Science (English Medium) इयत्ता १२ - CBSE Important Questions

The presence of nitro group (−NO₂) at o/p positions increases the reactivity of haloarenes towards nucleophilic substitution reactions.

What is the principle behind the zone refining of metals?

Identify the chiral molecule in the following pair :

Explain the principle of the method of electrolytic refining of metals. Give one example.

Write the structures of A, B and C in the following:

p-Dichlorobenzene has higher m.p. and lower solubility than those of o- and m-isomers. Discuss.

Give reasons:

The dipole moment of chlorobenzene is lower than that of cyclohexyl chloride.

Which reducing agent is employed to get copper from the leached low-grade copper ore?

Draw the structure of major monohalo product in each of the following reactions :

Arrange the following compounds in increasing order of their boiling points.

(a)  \[\begin{array}{cc}
\ce{CH3}\phantom{..................}\\
\backslash\phantom{...........}\\
\ce{CH - CH - CH2Br}\\
/\phantom{.............}\\
\ce{CH3}\phantom{..................}
\end{array}\]

(b) \[\ce{CH3CH2CH2CH2Br}\]

(c) \[\begin{array}{cc}
\phantom{...}\ce{CH3}\\
\phantom{}|\\
\ce{H3C - C - CH3}\\
\phantom{}|\\
\phantom{..}\ce{Br}
\end{array}\]

Arrange the following compounds in increasing order of their boiling points:

CH₃CH₂OH, CH₃−CHO, CH₃−COOH

Arrange the following compounds in increasing order of reactivity towards S_N2 reaction.

2-Bromopentane, 1-Bromopentane, 2-Bromo-2-methylbutane

Complete the reaction with the main product formed:

Convert bromoethane to propanamine.

Give the mechanism of the following reaction:

\[\ce{CH3CH2OH ->[H2SO4][413 K] CH3CH2-O-CH2CH3 + H2O}\]

The following questions are case-based questions. Read the passage carefully and answer the questions that follow:

Answer the following questions:

(a) Why racemisation occurs in S_N1? (1)

(b) Why is ethanol less polar than water? (1)

(c) Which one of, the following in each pair is more reactive towards S_N2 reaction? (2)

(i) CH₃ – CH₂ – I or CH₃CH₂ – Cl

(ii)

OR

(c) Arrange the following in the increasing order of their reactivity towards S_N1 reactions: (2)

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

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

Account for the following:

Helium is used in diving apparatus.

Draw the structures of the following molecules: XeF₂

Draw the structures of the following: H₄P₂O₇ (Pyrophosphoric acid)

What happens when 

H₃PO₃ is heated ?

Write the reactions involved.