Subject

Chemistry

Class

CBSE Class 12

Pre Boards

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Sample Papers

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 Multiple Choice QuestionsShort Answer Type

21.

A first-order reaction is 50% completed in 40 minutes at 300 K and in 20 minutes at 320 K. Calculate the activation energy of the reaction.

(Given: log 2 = 0.3010, log 4 = 0.6021, R = 8.314 JK–1 mol–1)


22.

What happens when

A freshly prepared precipitate of Fe(OH)3 is shaken with a small amount of FeCl3 solution?


23.

What happens when

Persistent dialysis of a colloidal solution is carried out?


24.

What happens when

An emulsion is centrifuged?


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25.

For the reaction

2AgCl (s) + H2 (g)  (1 atm)   2 Ag (s) + 2H+ (0.1 M) + 2Cl- (0.1 M),Go = - 43600 J at 25o C

Calculate the e.m.f. of the cell.
[log 10–n = – n]


26.

Define fuel cell and write its two advantages.


27.

Give reasons:

H3POundergoes disproportionation reaction but H3PO4 does not.


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28.

Give reason:

When Cl2 reacts with an excess of F2. ClF3 is formed and not FCl3


Chlorine has empty d-orbital and it acquires excited state at the time of bonding when an electron from 3p-orbital are promoted to 3d- orbital.



In first excited state chlorine atom can exhibit a covalency of three, hence cannot expand its octet due to the absence of empty d- orbitals in 2nd energy shell.

Hence, it cannot exhibit covalency more than 1therefore FCl3 is not possible.


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29.

Give Reason:

Dioxygen is a gas while Sulphur is a solid at room temperature.


30.

Draw the structures of the following.
(i) XeF4
(ii) HClO3


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