This document provides information on electrochemistry and electrochemical cells. It defines electrochemistry as the study of electricity production from spontaneous chemical reactions and use of electrical energy for non-spontaneous reactions. It describes different types of electrochemical cells including galvanic cells that convert chemical to electrical energy and electrolytic cells that do the opposite. Key concepts discussed include electrode potentials, standard hydrogen electrode, Nernst equation, and factors affecting cell potential. Common electrochemical devices like batteries and the corrosion process are also summarized.
Energy required to beak a chemical bond, almost same amount of energy is used to form the same bond between reactants. Bond energies can be used to predict exothermic and endothermic nature of chemical reactions
Energy required to beak a chemical bond, almost same amount of energy is used to form the same bond between reactants. Bond energies can be used to predict exothermic and endothermic nature of chemical reactions
This is the power point presentation for the students of class XII. This includes: Types of solutions, concentration of solutions, Solution of solid in liquid, solution of gas in liquid: Henry's law, vapour pressure of solutions, Raoult's law, Ideal & non ideal solutions, azeotropic mixtures, Colligative properties - (1) relative lowering of vapour pressure of solution of volatile solute, (2) elevation in boiling point of solution (3) depression in freezing point of solution (4) osmotic pressure, abnormal molar mass of solute, Van't Hoff's factor, numerical problems.
Valence shell electron pair repulsion theory (VSEPR THEORY)Altamash Ali
Designed in a very easy manner so that u all are able to understand each and everything easily.
Gillespie & Nyholm proposed this theory ion 1957 and its is based on the direction of bonds in a polyatomic molecule.
Based on this there are several postulate that are very necessary to know before any molecule to study.
Class XII Electrochemistry - Nernst equation.Arunesh Gupta
Introduction, application of electrochemistry, metallic conduction & electrolytic conduction, electrolytes, electrochemical cell & electrolytic cell, Galvanic cell (Daniell cell), Standard reduction & oxidation potential, SHE as reference electrode, Standard emf of a cell or standard cell potential, Electrochemical series & its application, Nernst equation, Relationship between (i) Standard cell potential & equilibrium constant (ii) standard cell potential & standard Gibbs energy, some numerical problems.
A detailed presentation about what is MOT. Explaining its principles, sigma and pi bonds, bond order, and molecular stability. A good and knowledgeable presentation to understand these concepts.
CONTENTS
Electrochemistry: definition & importance
Conductors: metallic & electrolytic conduction,
Electrolytes, Electrochemical cell & electrolytic cell
A simple electrochemical cell: Galvanic cell or (Daniell Cell)
Cell reaction, cell representation, Salt bridge & its use,
Electrode potential, standard electrode potential, SHE,
Standard cell potential or standard electromotive force of a cell
Electrochemical series (Standard reduction potential values)
Nernst Equation, Relationship with Standard cell potential with Gibbs energy & also equilibrium constant
Resistance (R) & conductance (G) of a solution of an electrolyte
Conductivity (k) of solution, Cell constant (G*) & their units,
Molar conductivity (Λm) & its variation with concentration & temperature,
Debye Huckel Onsager equation & Limiting molar conductivity,
Kohlrausch’s law & its application & numerical problems.
Electrolytic cells & electrolysis.
Some examples of electrolysis of electrolytes in molten / aq. state.
Faraday’s laws of electrolysis: First & second law- numerical problems. Corrosion, Electrochemical theory of rusting.
Prevention of rusting.
This is the power point presentation for the students of class XII. This includes: Types of solutions, concentration of solutions, Solution of solid in liquid, solution of gas in liquid: Henry's law, vapour pressure of solutions, Raoult's law, Ideal & non ideal solutions, azeotropic mixtures, Colligative properties - (1) relative lowering of vapour pressure of solution of volatile solute, (2) elevation in boiling point of solution (3) depression in freezing point of solution (4) osmotic pressure, abnormal molar mass of solute, Van't Hoff's factor, numerical problems.
Valence shell electron pair repulsion theory (VSEPR THEORY)Altamash Ali
Designed in a very easy manner so that u all are able to understand each and everything easily.
Gillespie & Nyholm proposed this theory ion 1957 and its is based on the direction of bonds in a polyatomic molecule.
Based on this there are several postulate that are very necessary to know before any molecule to study.
Class XII Electrochemistry - Nernst equation.Arunesh Gupta
Introduction, application of electrochemistry, metallic conduction & electrolytic conduction, electrolytes, electrochemical cell & electrolytic cell, Galvanic cell (Daniell cell), Standard reduction & oxidation potential, SHE as reference electrode, Standard emf of a cell or standard cell potential, Electrochemical series & its application, Nernst equation, Relationship between (i) Standard cell potential & equilibrium constant (ii) standard cell potential & standard Gibbs energy, some numerical problems.
A detailed presentation about what is MOT. Explaining its principles, sigma and pi bonds, bond order, and molecular stability. A good and knowledgeable presentation to understand these concepts.
CONTENTS
Electrochemistry: definition & importance
Conductors: metallic & electrolytic conduction,
Electrolytes, Electrochemical cell & electrolytic cell
A simple electrochemical cell: Galvanic cell or (Daniell Cell)
Cell reaction, cell representation, Salt bridge & its use,
Electrode potential, standard electrode potential, SHE,
Standard cell potential or standard electromotive force of a cell
Electrochemical series (Standard reduction potential values)
Nernst Equation, Relationship with Standard cell potential with Gibbs energy & also equilibrium constant
Resistance (R) & conductance (G) of a solution of an electrolyte
Conductivity (k) of solution, Cell constant (G*) & their units,
Molar conductivity (Λm) & its variation with concentration & temperature,
Debye Huckel Onsager equation & Limiting molar conductivity,
Kohlrausch’s law & its application & numerical problems.
Electrolytic cells & electrolysis.
Some examples of electrolysis of electrolytes in molten / aq. state.
Faraday’s laws of electrolysis: First & second law- numerical problems. Corrosion, Electrochemical theory of rusting.
Prevention of rusting.
22CYT12-Unit_I_Electrochemistry - EMF Series & its Applications.pptKrishnaveniKrishnara1
Electrochemistry:Introduction – cells – types - representation of galvanic cell - electrode potential - Nernst equation (derivation of cell EMF) - calculation of cell EMF from single electrode potential - reference electrode: construction, working and applications (Determination of potential of the unknown electrode and pH of the unknown electrode) of standard hydrogen electrode, standard calomel electrode - glass electrode – EMF series and its applications - potentiometric titrations (redox) - conductometric titrations - mixture of weak and strong acid vs strong base.
Conductors and Non-Conductors
Substances can be classified as conductors and non-conductors based on their ability to conduct electricity.
Conductors: Substances that allow electric current to flow through them are called conductors. For example, Plastic, Wood, etc.
Non-Conductors: Non-conductors are insulators that do not allow electricity to pass through them. For example, Copper, Iron, etc.
Types of Conductors
Conductors are divided into two groups: Metallic conductors and Electrolytes.
Metallic Conductors: These conductors conduct electricity by the movement of electrons without any chemical change during the process. This type of conduction happens in solids and in the molten state.
Electrolytes: They conduct electricity by the movement of the ions in the solutions. It is present in the aqueous solution.
Distinguish between Metallic and Electrolytic Conduction
Metallic Conduction Electrolytic Conduction
The movement of electrons causes the electric current The movement of ions causes the electric current
There is no chemical reaction Ions get ionised or reduced at the electrodes
There is no transfer of matter It involves the transfer of matter in the form of ions
Follows Ohm’s law Follows Ohm’s law
Resistance increases with an increase in temperature Resistance decreases with an increase in temperature
Faraday’s law is not followed Follows Faraday’s law
Electrolytes
(a) Substances whose aqueous solutions allow the conductance of electric current and are chemically decomposed are called electrolytes.
(b) The positively charged ions furnished by the electrolyte are called cations, while the negatively charged ions furnished by the electrolyte are called anions.
Types of Electrolytes
(a) Weak electrolytes: Electrolytes that are decomposable to a very small extent in their dilute solutions are called weak electrolytes. For example, organic acids, inorganic acids and bases etc.
(b) Strong electrolytes: Electrolytes that are highly decomposable in aqueous solution and conduct electricity frequently are called electrolytes. For example, mineral acid and salts of strong acid.
Electrode
For the electric current to pass through an electrolytic conductor, the two rods or plates called electrodes are always needed. These plates are connected to the terminals of the battery to form a cell. The electrode through which the electric current flows into the electrolytic solution is called the anode, also called the positive electrode, and anions are oxidised here.
An electrode through which the electric current flows out of the electrolytic solution is called the cathode, also called the negative electrode, and cations are reduced there.
Electrolysis
Electrolysis is the process of chemical deposition of the electrolyte by passing an electric current. Electrolysis takes place in an electrolytic cell. This cell will convert the electrical energy to chemical energy.
Introduction to Electrochemistry
- Electrochemistry explores the interplay between electrical energy and chemical reactions, focusing on oxidation-reduction (redox) reactions and electrochemical cells.
**Oxidation and Reduction**
- Oxidation involves the loss of electrons, while reduction involves the gain of electrons, summed up by the mnemonic OIL RIG. An example reaction is Zn + Cu²⁺ → Zn²⁺ + Cu.
**Redox Reactions in Everyday Life**
- Examples include the rusting of iron, cellular respiration, and the combustion of fuels.
**Electrochemical Cells**
- Two main types are Galvanic (Voltaic) cells, which convert chemical energy into electrical energy, and Electrolytic cells, which use electrical energy to drive chemical reactions. Components include the anode (where oxidation occurs), the cathode (where reduction occurs), and an electrolyte.
**Galvanic Cells**
- A common example is the Daniell Cell, which generates electrical energy through spontaneous redox reactions.
**Electrolytic Cells**
- These cells drive non-spontaneous reactions using electrical energy, such as the electrolysis of water to produce hydrogen and oxygen gases.
**Applications of Electrochemistry**
- Includes batteries (e.g., lithium-ion, alkaline), electroplating, corrosion prevention methods like galvanization, and fuel cells that directly convert chemical energy into electrical energy.
**Electrochemistry in Nature**
- Involves biochemical processes like the electron transport chain in mitochondria and natural galvanic cells, such as those influenced by lightning in soil.
**Summary**
- Understanding redox reactions and electrochemical cells is essential. Electrochemistry has a wide range of practical applications, making it a significant field of study.
**Discussion and Q&A**
- Engage with the audience to explore real-life applications and recent advancements in electrochemistry.
This summary encapsulates the key points and themes of the presentation, providing a concise overview of the fundamental concepts and applications of electrochemistry.
Nutraceutical market, scope and growth: Herbal drug technologyLokesh Patil
As consumer awareness of health and wellness rises, the nutraceutical market—which includes goods like functional meals, drinks, and dietary supplements that provide health advantages beyond basic nutrition—is growing significantly. As healthcare expenses rise, the population ages, and people want natural and preventative health solutions more and more, this industry is increasing quickly. Further driving market expansion are product formulation innovations and the use of cutting-edge technology for customized nutrition. With its worldwide reach, the nutraceutical industry is expected to keep growing and provide significant chances for research and investment in a number of categories, including vitamins, minerals, probiotics, and herbal supplements.
Earliest Galaxies in the JADES Origins Field: Luminosity Function and Cosmic ...Sérgio Sacani
We characterize the earliest galaxy population in the JADES Origins Field (JOF), the deepest
imaging field observed with JWST. We make use of the ancillary Hubble optical images (5 filters
spanning 0.4−0.9µm) and novel JWST images with 14 filters spanning 0.8−5µm, including 7 mediumband filters, and reaching total exposure times of up to 46 hours per filter. We combine all our data
at > 2.3µm to construct an ultradeep image, reaching as deep as ≈ 31.4 AB mag in the stack and
30.3-31.0 AB mag (5σ, r = 0.1” circular aperture) in individual filters. We measure photometric
redshifts and use robust selection criteria to identify a sample of eight galaxy candidates at redshifts
z = 11.5 − 15. These objects show compact half-light radii of R1/2 ∼ 50 − 200pc, stellar masses of
M⋆ ∼ 107−108M⊙, and star-formation rates of SFR ∼ 0.1−1 M⊙ yr−1
. Our search finds no candidates
at 15 < z < 20, placing upper limits at these redshifts. We develop a forward modeling approach to
infer the properties of the evolving luminosity function without binning in redshift or luminosity that
marginalizes over the photometric redshift uncertainty of our candidate galaxies and incorporates the
impact of non-detections. We find a z = 12 luminosity function in good agreement with prior results,
and that the luminosity function normalization and UV luminosity density decline by a factor of ∼ 2.5
from z = 12 to z = 14. We discuss the possible implications of our results in the context of theoretical
models for evolution of the dark matter halo mass function.
Toxic effects of heavy metals : Lead and Arsenicsanjana502982
Heavy metals are naturally occuring metallic chemical elements that have relatively high density, and are toxic at even low concentrations. All toxic metals are termed as heavy metals irrespective of their atomic mass and density, eg. arsenic, lead, mercury, cadmium, thallium, chromium, etc.
What is greenhouse gasses and how many gasses are there to affect the Earth.moosaasad1975
What are greenhouse gasses how they affect the earth and its environment what is the future of the environment and earth how the weather and the climate effects.
The ability to recreate computational results with minimal effort and actionable metrics provides a solid foundation for scientific research and software development. When people can replicate an analysis at the touch of a button using open-source software, open data, and methods to assess and compare proposals, it significantly eases verification of results, engagement with a diverse range of contributors, and progress. However, we have yet to fully achieve this; there are still many sociotechnical frictions.
Inspired by David Donoho's vision, this talk aims to revisit the three crucial pillars of frictionless reproducibility (data sharing, code sharing, and competitive challenges) with the perspective of deep software variability.
Our observation is that multiple layers — hardware, operating systems, third-party libraries, software versions, input data, compile-time options, and parameters — are subject to variability that exacerbates frictions but is also essential for achieving robust, generalizable results and fostering innovation. I will first review the literature, providing evidence of how the complex variability interactions across these layers affect qualitative and quantitative software properties, thereby complicating the reproduction and replication of scientific studies in various fields.
I will then present some software engineering and AI techniques that can support the strategic exploration of variability spaces. These include the use of abstractions and models (e.g., feature models), sampling strategies (e.g., uniform, random), cost-effective measurements (e.g., incremental build of software configurations), and dimensionality reduction methods (e.g., transfer learning, feature selection, software debloating).
I will finally argue that deep variability is both the problem and solution of frictionless reproducibility, calling the software science community to develop new methods and tools to manage variability and foster reproducibility in software systems.
Exposé invité Journées Nationales du GDR GPL 2024
Observation of Io’s Resurfacing via Plume Deposition Using Ground-based Adapt...Sérgio Sacani
Since volcanic activity was first discovered on Io from Voyager images in 1979, changes
on Io’s surface have been monitored from both spacecraft and ground-based telescopes.
Here, we present the highest spatial resolution images of Io ever obtained from a groundbased telescope. These images, acquired by the SHARK-VIS instrument on the Large
Binocular Telescope, show evidence of a major resurfacing event on Io’s trailing hemisphere. When compared to the most recent spacecraft images, the SHARK-VIS images
show that a plume deposit from a powerful eruption at Pillan Patera has covered part
of the long-lived Pele plume deposit. Although this type of resurfacing event may be common on Io, few have been detected due to the rarity of spacecraft visits and the previously low spatial resolution available from Earth-based telescopes. The SHARK-VIS instrument ushers in a new era of high resolution imaging of Io’s surface using adaptive
optics at visible wavelengths.
Professional air quality monitoring systems provide immediate, on-site data for analysis, compliance, and decision-making.
Monitor common gases, weather parameters, particulates.
2. ELECTROCHEMISTRY
Electrochemistry is that branch of chemistry which deals with 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.
Importance of Electrochemistry
1. Production of metals like Na, Mg. Ca and Al.
2. Electroplating.
3. Purification of metals.
4. Batteries and cells used in various instruments.
3. Conductors
Substances that allow electric current to pass through them are known as
conductors.
Metallic Conductors or Electronic Conductors
Substances which allow the electric current to pass through them by the
movement of electrons are called metallic conductors, e.g.. metals.
Electrolytic Conductors or Electrolytes
Substances which allow the passage of electricity through their fused
state or aqueous solution and undergo chemical decomposition are
called electrolytic conductors, e.g., aqueous solution of acids. bases
and salts.
Electrolytes are of two types:
1. Strong electrolytes
The electrolytes that completely dissociate or ionise into ions are called
strong electrolytes. e.g., HCl, NaOH, K2SO4
2. Weak electrolytes
The electrolytes that dissociate partially are called weak electrolytes,
e.g., CH3COOH, H2CO3, NH4OH,H2S, etc.
4. ELECTROCHEMICAL CELL
The cell which converts chemical energy to
electrical energy and vice versa is called an
electrochemical cell.
TYPES
Galvanic Cells -Converts chemical energy into
electrical energy.
Galvanic cell is also called voltaic cell.
Electrolytic Cells -Converts electrical energy into
chemical energy.
7. EXAMPLE
The Daniel cell is represented as follows :
Zn(s) | Zn2+ (C1 ) || Cu2+ (C2 ) | Cu (s)
Salt bridge
When the oxidation takes place then it is anode when there is
reduction takes place then thereis cathode.
8. GALVANIC CELL
DANIEL CELL
It is a Galvanic Cell in which Zinc and Copper are used for
the redox reaction to take place.
Zn (s) + Cu2+ (aq) Zn2+ (aq) + Cu(s)
Oxidation Half : Zn (s) Zn2+ (aq) + 2e–
Reduction Half : Cu2+(aq) + 2e– Cu(s)
NOTES:-
Anode is assigned negative polarity
cathode is assigned positive polarity.
In Daniel Cell, Zn acts as the anode and Cu acts as the
cathode
Ques…. What is the difference between electrolytic cell
and galvanic cell.
10. FUNCTION OF SALT BRIDGE
1. It completes the circuit and allows the flow of
current.
2. It maintains the electrical neutrality on both sides.
3. Salt-bridge generally contains solution of strong
electrolyte such as KNO3, KCL etc. KCl is
preferred because the transport numbers of
K+ and Cl-are almost same.
11. SOME TERMS
CELL POTENTIAL
It is the difference between electrode potentials (of
both electrodes i.e anode and cathode) of the given cell. It is denoted by E cell.
Electrode Potential
When an electrode is in contact with the solution of its ions
in a half-cell, it has a tendency to lose or gain electrons
which is known as electrode potential. It is expressed in
Volts.
OR
Potential difference between the electrode and electrolyte.
Oxidation potential
The tendency to lose electrons in the above case is known as oxidation
potential. Oxidation potential of a half-cell is inversely proportional to the
concentration of ions in the solution.
Reduction potential
The tendency to gain electrons in the above case is known as reduction
potential.
12. E cell is written as :
E cell = E right – Eleft
EXAMPLE:-
Cell reaction:
Cu(s) + 2Ag+ (aq) → Cu2+(aq) + 2 Ag(s)
Half-cell reactions:
Cathode (reduction): 2Ag+ (aq) + 2e– → 2Ag(s)
Anode (oxidation): Cu(s) → Cu2+(aq) + 2e
The cell can be represented as:
Cu(s)|Cu2+(aq)||Ag+ (aq)|Ag(s)
Ecell = Eright – Eleft
=E Ag+/ Ag – E Cu2+ /Cu
NOTES:-It is not possible to determine the absolute value
of electrode potential. For this a reference electrode [NHE
or SHE] is required.
13. STANDARD HYDROGEN
ELCTRODE(SHE)
It is related to standard conditions.
The standard conditions taken are :
(i) 1M concentration of each ion in the solution.
(ii) A temperature of 298 K.
(iii) 1 bar pressure for each gas
14. EMF(ELECTROMOTIVE FORCE)
It is the difference between the electrode potentials of
two half-cells and cause flow of current from
electrode at higher potential to electrode at lower
potential. It is also the measure of free energy
change. Standard emf of a cell. It is denoted by
E0(prnounced as e not).
15.
16. ELECTROCHEMICAL SERIES
The half cell potential values are standard values and are
represented as the standard reduction potential values as
shown in the table at the end which is also called
Electrochemical Series.
17.
18. APPLICATIONS OF ELECTROCHEMICAL
SERIES
The lower the value of E°, the greater the tendency
to form cation.
M → Mn+ + ne
Reducing character increases down the series.
Reactivity increases down the series.
Determination of emf; emf is the difference of
reduction potentials of two half-cells.
•Eemf = ERHS – ELHS
If the value of emf is positive. then reaction take
place spontaneously, otherwise not.
19. NERNST EQUATION
It relates electrode potential with the concentration
of ions.
.
23. CONDUCTANCE: It is the reciprocal of resistance.
The ease with which the electric current flows
through a conductor.It is denoted by G.
G = (1/R), units ohm-1 mhos or Ω-1
SPECIFIC CONDUCTIVITY -It is the reciprocal of
resistivity .It is denoted by kappa(k).
24. NOTE:-Specific conductivity decreases on dilution. This is
because concentration of ions per cc decreases upon dilution.
Molar Conductivity (Λm)
The conductivity of all the ions produced when 1 mole of an
electrolyte is dissolved in V mL of solution is known as molar
conductivity.It is related to specific conductance as
Λm = (k x 1000/M) where. M = molarity.
It units are Ω-1 cm2 mol-1 or S cm2 mol-1.
Equivalent conductivity (Λe)
The conducting power of all the ions produced when 1 g-
equivalent of an electrolyte is dissolved in V mL of solution, is
called equivalent conductivity. It is related to specific
conductance as
Λe = (k x 1000/N) where. N = normality.
Its units are ohm-1 cm2 (equiv-1) or mho cm2 (equiv-1) or S
cm2 (g-equiv-1).
26. FACTORS AFFECTING ELECTROLYTIC
CONDUCTANCE
Electrolyte -is a substance that dissociates in
solution to produce ions and hence conducts
electricity in dissolved or molten state.
Examples : HCl, NaOH, KCl (Strong electrolytes).
CH3COOH, NH4OH (Weak electrolytes).
Nature of electrolyte or interionic attractions
Temperature
27.
28. VARIATION OF CONDUCTIVITY AND MOLAR
CONDUCTIVITY WITH DILUTION
Conductivity always decreases with decrease in
concentration both, for weak and strong
electrolytes. This can be explained by the fact that
the number of ions per unit volume that carry the
current in a solution decreases on dilution.
Molar conductivity increases with decrease in
concentration. This is because the total volume, V,
of solution containing one mole of electrolyte also
increases
29.
30. LIMITING MOLAR CONDUCTIVITY (Λ0M )
The value of molar conductivity when the
concentration approaches zero is known as limiting
molar conductivity or molar conductivity at infinite
dilution.
It is possible to determine the molar conductivity at
infinite dilution λ0m.
In case of strong electrolyte by extrapolation of
curve of λ0mvs c.
In caseof weak electrolyte at infinite dilution cannot
be determined by extapolation of the curve as the
curve becomes almost parallel to y-axis when
concentration approaches to zero.
31. KOHLRAUSCH’S LAW
It states that the limiting molar conductivity of an
electrolyte can be represented as the sum of the
individual contributions of the anion and cation of
the electrolyte.
In general, if an electrolyte on dissociation gives v+
cations and v– anions then its limiting molar
conductivity is given by:-
33. ELECTROLYSIS
It is the process of decomposition of an electrolyte when
electric current is passed through either its aqueous
solution or molten state.
PREDICT THE PRODUCT OF ELECTROLYSIS:-
when an aqueous solution of an electrolyte is
electrolysed, if the cation has higher reduction potential
than water (-0.83 V), cation is liberated at the cathode
(e.g.. in the electrolysis of copper and silver salts)
otherwise H2 gas is liberated due to reduction of water
(e.g., in the electrolysis of K, Na, Ca salts, etc.)
Similarly if anion has higher oxidation potential than
water (- 1.23 V), anion is liberated (e.g., Br-), otherwise
O2 gas is liberated due to oxidation of water (e.g., in
caseof F-, aqueous solution of Na2SO4 as oxidation
potential of SO2-
4 is – 0.2 V).
34.
35.
36.
37. BATTERIES
Cells and batteries are available in a wide variety of
types.
TYPES
A primary cell cannot be recharged and cannot be
used.
A secondary cell, or storage cell, can be recharged
and can be use.
38. PRIMARY CELL
DRY CELL:-
Anode : Zn container
Cathode : Carbon (graphite) rod surrounded by powdered MnO2
and carbon.
Electrolyte : NH4 Cl and ZnCl2
Reaction :
Anode : Zn → Zn2+ + 2e–
Cathode : MnO2 + NH4
+ + e – → MnO (OH) + NH3
The standard potential of this cell is 1.5 V and it falls as the
cell gets discharged continuously and once used it cannot be
recharged.
39.
40. MERCURY CELL:
It offers a rather more stable voltage.
The emf of the Mercury Cell is 1.35 V.
Usually, the mercury cell is costlier. This is the reason, why they
are used only in sophisticated instruments such as camera,
hearing aids, and watches etc.
41. The reactions during discharge are,
At anode: Zn(Hg) + 2OH– →Zn (OH)2 + 2e–
At cathode: HgO + H2O + 2e– →Hg + 2OH–
Overall reaction:
Zn(Hg) + HgO(s) →Zn(OH)2+ Hg(l)
42. SECONDARY CELL
Secondary cells are those which can be recharged
again and again for multiple uses. e.g. lead storage
battery and Ni – Cd battery.
43. LEAD STORAGE
Anode : Lead (Pb)
Cathode : Grid of lead packed with lead oxide (PbO2 )
Electrolyte : 38% solution of H2 SO4
Discharging Reactions
Anode:
Pb(s) + SO4
2–(aq) PbSO4 (s) + 2e–
Cathode:
PbO2 (s) + 4H+ (aq) + SO4 2–(aq) + 2e– PbSO4 (s) +
2H2O(l)
Overall Reaction :
Pb(s) + PbO2 (s) + 2H2 SO4 (aq) 2PbSO4 (s) + 2H2O(l)
44. CORROSION
It involves a redox reaction and formation of an
electrochemical cell on the surface of iron or any other metal.
Anode : 2Fe (s) → 2 Fe2+ + 4e– Eº = + 0.44 V
Cathode : O2 (g) + 4H+ + 4e– → 2H2 O(l) Eº = 1.23 V
Overall reaction:
2Fe (s) + O2 (q) + 4H+ → 2Fe2+ + 2H2O
45.
46. IMPORTANT QUESTIONS
a) Following reactions occur at cathode during the electrolysis of aqueous
silver chloride solution :
Ag+(aq) + e– → Ag(s) E° = +0.80 V
H+(aq) + e– →1/2 H2 (g) E° = 0.00 V
On the basis of their standard reduction electrode potential (E°) values,
which reaction is feasible at the cathode and why ?
(b) Define limiting molar conductivity. Why conductivity of an electrolyte solution
decreases with the decrease in concentration ?
(c) Calculate emf of the following cell at 25 °C :
Fe | Fe2+(0.001 M) || H+(0.01 M) | H2(g) (1 bar) | Pt(s)
E°(Fe2+ | Fe) = –0.44 V E°(H+ | H2) = 0.00 V
(d) From the given cells : Lead storage cell, Mercury cell, Fuel cell and Dry cell .
Answer the following :
(i) Which cell is used in hearing aids ?
(ii) Which cell was used in Apollo Space Programme ?
(iii) Which cell is used in automobiles and inverters ?
(iv) Which cell does not have long life ?
47. (e)Calculate the degree of dissociation (α) of acetic acid if its molar
conductivity (∧m) is 39.05 S cm2mol–1. Given λo (H+) = 349.6 S cm2
mol–1 and λo(CH3COO–) = 40.9 S cm2mol–1.
(f) Calculate the mass of Ag deposited at cathode when a current of 2
amperes was passed through a solution of AgNO3 for 15 minutes. (Given
: Molar mass of Ag = 108 g mol–1 1F = 96500 C mol–1)
(g) Define fuel cell.
(h) Write the cell reaction and calculate the e.m.f. of the following cell at 298
K :
Sn (s) | Sn2+ (0·004 M) || H+(0·020 M) | H2(g) (1 bar) | Pt (s) (Given :E0
Sn2+/Sn = – 0·14 V)
(i) Give reasons :
On the basis of Eo values, O2 gas should be liberated at anode but it is
Cl2 gas which is liberated in the electrolysis of aqueous NaCl.
Conductivity of CH3COOH decreases on dilution.
(j) For the reaction 2AgCl (s) + H2 (g) (1 atm) 2Ag (s) + 2H+ (0·1 M)
+ 2Cl–(0·1 M),
∆Go= – 43600 J at 25 C. Calculate the e.m.f. of the cell. [log 10–n= – n]
(k) Define fuel cell and write its two advantages.
48. (l) E°cell for the given redox reaction is 2.71 V
Mg+ Cu2+(0.01v) Mg2+(0.001V) + Cu (s)
Calculate Ecell for the reaction. Write the direction of flow of
current when an external opposite potential applied is i) less
than 2.71 V and (ii) greater than 2.71 V
(m) A steady current of 2 amperes was passed through two
electrolytic cells X and Y connected in series containing
electrolytes FeSO4 and ZnSO4 until 2.8 g of Fe deposited at
the cathode of cell X. How long did the current flow? Calculate
the mass of Zn deposited at the cathode of cell Y. (Molar mass
: Fe = 56 g mol–1 Zn = 65.3 g mol–1, 1F = 96500 C mol–1)