Tag: extraction of metals by electrolysis

Questions Related to extraction of metals by electrolysis

Cost of electricity for the production of $X$ litres of $H _2$ at $NTP$ at the cathode is Rs $X$, then cost of electricity for the production $X$ litres of $O _2$ gas at $NTP$ at the anode will be:


[Assume $1$ mole of electrons as one unit of electricity]

chemistry chemical changes applications of electrolysis electroplating extraction of metals by electrolysis

  1. $2X$

  2. $4X$

  3. $16X$

  4. $32X$

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Correct Option: A
Explanation:

Electrolysis of water gives:


${ H } _{ 2 }O\rightarrow { H } _{ 2 }+\tfrac { 1 }{ 2 } { O } _{ 2 }$


On electrolysis of water, hydrogen, and oxygen formed in the ratio $2:1$.
Since $X$ litres of ${ H } _{ 2 }$ is formed. Amount of ${ O } _{ 2 }$ formed will be $\tfrac { X }{ 2 } $. Since cost of production of electricity from $\tfrac { X }{ 2 } $ litres of ${ O } _2$ = Rs $X$

So, cost of production of electricity from $X$ litres of ${ O } _2$ = Rs $2X$.

So, the correct answer is option $A$.

A solution of $CuSO _4$ is electrolysed for $7$ minutes with a current of $0.6A$. The amount of electricity passed is equal to:

chemistry chemical changes applications of electrolysis electroplating extraction of metals by electrolysis

  1. $4.2C$

  2. $2.6\times 10^{-3}F$

  3. $126C$

  4. $36C$

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Correct Option: B
Explanation:

Quantity of electricity passed $\displaystyle Q(C) = I(A) \times t(s)$
$\displaystyle Q(C)=0.6 \ A \times 7 \ min \times 60 \ s/min$
$\displaystyle Q(C)=252 \ C$
Number of faraday passed $\displaystyle = \dfrac {252 \ C}{96500 \ C/F}=2.6 \times 10^{-3} \ F$

State True or False.
Electrotyping is an application of electrolysis.

chemistry chemical changes applications of electrolysis electroplating extraction of metals by electrolysis

  1. True

  2. False

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Correct Option: A
Explanation:

Electrotyping is a chemical method for forming metal parts that exactly reproduce a model.
Electrotyping is related to electroplating, which permanently adds a thin metallic overlayer to a metallic object instead of creating a freestanding metal part. So it is basically an application of electrolysis.

In the electroplating of iron by nickel, nickel sulphate solution is taken as electrolyte. What is the acid that is added to the electrolyte during the process?

chemistry chemical changes applications of electrolysis electroplating extraction of metals by electrolysis

  1. $HCl$

  2. $HCN$

  3. $HNO _3$

  4. $H _2SO _4$

Show answer
Correct Option: D
Explanation:

Sulphuric acid is used for pH adjustment during electroplating of nickel.

During electrolysis of an aqueous solution of a salt, pH in the space near one of the electrodes is increased, which of the following salt solution was electrolysed?

chemistry chemical changes applications of electrolysis electroplating extraction of metals by electrolysis

  1. $KCl$

  2. ${ CuCl} _{ 2 }$

  3. ${ Cu(NO } _{ 3 }{ ) } _{ 2 }$

  4. ${ CuSO } _{ 4 }$

Show answer
Correct Option: A
Explanation:
As the cation $\left( {K}^{+} \right)$ in $KCl$ has lower electrode potential than $H$, hydrogen is liberated at cathode.

There is an accumulation of ${H}^{+}$ at one electrode, resulting in an increase in pH.

Hence, option A is correct.

A 5-ampere current is passed through a solution of zinc sulphate for $40 $ minutes. The amount of zinc deposited at the cathode is:

chemistry chemical changes applications of electrolysis electroplating extraction of metals by electrolysis

  1. $0.4065 g$

  2. $65.04 g$

  3. $40.65 g$

  4. $4.065 g$

Show answer
Correct Option: D
Explanation:

$\because$ $W=z.i.t$=$\cfrac{E}{F}\times{i}.{t}$$=\left(\cfrac{65.38\times5\times40\times60}{2\times96500}\right)g$.


                                $=4.065 g.$

The same amount of electricity was passed through two separate electrolytic cells containing solutions of nickel nitrate $\left[ Ni{ \left( { NO } _{ 3 } \right)  } _{ 2 } \right]$ land chromium nitrate $\left[Cr{ \left( { NO } _{ 3 } \right)  } _{ 3 } \right]$ respectively. If $0.3g$ of nickel was deposited in the first cell, the common of chromium deposited is :
$(at. Wt. Of Ni=59, at. Wt. Of Cr=52)$

chemistry chemical changes applications of electrolysis electroplating extraction of metals by electrolysis

  1. $0.1g$

  2. $0.17g$

  3. $0.3g$

  4. $0.6g$

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Correct Option: B

A certain quantity of electricity when passed through solution of ${ AgNO } _{ 3 }$, ${ ZnSO } _{ 4 }$, ${ CrI } _{ 3 }$. If X moles of Cr are deposited at its cathode, how many moles of Ag and Zn are deposited at their respective cathodes.

chemistry chemical changes applications of electrolysis electroplating extraction of metals by electrolysis

  1. X, X

  2. 3X, 2X

  3. 3X, 1.5X

  4. none of these

Show answer
Correct Option: C
Explanation:

$Ag^++e^- \longrightarrow Ag$

$Zn^{2+}+2e^- \longrightarrow Zn$
$Cr^{3+}+3e^-\longrightarrow Cr$
Given that $x$ moles of $Cr$ is deposited at it's cathode means in case of $Ag$ it will be $3X$  and for $Zn$ it will be $\cfrac {3X}{2}$ moles deposits at cathode.

How long (approximate) should water be electrolysed by passing through $100$ amperes current so that the oxygen realised can completely burn $27.66\ g$ of diborane?


(Atomic weight of $B=10.8\ u$ )

chemistry chemical changes applications of electrolysis electroplating extraction of metals by electrolysis

  1. $0.8$ hours

  2. $3.2$ hours

  3. $1.6$ hours

  4. $6.4$ hours

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Correct Option: B

The mass of carbon anode consumed (giving only carbondioxide) in the production of 270 kg of Aluminium metal from bauxite by the Hall process is :

chemistry chemical changes applications of electrolysis electroplating extraction of metals by electrolysis

  1. 270 kg

  2. 540 kg

  3. 90 kg

  4. 180 kg

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Correct Option: B