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Chemistry 1 Marks Question

Electrochemistry · Rajasthan Board (RBSE) STD 12 Science (Rajasthan - English Medium). 25 questions.

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Question 11 Mark
Which of the following will have higher molar conductivity between them : (i) One mole NaCl in 100 ml solution (ii) One mole NaCl in 250 ml solution and why?
Answer
Molar conductivity of solution (ii) will be higher because $\Lambda_{ m }=\kappa \times V$ i.e. the molar conductivity increases with the increase in volume.
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Question 21 Mark
Write the cell diagram of the following cell reactions :
$
2 Fe_{(s)}+3 Cd_{(aq)}^{2+} \rightarrow 2 Fe_{(aq)}^{+3}+3 Cd_{(s)}
$
Answer
The cell diagram of the above cell reaction is as follows:
Anode ${ }^{-} Fe _{( s )}\left| Fe _{( aq )}^{+3} \| Cd _{(\text {aq })}^{2+}\right| Cd _{( s )}{ }^{+}$Cathode
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Question 31 Mark
Explain the function of platinum in standard hydrogen electrode (SHE).
Answer
For standard hydrogen electrode (SHE), platinum, catalyst, and metallic contact acts as inert metals.
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Question 41 Mark
Why it is not possible to determine the electrode potential of any one electrode?
Answer
Electrode potential of any one electrode cannot be determined because electromotive force (EMF) can be measured only when the circuit is complete and the circuit is not complete with just one electrode.
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Question 51 Mark
Why does rust occur quickly in salt water?
Answer
Salt $( NaCl )$ does not increase ionization of $H _2 O$, thereby increasing the concentration of $H ^{+}$which helps in rusting.
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Question 61 Mark
If a dry cell is not used for a long time, it gets destroyed. Why?
Answer
If a dry cell is not used for a long time, the ammonium chloride present in it corrodes its zinc vessel and it destroys.
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Question 71 Mark
Why does the potential remain constant throughout the working period in mercury cell?
Answer
In the entire cell reaction of mercury cell, there is no such ion, whose concentration changes due to being in solution.
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Question 81 Mark
Why is Al metal not obtained by electrolysis of Al salts?
Answer
Al metal is not obtained by electrolysis of Al salts because it reacts with water to form $Al _2 O _3$.
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Question 91 Mark
What is Debye-Huckel-Onsagar equation?
Answer
$\Lambda_m=\Lambda_m^{\circ}- A \sqrt{C}$ $\Lambda_{ m }=$ Molar conductivity, $\Lambda_{ m }{ }^{\circ}=$ limiting molar conductivity, $A =$ constant and $C =$ concentration.
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Question 101 Mark
What will be the products obtained by electrolysis of molten $PbBr _2$ ? If inert electrode is taken.
Answer
On electrolysis of molten $PbBr _2, Pb$ is obtained at the cathode and $Br _2$ at anode.
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Question 111 Mark
What is relationship between molar conductivity and equivalent conductivity?
Answer
$
\frac{\text { Molar conductivity }}{\text { Equivalent conductivity }}=n, \quad n=\frac{\text { Molecular weight }}{\text { Equivalent weight }}
$
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Question 121 Mark
Write the formula to determine molar conductivity.
Answer
Molar conductivity, $\Lambda_{ m }=\frac{\kappa \times 1000}{ M }$ ( $M =$ molarity).
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Question 131 Mark
Explain the relationship between specific conductivity ( $\kappa$ ) of cell and cell constant.
Answer
$\kappa=\frac{1}{ R } \times \frac{l}{A}\left(\frac{l}{A}=\right.$ cell constant $)$.
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Question 141 Mark
What will be the charge in pH of the solution when electricity is passed through aqueous solution of NaCl ?
Answer
When electricity is passed through an aqueous solution of NaCl , the pH of the solution increases ( $pH >7)$ because a strong base $( NaOH )$ is formed in it.
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Question 151 Mark
Write the product obtained on electrolysis of $CuSO _4$ solution using platinum electrode.
Answer
On electrolysis of $CuSO _4$ solution, copper is obtained at the cathode and oxygen at anode.
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Question 161 Mark
What does the negative value of $E_{\text {cell }}^{\circ}$ indicates?
Answer
$E _{\text {cell }}^{\circ}$ being negative means $\Delta G =+ ve$ and in this situation, no work will be done in the cell.
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Question 201 Mark
Explain the reaction between $pH$ of the solution and the hydrogen electrode potential.
Answer
$E_{H^{+} / H_2}=0.059 \log \left[H^{+}\right]$
$E_{H^{+} / H_2}=-0.059 \ pH$
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Question 211 Mark
What will be the effect on the value of electrode potential of Zn electrode if the concentration of $Zn ^{2+}$ is increased?
Answer
By increasing the concentration of $Zn ^{2+}$, the value of electrode potential of Zn increases.
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Question 221 Mark
Will the following reaction occur or not :
$
ZnSO_{4(aq)}+2 Ag_{(s)} \rightarrow Ag_2 SO_{4(aq)}+Zn_{(s)}
$
Answer
The reaction will not occur because the tendency of Ag to be oxidized is less than the tendency of Zn to be oxidized.
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Question 231 Mark
Equilibrium constant $\left( K _{ C }\right)$ is related to $E _{\text {cell }}$ and not $E _{\text {cell }}$. Why?
Answer
$K _{ C }$ is related to $E _{\text {cell }}^{\circ}$ because at equilibrium, the value of $E _{\text {cell }}$ is zero.
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Question 241 Mark
The conductivity of 0.20 M solution of KCl at 298 K is 0.0248 S cm-1. Calculate its molar conductivity.
Answer
Molar conductivity $\left(\Lambda_{ m }\right)=\frac{\kappa \times 1000}{\text { Molarity }}$
$\kappa=$ conductivity $=0.0248 S cm ^{-1}$, Molarity $=0.20 M$
Hence, $\Lambda_{ m }=\frac{0.0248\left(S cm ^{-1}\right) \times 1000 cm^3}{0.20 mol}$
$\Lambda_{ m }=124 S cm ^2 mol^{-1}$
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Question 251 Mark
Arrange the following metals in the order in which they displace each other from the solution of their salts.
Al, Cu, Fe, Mg and Zn.
Answer
The order in which the given metals replace each other in their salt solution is as follows. This is the decreasing order of their reactivity :
$Mg > Al > Zn > Fe > Cu$
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