241.
Which of the following statements is correct about the given Daniell cell?
A
This cell converts the electrical energy liberated during the redox reaction to chemical energy.
B
This cell has an electrical potential greater than $$1.1\,V$$ when concentration of $$Z{n^{2 + }}$$ and $$C{u^{2 + }}$$ ions is unity $$\left( {1\,mol\,d{m^{ - 3}}} \right).$$
C
In this cell, copper is acting as cathode and zinc is acting as anode.
D
Redox reaction occurring in this cell is $$C{u_{\left( s \right)}} + Zn_{\left( {aq} \right)}^{2 + } \to Cu_{\left( {aq} \right)}^{2 + } + Z{n_{\left( s \right)}}$$
Answer :
In this cell, copper is acting as cathode and zinc is acting as anode.
No explanation is given for this question. Let's discuss the answer together.
242.
For the electrochemical cell, $$M\left| {{M^ + }} \right|\left| {{X^ - }} \right|X,{E^o}{M^ + }/M = 0.44V\,{\text{and}}\,{E^ \circ }\left( {X/X} \right) = 0.33V.$$ From this data one can deduce that
A
$$M + X \to {M^ + } + {X^ - }$$ is the spontaneous reaction
B
$${M^ + } + {X^ - } \to M + X$$ is the spontaneous reaction
C
$${E_{cell}} = 0.77V$$
D
$${E_{cell}} = - 0.77V$$
Answer :
$${M^ + } + {X^ - } \to M + X$$ is the spontaneous reaction
Key Idea This problem is based on Faraday's first law of electrolysis which states that when an electric current is passed through an electrolytic solution, the amount of substance $$(w),$$ deposited at the electrode, is proportional to the electric charge $$(q)$$ passed through the electrolytic solution.
The formula used in the problem is
$$w = \frac{{Eit}}{{96500}}\,\,\,...{\text{(i)}}$$
where, $$E = $$ gram-equivalent mass of $$C{l^ - }$$
$$i =$$ current, $$t =$$ time, $$it= q$$
Given, $$w = 0.10\,mol = \left( {0.10 \times 71} \right)g,$$
$$i = 3A,E = 35.5$$
The following reactions occured,
\[\begin{align}
& \text{At cathode :}\,2{{H}_{2}}O\xrightarrow{+2{{e}^{-}}}{{H}_{2}}+2O{{H}^{-}} \\
& \text{At anode : }\underset{35.5\,g}{\mathop{2C{{l}^{-}}}}\,\xrightarrow{-2{{e}^{-}}}\underset{71\,g}{\mathop{C{{l}_{2}}}}\, \\
\end{align}\]
Putting all values in expression (i) we get
\[\begin{align}
& \left( 0.10\times 71 \right)=\frac{35.5}{96500}\times 3\times t\,\,\text{or}\,\,t=6433\,s \\
& \,\text{or}\,\,t=107.22\,\min \\
& \simeq \,110\,\min \,\,\left[ 1\,s=\frac{1}{60}\min \right] \\
& \\
\end{align}\]
244.
The Nernst equation $$E = {E^ \circ } - \frac{{RT}}{{nF}}\,\ln \,Q$$ indicates that the $$Q$$ will be equal to equilibrium constant $${K_c}$$ when :
245.
Following cell has $$EMF\,0.7995\,V.$$
$$Pt\left| {{H_2}\left( {1\,atm} \right)} \right|\left. {HN{O_3}\left( {1\,M} \right)} \right|\left| {AgN{O_3}\left( {1\,M} \right)} \right|Ag$$
If we add enough $$KCl$$ to the $$Ag$$ cell so that the final $$C{l^ - }$$ is $$1M.$$ Now the measured emf of the cell is $$0.222V.$$ The $${K_{sp}}$$ of $$AgCl$$ would be-
In eclectrochemical series, $$Al$$ is placed above $$Zn$$ and all other are present below $$Zn.$$ So, aluminium displaces zinc from $$ZnC{l_2}$$ solution. Hence, it cannot keep in contact with $$Al.$$
247.
Which of the following statement is correct ?
A
Cathode is $$–ve$$ terminal in both, glavanic and electrolytic cells.
B
Anode is $$+ve$$ terminal in both, galvanic and electrolytic cells.
C
Cathode and anode are $$–ve$$ terminal in electrolytic and galvanic cell.
D
Cathode and anode are $$+ve$$ terminal in electrolytic and galvanic cell.
Answer :
Cathode and anode are $$–ve$$ terminal in electrolytic and galvanic cell.
$$2H{I^{ - 1}} + {H_2}\mathop {S{O_4}}\limits^{ + 6} \to I_2^0 + \mathop {S{O_2}}\limits^{ + 4} + 2{H_2}O$$ in this reaction oxidation number of $$S$$ is decreasing from $$+ 6$$ to $$+4$$ hence undergoing reduction and for $$HI$$ oxidation Number of $$I$$ is increasing from $$-1$$ to $$0$$ hence underegoing oxidation therefore $${H_2}S{O_4}$$ is acting as oxidising agent.
250.
Standard reduction electrode potentials of three metals $$A, B$$ & $$C$$ are respectively $$+ 0.5 V, -3.0 V$$ & $$-1.2 V.$$ The reducing powers of these metals are
\[\begin{matrix}
A \\
+0.5C \\
\end{matrix}\,\,\,\begin{matrix}
B \\
-3.0V \\
\end{matrix}\,\,\,\begin{matrix}
C \\
-1.2V \\
\end{matrix}\]
NOTE : The higher the negative value of reduction potential, the more is the reducing power.
Hence $$B > C > A.$$