ELECTRO PLATING

                          ELECTRO PLATING

It is the process of coating a metal on the surface of a conductor by electrolysis. A solution containing the metallic salt is used for this. This is the electrolyte.

Which metal is to be used for electroplating, that metal should be used as the positive electrode, and the solution of the same metal is to be used  as the electrolyte. The object which is to be electroplated is to be used as the negative electrode.

What is the mechanism of electroplating?

When electricity flows through electrolyte changes into ions.it  should contain the ions of the metals to be coated. Metal ions are positive. Therefore the metal ions have a tendency to move towards negative electrode(Cathode) so there we place the object to be coated

Is the DC current is necessary  for electroplating?

Yes,DC is direct current from battery. it has no variation. It always keep anode as positive and cathode as negative. AC is alternating current. So its positive and negative half cycles continuously changes. So the polarity of electrodes continuously changes.

Suppose you you have not a DC supply, But a AC supply is provided how can you produce DC?

Using a Bridge rectifier or center tape rectifier convert AC to DC it is called rectification. Remove resistor from the output and connct the electrodes in that place

Positive electrode       negative  electrode        electrolyte

Anode                            Cathode                        

Metal to coated             Object

Copper                           iron spoon                       Copper Sulphate

Silver                                 "   "                                    Silver nitrate/

                                                                            Silver cyanide+sodium cyanide

Gold                                   "      "                           gold cyanide+sodium cyanide

chromium                          "        "                           chromic acid

Faraday's laws of Electrolysis

First law

The mass of the substance(m) deposited on  an electrolyte is directly proportional to the amount of electric charge(Q) pass through the electrolyte

m=zQ (z is called electrochemical equivalent)

Q=It

Second law

When the same current is passed through different electrolytes, the masses deposited at the electrodes are proportional to their chemical equivalents

If mass m1 and m2  of two different substances of chemical equivalents E1 and E2  are deposited by the passage of same charge Q Then m1/m2=E1/E2

Faraday's constant

It is the ratio of chemical equivalent to electro chemical equivalent 

F=E/z   F=96500 coulomb

It is also defined as the quantity of electricity required to liberate one equivalent mass of the substance during electrolysis