Subject

Chemistry

Class

CBSE Class 12

Pre Boards

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Sample Papers

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 Multiple Choice QuestionsLong Answer Type

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31.

(a) Define the terms osmosis and osmotic pressure. Is the osmotic pressure of a solution a colligative property? Explain. 

(b) Calculate the boiling point of a solution prepared by adding 15.00 g of NaCl to 250.0 g of water. (Kb for water = 0.512 K kg mol-1), (Molar mass of NaCl = 58.44 g)


(a) Osmosis: The process of flow of solvent molecules from pure solvent to a solution or from a solution of lower concentration to a solution of higher concentration through a semi-permeable membrane is called osmosis. 

Osmotic Pressure: The pressure required to just stop the flow of solvent due to osmosis is called osmotic pressure (π) of the solution. 

 Yes, the osmotic pressure of a solution is a colligative property. The osmotic pressure is expressed as. 

 
Where,  

π  = osmotic pressure 

n = number of moles of solute 

V = volume of solution 

T = temperature 

 

From the equation, it is clear that osmotic pressure depends on upon the number of moles of solute ‘n’ irrespective of the nature of the solute. 

 

Hence, osmotic pressure is a colligative property. 

 

(b) Given

 Kb = 0.512 k kg mol-1

w2 = 15.00 g 

w1 = 250.0 g 

M2 = 58.44 g 

 

Using the formula, 

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32.

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

(ii) F2 is most reactive of all the four common halogens. 

(b) Complete the following chemical equations: 

(i) C + H2SO4 (conc.)-->

(ii) P4 + NaOH + H2O-->

(iii) Cl2+F2  ------>
           (excess)

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33.

(a) Account for the following: 

(i) The acidic strength decreases in the order HCl > H2S > PH3

(ii) Tendency to form pentahalides decreases down the group in group 15 of the periodic table. 

 (b) Complete the following chemical equations: 

 (i) P4 + SO2Cl2-->

 (ii) XeF2 + H2O---> 

 (iii) I2+HNO3(conc.)---> 

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34.

Answer the following: 

(i) Haloalkanes easily dissolve in organic solvents, why? 

(ii) What is known as a racemic mixture? Give an example. 

(iii) Of the two Bromo derivatives, C6H5CH(CH3)Br and C6H5CH(C6H5)Br, which one is more reactive in Sn1 substitution reaction and why? 

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35.

Describe the following giving one example for each: 

 (i) Detergents 

(ii) Food preservatives 

(iii) Antacids 

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36.

Give chemical tests to distinguish between 

(i) Propanal and propanone, 

(ii) Benzaldehyde and acetophenone. 

(b) How would you obtain 

(i) But-2-enal from ethanal, 

(ii) Butanoic acid from butanol, 

(iii) Benzoic acid from ethylbenzene? 

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37.

(a) Describe the following giving linked chemical equations: 

 (i) Cannizzaro reaction 

 (ii) Decarboxylation 

(b) Complete the following chemical equations: 

 

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