Subject

Chemistry

Class

ICSE Class 12

Pre Boards

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Sample Papers

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 Multiple Choice QuestionsShort Answer Type

31.

A compound AB has a simple cubic structure and has molecular mass 99. Its density is 3.4 g cm-3. What will be the edge length of the unit cell?

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32.

The molecular weight of an organic compound is 58 g mol-1. What will be the boiling point of a solution containing 48 grams of the solute in 1200 grams of water?

[Kb for water = 0.213 C kg mole-1; Boiling point of water = 1000 C]

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33.

In the first order reaction,10% of the reactant is consumed in 25 minutes. Calculate:
i) The half-life period of the reaction.
ii) The time required for completing 87.5% of the reaction.

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34.

Consider the following cell reaction at 298K:

2Ag+ +Cd--> 2Ag +Cd2+

The standard reduction potentials (E0) for Ag+/Ag and Cd2+/Cd are 0.80V and -0.40 V respectively:
1) write the cell representation.
2) what will be the emf of the cell if the concentration of Cd2+ os 0.1 M and that of Ag+ is 0.2M?
3) Will the cell work spontaneously for the condition given in (2) above?


From the given chemical equation:

2Ag+ +Cd--> 2Ag +Cd2+

Ag+/Ag = 0.80V
Cd2+/Cd =-0.40V


The Ered for silver> Ered for cadmium, sliver ion will be reduced and cadmium metal will be oxidized.

anode reaction: Cd--> Cd2+ +2e-
cathode reaction: 2Ag+ +2e- --> 2Ag

straight I right parenthesis space space Cell space reaction

straight E subscript cell superscript 0 space equals space straight E subscript cathode superscript 0 space minus space straight E subscript anode superscript 0

space equals space 0.80 minus left parenthesis negative 0.40 right parenthesis space equals 1.20 space straight V

ii right parenthesis space Using space nernst space equation colon

straight E subscript cell space equals space straight E subscript cell superscript 0 minus open square brackets fraction numerator 2.303 RT over denominator nF end fraction close square brackets log space open square brackets Cd to the power of 2 plus end exponent over Ag to the power of plus close square brackets

straight E subscript cell space equals space 1.20 minus space open square brackets fraction numerator 0.591 over denominator 2 end fraction close square brackets space log open square brackets fraction numerator 0.1 over denominator 0.2 end fraction close square brackets

straight E subscript cell space equals space 1.20 minus space open square brackets fraction numerator 0.591 over denominator 2 end fraction close square brackets log left parenthesis 0.5 right parenthesis

straight E subscript cell space equals space 1.20 minus open square brackets fraction numerator 0.591 over denominator 2 end fraction close square brackets left parenthesis negative 0.301 right parenthesis
straight E subscript cell space equals space 1.20 minus left parenthesis negative 0.088 right parenthesis
straight E subscript cell space space equals 1.288 space straight V

iii right parenthesis space Since space the space straight E subscript cell space reaction space is space positive space hence comma space the space reaction space is space spontaneously.

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35.

What is a buffer solution? How is it prepared to explain the buffer action of as basic buffer with a suitable example?

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36.

Explain the following:
i) when NaCl is added to AgNO3 solution, a white precipitate is formed.
ii) An aqueous solution of ammonium chloride is acidic in nature.

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37.

A 0.05 M NH4OH solution offers the resistance of 50 ohms to a conductivity cell at 298K. If the cell constant is 0.50 cm-1 and molar conductance of NH4OH at infinite dilution is 471.4 ohm-1cm2mol-1, calculate:

i) Specific conductance
ii) Molar conductance
iii) Degree of dissociation

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38.

Water acts as Bronsted acid as well as a Bronsted base. Give one example each to illustrate this statement.

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39.

What type of isomerism is exhibited by the following pairs of compounds:
i) [PtCl2(NH3)4]Br2 and [PtBr2(NH3)4Cl2
ii) [Cr(SCN)(H2O)5]2+ and [Cr(NCS)(H2O)5]2+

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40.

Give balanced equations for the following reaction:

i) Silver nitrate si added to the dilute solution of sodium thiosulphate.

ii) Potassium dichromate is treated with acidified ferrous sulphate solution.

iii) Phosphorus reacts with conc. sulphuric acid.

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