3 Marks Question

Question 13 Marks

Explain with examples the terms weak and strong electrolytes.

Answer

Weak electrolytes$:$ Weak electrolytes are those which do not dissociate into ions completely in aqueous solution $e.g.$ $CH_3COOH$
Strong electrolytes$:$ Strong electrolytes are those which dissociate into ions completely in aqueous solution $e.g. NaCl$

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Question 23 Marks

What are ambident nucleophiles? Explain with an example.

Answer

Ambident nucleophiles are nucleophiles having two nucleophilic sites. Thus, ambident nucleophiles have two sites through which they can attack.
For example, nitrite ion is an ambident nucleophile.
$[-O-\ddot{N}=O]$
Nitrite ion can attack through oxygen resulting in the formation of alkyl nitrites. Also, it can attack through nitrogen resulting in the formation of nitroalkanes.

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Question 33 Marks

Calculate the emf of the following cell at $25^{\circ} C$.$Fe \left| Fe ^{2+}(0.001 M )\right|\left| H ^{+}(0.01 M )\right| H _2(g)(1 bar ) \mid Pt ( s )$
Given that, $E_{ Fe ^{2+} / Fe }^o=-0.44 V ; E_{H^{+} / H_2}^o=0.00 V$

Answer

At anode, $Fe ( s ) \rightarrow Fe ^{2+}( aq )+2 e ^{-}$
At cathode, $\left[ H ^{+}( aq )+ e ^{-} \rightarrow \frac{1}{2} H _2(g)\right] \times 2$
Overall reaction:
$Fe(s)+2 H^{+}(aq) \rightarrow Fe^{2+}(aq)+H_2(g)$
Given, $E_{ Fe ^{2+} / Fe }^o=-0.44 V$ and $E_{H^{+} / H_2}^o=0.00 V$
$\left.E^0(\text { cell })=E^0 \text { (cathode) }-E^0 \text { (anode }\right)=[0.00-(-0.44)]=0.44 V$
Now, Applying Nernst equation:
$E_{\text {cell }}=E_{\text {cell }}^o-\frac{0.00591}{2} \log \frac{\left[Fe^{2+}\right]}{\left[H^{+}\right]^2}=0.44-\frac{0.00591}{2} \log \frac{10^{-3}}{\left(10^{-2}\right)^2}$
$=0.44-\frac{0.00591}{2}=0.4104 V$

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Question 43 Marks

Write the major products in the following:

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Question 53 Marks

Give the structures and IUPAC names of the products expected from the following reactions:
a. Catalytic reduction of butanol.
b. Hydration of propene in the presence of dilute sulphuric acid.
c. Reaction of propanone with methyl magnesium bromide followed by hydrolysis.

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Question 63 Marks

While separating a mixture of ortho and para nitrophenols by steam distillation, name the isomer which will be steam volatile. Give reason.

Answer

Intramolecular H-bonding is present in o-nitrophenol. In p-nitrophenol, the molecules are strongly associated due to the presence of intermolecular bonding. Hence, o-nitrophenol is steam volatile.

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Question 73 Marks

$i.$ Define rate constant of reaction.
$ii.$ A first order reaction takes $40$ mins for $30\%$ decomposition. Calculate $t_\frac{1}{2}.$

Answer

$i.$ Rate constant $:$ It is the rate of chemical reaction when the concentration of reactant taken as unity at a given temperature.
$ii.$ Let initial
conc. $=$ a conc. after $40 \ min$. $=a-\frac{a \times 30}{100}$
$=0.70 \ a$
$K=\frac{2.303}{t} \ \log \frac{[A]_0}{[A]}$
$=\frac{2.303}{40} \ \log \frac{a}{0.70 a}$
$=\frac{2.303}{40} \ \log \frac{1}{0.70}$
$=\frac{2.303}{40} \times 0.1549$
$=8.92 \times 10^{-3} min^{-1}$
$t_{1 / 2}=\frac{0.693}{K}$
$=\frac{0.693}{8.92 \times 10^{-3}}$
$=77.7 \ min$

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Question 83 Marks

What is the difference between Galvanic cell (Electrochemical cell) and Electrolytic cell.

Answer

Electrochemical cell	Electrolytic cell
(1) It is a device to convert chemical energy into electrical energy.	(1) It is a device to convert electrical energy into chemical energy.
(2) It is based upon the redox reaction which is spontaneous.	(2) The redox reaction is non-spontaneous and takes place only when electric energy is supplied.
(3) To set up this cell, a salt bridge or porous pot is used.	(3) No salt bridge is used in this case.

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Chemistry 3 Marks Question

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