Electrochemistry: Important Two Marks Questions and Answers

UNIT 3: Electrochemistry

Two Marks Questions and Answers

1. Define a conductor and conductance.

A substance (or) material that allows electric current to pass through it is called a conductor. The ability of a material to conduct electric current is called conductance.

2. What are electrolytic conductors? Give examples.

Electrolytic conductors conduct electric current due to the movement of ions in solution or in fused state. The conduction increases with increase of temperature.

Examples: Acids, bases, electrovalent substances.

3. What are strong electrolytes?

Strong electrolytes are substances, which ionise completely almost at all dilutions.

4. Define conductance. Give its unit.

The conductance of an electrolyte is the reciprocal of its resistance

 c = 1/R

Unit of conductance:

 c = 1/ ohm = ohm^‒1 (or) mho.

5. Define specific conductance.

The reciprocal of specific resistance is called specific conductance. (or) It is the conductance of 1 cm³ of a material.

 κ = c × l/a

6. Give the unit of specific conductance.

κ = cm / [ ohm × cm² ]

Unit:

 κ = 1 / [ ohm × cm ]

= ohm^‒1 cm^‒1

 = mho.cm^‒1

7. Define equivalent conductance. Give its unit.

It is defined as the conducting power of all the ions produced by dissolving 1 gram equivalent of an electrolyte in the solution.

˄eq = 1000κ / C

Unit:

˄ = [ cm³ / gm.equivalent ] × mho.cm^‒1

= mho. cm² . gm . equ^‒1

8. What is cell constant?

It is the ratio of distance between two electrodes (l) and area of the electrodes (a).

 x = l/a

9. How will temperature affect conductivity?

Increasing the temperature increases the conductivity of an electrolyte.

10. How size and charge of the ions affect conductance?

Smaller ions with higher charges tend to have higher mobility and thus contribute more to the conductivity.

11. Define oxidation. Give an example.

It is a process, which involves loss of electrons by a substance. Oxidation occurs at the anode.

Zinc atom (Zn) loses two electrons and gets oxidized to zinc ion (Zn²⁺).

Zn_(s) → Zn(aq)²⁺_(aq) + 2e ̄

12. Define reduction. Give an example.

It is a process, which involves gain of electrons by a substance. Reduction occurs at the cathode.

Copper ion (Cu²⁺) gains two electrons, liberated by Zn and gets reduced to copper (Cu).

Cu²⁺_(aq) + 2e^‒ →  Cu_(s)

13. What is a cell? Mention its types.

A cell is a device consisting two half cells. Each half cell contains an electrode dipped in an electrolytic solution. The two half cells are connected through one wire. The followings are two types of cells.

1. Electrolytic cells.

2. Electrochemical cells (or) voltaic cells (or) galvanic cells.

14. Define electrochemical cell.

Electrochemical cell is the one, in which chemical energy is converted into electrical energy.

15. What are galvanic cells?

Galvanic cells are electrochemical cells in which the electrons, transferred due to redox reaction, are converted to electrical energy.

16. What is salt bridge? Explain its functions.

(or)

Why salt bridge is used in the construction of a cell.

It consists of a U‒tube containing saturated solution of KCl or NH₄NO₃ in agar‒agar gel. It connects the two half cells of the galvanic cells.

Functions of salt bridge

(i) It eliminates liquid junction potential.

(ii) It provides the electrical continuity between the two half cells.

17. What are the conditions for an electrochemical cell to act as a standard cell.

The conditions for an electrochemical cell to act as a standard cell are

(i) The e.m.f of the cell is reproductive.

(ii) The temperature‒coefficient of e.m.f (change in e.m.f with temperature) should be very low.

18. What is electrode potential? How is it developed?

It is the measure of tendency of a metallic electrode to lose or gain electrons, when it is in contact with a solution of its own salt.

It is developed when a metal is placed in a solution of its own salt.

19. Define single electrode potential. Mention the factors affecting it.

It is the measure of tendency of a metallic electrode to lose or gain electrons, when it is in contact with a solution of its own salt.

Factors

The following factors affect the electrode potential.

(i) The nature of the metal.

(ii) The temperature.

(iii) The concentration of metal ions in solution.

20. Define Helmholtz electrical double layer.

It is a sort of layer, (+ve (or) ‒ve ions) formed all around the metal, which prevents further passing of the positive ions from or to the metal.

21. Write Nernst equation.

 E = E° + ( 2.303RT/nF . log [Mⁿ⁺] )

22. Explain oxidation and reduction potentials of an electrode.

The tendency of an electrode to lose electrons, when it contacts with the solution of its own salts, is called the oxidation potential, and the tendency of an electrode to gain electrons is called the reduction potential

23. Zinc reacts with dil. H₂SO₄ to give hydrogen but Ag does not explain.

Given that:

 E° (Ag⁺, Ag) = +0.80 V and

 E° (Zn²⁺, Zn) = − 0.76 V.

Since zinc possesses negative reduction potential and also it is placed above hydrogen in emf series Zn liberates hydrogen.

But silver possesses positive reduction potential and also it is placed below hydrogen in emf series, so Ag does not liberates hydrogen.

24. Mention the applications of Nernst equation.

1. Nernst equation is used to calculate electrode potential of unknown metal.

2. Corrosion tendency of metals can be predicted.

25. Suggest a method to determine the electrode potential of zinc.

Emf measurement: Zn electrode is coupled with saturated calomel electrode and the emf of the cell is measured. From the emf, using the following formula, electrode potential of Zn is calculated.

E_cell = E⁰_cal ‒ E⁰_Zn

E⁰_Zn = +0.2422‒1.0025

 = ‒0.7603 V.

26. Define the term Single Electrode Potential.

It is the measure of tendency of a metallic electrode to lose or gain electrons, when it is in contact with a solution of its own salt.

27. Define Standard Electrode Potential.

It is the measure of tendency of a metallic electrode to lose or gain electrons, when it is in contact with solution of its own salt or 1 molar concentration at 25°C.

28. What is electrochemical series? What is its significance.

When various metals are arranged in the order of their increasing values of standard reduction potential on the hydrogen scale, then the arrangement is called electrochemical series..

Significance:

1. Standard emf of the cell can be calculated.

2. Equilibrium constant can be calculated.

29. List any applications of EMF series.

1. Standard e.m.f of a cell can be calculated.

2. Hydrogen displacement behaviour can be predicted.

3. Standard free energy change & equilibrium constant can be calculated.