Electrochemistry 1

Question 1

what is electrochemistry

Answer 1

Electrochemistry is the study of production of
electricity from energy released during spontaneous
chemical reactions and the use of electrical energy
to bring about non-spontaneous chemical
transformations.

Question 2

describe daniell cell in brief

Answer 2

Cathode and Anode
Anode( -ve) : The zinc electrode (Zn) serves as the anode, where oxidation occurs. Zinc loses electrons and is oxidized to zinc ions (

Cathode(+ve) : The copper electrode (Cu) serves as the cathode, where reduction takes place. Copper ions in the solution gain electrons and are reduced to copper metal:

2. Flow of Electrons and Current
   Flow of Electrons: Electrons flow from the anode (zinc) to the cathode (copper) through an external circuit.
   Flow of Current: By convention, the current flows from the positive electrode (cathode) to the negative electrode (anode) in the external circuit, opposite to the direction of electron flow.
3. Salt Bridge and Its Functions
   Salt Bridge: The salt bridge is a a glass u- tube or rubber tube filled with s paste of nh4cl, kcl of kno3 in agar-agar or gelatin. that connects the two half-cells.

Functions of the Salt Bridge:
Maintains Electrical Neutrality: It allows the flow of ions between the two half-cells, preventing charge buildup that would otherwise stop the reaction.
Completes the Circuit: It completes the internal circuit by allowing the exchange of ions, which balances the charges in each half-cell.

Zn(s) + Cu2+(aq) ® Zn2+ (aq) + Cu(s)
This reaction is a combination of two half reactions whose addition
gives the overall cell reaction:
(i) Cu2+ + 2e– —–> Cu(s)
(reduction half reaction)

(ii) Zn(s) ——> Zn2+ + 2e–
(oxidation half reaction)

Question 3

what kind of ions should the salt bridge should not contain

Answer 3

The salt bridge must not have a salt whose ions forms precipitate with the existing ions in the solution. Only inert electrolytes can be used. it cannot interact chemically with existing ions.
For eg: Pb2+ or Ag+

Question 4

what happens to the daniell cell when an external voltage less than 1.10V is applied

Answer 4

(i) Electrons flow from Zn rod to
Cu rod hence current flows
from Cu to Zn.
(ii) Zn dissolves at anode and
copper deposits at cathode.

Zn=anode=-ve
Cu=cathode= +ve

Question 5

what happens to the daniell cell when an external voltage of 1.10V is applied

Answer 5

(i) No flow of
electrons or
current.
(ii) No chemical
reaction.

Question 6

what happens to the daniell cell when an external voltage greater than 1.10V is applied

Answer 6

(i) Electrons flow
from Cu to Zn
and current flows
from Zn to Cu.
(ii) Zinc is deposited
at the zinc
electrode and
copper dissolves at
copper electrode.

iii) Zinc becomes cathode (+ve) and copper becomes anode (-ve)

iv) It behaves like an electrolytic cell

Question 7

differentiate between electorlytic and electrochemical cells?

Answer 7

Electrochemical cell:
- Converts gibbs free energy( chemical energy) to electrical energy
- based on a spontaneous redox reaction
-chemical changes are taking place in 2 different beakers
- anode is -ve, cathode is +ve
- oxidation takes place at anode
- reduction takes place at cathode

Electrolytic cell:
- converts electrical energy into chemical energy
- based on a non spontaneous redox reaction, that takes place only on the supply fo energy
- only one compound undergoes decomposition
- anode is +ve and cathode is -ve
- oxidation takes place at anode
-reduction takes place at cathode

Question 8

What is a galvanic cell

Answer 8

a galvanic cell is an electrochemical cell that
converts the chemical energy of a spontaneous redox reaction into
electrical energy. In this device the Gibbs energy of the spontaneous
redox reaction is converted into electrical work which may be used for
running a motor or other electrical gadgets

Question 9

what is a half cell or redox couple

Answer 9

The reduction half reaction occurs on the copper electrode while the
oxidation half reaction occurs on the zinc electrode.

A half-cell, also known as a redox couple, is a part of an electrochemical cell where either oxidation or reduction takes place. It consists of an electrode (a solid conductor, typically a metal) and an electrolyte (a solution containing ions).

Question 10

what is electrode potential

Answer 10

A potential difference
develops between the electrode and the electrolyte which is called
electrode potential.

It represents the tendency of a metal to get oxidised or reduced when placed in a solution of its own salt.

If the metal has a tendency to get oxidised, then it will lose elctrons and pass ions into the solution. the electrons deposit on metal and it becomes -vely charged
.

If the metal has a tendency to get reduced, it will gain electrosn and deposit on the electrode as solid metal. electrons gained by ions are lost by the metal so it becomes +vely charged.

Question 11

what is standard electrode potential

Answer 11

tendency of a metal electrode to gain or lose electrons when placed in a solution of its own salt of 1M conc at 298K.

electrode potential when the electrolyte conc is unity and temp is 298k, 1 atm pressure

According to IUPAC convention, standard
reduction potentials are now called standard electrode potentials.

Question 12

electode potentials in a galvanic cell

Answer 12

In a
galvanic cell, the half-cell in which oxidation takes place is called anode
and it has a negative potential with respect to the solution. It is -vely charged.

The other
half-cell in which reduction takes place is called cathode and it has a
positive potential with respect to the solution. it is +vely charged,

Question 13

define cell potential

Answer 13

The potential difference between the two electrodes of a galvanic
cell is called the cell potential and is measured in volts. The cell
potential is the difference between the electrode potentials (reduction
potentials) of the cathode and anode.

Question 14

what is emf

Answer 14

The potential diff between the two electrodes is called as electromotive force (emf) when no current is drawn through the cell.

Question 15

describe how the standard hydrogen electrode is constructed

Answer 15

It consists of a platinum electrode coated with platinum black, which is enclosed in an inverted glass tube. Pure Hydrogen gas at 1 bar pressure is bubbled through the tube. The tube is immersed in an acidic medium with 1M H+.
The concentration of both the
reduced and oxidised forms of hydrogen is
maintained at unity

Question 16

what is the special feature of SHE? what is it used for?

Answer 16

The electrode potential of the SHE at all temperatures is arbitrarily assumed to be 0.

The potential of individual half-cell cannot be measured. We can
measure only the difference between the two half-cell potentials that
gives the emf of the cell.

At 298 K the emf of the cell, standard hydrogen electrode ||second
half-cell constructed by taking standard hydrogen electrode as anode
(reference half-cell) and the other half-cell as cathode, gives the reduction
potential of the other half-cell.

If the concentrations of the oxidised and
the reduced forms of the species in the right hand half-cell are unity,
then the cell potential is equal to standard electrode potential, EoR of the given half-cell.

Question 17

what does +ve value of reduction potential indicate and what abt +ve value when coupled with she

Answer 17

The positive value of the standard electrode potential in the first
case indicates that Cu2+ ions get reduced more easily than H+
ions. The
reverse process cannot occur, that is, hydrogen ions cannot oxidise Cu
(or alternatively we can say that hydrogen gas can reduce copper ion)
under the standard conditions described above. Thus, Cu does not
dissolve in HCl. In nitric acid it is oxidised by nitrate ion and not by
hydrogen ion. The negative value of the standard electrode potential
in the second case indicates that hydrogen ions can oxidise zinc (or
zinc can reduce hydrogen ions).

Question 18

what do you mean by inert electrodes?

Answer 18

Sometimes metals like platinum or gold are used as inert electrodes.
They do not participate in the reaction but provide their surface for
oxidation or reduction reactions and for the conduction of electrons.

They serve as a source or sink for electrons.

Eg: Pt is used in following cells:

i) SHE
Pt(s)| H2(g)| H+ ( aq)

half cell reacn: H+ (aq)+ e– ® ½ H2(g)

ii) bromine elctrode
Pt(s)| Br2(g)| Br- ( aq)
With half-cell reaction: ½ Br2(aq) + e– ® Br–(aq