electrochemistry engineering chemistry KTU syllabus

Electrochemistry

1. CORROION: It is basically defined as a natural process that causes the transformation of pure metals into undesirable substances when they react with substances like water or air Types of corrosion: Dry or chemical corrosion: direct chemical attack on metals in dry conditions. Electrochemical or wet corrosion: under moist conditions due to formation of galvanic cells. Corrosion of Iron (Rusting) Rusting of iron, which is the most commonly seen example, happens when iron comes in contact with air or water. Here, metal iron loses electrons and gets converted to Fe 2+ . The electrons lost will move to the other side, where they combine with H +  ions .

2. Anode reaction 2Fe (s)  → 2Fe 2+  + 4e –  Cathode reaction 𝑂 2 +4𝐻 + +4𝑒−⟶2𝐻 2 𝑂 Overall reaction 2Fe (s)  + O 2(g)  + 4H +  → 2Fe 2+  + 2H 2 O The Fe 2+  ions formed at the anode react with oxygen in the atmosphere, thereby getting oxidised to Fe 3+  and forming Fe 2 O 3,  which comes out in the hydrated form as Fe 2 O 3 .xH 2 O Fe 2 +  + 3O 2  → 2Fe 2 O 3 Fe 2 O 3  + xH 2 O → Fe 2 O 3 . xH 2 O (rust)

3. Electrochemical series galvanic series Orderly arrangement of the metals and non-metals in their standard electrode potential. The arrangement of metals, alloys are according to their corrosion tendencies. E is measured for metals and non-metals E is measured for metals and alloys E is measured by dipping pure metals in their salt solution E is measured by dipping metal and alloys in unpolluted sea water. SHE is used as reference electrode. Calomel electrode is used as reference electrode. Position of metal is fixed Position of metal and alloy may change Electrochemical series galvanic series

4. Iron pipes buried along with zinc in the ground. In a redox reaction involving iron and zinc, the zinc will serve as the anode, and iron the cathode. The zinc anode will oxidize and provide electrons for the reduction of Fe 2+  to elemental iron. This is called cathodic protection. The zinc anode is termed a sacrificial anode.

5. Corrosion control through impressed current method: The metal to be protected is converted to cathode by applying an impressed current. A DC current is applied to an anode (graphite) buried inside the soil to the corroding metal. The impressed current is slightly higher than the corrosion current. Thus the anodic corroding metal becomes cathodic and protected from corrosion.

6. Explain the Electroless plating of Nickel. Metal ions + Reducing Agent   Metal (Deposited) + Oxidised Product Definition:  it is a technique of depositing of a noble metal from its salt solution on a catalytically active surface of a base metal by using a suitable reducing agent. Electroless Nickel plating: Step 1: Pretreatment and activation of the surface:   The surface to be plated is first degreased by using organic solvents or alkali followed by acid treatment. Step 2: preparation of plating bath composition:

7. Potentiometric titration : In potentiometric titration, the electric potential is measured across the analyte solution using an indicator and a reference electrode. Electric potential depends on the concentration of the metal ions involved. For a reduction reaction, M n + + ne -  M E = E – 2.303RT log 1 nF [ M n + ]   As the concentration of M n + changes the E cell changes correspondingly.  

8. Titration of Fe 2+ with Ce 4+ Reactions involved are: Fe 2+  Fe 3+ + e (oxidation ) Ce 4+ + e  Ce 3+ (reduction) Over all reaction Fe 2+ + Ce 4+  Fe 3+ + Ce 3+ Ferrous solution is taken in a beaker. A reference electrode and indicator electrode is introduced to it. Cerium solution is added from a burette. During the addition of Ce 4+ , Fe 2+ oxidizes to Fe 3+ The Fe 2+ /Fe 3+ electrode is set up and during the addition due to change in concentration of Fe 2+ and Fe 3+ changes, the potential slightly changes. After the end point, there is no Fe 2+ left in the beaker. Then the addition of Ce 4+ results in the formation of Ce 4+ / Ce 3+ electrode and potential increases sharply at the end point.