Corrosion Engineering Multiple Choice Questions on “Modern Theory Principles – Polarization – 1”.
1. What is meant by an anode?
a) An electrode at which reduction process takes place
b) An electrode at which oxidation process takes place
c) An electrode at which neither the oxidation nor reduction takes place
d) An electrode at which both oxidation and reduction takes place
Answer: b
Clarification: An electrode at which the oxidation process takes place is known as anode whereas the electrode at which reduction process takes place is known as the cathode.
2. Which of the following is correct regarding Polarization?
a) It is the deviation from equilibrium potential
b) It results from the change in net current flow
c) Magnitude is measured in terms of overvoltage
d) It is the deviation from equilibrium potential that occurred due to the change in net current flow and its magnitude is measured in terms of overvoltage.
Answer: d
Clarification: Polarization is the deviation from equilibrium potential that occurred due to the change in net current flow and its magnitude is measured in terms of overvoltage.
3. What is the symbol of overvoltage?
a) Alpha (α)
b) Beta (β)
c) Eta (η)
d) Delta (Δ)
Answer: c
Clarification: 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.
4. Exchange current density is the current per unit area of either oxidation or reduction process at the equilibrium.
a) True
b) False
Answer: a
Clarification: 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.
5. What is the formula to calculate rate of oxidation or rate of reduction during equilibrium?
a) r0=rR=i0nF
b) r0=rR=i0/nF
c) r0=rR=i0n/F
d) r0=rR=nF/i0
Answer: b
Clarification: 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.
6. Which of the following metal shows the highest exchange current density for hydrogen-hydrogen ion as per given figure?
a) Mercury
b) Iron
c) Platinized platinum
d) Platinum
Answer: c
Clarification: Platinized platinum shows the highest exchange current density for hydrogen-hydrogen ion due to its high inertness and electrically conductivity. The order follows as (i0)PtH+/H2>(i0)FeH+/H2>(i0)HgH+/H2.
7. Which of the following is the controlling factor of Activation polarization?
a) The activation energy of a reaction
b) Diffusion of ions in the solution
c) The temperature of a solution
d) The velocity of a solution
Answer: a
Clarification: 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.
8. Which of the following mentioned is/are the types of polarization?
a) Activation polarization
b) Concentration polarization
c) Resistance polarization
d) Activation, concentration and resistance polarization
Answer: d
Clarification: Types of polarization:
9. What is the relationship between reaction rate and overvoltage for activation polarization?
a) na=±βlog(i0/i)
b) na=±βlog(I/i0)
c) na=±βlog(1-i0/i)
d) na=±βlog(1-i/i0)
Answer: b
Clarification: 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.
10. What is depicted in the given figure?
a) Concentration polarization of hydrogen-hydrogen ion
b) Resistance polarization of hydrogen-hydrogen ion
c) Activation polarization of hydrogen-hydrogen ion
d) Both activation and concentration polarization of hydrogen-hydrogen ion
Answer: c
Clarification: The given figure depicts the activation polarization of the hydrogen-hydrogen ion electrode. Curve1 indicates the cathodic polarization whereas curve2 indicates the anodic polarization.