Electroplating - class-XI

Using the Nernst equation: E = E_cell - (0.059/n) * log(1/[Zn+2]). Diluting 100 times increases the concentration of the denominator in the log term, making the log term more negative, which increases the overall potential by (0.059/2) * log(100) = 0.059 V = 59 mV.

Electroplating is the process of plating one metal onto another, for decorative purposes or to prevent corrosion of a metal. 

One Faraday (96500 C) of charge deposits or releases 1 gram equivalent of a substance. For H2 gas (n=2), 1 Faraday releases 0.5 moles of H2. Volume at STP = 0.5 * 22400 mL = 11200 mL.

Faraday's first law of electrolysis states that the mass of a substance deposited is directly proportional to the quantity of electricity (charge Q) passed through the electrolyte.

Answer is D.
Electrolysis has wide applications in industries. Some of the important applications are, as follows, 
(i) Production of hydrogen by electrolysis of water. 
(ii) Manufacture of heavy water. 
(iii) The metals like K, Mg, Al, etc., are obtained by electrolysis of fused electrolytes. 
(iv) Non-metals like hydrogen, fluorine, chlorine are obtained by electrolysis. 
(v) In this method pure metal is deposited at cathode from a solution containing the metal ions, etc. 
(vi) Compounds like NaOH, KOH, white lead, etc. are synthesised by electrosynthesis method.
(vii) Electroplating: The process of coating an inferior metal with a superior metal by electrolysis is known as electroplating. 
Hence, the options A, B and C are correct.

Refining an impure metal to give a pure metal is known as electrorefining.

Metal plating protects the iron against corrosion by forming a sacrificial layer. This metal layer itself gets oxidize instead of iron and thus protects the iron itself. 

Extracting metals in the pure form from its compound is known as extraction of metals.

The deposition of superior metal on the surface of inferior metal is known as electroplating.

The electrodes are inert so that they do not involve the electrode reactions but transfer electrons through them. Since the silvery metal i.e. $Al$ is produced at cathode.

Electrolysis of water gives:

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 $\displaystyle = \dfrac {252 \ C}{96500 \ C/F}=2.6 \times 10^{-3} \ F$

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

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

According to Faraday's laws of electrolysis, the mass deposited is proportional to the equivalent weight. Equivalent weight of Ni is 59/2 = 29.5, and for Cr is 52/3 = 17.33. Mass of Cr = (Mass of Ni * Eq. Wt. Cr) / Eq. Wt. Ni = (0.3 * 17.33) / 29.5 = 0.176g.

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

The combustion of diborane (B2H6 + 3O2 -> B2O3 + 3H2O) requires 3 moles of O2 per mole of B2H6. 27.66g of B2H6 is 1 mole (MW=27.66). Thus, 3 moles of O2 are needed. Electrolysis of water (2H2O -> 2H2 + O2) requires 4 moles of electrons per mole of O2. Total charge Q = 3 * 4 * 96500 C. Time = Q / I = 1158000 / 100 = 11580 seconds, which is approximately 3.2 hours.

The reaction taking place at anode is given by:

At a nickel anode in an electrolytic cell, the metal itself undergoes oxidation (Ni -> Ni2+ + 2e-) because nickel is an active electrode.

Delta G = -nFE. For the reaction 4Al + 3O2 -> 2Al2O3, n = 12 electrons. Delta G = -965 kJ/mol O2. Since 3 moles of O2 are used, total Delta G = 3 * -965 = -2895 kJ. E = -Delta G / nF = 2895000 / (12 * 96500) = 2.5 V.

For high-quality electroplating, a low current density is required to ensure a smooth, uniform, and firm deposit. A high current would result in a rough, powdery, or non-adherent deposit.

Sodium argentocyanide (Na[Ag(CN)2]) is used as the electrolyte for silver plating because it provides a very low concentration of Ag+ ions, which ensures a smooth and uniform deposit.

During silver plating of an article using potassium argentocyanide as an electrolyte,
Cathode - Article to be electroplated.
Anode - Block of silver metal

No matter what, reduction always occurs at cathode. 

The process of depositing a thin layer of silver electrolytically on the metal surface is called silver plating. The article to be silver-plated is used as cathode while anode consists of pure silver. 

Reactions:
At cathode:
$Ag^+ +e^-\rightarrow Ag$
At anode:
$2 H _2O \rightarrow O _2 + 4H^+ + 4 e^-$

Galvanization is the process of applying a protective zinc coating to steel or iron, to prevent rusting. Galvanization of Iron meaning coating with zinc.

Both transmission of nerve impulse and  rusting of iron are results of electrochemical reactions.In transmission of nerve impulse numerous small molecules function as neurotransmitters at various chemical synapses.Rust is an iron oxide, usually red oxide formed by the redox reaction of iron and oxygen in the presence of water or air moisture. Lightning is a sudden electrostatic discharge during an electrical storm between electrically charged regions of a cloud. 

Galvanization is the process of applying a protective zinc coating to steel or iron in order to prevent it from rusting.

This method is based upon the phenomenon of electrolysis. The crude metal is made anode whereas the thin sheet of a pure metal is made cathode. The electrolyte is the solution of the soluble salt of the same metal, preferably a double salt on passing electricity the metal from anode goes into solutions as ions due to oxidation while the pure metal gets deposited at the cathode due to the reduction of metal ions the impurities settle down below the anode as Anode Mud.

Rusting of iron is a chemical change because it involves the formation of a new substance, hydrated iron(III) oxide, through a chemical reaction with oxygen and water.

Silver plating is an electroplating process utilizing an electrolyte containing silver cyanide solution and some free cyanide ions and operating at pH value not less than $8$. Free cyanide prevents precipitation of silver cyanide salt from the solution, provides electrical conductivity of the electrolyte and helps in the dissolution of silver anodes.

Electroplating is a process of deposition of superior metal on the surface of inferior metal.

Anode is the impure block and cathode is the pure block in electro-refining of metal.

Electroplating is $depositing$ of metals and electro-refining is $refining$ of metals.

The main application of electrolysis are:

The main application of electrolysis are:

Electrolysis is the process of using an external electric current to drive a non-spontaneous chemical reaction.

In the electrolysis process,

$2{ H } _{ 2 }O(l)\rightarrow2{ H } _{ 2 }(g)+{ O } _{ 2 }(g)$

$\dfrac {W _{1}}{W _{2}} = \dfrac {E _{1}}{E _{2}}$
$\dfrac {1.008}{W _{2}} = \dfrac {1.008}{8}$
$\therefore W _{2} = 8\ g$
where, $E _{1}$ and $E _{2}$ are equivalent masses of hydrogen and oxygen respectively.

Given:

Molar Mass of Ag = 108 g/mol

$1F = 96500\ C mol^{−1}$

Reaction at cathode = $Ag + e^-  \rightarrow   Ag(s)$ 

$w = Zlt$

Where, w = Mass deposited at cathode

Z = electrochemical constant

I = current

t = time

Now I = 2amp

$t = 15\ min = 15\times 60 = 900\ seconds$

Z = Eq. wt of substance $/ 96500 = 108/96500$ 

So,

$w = \dfrac{108}{96500} \times 900 \times 2 $

= $2.015g$

According to the data given when $1$ e is passed the amount of silver,

Electrolysis of brine (NaCl solution) produces NaOH, Cl2, and H2. Oxygen gas is not produced at the electrodes under standard conditions for this process.

Iron cannot be property plated with silver it becomes peel if plated with silver are to peeling of silver it cannot properly plated iron.

Silver plating on Steel spoon: A silver rod is made as anode and steel spoon as cathode. Potassiumargentocyanide $(K[Ag(CN) _2])$ is used as electrolyte.
$AgNO _3$ is not used as electrolyte because in that case the silver coating will be non-uniform as the electrolysis takes place rapidly.
In electroplating of copper by silver, silver rod is taken as anode.

Electrolysis of brine or NaCl produces hydrogen at cathode and chlorine at anode while the electrolyte NaOH sodium hydroxide remains in the solution.

Option D is correct 

The reaction taking place on the given reaction are,

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.

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).

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

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

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. 

Answer is A.
Electroplating is a very useful process. It is widely used in industry for coating metal objects with a thin layer of a different metal. The layer of metal deposited has some desired property, which the metal of the object lacks. For example, chromium plating is done on many objects such as car parts, bath taps, kitchen gas burners, bicycle handlebars, wheel rims and many others.
Chromium has a shiny appearance. It does not corrode. It resists scratches. However, chromium is expensive and it may not be economical to make the whole object out of chromium. So the object is made from a cheaper metal and only a coating of chromium over it is deposited.
Hence, electroplating of chromium is done on objects like water taps and cycle bell to give them a shiny appearance and prevent them from corrosion. The statement is true.

The object on which we have to deposit a material, should always be at cathode

The material which should be deposited on the object is always at anode.

The silver spoon is cleaned with a dilute acid solution to remove the oxide layer from its surface and washed in running water until it is free from the acid.