Electrochemistry 1 Question 31
Passage
Chemical reactions involve interaction of atoms and molecules. A large number of atoms/molecules (approximately $6.023 \times 10^{23}$ ) are present in a few grams of any chemical compound varying with their atomic/molecular masses. To handle such large numbers conveniently, the mole concept was introduced. This concept has implications in diverse areas such as analytical chemistry, biochemistry, electrochemistry and radiochemistry. The following example illustrates a typical case, involving chemical/electrochemical reaction, which requires a clear understanding of the mole concept. A $4.0 M$ aqueous solution of NaCl is prepared and $500$ mL of this solution is electrolysed. This leads to the evolution of chlorine gas at one of the electrodes (atomic mass : $\mathrm{Na}=23, \mathrm{Hg}=200,1 \mathrm{~F}=96500 \mathrm{C}$ ).
$ (2007,3 \times 4 M=12 M) $
30. If the cathode is a $\mathrm{Hg}$ electrode, the maximum weight (in gram) of amalgam formed from this solution is
(a) 200
(b) 225
(c) 400
(d) 446
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Answer:
Correct Answer: 30. (d)
Solution:
- At cathode $\mathrm{Na}^{+}+e^{-} \xrightarrow{\mathrm{Hg}} \underset{\text { Amalgam }}{\mathrm{Na}(\mathrm{Hg})}$
Two moles of $\mathrm{Na}$ formed during electrolysis would produce two moles of $\mathrm{Na}(\mathrm{Hg})$ amalgam.
$\Rightarrow$ mass of amalgam $=2 \times(23+200)=446 \mathrm{g}$
BETA
