Tag: electroplating

Questions Related to electroplating

Electrolysis of a solution of $Mn{ SO } _{ 4 }$ in aqueous sulphuric acid is a method for the preparation of $MnO _ 2$. Passing a current of $27A$ for $24$ hours gives $1kg$ of $MnO _2$. The current efficiency in this process is:

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

  1. $100$%

  2. $95.185$%

  3. $80$%

  4. $82.951$%

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Correct Option: B
Explanation:

The reaction taking place on the given reaction are,

$Mn^{2+}+2H _2O\rightarrow MnO _2+2H^{+}+H _2$

Amount of current is given by,
$m= Z \times I \times t$

$I=m\dfrac{F\times x}{t\times M}$

    $=1000g\times{\dfrac{96500\times 2}{24\times 60 \times 60 \times 86.9}}$

    $\implies I=25.70A$

Now current efficiency$=\dfrac{25.7}{27} \times 100=95.185$ %

Hence,option B is correct answer.

Consider the reaction : $Cr _2O _7^{2-} + 14H^+ + 6e^- \to 2Cr^{3+}+7H _2O$


What is the quantity of electricity in coulombs needed to reduced $1\ mol$ of $Cr _2O _7^{2-}$?

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

  1. $6 \times 10^6C$

  2. $5.79\times 10^5C$

  3. $5.25 \times 10^5C$

  4. None of these

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Correct Option: B
Explanation:
$Cr _2O _7^{2-} + 14H^+ + 6e^- \to 2Cr^{3+}+7H _2O$

The valency factor for Chromium is $6$.

Applying faraday's first law-
$ \dfrac{Q} {F} =mole \times V.f.$

$  Q            =mole \times V.f. \times F$ 

$  Q            =1 \times 6 \times 96500$

$  Q            =5.79\times 10^5\ C$

Calculate the amounts of Na and chlorine gas produced during the electrolysis of fused $NaCl$ by the passage of 1 ampere current for 25 minutes. 

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

  1. 0.3565 gm and 0.55 gm

  2. 0.3565 gm and 0.66 gm

  3. 0.55 gm and 0.3565

  4. None of above

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Correct Option: A
Explanation:
$i= 1 \ amp$
$t= 25 \ min = 25 \times 60 \ sec$
Molar mass of $Na= 23 \ g \ mol^{-1}$
Molar mass of $Cl _2= 71 \ g \ mol^{-1}$
$Cl^-= \cfrac 12 {(12)}=35.5 \ g$
Formula used, $m= \cfrac {Molar \ mass}{n \times F} \times i \times t$
For $Na$, $n=1$
$m= \cfrac {23}{1 \times 96500} \times 1 \times 25 \times 60$
$=0.3575 \ g$

For $Cl$, $n=1$
$m= \cfrac {35.5}{1 \times 96500} \times 1 \times 25 \times 60$
$=0.5518 \ g$

$\therefore$ The amounts of $Na$ and $Cl$ gas produced are $0.3575 \ g$ and $0.5518 \ g$ respectively.

A current of  $13.4\mathrm { A }$  is passed through  $1.0\mathrm { L }$  of  $1.0\mathrm { M }$  $HCl$  solution by using  $Pt$  electrodes for  $1.0\  \mathrm { hr }.$  The  $pH$  of the solution after the experiment is over at  $298 K$  will be about.

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

  1. $0.20$

  2. $0.30$

  3. $0.40$

  4. $0.50$

Show answer
Correct Option: B
Explanation:
$ (B) 0.30 $ 
Change in coulombs $ = 13.4\times 1\times 60\times 60 = 48240 $

Moles of electric charge $ = \dfrac{48240}{96500} = 0.5 F $

Equivalent of HCl decomposed on electrolysis $ = 0.5 $

Mili equivalents of HCl along electrolysis $ = 500 $

Molarity of HCl after electrolysis $ = \dfrac{500}{1000} = 0.5 M$

$ [H ^{+}] = 5\times 10^{-1} $

$ p{H} = -\log [H^{+}] $

$ p{H} = -\log 5\times 10^{-1} = 0.30. $

A solution of ${ AgNO } _{ 3 }$ is a good electrolyte but is not used for electroplating an article with silver because :

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

  1. rapid deposition of silver takes place resulting in uneven coating

  2. slow deposition of silver takes place resulting in uneven coating

  3. poor conduction of silver

  4. none of the above

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Correct Option: A
Explanation:

A solution of $AgNO _3$ is a good electrolyte but is not used for electroplating an article with silver because it undergoes very fast redox process and electroplating done through this process is not uniform.

The electrical process of coating an inexpensive conductor with a metal is called electroplating.

chemistry chemical effects of electric current applications of electrolysis electroplating extraction of metals by electrolysis

  1. True

  2. False

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Correct Option: A
Explanation:
Electroplating is a process that uses electric current to deposit/reduce dissolved metal cations so that they form a thin coherent metal coating on an electrode.

It is used to coat a relatively mundane metal, such as copper, with a thin layer of another, more precious metal, such as gold or silver. 

Hence, option $\text{A}$ is correct.

Chromium plating is done to make the object scratch proof and appear shiny.

chemistry chemical effects of electric current applications of electrolysis electroplating extraction of metals by electrolysis

  1. True

  2. False

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Correct Option: A
Explanation:

Chromium plating is a technique of electroplating in which a thin layer of chromium is coated onto a metal object. The layer is decorative (shiny), provide corrosion resistance, ease cleaning procedures, and increase surface hardness (scratch resistance).


Hence, option A is correct.

To protect iron from corrosion and rusting , it is electroplated with 

physics chemical effects of electric current applications of electrolysis electroplating extraction of metals by electrolysis

  1. Zinc

  2. Chromium

  3. Nickel

  4. Aluminum

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Correct Option: A
Explanation:

Iron is coated with a more active metal like Zinc. This is a sacrificial method. If the rusting conditions are met, zinc rusts before iron and prevents iron from rusting. Zinc makes a protective layer with Zn(OH)2 and ZnCO3

The process of depositing a thin layer of desired metal over another metal by passing an electric current through some electrolyte is called :

chemistry chemical effects of electric current applications of electrolysis electroplating extraction of metals by electrolysis

  1. electric shielding

  2. electric polishing

  3. electric coating

  4. electroplating

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Correct Option: D
Explanation:

Electroplating is the application of electrolytic cells in which a thin layer of metal is deposited onto an electrically conductive surface.


Hence, option D is correct.

Electroplating does not help

physics chemical effects of electric current applications of electrolysis electroplating extraction of metals by electrolysis

  1. fine finish to the surface

  2. shining appearance

  3. metals to become hard

  4. protect metals against corrosion

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Correct Option: C
Explanation:

Electroplating is primarily used to change the surface properties of an object like appearance, corrosion protection, lubricity etc.  Thus, electroplating does not help in making the metals become hard.