.

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3.

How is copper extracted from a low-grade ore of it?

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4.

What is the basicity of H3PO2 acid and why?

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5.

A reaction is of second order with respect to a reactant. How is its rate affected if the concentration of the reactant is (i) doubled (ii) reduced to half?

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6.

Express the relation among cell constant, the resistance of the solution in the cell and conductivity of the solution. How is molar conductivity of a solution related to its conductivity?

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7.

The molar conductivity of a 1.5 M solution of an electrolyte is found to be 138.9S cm2mol-1. Calculate the conductivity of the conductivity of this solution.

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8.

Explain the role of each of the following:

(i) NaCN in the extraction of silver

(ii) SiO2 in the extraction of copper

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9. Complete the following chemical equations:


bold i bold right parenthesis bold space bold Cr subscript 2 bold O subscript 7 superscript 2 minus end superscript space plus space bold H to the power of plus space plus space bold I to the power of minus space rightwards arrow

ii right parenthesis space bold MnO subscript 4 superscript minus space plus space bold NO subscript 2 superscript minus space plus space bold H to the power of plus rightwards arrow
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10.

Explain the following facts giving appropriate reason in each case:

(i) NF3 is an exothermic compound whereas NCl3 is not.

(ii) All the bonds in SF4 are not equivalent.

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