electroplating ,Aluminum extraction and Copper purification

Applications of electrolysis :

Electrolysis is a process that involves the use of an electric current to cause a chemical reaction to occur. The process has a variety of practical applications in different fields. Some of the applications of electrolysis are:

• Production of metals: Electrolysis is used in the production of metals such as aluminum, copper, and zinc from their ores.

• Electroplating: Electroplating is the process of depositing a thin layer of metal on an object’s surface. Electrolysis is used in this process to transfer the metal ions to the object’s surface.

• Electrolytic refining: Electrolysis is used to purify metals such as copper, silver, and gold.

• Production of chemicals: Electrolysis is used to produce a variety of chemicals, such as chlorine, sodium hydroxide, and hydrogen.

• Electrolysis in medicine: Electrolysis is used in a medical procedure called electrolysis hair removal, which involves the use of an electric current to destroy hair follicles.

• Corrosion prevention: Electrolysis can be used to prevent corrosion in metal structures. This process involves applying an electric current to the metal, which creates a protective layer on the surface.

we will study 3 Applications to electrolysis as the following:

1)electroplating     2)Aluminum extraction           3)Copper purification

1)Electroplating process

A process of formation of a thin layer of certain metal on the surface of  another metal to give it a nice shiny view or protect it from corrosion 

Importance of electroplating

• Protect the substance from corrosion
• Rising the value of some cheap metals by plating them by chromium ,silver and gold
• Give them a nice shiny view

Examples:

-Electroplating car parts that made of steel by chromium layer to give it beautiful appearance and protect them from corrosion

-Electroplating water taps with chromium or gold

Steps of Electroplating  Fork with layer of silver:

 Clean the Jug

• Connect a pure plate of silver to the positive pole of battery  to act as an anode
• Connect the Jug to the negative pole of battery to act as a cathode
• The anode and cathode are dipped in silver nitrate solution(electrolyte)
• At the anode :Oxidation of Silver atoms of the anode :

Ag⁰_(s)  ⇒  Ag⁺ +   e^– 

• At the cathode :Reduction of The sliver ions (Ag+) solution to silver that deposit on the surface of the Jug

Ag⁺ _(aq)     +   e^– ⇒ Ag⁰_(s)

Example

Electric current with strength 18 A is passed for 1 hour in a nickel (II) sulphate solution (NiSO₄) to electroplate the two faces of a thin square sheet of a cheap metal with side length =4 cm calculate the thickness of the plating layer

(Ni density=8.9g/cm3  – Ni=58.7)

Answer:

Mass equivalent of Ni = atomic mass/charge(valence)=58.7/2=29.35

The deposited substance= quantity of electricity x mass equivalent/96500

=18 x 1x60x60x29.35  /96500=19.88 g

Surface area of nickel =one face surface area x 2= (side length)² x 2

= 4 x 4 x 2 = 32 cm2

Density =mass/volume

8.9=19.88/v

V=mass/density =19.88/8.9=2.233cm³

The thickness of Ni layer = volume/ surface area= 2.23/32=0.07  cm

2)Extraction of aluminum from bauxite ore

The device of ُExtration of aluminum:

• the graphite (carbon) cylinder are connected to the positive pole of the electric source to act as an anode
• the graphite lining (plating) the cell s container which is made of iron is connected to the negative pole of the electric source at as cathod

-By dissolving of bauxite(Al₂O₃) in a molten of Cryolite (Na₃AlF₆) which contains a little of fluorspar (CaF₂)  GR?

-To decrease the melting point of the mixture from 2045 c to 950 C

-recently Cryolite is exchanged by a mixture of fluoride salts of aluminum .sodium and calcium GR?

– to get mixture with low melting point and low density to easy separate  the aluminum

-The bauxite melt decomposes according :

  Al₂O_{3 (L)} ⇒ 2Al³⁺ _(L)   +3O^2- _(L)

1)oxidation of oxygen ions at the anode 

    3O^2- ⇒  3/2 O_2(g)  + 6 e^–

2)Reduction of aluminum ions at the cathode    2Al³⁺   + 6 e^– ⇒ 2Al⁰

     The total equation:

     2Al³⁺  + 3O^2- ⇒ 2Al^o + 3/2O_{2 (g)}

Give reason: graphite cylinders need to be changed in electrolytic cell of of bauxite from time to time?

Due to their corrosion sue to their reaction with O2 gas which evolves from oxidation  process forming CO2 and CO

2C_(s) + 3/2 O_2(g) ⇒CO _(g)  + CO_2(g)

3)Purification of Copper

-Copper of 99% degree of purity contains Zinc ,gold iron and silver

These impurities decreases it quality to conduct electricity

– Electrolysis is used in purification of copper that is used in making of electric wires

Steps of purification of Copper

1) a pure copper is connected to the negative pole of electric source to act as cathode

2) impure copper wire is connected to the  the positive pole of the electric source to act as anode

3) both of the are dipped in electrolyte solution of Copper (II) sulphate

  CuSO_{4 (aq)}    ⇒ Cu²⁺_(aq)  + SO4^2-_(aq)

4) on passing electric current :

-Oxidation occurs to copper atoms at the anode

  Cu⁰ _(s) ⇒ Cu²⁺_(aq)

-a reduction process occurs to copper ions at the cathode to form pure copper atoms that are deposited on the cathode

The impurities

Some of (Zn and Iron ) are oxidized and dissolves  in the solution

  Zn⁰    ⇒ Zn²⁺ _(aq) + 2e^–

   Fe⁰_(s)      ⇒  Fe²⁺ _(aq)  +  2e^–

-The Sliver and gold are not oxidizes  and the are deposited in the solution below the anode

By the time: the anode mass decreases – the cathode mass increases and the concentration of copper(II) ions (Cu²⁺) in the electrolyte decreases

Give reasons

1)Zinc and iron atoms are not deposited on the cathode of the copper purification cell?

-due to difficulty of reduction of zinc ions and iron(II) ions due to their lower reduction potential

2)importance of purification of copper after extraction from its ore?

-to get copper of 99.95 % pure to make electric wires and to separate some  rich elements such as silver and gold

-Question: explain the steps of separation of copper from a copper-iron alloy ?