Explore topic-wise InterviewSolutions in .

Correct answer is (b) na=±βlog(I/i0)

The best explanation: The relationship between REACTION RATE and OVERVOLTAGE for activation POLARIZATION can be noted as na=±βlog(I/i0) where β is a Tafel constant and i0 is exchange current density.

Right answer is (a) False

Easy explanation: The change in Gibbs free ENERGY is a state FUNCTION and it is independent of the path FOLLOWED by the system to reach that state. It is denoted by ΔG (DELTA G).

The CORRECT answer is (d) Platinized platinum

For explanation: Platinized platinum metal is USED as the solid interface for hydrogen gas in the STANDARD hydrogen electrode. It is due to the inertness of the metal and ease with which electron transfer occurs on its SURFACE. Platinized platinum is black platinum-coated platinum.

The CORRECT CHOICE is (c) 2Ag^+1+2e==>2Ag and Cu==>Cu^+2+2e

For explanation I WOULD say: Standard HYDROGEN potential of silver (Ag) is +0.80V and copper is +0.34V.

Cathodic reaction: 2Ag^+1+2e==>2Ag

Anodic reaction: Cu==>Cu^+2+2e

The correct option is (a) The activation energy of a reaction

The best I can EXPLAIN: Activation polarization is the mechanism of polarization that depends on the activation energy of a reaction. Activation energy is the MINIMUM energy required for reacting SPECIES to undergo CHEMICAL reactions.

Right choice is (b) Pourbaix DIAGRAMS

The best explanation: Pourbaix diagrams show the STABILITY of metal over a range of pH and POTENTIAL of a SYSTEM. It also includes native zone, PASSIVE zone, and corrosive zone. It is also called as potential-pH diagrams.

Correct answer is (B) r0=rR=I0/nF

The best I can explain: Equilibrium is defined as the state at which rate of oxidation is equal to the rate of reduction. And the formula to calculate rate of oxidation or reduction is r0=rR=i0/nF where i0 is exchange current density, N is number of electrons INVOLVED and F is FARADAY’s constant.

Right ANSWER is (a) True

Best EXPLANATION: Exchange CURRENT density is the current per unit AREA of either oxidation or reduction PROCESS at the equilibrium. Type of metal and environment are the factors of exchange current density and it is denoted by i0.

Correct answer is (a) True

Easiest explanation: Corrosion is USUALLY an electrochemical process which is a combination of OXIDATION half-cell and REDUCTION half-cell. Oxidation and reduction reactions are simultaneous in nature and it is also called Redox reactions.

Correct choice is (c) To reduce CORROSION attack, to predict the direction of spontaneous reaction and to estimate the COMPOSITION of corrosion product

To explain I WOULD say: Applications of POURBAIX diagrams:

i. Predicting the spontaneous direction of reactions

ii. To reduce corrosion attack

iii. To estimate the composition of corrosion product.

Correct option is (a) True

For EXPLANATION I would say: If the TRANSITION of a system from one state to another state resulted in negative free energy CHANGE then it is known as a spontaneous reaction. It MEANS the free energy of products is less than the free energy of reactants.

Right option is (c) ΔG=-nFEcell

The explanation: ΔG=-nFEcell where N is the electrons PARTICIPATED in the reaction, F is the FARADAY CONSTANT (96500 COULOMBS), Ecell is the overall cell potential and E^0cell is the standard cell potential.

Right answer is (d) ANODIC PROTECTION, noble metal alloying and methods to measure corrosion rates rapidly

Easiest explanation: MODERN electrode kinetics deals with electrochemical corrosion of aqueous solution and it RESULTS in the APPLICATIONS of

Anodic protection

Noble metal alloying

Methods to measure corrosion rates rapidly.

Correct option is (b) Titanium

Best EXPLANATION: Stainless steels and titanium passivates spontaneously in acid solutions containing OXIDIZERS or dissolved OXYGEN. A decrease in passive potential and critical current DENSITY is the driving FORCE for the spontaneous passivation.

Correct choice is (c) Any ELECTROCHEMICAL reaction can be divided into two or more PARTIAL reactions and no net accumulation of ELECTRIC CHARGE during the reaction

The best I can explain: Hypothesis of mixed potential theory:

i. Any electrochemical reactions can be divided into two or more partial reactions

ii. No net accumulation of electric charge during the reaction.

Right answer is (b) Silver (Ag) and Iron (Fe)

Easy explanation: In the Ag-Fe system, Silver (Ag) (+0.80V) acts as a cathode as the standard HYDROGEN POTENTIAL is RELATIVELY higher than the Iron (Fe) (-0.44V) and Iron acts as ANODE due to relatively LESS standard hydrogen potential.

Correct answer is (a) True

For explanation: AGITATION tends to decrease the thickness of the diffusion LAYER by supply ENOUGH ions to the metal interface hence there will be an increase in limiting diffusion current DENSITY of concentration polarization.

Correct option is (c) It is a non-spontaneous reaction

To explain: If the transition of a system from ONE state to another state resulted in positive free ENERGY change then it is known as a non-spontaneous reaction. It means the free energy of reactants is less than the free energy of products. It requires external HEAT or FORCE to proceeds with the reaction.

Correct option is (b) Corrosion of metals

Explanation: Spontaneous reaction is a reaction in which the reactants convert into products without any supply of external energy. OXIDATION of metal ATOMS into metal IONS due to the INSTABILITY of METALLIC atoms is known as the corrosion of metals.

Right answer is (d) It FOLLOWS typical TAFEL behavior and corrosion rates INCREASES exponentially

To explain I would say: ACTIVE region is the first STAGE of active-passive transition in which the corrosion rates increase exponentially and it follows typical Tafel behavior.

Correct OPTION is (a) True

The explanation is: Trans passive region is the last region of active-passive transitions of metal in which the corrosion rate INCREASES with an increase in potential. It is formed due to the instability of the passive layer at that high POTENTIALS.

The correct CHOICE is (d) It is a CONTINUATION of activation polarization, diffusion of IONS in the bulk solution is the controlling FACTOR and it usually OPERATES at high current densities

The explanation: Concentration polarization is the mechanism of polarization in which diffusion of ions in the bulk solution is the controlling factor, it is a continuation of activation polarization and it usually operates at high current densities.

The CORRECT CHOICE is (b) Change in Gibbs FREE energy

Explanation: Change is Gibbs free energy is the difference of free energies of the REACTION products and REACTANTS. And it is a direct measure of the work capacity or maximum electrical energy available in from a system.

Correct choice is (a) True

To explain I would say: Passivation is the LOSS of chemical reactivity of a metal due to the formation of the oxide layer. It is RELATIVELY unstable and subject to damage. Chemical properties, wear RESISTANCE and thickness are the FACTORS for the STABILITY of the passive layer.

Correct answer is (C) ETA (η)

The EXPLANATION is: The MAGNITUDE of polarization is measured in TERMS of over voltage and it is denoted with symbol Eta (η). It is the difference of corrosion potential (Ecorr) and the standard potential of an electrode.

Right answer is (d) Wilsmore and Nernst

Easy EXPLANATION: Mixed potential THEORY is the ELECTROCHEMICAL hypothesis of modern CORROSION presented by Wagner and Traud in the year 1938. It relates the potentials and currents of the corrosion SYSTEM to determine corrosion potential (Ecorr) and corrosion current (icorr).

Right option is (d) Rate of REACTION is not predicted and it neglects the impurities of working conditions

Easy EXPLANATION: Limitations of Pourbaix DIAGRAMS:

i. Rate of reaction can’t be predicted

ii. It neglects the impurities of working conditions

iii. Alloying elements of ALLOYS are also NEGLECTED.

Correct answer is (c) iL=DnFCB/x

The explanation is: iL=DnFCB/x is the formula to determine the LIMITING diffusion current DENSITY (iL) of concentration polarization. Where IL is the limiting diffusion current density, D is the diffusion COEFFICIENT, CB concentration of ions in bulk SOLUTION and x is the thickness of diffusion layer.