Tag: extraction of metals by electrolysis

Questions Related to extraction of metals by electrolysis

The same amount of electricity was passed through two separate electrolytic cells containing solutions of nickel nitrate $[Ni(NO _{3}) _{2}$] and chromium nitrate $[Cr(NO _{3}) _{3}$] respectively.If 0.3 g of nickel was deposited in the first cell, the amount 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. 0.1 g

  2. 0.17 g

  3. 0.3 g

  4. 0.6 g

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Correct Option: C

On electrolysing a solution of dilute ${ H } _{ 2 }{ SO } _{ 4 }$ between platinum electrodes, the gas evolved at the anode is 

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

  1. ${ SO } _{ 2 }$

  2. ${ SO } _{ 3 }$

  3. ${ O } _{ 2 }$

  4. ${ H } _{ 2 }$

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Correct Option: A

In the manufacture of $NaOH$ by the electrolysis of $NaCl$ solution, the cathode and anode are separated using a diaphragm because :

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

  1. it prevents the reaction betweeen ${H _2}$ and $C{l _2}$ formed

  2. it prevents the mixing of $NaOH$ and $NaC{l _2}$

  3. it prevents the reaction betweeen $Na$ and $C{l _2}$ formed

  4. it increases the yield of $NaOH$

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Correct Option: B

Charge required for liberating $710 g$ of $Cl _{2}(g)$ by electrolyzing a concentrated solution of $NaCl$ will be:

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

  1. $1.93$ x $10^{5}$ $C$

  2. $1.93$ x $10^{6}$ $C$

  3. $9.65$ x $10^{6}$ $C$

  4. $9.65$ x $10^{5}$ $C$

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Correct Option: B
Explanation:

The reaction taking place at anode is given by:

$2Cl^- \rightarrow Cl _2+2e^-$
Thus, $2$ moles of $e^-$ are required to liberate $1$ mole of $Cl _2$
Moles of $Cl _2=\dfrac{710}{71}=10$
Hence moles of $e^-$ required $=2\times10=20$
Hence $Q=20F$
$\Rightarrow Q=20\times 96500$
$\Rightarrow Q=1.93\times10^6 C$

The correct relation is

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

  1. $\triangle G = -RT\ ln\ K/Q$

  2. $\triangle G = -RT\ ln\ K$

  3. $\triangle G = -RT\ ln\ Q/K$

  4. $\triangle G = +RT\ ln\ Q$

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Correct Option: B
Explanation:

$\triangle G = \triangle G^{\circ} + RT\ ln Q$
$\triangle G = -RT\ ln \dfrac {K}{Q}$.

Which process occurs in the electrolysis of an aqueous solution of nickel chloride at nickel anode?

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

  1. $Ni\rightarrow Ni^{2+}+2e^{-}$

  2. $Ni^{2+}+2e^{-}\rightarrow Ni$

  3. $2CI^{-}\rightarrow 2CI _{2}+2e^{-}$

  4. $2H^{+}+2e^{-}\rightarrow H _{2}$

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Correct Option: A

On the basic of information available from the reaction
$ 4AI + 3O _{2} \rightarrow 2AI _{2}O _{3}; \triangle G = -965$ kJ/mol of $O _{2}$
The minimum EMF required to carry out electrolysis of $ AI _{2}O _{3}$ is

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

  1. 0.833 V

  2. 2.5 V

  3. 5.0 V

  4. 1.67 V

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Correct Option: B

By selecting electrolyte as sodium argentocyanide for electroplating of the metal article with silver. Which of the following condition ensures that deposit is smooth, firm and long-lasting?

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

  1. low direct current should be passing for long time

  2. low indirect current should be passing for long time

  3. low direct current should be passing for short time

  4. low indirect current should be passing for long time.

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Correct Option: A

A current of 3.7 A is passed for 6 h between nickel electrodes in 0.50 1 of 2 M solution of $Ni(NO _{3}) _{2}$. The molarity of $Ni^{2+}$ at the end of electrolysis is

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

  1. 1.172 M

  2. 0.172 M

  3. 0.586 M

  4. 2 M

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Correct Option: D

Which of the following reaction taken place at anode during electroplating of metal with silver using sodium argentocyanide as an electrolyte?

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

  1. $Ag\quad -{ e }^{ \ _ }\longrightarrow { Ag }^{ \ + }$

  2. ${ Ag }^{ + }+{ e }^{ \ _ }\longrightarrow Ag$

  3. $Ag\quad -2{ e }^{ \ _ }\longrightarrow { Ag }^{ \ +}\quad +{ e }^{ \ - }$

  4. $2{ Ag }^{ + }+{ e }^{ \ _ }\longrightarrow Ag$

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Correct Option: A
Explanation:

In electroplating with silver, oxidation reaction at anode takes place:


$Ag - e^-\rightarrow Ag^+$.