2 Marks Questions

Question 12 Marks

(a) Calculate $\Delta G^{0}$ for the reaction
$Zn(s) + Cu^{2+}(aq) \longrightarrow Zn^{2+}(aq) + Cu(s)$.
Given: $E^{0}$ for $Zn^{2+}/Zn = -0.76 V$ and
$E^{0}$ for $Cu^{2+}/Cu = +0.34 V$,
$R = 8.314 J K^{-1} mol^{-1}$,
$F = 96500 C mol^{-1}$.
(b) Give two advantages of fuel cells.

Answer

(a) $E ^{\circ}{ }_{\text {cell }}= E ^{\circ}{ }_{ L }- E ^{\circ}{ }_{ A }$
$=0.34-(-0.76)=1.10 V$
$\Delta G ^{\circ}=-n FE ^{\circ}$
$=-2 \times 1.10 \times 96500$
$=-212300 J / mol$
$=-212.3 kJ / mol$
(b) (i) Pollution free, (ii) High efficiency.

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Question 22 Marks

Calculate the mass of Ag deposited at cathode when a current of 2 amperes was passed through a solution of $AgNO_{3}$ for 15 minute. (Given: Molar mass of $Ag = 108 g mol^{-1}$, $1 F = 96500 C mol^{-1}$)

Answer

$Q = I \times t = 2 \times 15 \times 60 = 1800 C$
$Ag^{+} + e^{-} \rightarrow Ag(s)$
96500 C of current deposit silver = 108 g
1800 C of current will deposit = $\frac{108 \times 1800}{96500}$
Amount of Ag deposited = 2.01 g

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Question 32 Marks

Faraday's first law of electrolysis.

Answer

Faraday's first law: According to this law the amount of substance is directly proportional to the quantity of electricity passed.
$M \propto Q$ $m =$ Amount or mass of substance,
$Q =$ Quantity of electricity or charge,
$Q = I \times t,$
$I =$ Current in ampere,
$t =$ Time in second,
$m \propto I \times t$
or $\quad$ $m = Z \times It$ or $m = ZQ$

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Question 42 Marks

State Faraday's second law of electrolysis.

Answer

Faraday's second law: According to this law when same quantity of electricity is passed through solution of different electrolytes, the amount of substance liberated at the electrodes is proportional to their equivalent masses.
If $m_{1}$ and $m_{2}$ are the masses of metal deposited by passing same quantity of electricity and $E_{1}$ and $E_{2}$ are their equivalent masses respectively then $\frac{m_{1}}{m_{2}} = \frac{E_{1}}{E_{2}}$

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Question 52 Marks

What do you mean by Primary Cell?

Answer

A primary cell is that in which redox reaction occurs only once i.e., it is not rechargeable.
It means in primary cells the electrode reaction cannot be reversed by an external electrical energy source and it becomes dead over a period of time. It cannot be used again. Typical primary cells are Daniell cell, Dry cell and Mercury cell.

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Question 62 Marks

Define electrode and electrode potential.

Answer

Electrode: An electrode is a small piece of metal or metal rod that is used to flow current through electrolyte.
Electrode Potential: The electrical potential difference set up between the metal and solution of its ions is known as the electrode potential or half cell potential. It is denoted by the letter E.

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Chemistry 2 Marks Questions

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