Subject

Chemistry

Class

ICSE Class 12

Pre Boards

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Sample Papers

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 Multiple Choice QuestionsShort Answer Type

21. The pH of an acidic buffer remains constant even when a few drops of a strong acid are added to it. Give reasons.  
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22. Draw a graph which is used to calculate the activation energy of a reaction. Give the appropriate expressions used to calculate the activation energy graphically.
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23.

(i) 10 g of an organic compound was present in 100 cm3 of water. It was extracted twice with fresh 50 cm3portions of ether. How much organic compound was extracted ? (The organic compound is three times more soluble in ether than in water.)

(ii) Give one example each of homogeneous and heterogeneous catalysis.


(i) Suppose x gm of water solute is extracted by the first application of 50 cc of other.
Concentration space in space ether space left parenthesis straight C subscript ether right parenthesis space equals space straight x over 50
Concentration space in space water space left parenthesis straight C subscript water right parenthesis space equals space fraction numerator 10 minus straight x over denominator 100 end fraction
Given comma space straight C subscript ether over straight C subscript water space equals space 3
substituting space the space values
fraction numerator begin display style straight x over 50 end style over denominator begin display style fraction numerator 10 minus straight x over denominator 100 end fraction end style end fraction space equals space 3 space Or space straight x over 50 space straight x space fraction numerator 100 over denominator 10 minus straight x end fraction space equals 3
Or
2 straight x space equals space 30 minus 3 straight x
5 straight x space equals space 30
straight x space equals space 6 space gm
The space amount space left space in space the space solution space after space first space application
equals space 10 minus 6 space equals space 4 gm
If space straight x subscript 1 space be space the space quantity space extracted space in space second space operation comma space then
fraction numerator begin display style straight x subscript 1 over 50 end style over denominator begin display style fraction numerator 40 minus straight x subscript 1 over denominator 100 end fraction end style end fraction space equals space 3 space or space straight x subscript 1 over 50 space straight x space fraction numerator 100 over denominator 40 minus straight x subscript 1 end fraction space equals 3

Or space 2 straight x subscript 1 space equals space 12 minus 3 straight x subscript 1
5 straight x subscript 1 space equals space 12
straight x subscript 1 space equals space 2.4 space gm space
Total space organic space compound space extracted space space equals 6 space plus 2.4 space equals space 8.4 space gm

ii right parenthesis space Homogeneous space catalysis colon space Homogeneous space catalyst space are space those space which space have space same space phase.

SO subscript 2 space left parenthesis straight g right parenthesis space space plus 1 half straight O subscript 2 left parenthesis straight g right parenthesis space rightwards arrow with No left parenthesis straight g right parenthesis space on top space SO subscript 3 left parenthesis straight g right parenthesis
Heterogeneous space catalysis colon space Heterogeneous space catalyst space are space those space which space have space different space phase space then space reactant.
3 straight H subscript 2 left parenthesis straight g right parenthesis space plus straight N subscript 2 left parenthesis straight g right parenthesis space space rightwards arrow with Fe left parenthesis straight s right parenthesis space on top space 2 NH subscript 3 left parenthesis straight g right parenthesis space

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24.

(i) Name the crystal structure of the copper metal.   

(ii) What is the coordination number of copper in its crystalline state ?

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25.

ΔH and ΔS for vaporization of water at 1 atm pressure are 40.63 KJ mole 1 and 108.8 JK– 1mole–  1 respectively. Calculate the temperature at which the free energy change for the transformation will be zero. Predict the sign of free energy change below this temperature.

(ii) The heat supplied to a Carnot engine is 1958.22 KJ. How much useful work can be done by the engine which works between 0 °C and 100 °C ?

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26. Calculate the enthalpy of formation of methane from the following data:

straight C space left parenthesis straight s right parenthesis space plus straight O subscript 2 left parenthesis straight g right parenthesis space rightwards arrow CO subscript 2 left parenthesis straight g right parenthesis space space space space space space increment straight H space equals space minus 394 KJ space mol to the power of negative 1 end exponent
2 straight H subscript 2 left parenthesis straight g right parenthesis space plus straight O subscript 2 left parenthesis straight g right parenthesis space rightwards arrow 2 straight H subscript 2 straight O left parenthesis straight l right parenthesis space space space increment straight H space equals space minus 286 space KJ space mol to the power of negative 1 end exponent
CH subscript 4 left parenthesis straight g right parenthesis space plus 2 straight O subscript 2 left parenthesis straight g right parenthesis space rightwards arrow space CO subscript 2 left parenthesis straight g right parenthesis space plus 2 straight H subscript 2 straight O left parenthesis straight l right parenthesis space increment equals negative 890 KJ space mol to the power of negative 1 end exponent
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27.

Write balanced chemical equations for each of the following reactions : 

(i) Sodium thiosulphate with aqueous silver nitrate.

(ii) Copper sulphate with aqueous potassium iodide.

(iii) Hydrogen peroxide with acidified ferrous sulphate solution.

(iv) Ozone with moist iodine.

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28. What are the steps of the electro-thermic process for the manufacture of phosphorus from its mineral ?   
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29.

Give reasons :   

(i) Hydrogen peroxide is used for restoring the colour of lead paintings.

(ii) Silicones are used as lubricants at both high and low temperatures.

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30. Name the chief ore of lead. Write the steps involved in the extraction of lead from its sulphide ore by the self-reduction process. Give balanced equations wherever necessary.
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