chemistry

Question 1

how many types of electrodes are there? name them.

Answer 1

There are 5 types of electrode. They are
1.metal-metal ion electrode
2.metal-metal insoluble salt electrode
3.gas electrode
4.ion selective electrode
5.redox electrode
6.amalgam electrode

Question 2

Define single electrode potential.

Answer 2

The potential developed between a metal rod and its own ions in a
solution at equilibrium is called electrode potential. It is denoted by E and expressed in volts.

Question 3

Define standard electrode.

Answer 3

: The potential developed when a metal is in equilibrium with
1M solution of its own ions at 298K is called standard electrode potential. It is represented by E’ It is also called as standard reduction potential (SRP).

Question 4

explain what is metal-metal ion electrode and give examples

Answer 4

The electrode system consisting of metal in contact with a solution
containing its own metal ion.
Example: Cu|Cu2+ . Zn|Zn2+

Question 5

explain what is metal-metal insoluble salt electrode and give examples

Answer 5

The electrode system consisting of metal in with a
sparingly soluble salt of the same metal dipped in a solution containing anion if the salt. contact
Example: Calomel electrode (Hg|Hg2Cl2|Cl-) , Ag-AgCl electrode (Ag|AgCl|Cl-)

Question 6

explain what is gas electrode. give example

Answer 6

The electrode system consists of gas in contact with an inert metal wire which
is dipped in an ionic solution of the gas molecule.
Example: Standard hydrogen electrode (SHE)

Question 7

explain what is ion selective electrode and give examples

Answer 7

These are the electrodes which are sensitive to particular ionic species
and will develop a potential when a membrane is in contact with an ionic solution.
Example: Glass electrode

Question 8

explain what is redox electrode and give examples

Answer 8

Electrode in which potential arises due to the presence of oxidized and
reduced forms of the same substance in solution.
Example: Platinum electrode, Pt | Fe2+, Fe3+

Question 9

explain what is amalgam electrode and give examples

Answer 9

It is a modification of metal-metal ion electrode. Amalgam is the alloy
of any metal with mercury. In the place of metal, its solution in mercury is used.
Example: Zinc -amalgam electrode, where Zn(Hg) | Zn2+

Question 10

What is a reference electrode. What are the types of reference electrode.

Answer 10

Reference electrodes: These are the electrodes of constant potential which are used to determine
electrode potential of other electrodes. There are two types of reference electrodes.
❖ Primary reference electrode. Eg: Standard hydrogen electrode (SHE).
❖ Secondary reference electrode. Eg: Calomel electrode, Ag/AgCl electrode

Question 11

the construction of calomel electrode

Answer 11

• Calomel electrode is a metal- metal insoluble salt electrode and is a secondary reference
  electrode.
• It consists of a glass tube, a small amount of pure mercury is placed at the bottom of the glass
  tube and it is covered by a paste of Hg and calomel (mercurous chloride, Hg2Cl2).
• The remaining portion of the glass tube is filled with KCl solution of known concentration
  (saturated, 1N or 0.1N)
• A platinum wire is dipped into the mercury and is used to provide external electrical contact.
  The porous plug at the bottom acts as a salt bridge.
  Representation: Pt|Hg|Hg2Cl2|KCl(x) Where x = sat or 1N or 0.1N.

Question 12

explain the working of calomel electrode

Answer 12

Calomel Electrode can act as anode or cathode depending on the nature of the other
electrode.
When acts as anode: 2Hg + 2Cl- Hg2Cl2 + 2e-When acts as cathode: Hg2Cl2 + 2e-
2Hg + 2Cl-At equilibrium: Hg2Cl2 + 2e-
2Hg + 2Cl-
The electrode potential at 298K is given by
Ecal= E0
cal – 0.0591 log [Cl-]
From the above equation it is clear that as the concentration of Cl-ion increases, the electrode
potential decreases

Question 13

explain the advantages of calomel electrode

Answer 13

Advantages:
❖ It is easy to construct and maintain.
❖ Its potential can remain constant and it can easily be reproduced.
❖ It can be used in the presence of oxidizing agents.

Question 14

What are electrolyte concentration cells?

Answer 14

: The galvanic cell in which electrode and electrolyte present in
both half cells are same but only the concentration of electrolyte is different is called electrolyte
concentration cell

Question 15

explain the applications of calomel electrode

Answer 15

Applications:
❖ It is used as reference electrode in all potentiometric titrations.
❖ It is used as reference electrode with glass electrode in pH determination.
❖ It is used as a secondary reference electrode in the measurement of single electrode potential.

Question 16

Derive an expression for emf of an electrolyte
concentration cell.

Answer 16

DO IT IN THE BOOK

Question 17

Define Reference electrode

Answer 17

These are the electrodes of constant potential which are used to determine
electrode potential of other electrodes.

Question 18

Define Concentration cell

Answer 18

concentration cells are basically the galvanic cell which converts chemical energy to electrical energy which consists of 2 same electrodes and 2 same electrolytes but the concentration of the electrolytes differ from each other
example-zn cell

Question 19

define Standard
electrode potential

Answer 19

it is defined as the potential developed at the interface of a metal and its ion when it is in contact with 1M concentration of its own solution at stp

Question 20

Define EMF of the cell

Answer 20

the potential between 2 electrodes when there is a flow of current from higher potential to lower potential

Question 21

Define ion selective electrode.

Answer 21

These are the electrodes which are sensitive to particular ionic species
and will develop a potential when a membrane is in contact with an ionic solution. The potential
developed at these electrodes is a function of the concentration of that ion in the solution.

Question 22

Explain the construction of glass membrane electrode

Answer 22

Glass electrode is an ion selective electrode in which a thin glass membrane is present which is
permeable to H+
ion and not to other ions in the solution
A glass electrode consists of a thick–walled glass tube with a very thin walled glass membrane
(bulb) at the bottom. Its thickness varies from 0.01-0.03 mm.
* This glass membrane made up of special glass of low melting point and high electrical
conductivity. The approximate composition of this glass is 72%SiO2, 22%Na2O and 6%CaO.
* This glass membrane allows only H+
ions up to a pH range from 1 to 9.
* The glass bulb is filled with 0.1M HCl as internal reference solution in which a silver–silver
chloride electrode is dipped as an internal reference electrode which provides external electrical
contact
representation: ag|agcl|HCl(0.1M)|glass membrane

Question 23

explain the working of glass membrane electrode

Answer 23

When the glass electrode is dipped in the test solution, the Na+
ions of the glass membranes are
exchanged for H+
ions of the test solution.
Na+Gl- + H+ ↔ H+Gl- + Na+
When a glass electrode is placed between two H+ ion solutions of different concentrations (C1 and
C2), boundary potential is developed across the membrane. The boundary potential is given by the
equation
{DERIVATION}
Eb =0.0591/nlog[C2/C1]
Eb=0.0591/nlog[C2]-0.0591nlog[C1]–{n=1 for H+ ions}
Eb=0.0591log[C2]-0.0591log[C1]
lets take,
L=-0.0591log[C1]
L is constant because C1=0.1M HCl
therefore,
Eb=L+0.0591log[C2]
since C2 is the unknown concentration of H+
we can write,
Eb=L+0.0591log[H+]
we know,
PH=-log[H+]
Eb=L-0.0591pH
It is found that the potential of the glass electrode (EG) has three components:
* Boundary potential (Eb)
* Asymmetric potential (Eassy)
* Potential of the internal reference Ag – AgCl electrodes (EAg/AgCl)
∴ EG = Eb + Eassy + EAg/AgCl
Substitute equation (1) in (2), we get
EG= (L- 0.0591 pH) + Eassy + EAg/AgCl
EG= E0G - 0.0591 pH
Where E0G = L+ Eassy + EAg/AgCl .
E0G is the combination of three constant terms.

Question 24

Explain how glass electrode can be used in determination of pH of unknown solution?

Answer 24

The cell consists of a glass electrode as indicator electrode and a saturated calomel electrode (SCE)
as reference electrode, the cell is immersed in a solution whose pH is to be determined. The emf
cell is measured using vacuum tube voltmeter (VTVM).
The cell assembly is represented as
Pt|Hg|Hg2Cl2 |KCl(sat)||solution of unknown pH| glass membrane|HCl (0.1M) |AgCl|Ag
The emf of the cell is given by
Ecell = Ecathode – Eanode
Ecell = EG – ESCE
E cell = (E0G – 0.0591 pH) – ESCE—(Where EG =E0
G – 0.0591 pH)
𝒑𝑯 =𝑬𝑮𝟎 − 𝑬𝒄𝒆𝒍𝒍 − 𝑬𝑺𝑪𝑬/0.0591
E0G value of a glass electrode can be determined by using a solution of known pH.

Question 25

Define battery

Answer 25

A battery is a compact device consisting of two or more galvanic cells connected in series
or parallel or both. It stores chemical energy in the form of active materials and on demand converts
it into electrical energy through redox reactions. Thus, a battery acts as portable source of electrical
energy.

Question 26

how many types of batteries are there?

Answer 26

there are 3 types of batteries:-
1. Primary Battery
2. Secondary Battery
3. Reserve Battery

Question 27

What is Primary Battery?/

Answer 27

The batteries which cannot be recharged are called primary batteries or primary cells. In primary batteries, the cell reactions are not reversible. These batteries serve as a
source of energy only as long as the active chemical species are present in the battery. These are
designed for only single discharge and cannot be charged again.
Example: Dry cells, air batteries

Question 28

what are secondary batteries?

Answer 28

The batteries which can be recharged by passing the current in the opposite direction are called secondary batteries or rechargeable cells. A secondary cell can undergo large numbers of discharging and charging cycles. In a secondary battery the reactions are reversible. They are also called storage batteries. During discharging the cell acts as a galvanic cell and during charging the cells acts as an electrolytic cell
examples-lithium ion battery, nickel ion battry

Question 29

what are reserved batteries?

Answer 29

The batteries in which one of the components is stored separately and is
incorporated into the battery whenever electric energy is required is called reserve batteries.
Usually, the electrolyte is stored separately. Reserve batteries have long shelf life, deliver high
power and suitable for low temperature. These are used in missiles, torpedo (underwater weapon)
and other weapon systems.
Ex: Mg batteries activated by water (Mg-AgCl & Mg- CuCl), Li-V2O5 battery Batteries etc.

Question 30

Give the construction of Li-ion battery

Answer 30

These are rechargeable battery that stores energy by using a special process called intercalation.
These batteries are known for their high energy density (store a lot of energy in a small and
lightweight package), more efficient and have a longer lifespan compared to other types of
rechargeable batteries. In recent years, lithium-ion batteries have become increasingly popular due
to their widespread use in various applications
Anode-Lithium intercalated graphite (LiC6)
Cathode-Lithium cobalt oxide (Li1-xCoO2)
Electrolyte-Lithium salt like LiPF6 (lithium hexafluoro phosphate) dissolved in a mixture of ethylene carbonate and diethyl carbonate.
Separator-Fine porous polymer film
Type-Secondary battery
Representation-LiC6|LiPF6 dissolved in organic solvents|Li1-xCoO2
Cell potential-4.1V
{DIAGRAM}

Question 31

working of li ion battery

Answer 31

Cell reactions during discharge:
At anode: LixC6–>6C + xLi+ + xe-
At cathode: Li1-xCoO2 + xLi+ + xe—>LiCoO2
overall:LixC6+li1-xCoO2-><-6C+LiCoO2

Question 32

applications of Li ion battery

Answer 32

It is used in wireless headphones, mobile phones/smartphones, laptop computers,
electric vehicles, digital cameras, portable game machines, medical applications such as emergency
lighting, etc

Question 33

Give the construction of Na-ion battery

Answer 33

The main advantage of Na-ion batteries comes from the natural abundance and lower cost of sodium compared with lithium.
Construction:
Anode-Sodium ions absorbed on surface of hard carbon (NaxC6)
Cathode-Sodium transition metal oxides (Na1–xMO2), where M = Fe, Ni, Mn, Co, etc.
Electrolyte-Sodium salts such as NaPF6 and NaClO4 dissolved in mixture of organic
solvents-like ethylene carbonate (EC), propylene carbonate (PC)
Separator-Fine porous polymer film
Type-Secondary battery
Representation-NaxC6|NaPF6 dissolved in mixed organic solvents|Na1-xMO2
Cell potential-3.8V
{DIAGRAM}

Question 34

working of Na-ion battery

Answer 34

Cell reactions during discharge:
At anode: NaxC6–>6C + xNa+ + xe-
At cathode: Na1-xMO2 + xNa+ + xe- –>NaMO2
overall:Na1-xMO2+xNa+xe- -><- 6C+NaMO2

Question 35

applications of Na-ion battery

Answer 35

Applications
1. Na ion batteries are used in Electric Vehicles
2. They are used in portable electronics such as smartphones, tablets, and laptops
3. They can be used in Grid Energy Storage (where excess renewable energy generated from
sources such as solar and wind power can be stored)

Question 36

What is redox flow battery

Answer 36

A redox flow battery is a device that converts chemical energy into
electrical energy through reversible oxidation and reduction reaction of electrolytes. In redox flow
batteries, the electrolytes are stored in external storage tanks and are circulated through the cell.

Question 37

construction of VRB

Answer 37

It is a secondary battery which employs vanadium ions
as charge carriers.
Construction:
Anode and cathode-Both electrodes are made of carbon.
Electrolyte-Both electrolytes are vanadium-based which are prepared by dissolving vanadium pentoxide (V2O5) in H2SO4.
Anode electrolyte: V2+ and V3+ ions.
Cathode electrolyte : VO2+ and VO2+ ions.
Membrane-Hydrogen permeable polymer membrane like perfluorinated sulfonic acid (Nafion).
Cell potential-1.4 to 1.6 V
{DIAGRAM}

Question 38

working of VRB

Answer 38

Cell reactions:
Anode: V2+ ↔ V3+ + e−
Cathode: VO2+ + 2H+ + e− ↔ VO2+ + H2O
Overall reaction: V2+ + VO2+ +2H+
↔ VO2+ +V3+ +H2O
* Electrolytes present in the external storage tank is pumped to the positive and negative half-cells
by a pumping loop
* During discharging, in negative half-cell V2+ is oxidized to V3+ and the electron released travel in the external circuit. In the positive half-cell, V5+ in the form of VO2+ accepts an electron from
external circuit and reduced to V
4+ in the form of VO2+. H+ ions are transported through the
membrane from anode to cathode and maintain electrical neutrality.
* During charging, the cell is continuously charged until it reaches fully charged state confirmed
by the colour change of electrolytes. Vanadium electrolyte colour changes from green (V3+) to purple (V2+) at anode and blue VO2+ (V4+) to yellow VO2+ (V5+) at cathode. H+ ions are transported through the membrane from cathode to anode.

Question 39

applications of vanadium redox flow batteries

Answer 39

Applications: Battery can be used in utility-scale energy storage projects, micro grids, grid smoothing, backup power and in remote and off-grid power application.