Docstoc

Electroplating

Document Sample
Electroplating Powered By Docstoc
					      Electrolytic Cells



THE THEORY OF ELECTROPLATING
The Process of Electroplating
You must begin with a beaker that holds an
an electrolyte (aqueous solution of an ionic
compound) - like AgNO3
This means you have lots of free moving
ions [silver ion: Ag+1 and (NO3)-1] The
really important ion is that metal ion (Ag+1)!
This electrolyte solution of precious metal
ions is called the plating solution.
   Take Home Message:

This ionic solution is called the
“plating solution”. Therefore a
 plating solution must have the
      ions of a metal in it.
                                       beaker with silver ion
        Ag+1                    Ag+1
                      Ag+1
        Ag+1     Ag+1
                                       The solution of silver
       Ag+1                   Ag+1     ion is called the
                                       plating solution.
                       Ag+1
Ag+1
               Ag+1
Ag+1                          Ag+1
You still need two electrodes :

1 will be solid silver (or the pure metal of
whatever ion is in the plating solution… If
you are trying to plate gold, then use a bar
of gold..)
The other electrode may be another costly
metal – like copper, or the electrode could
be cheaper metals like lead or zinc.
Take Home Message:
The whole idea is to transfer these positive
ions of the silver solution to the zinc pin.

  …And make ‘em bond to the pin…
 by reducing the ions back to silver metal
           … Get the idea?
solid silver electrode




                                  Ag+1                   Ag+1

                         Ag+1            Ag+1             a zinc pin suspended in
                                  Ag+1                    solution

                         Ag+1
                                  Ag+1
                         Ag+1                           Ag+1
                                Ag+1       Ag+1
                                  Ag+1          Ag+1
                         Ag+1
                                                       Ag+1
Hook each electrode up to the opposite ends
of a battery. Connect the precious metal
(the silver electrode) to the positive
terminal             +    battery
                                   -

Hook the zinc pin to be electroplated to the
negative terminal
                                     +                             -
                                                 battery
solid silver electrode




                         Ag+1                     Ag+1
                                  Ag+1
                            Ag+1                            a zinc pin suspended in
                                         Ag+1
                                  Ag+1                      solution

                          Ag+1
                                  Ag+1                   Ag+1
                                          Ag+1
                           Ag+1            Ag+1          Ag+1
                                  Ag+1
                                                    Ag+1
                          Ag+1            Ag+1
Electrons begin to flow onto the zinc pin from
the battery – making the pin VERY negative
 The pin becomes highly negative. The Ag+1 ions
 are attracted to it.

 The silver ions are reduced back to silver atoms.
                Ag+1 + 1e-  Ag0
 When the ions get to the pin, they pick up loose
 electrons and the silver atoms coat the pin. New
 metallic bonds are made. The pin now looks as if
 the pin is solid silver!
                         e-   e-     e- e-
                                              +                       -
                    e-                            battery         e-
silver electrode   e-                                             e-
corroding          e-                                            e-
                   e-                                            e-
                   e-         Ag+1                          e-

                                       Ag+1
                              Ag+1
                                       Ag+1
                              Ag+1
                              Ag+1     Ag+1


                              Ag+1
                                         Ag+1
                                +                         -
                                    battery
solid silver electrode
                                                    e-
                                                    e-
                                               e-
                         Ag+1
                                     e-
                                                         a zinc pin suspended in
                         Ag+1       e-    e-
                                                         solution : Electrons
                                     e-   e-
                                                         build up on it, making
                                     e-   e-
                         Ag+1                            it negative.


                                               Silver ions are attracted to it
                         Ag+1
                                +                          -
                                    battery
solid silver electrode
                                                     e-
                                                     e-
                                                e-
                         Ag+1
                                      e-
                                    Ag                    a zinc pin suspended in
                         Ag+1       e-     e-
                                                          solution : Electrons
                                     e-    e-
                                                          build up on it, making
                                     e-
                                    Ag     e-
                         Ag+1                             it negative.
                                    Ag


                                                Silver ions are attracted to it
                          Ag+1
                            +                    -
                                battery
solid silver electrode




                                          a zinc pin suspended in
                         Ag+1             solution
   What’s happening with the silver
             electrode?
Electrons are being pulled off / drained away
from the silver and pumped into the battery.
The silver electrode is being oxidized!
            Ag0  1e- + Ag+1

Silver ion, (Ag+1) is soluble in water and moves
into the solution.
The silver electrode is corroded – but the plating
solution is replenished with the necessary ions!
                         e-   e-     e- e-
                                              +                                -
                    e-                                   battery           e-
silver electrode   e-                                                      e-
corroding          e-                                                     e-
                   e-                                                     e-
                   e-         Ag+1            Ag+1                   e-

                                       Ag+1                        a zinc pin electroplated in

                              Ag+1            Ag+1                         silver

                              Ag+1       Ag+1
                              Ag+1 Ag+1
                                                  Ag+1
                                                                               Replenished
                              Ag+1                                             silver ion… put
                                                                               in another pin!
                                         Ag+1               Ag+1
         Wrappin’ It Up…
Electroplating is an an electrolytic process
designed to use the electrons of an external
energy source to reduce metallic cations of
the solution and to cause them to plate out
onto an object.
         Plating Solution
An ionic compound containing the metal
ion you want to “plate out” onto a pin,
spoon, car bumper, bike frame….

Chromium, Gold, Silver are very common
(bike frames, everyday forks /spoons/knives
or electroplated jewelry… “gold-plated”)
                   The Anode
A hunk of metal – the same metal as the
metal ions of the plating solution.
The anode is oxidized (An Ox)
The anode is corroded and gets smaller
The anode is the positive electrode!
      (this is different from the voltaic cell)
             The Cathode
The object to be plated is the cathode.

It it the site of reduction – positive ions are
attracted to it. They are reduced by excess
electrons when they contact the cathode.
The cathode is negative! Electrons are
being forced onto it.
     Voltaic vs. Electrolytic
There are some differences between a
voltaic cell and an electrolytic cell. I can
think of two or three biggies … It’s up to
you now …

				
DOCUMENT INFO
Shared By:
Categories:
Tags:
Stats:
views:6
posted:6/14/2012
language:English
pages:23