# Important Questions and Answers: Electrochemistry

1. What is electrochemical equivalent?

Ans: From Faraday’s first law:

W ∝ Q

or, W ∝ It [∵ Q = It]

∴W = ZIt

Here, Z is the constant called electrochemical equivalent (E.C.E.). If I = 1 ampere, t = 1 second, then:

W = Z

So, electrochemical equivalent is defined as the weight of the substance deposited or liberated by passing a current of one ampere in one second.

2. How does specific conductance decreases and equivalent conductance increase with dilution.

Ans: The conductance of a conductor having unit length and unit area is called as specific conductance. As the solution is diluted, the number of ions present in the solution per unit length and area decreases. Hence, the specific conductance decreases with dilution.

Equivalent conductance is the conductance of all ions produced by 1 gram equivalent of electrolyte in any of its solution. As the solution is diluted, the degree of ionization of weak electrolyte increases thereby increasing the number of ions.  In case of strong electrolyte, inter ionic interaction decreases and mobility of the ions increases. So, equivalent conductance of any electrolyte increases with dilution.

3. Differentiate between electrolytic conduction and metallic conduction.

 Metallic conduction Electrolytic conduction In this type of conduction, electricity is passed due to the movement of electrons. In this type of conduction, electricity is passed due to the movement of ions. There is no decomposition of substance. The compound decomposes into its constituent ions. Electrical conductance decrease with increase in temperature. Electrolytic conductance  increases with increase in temperature.

4. What is standard electrode potential ?

Ans: The potential difference developed at the metal solution interface when a metal strip is dipped inside its molar electrolytic solution at 25oC and 1 atmospheric pressure is  called standard electrode potential. It is represented by Eo.

5. Define the term:

a. Cell constant

b. Molar conductance

Ans:

a. Cell constant: The ratio of distance between two electrodes and area of the cross section of the electrodes is called cell constant.

i.e., Cell constant = l/A

b. Molar conductance: The conductance of the solution containing one mole of electrolyte in the given volume of solution is called molar conductance. It is denoted by μ.

6. Can a nickel spatula be used to stir copper sulphate solution?

Ans: The standard reduction potential of nickel is less than that of copper. So, nickel is more reactive than copper. Thus, when nickel is used to stir copper, nickel will dissolve to precipitate copper. So, nickel spatula cannot be used stir copper sulphate solution.

7. What is Standard Hydrogen Electrode (SHE) ? Mention one application of SHE.

The standard hydrogen electrode, is a redox electrode which forms the basis of the thermodynamic scale of oxidation-reduction potentials.

It is used as a reference electrode.

8. Standard Hydrogen Electrode acts as both anode and cathode. Give reason.

Ans: The oxidation and reduction in the Standard Hydrogen Electrode take place in platinum foil. So, it acts as cathode as well as anode.

9. What do you mean by single electrode potential? How does it arise? Name any two factors that affect the magnitude of single electrode potential.

Ans: When a metal rod is made in contact with its own ion solution, then a potential difference is created. This potential difference is called single electrode potential. It arises due to the formation of electric double layer. The two factors affecting single electrode potential are:

(i). Temperature

(ii). Concentration of metal ions in its solution

10. Differentiate between electrolytic cell and voltaic cell.

Ans:

 Electrolytic cell Voltaic cell It is a device in which electricity produces chemical reaction. It is a device in which electricity is produced by chemical reaction. Electricity energy is converted into chemical energy. Chemical energy is converted into electrical energy. Anode is positive electrode and cathode is negative electrode. Anode is negative electrode and cathode is positive electrode. Ions are discharged on both electrodes. Ions are discharged only on the cathode. Salt bridge is not used. Salt bridge is used.

11. What is electrochemical series? What are the applications of electrochemical series.

Ans: The sequential arrangement of various electrodes in the order of increasing standard reduction potential  is called electrochemical series. Application of electrochemical series are as follows:

• To calculate the standard cell potential of a cell.
• To determine the relative strength of oxidizing and reducing agent.
• To predict the feasibility of reaction.

12. What is oxidation and reduction potential?

Ans: The measure of tendency of an electrode to lose electron when it is dipped in a solution containing ions is called oxidation potential.

The measure of tendency of an electrode to lose electron when it its dipped in a solution containing ions is called reduction potential.

13. Write down the unit of conductance, specific conductance, molar conductance, equivalent conductance and cell constant?

Ans: The unit of:

Conductance: ohm-1 or mho or siemen

Specific conductance: ohm-1cm-1 or Scm-1

Molar conductance: ohm-1cm2mol-1

Equivalent conductance: ohm-1cm2equiv-1

Cell constant: cm-1

14. What is cell notation? Write down the rules for writing cell notation.

Ans: The symbolic representation of redox reaction taking place in a galvanic cell or electrochemical cell is called cell notation. Example: Zn-Cu galvanic cell notation is represented as:

Zn (s)/Zn++ (aq)   ||          Cu++ (aq)/Cu(s)

Anode                salt bridge     cathode

Rules for writing cell notation:

• Anode is written in left hand side and cathode is written in right hand side.
• Anode and cathode are separated by two vertical lines (||), known as salt bridge.
• Anode is written as: M(s)/Mn+(aq)
• Cathode is written as: Mn+(aq)/M(s)

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