Class 12 > PYQ CHEMISTRY > 2020 > Set 2

2020

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Q22
For a 5% solution of urea (Molar mass = 60 g/mol), calculate the osmotic pressure at 300 K. [R = 0·0821 L atm K⁻¹ mol⁻¹]
OR
Visha took two aqueous solutions — one containing 7·5 g of urea (Molar mass = 60 g/mol) and the other containing 42·75 g of substance Z in 100 g of water, respectively. It was observed that both the solutions froze at the same temperature. Calculate the molar mass of Z.

Q23
Write the names and structures of monomers in the following polymers :
(a) Nylon-6,6
(b) Buna-S

Q27
Account for the following :
(a) Sulphurous acid is a reducing agent.
(b) Fluorine forms only one oxoacid.
(c) Boiling point of noble gases increases from He to Rn.
OR
Complete the following chemical reactions :
(a) MnO₂+ 4HCl —>

(b) XeF₆+ KF —>

(c) I⁻ (aq) + H⁺ (aq) + O₂(g) —>

Q28
Give the structures of A and B in the following sequence of reactions :
<p><img alt="" src="" style="height:144px; width:400px" /></p>

OR
(a) How will you distinguish between the following pairs of compounds :
(i) Aniline and Ethanamine (ii) Aniline and N-methylaniline

(b) Arrange the following compounds in decreasing order of their boiling points :
Butanol, Butanamine, Butane

Q29
Give the plausible explanation for the following :
(a) Glucose doesn’t give 2,4-DNP test.
(b) The two strands in DNA are not identical but are complementary.
(c) Starch and cellulose both contain glucose unit as monomer, yet they are structurally different.

Q30
How will the rate of the reaction be affected when
(a) surface area of the reactant is increased,
(b) temperature of the reaction is decreased, and
(c) catalyst is added in a reversible reaction?

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