Subject

Chemistry

Class

CBSE Class 12

Pre Boards

Practice to excel and get familiar with the paper pattern and the type of questions. Check you answers with answer keys provided.

Sample Papers

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 Multiple Choice QuestionsShort Answer Type

21.

Write the main structural difference between DNA and RNA. Of the four bases, name those which are common to both DNA and RNA.

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22.

Write such reactions and facts about glucose which cannot be explained by its open chain structure.

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23.

State reasons for the following:

(i) pKb value for aniline is more than that for methylamine.

(ii) Ethylamine is soluble in water whereas aniline is not soluble in water.

(iii) Primary amines have higher boiling points than tertiary amines.
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24.

Rearrange the compounds of each of the following sets in order of reactivity towards SN2 displacement:

(i) 2-Bromo-2-methylbutane, 1-Bromopentane, 2-Bromopentane

(ii) 1-Bromo-3-methylbutane, 2-Bromo-2-methylbutane, 3-Bromo-2-methylbutane

(iii) 1-Bromobutane, 1-Bromo-2, 2-dimethylpropane, 1-Bromo-2-methylbutane
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25.

How would you obtain the following?

(i) Benzoquinone from phenol

(ii) 2-methyl propan-2-ol from methyl-magnesium bromide

 (iii) Propane-2-ol from propene

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26.

Write the names and structures of the monomers of the following polymers:

(i) Buna-S

(ii) Dacron

(iii) Neoprene
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27.

What are the following substances? Give one example of each.

(i) Food preservatives

(ii) Synthetic detergents

(iii) Antacids


(i) Food Preservatives: These are the chemical substances which are added to the food materials to prevent their spoilage due to microbial growth and to retain their nutritive value for a long time. Sodium benzoate, sodium metabisulphite are some common preservatives. Preservatives prevent rancidity and kill or inhibit the growth of the microorganism.

(ii) Synthetic Detergents: Detergents are cleaning agents which have all the properties of soaps, but actually do not contain any soap e.g., sodium dodecylbenzene sulphonate. These can be used both in soft and hard water as they give foam even in hard water.

Detergents are mainly classified into three categories:

(i) Anionic detergents

(ii) Cationic detergents

(iii) Non-ionic detergents

(iii) Antacids: These are the chemical substances which neutralize the excess acid and raise the pH to an appropriate level in the stomach. Sodium hydrogen carbonate or a mixture of aluminium and magnesium hydroxide are some common antacids.

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 Multiple Choice QuestionsLong Answer Type

28.

(a) Draw the structures of the following molecules:

(i) (HPO3)3

(ii) BrF3

(b) Complete the following chemical equations:

(i) HgCl2 + PH3-->

(ii) SO3 + H2SO4 -->

(iii) XeF4 + H2O  -->

 OR

(a) What happens when?

(i) Chlorine gas is passed through a hot concentrated solution of NaOH?

(ii) Sulphur dioxide gas is passed through an aqueous solution of a Fe (III) salt?

(b) Answer the following:

(i) What is the basicity of H3PO3 and why?

(ii) Why does fluorine not play the role of a central atom in inter-halogen compounds?

(iii) Why do noble gases have very low boiling points?

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29.

(a) What type of a battery is lead storage battery? Write the anode and cathode reactions and the overall cell reaction occurring in the operation of a lead storage battery.

(b) Calculate the potential for half-cell containing 0.10 M K2Cr2O7 (aq), 0.20 M Cr3+(aq) and 1.0 x 10-4 M H+ (aq)

The half-cell reaction is Cr subscript 2 straight O subscript 7 superscript 2 minus end superscript left parenthesis aq right parenthesis straight space plus straight space 14 straight space straight H to the power of plus subscript left parenthesis aq right parenthesis end subscript straight space plus straight space 6 straight e to the power of minus straight space rightwards arrow straight space 2 Cr subscript left parenthesis aq right parenthesis end subscript superscript 3 plus end superscript straight space plus straight space 7 straight H subscript 2 straight O subscript left parenthesis straight l right parenthesis end subscript

And the standard electrode potential is given as E0 = 1.33 V.

 OR

(a) How many moles of mercury will be produced by electrolysing 1.0 M?

Hg (NO3)2 solution with a current of 2.00 A for 3 hours?

[Hg (NO3)2 = 200.6 g mol-1]

(b) A voltaic cell is set up at 25°C with the following half-cells Al3+ (0.001 M) and Ni2+ (0.50 M). Write an equation for the reaction that occurs when the cell generates an electric current and determine the cell potential.

 Error converting from MathML to accessible text.

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30.

(a) Illustrate the following name reactions:

(i) Cannizzaro’s reaction

(ii) Clemmensen reduction

(b) How would you obtain the following?

(i) But-2-enal from ethanal

(ii) Butanoic acid from butanol

(iii) Benzoic acid from ethylbenzene

 OR

 (a) Given chemical tests to distinguish between the following:

(i) Benzoic acid and ethyl benzoate

(ii) Benzaldehyde and acetophenone


(b) Complete each synthesis by giving missing reagents or products in the following:

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