This document discusses electrogravimetry, which is the quantitative analysis of substances by electrolysis. It defines key terms used in electrogravimetry like cathode, anode, current density, and overpotential. It explains Faraday's laws of electrolysis and how they relate to the amount of material deposited. It also describes how controlling variables like cathode potential can be used to selectively deposit metals and separate them from each other.
The Detailed Theory and instrumentation of Both Amperometry and Biamperometric analysis is given with Titration curves and Applications.
Medha Thakur (M.Sc Chemistry)
ELECTRICAL DOUBLE LAYER-TYPES-DYNAMICS OF ELECTRON TRANSFER-MARCUS THEORY-TUNNELING - BUTLER VOLMER EQUATIONS-TAFEL EQUATIONS-POLARIZATION AND OVERVOLTAGE-CORROSION AND PASSIVITY-POURBAIX AND EVAN DIAGRAM-POWER STORAGE-FUEL CELLS
ELECTROCHEMISTRY - I
4.1 - Metallic and Electrolytic Conductors-Faraday’s Laws-Electro plating Specific conductance and Equivalent conductance - Measurement of equivalent conductance - Variation of Equivalent Conductance and Specific Conductance with Dilution Kohlrausch Law and its applications - Ostwald’s Dilution Law and its Limitations.
The Detailed Theory and instrumentation of Both Amperometry and Biamperometric analysis is given with Titration curves and Applications.
Medha Thakur (M.Sc Chemistry)
ELECTRICAL DOUBLE LAYER-TYPES-DYNAMICS OF ELECTRON TRANSFER-MARCUS THEORY-TUNNELING - BUTLER VOLMER EQUATIONS-TAFEL EQUATIONS-POLARIZATION AND OVERVOLTAGE-CORROSION AND PASSIVITY-POURBAIX AND EVAN DIAGRAM-POWER STORAGE-FUEL CELLS
ELECTROCHEMISTRY - I
4.1 - Metallic and Electrolytic Conductors-Faraday’s Laws-Electro plating Specific conductance and Equivalent conductance - Measurement of equivalent conductance - Variation of Equivalent Conductance and Specific Conductance with Dilution Kohlrausch Law and its applications - Ostwald’s Dilution Law and its Limitations.
Knocking Door of Cyclic Voltammetry - cv of CV by Monalin MishraMONALINMISHRA
This ppt presentation shares some short basic knowledge on the electroanalytical technique of Cyclic Voltammetry. It also covers the working of CV with some short videos and photos.It also provides general explanation on some relevent techniques
Slide 1: Title Slide
Extrachromosomal Inheritance
Slide 2: Introduction to Extrachromosomal Inheritance
Definition: Extrachromosomal inheritance refers to the transmission of genetic material that is not found within the nucleus.
Key Components: Involves genes located in mitochondria, chloroplasts, and plasmids.
Slide 3: Mitochondrial Inheritance
Mitochondria: Organelles responsible for energy production.
Mitochondrial DNA (mtDNA): Circular DNA molecule found in mitochondria.
Inheritance Pattern: Maternally inherited, meaning it is passed from mothers to all their offspring.
Diseases: Examples include Leber’s hereditary optic neuropathy (LHON) and mitochondrial myopathy.
Slide 4: Chloroplast Inheritance
Chloroplasts: Organelles responsible for photosynthesis in plants.
Chloroplast DNA (cpDNA): Circular DNA molecule found in chloroplasts.
Inheritance Pattern: Often maternally inherited in most plants, but can vary in some species.
Examples: Variegation in plants, where leaf color patterns are determined by chloroplast DNA.
Slide 5: Plasmid Inheritance
Plasmids: Small, circular DNA molecules found in bacteria and some eukaryotes.
Features: Can carry antibiotic resistance genes and can be transferred between cells through processes like conjugation.
Significance: Important in biotechnology for gene cloning and genetic engineering.
Slide 6: Mechanisms of Extrachromosomal Inheritance
Non-Mendelian Patterns: Do not follow Mendel’s laws of inheritance.
Cytoplasmic Segregation: During cell division, organelles like mitochondria and chloroplasts are randomly distributed to daughter cells.
Heteroplasmy: Presence of more than one type of organellar genome within a cell, leading to variation in expression.
Slide 7: Examples of Extrachromosomal Inheritance
Four O’clock Plant (Mirabilis jalapa): Shows variegated leaves due to different cpDNA in leaf cells.
Petite Mutants in Yeast: Result from mutations in mitochondrial DNA affecting respiration.
Slide 8: Importance of Extrachromosomal Inheritance
Evolution: Provides insight into the evolution of eukaryotic cells.
Medicine: Understanding mitochondrial inheritance helps in diagnosing and treating mitochondrial diseases.
Agriculture: Chloroplast inheritance can be used in plant breeding and genetic modification.
Slide 9: Recent Research and Advances
Gene Editing: Techniques like CRISPR-Cas9 are being used to edit mitochondrial and chloroplast DNA.
Therapies: Development of mitochondrial replacement therapy (MRT) for preventing mitochondrial diseases.
Slide 10: Conclusion
Summary: Extrachromosomal inheritance involves the transmission of genetic material outside the nucleus and plays a crucial role in genetics, medicine, and biotechnology.
Future Directions: Continued research and technological advancements hold promise for new treatments and applications.
Slide 11: Questions and Discussion
Invite Audience: Open the floor for any questions or further discussion on the topic.
THE IMPORTANCE OF MARTIAN ATMOSPHERE SAMPLE RETURN.Sérgio Sacani
The return of a sample of near-surface atmosphere from Mars would facilitate answers to several first-order science questions surrounding the formation and evolution of the planet. One of the important aspects of terrestrial planet formation in general is the role that primary atmospheres played in influencing the chemistry and structure of the planets and their antecedents. Studies of the martian atmosphere can be used to investigate the role of a primary atmosphere in its history. Atmosphere samples would also inform our understanding of the near-surface chemistry of the planet, and ultimately the prospects for life. High-precision isotopic analyses of constituent gases are needed to address these questions, requiring that the analyses are made on returned samples rather than in situ.
Cancer cell metabolism: special Reference to Lactate PathwayAADYARAJPANDEY1
Normal Cell Metabolism:
Cellular respiration describes the series of steps that cells use to break down sugar and other chemicals to get the energy we need to function.
Energy is stored in the bonds of glucose and when glucose is broken down, much of that energy is released.
Cell utilize energy in the form of ATP.
The first step of respiration is called glycolysis. In a series of steps, glycolysis breaks glucose into two smaller molecules - a chemical called pyruvate. A small amount of ATP is formed during this process.
Most healthy cells continue the breakdown in a second process, called the Kreb's cycle. The Kreb's cycle allows cells to “burn” the pyruvates made in glycolysis to get more ATP.
The last step in the breakdown of glucose is called oxidative phosphorylation (Ox-Phos).
It takes place in specialized cell structures called mitochondria. This process produces a large amount of ATP. Importantly, cells need oxygen to complete oxidative phosphorylation.
If a cell completes only glycolysis, only 2 molecules of ATP are made per glucose. However, if the cell completes the entire respiration process (glycolysis - Kreb's - oxidative phosphorylation), about 36 molecules of ATP are created, giving it much more energy to use.
IN CANCER CELL:
Unlike healthy cells that "burn" the entire molecule of sugar to capture a large amount of energy as ATP, cancer cells are wasteful.
Cancer cells only partially break down sugar molecules. They overuse the first step of respiration, glycolysis. They frequently do not complete the second step, oxidative phosphorylation.
This results in only 2 molecules of ATP per each glucose molecule instead of the 36 or so ATPs healthy cells gain. As a result, cancer cells need to use a lot more sugar molecules to get enough energy to survive.
Unlike healthy cells that "burn" the entire molecule of sugar to capture a large amount of energy as ATP, cancer cells are wasteful.
Cancer cells only partially break down sugar molecules. They overuse the first step of respiration, glycolysis. They frequently do not complete the second step, oxidative phosphorylation.
This results in only 2 molecules of ATP per each glucose molecule instead of the 36 or so ATPs healthy cells gain. As a result, cancer cells need to use a lot more sugar molecules to get enough energy to survive.
introduction to WARBERG PHENOMENA:
WARBURG EFFECT Usually, cancer cells are highly glycolytic (glucose addiction) and take up more glucose than do normal cells from outside.
Otto Heinrich Warburg (; 8 October 1883 – 1 August 1970) In 1931 was awarded the Nobel Prize in Physiology for his "discovery of the nature and mode of action of the respiratory enzyme.
WARNBURG EFFECT : cancer cells under aerobic (well-oxygenated) conditions to metabolize glucose to lactate (aerobic glycolysis) is known as the Warburg effect. Warburg made the observation that tumor slices consume glucose and secrete lactate at a higher rate than normal tissues.
This pdf is about the Schizophrenia.
For more details visit on YouTube; @SELF-EXPLANATORY;
https://www.youtube.com/channel/UCAiarMZDNhe1A3Rnpr_WkzA/videos
Thanks...!
Richard's entangled aventures in wonderlandRichard Gill
Since the loophole-free Bell experiments of 2020 and the Nobel prizes in physics of 2022, critics of Bell's work have retreated to the fortress of super-determinism. Now, super-determinism is a derogatory word - it just means "determinism". Palmer, Hance and Hossenfelder argue that quantum mechanics and determinism are not incompatible, using a sophisticated mathematical construction based on a subtle thinning of allowed states and measurements in quantum mechanics, such that what is left appears to make Bell's argument fail, without altering the empirical predictions of quantum mechanics. I think however that it is a smoke screen, and the slogan "lost in math" comes to my mind. I will discuss some other recent disproofs of Bell's theorem using the language of causality based on causal graphs. Causal thinking is also central to law and justice. I will mention surprising connections to my work on serial killer nurse cases, in particular the Dutch case of Lucia de Berk and the current UK case of Lucy Letby.
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.
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.
1. Prof. Santosh S. Dipke
(Assistant Professor)
Department of Chemistry
Pratap College, Amalner
ELECTROGRAVIMETRY
2. 2
Theory of electrogravimetric analysis
Terms used in electrogravimetric analysis
Completeness of deposition
Electrolytic separation of metals
Character of the deposit
Electrolytic separation of metals with controlled cathode potential
Apparatus, Determination of copper ( constant current procedure )
Determination of antimony, copper, lead and tin in bearing metal (controlled
current procedure)
Content
3. 3
Element to be determined is deposited electrolytically upon a suitable electrode
Filtration is not required
Co-deposition of two metals can often be avoided with controlled experimental conditions
Electro-deposition is governed by Ohm's Law and by Faraday's two Laws of Electrolysis
1. The amounts of substances liberated (or dissolved) at the electrodes of a cell are directly
proportional to the quantity of electricity which passes through the solution. i.e.
(mass of chemical deposition) 𝑚 𝑄 𝑞𝑢𝑎𝑛𝑡𝑖𝑡𝑦 𝑜𝑓 𝑒𝑙𝑒𝑐𝑡𝑟𝑖𝑐𝑖𝑡𝑦
𝑚
𝑄
= 𝑍 = 𝑃𝑟𝑜𝑝𝑜𝑟𝑡𝑖𝑜𝑛𝑎𝑙𝑖𝑡𝑦 𝑐𝑜𝑛𝑠𝑡𝑎𝑛𝑡,
𝑒𝑙𝑒𝑐𝑡𝑟𝑜𝑐ℎ𝑒𝑚𝑖𝑐𝑎𝑙 𝑒𝑞𝑢𝑖𝑣𝑎𝑙𝑒𝑛𝑡 𝑜𝑓 𝑡ℎ𝑒 𝑠𝑢𝑏𝑠𝑡𝑎𝑛𝑐𝑒 (𝑒. 𝑐. 𝑒)
Introduction
4. 4
2. The amounts of different substances liberated or dissolved by the same quantity of electricity
are proportional to their relative atomic (or molar) masses divided by the number of electrons
involved in the respective electrode processes.
𝑚 𝐸
𝐸 = 𝑚𝑜𝑙𝑎𝑟 𝑚𝑎𝑠𝑠/𝑉𝑎𝑙𝑒𝑛𝑐𝑒
Introduction
It follows from the Second Law that when a
given current is passed in series through
solutions containing copper(II) sulphate and
silver nitrate respectively, then the weights of copper and silver deposited in a given time will
be in the ratio of 63.55/2 to 107.87
Ohm's Law expresses the relation between the three fundamental quantities, current,
electromotive force, and resistance: The current I is directly proportional to the electromotive
force E and indirectly proportional to the resistance R, i.e. I = E/R
5. 5
Ampere (A): The fundamental SI unit of current, and which is defined as the constant current
which, if maintained in two parallel rectilinear conductors of negligible cross-section and of
infinite length and placed one meter apart in a vacuum, would produce between these
conductors a force equal to 2 x 10-7 newton per meter(N/m) length.
Volt (V): The unit of electrical potential, which is the difference of potential between two
points of a conducting wire which carries a constant current of one ampere, when the power
dissipated between these two points is one joule per second
Ohm (Ω): The unit of electrical resistance, which is the resistance between two points of a
conductor when a constant difference of potential of one volt applied between these two points
produces a current of one ampere
Coulomb (C): The unit of quantity of electricity, and is defined as the quantity of electricity
passing when a current of one ampere flows for one second.
To liberate one mole of electrons, or of a singly charged ion, will require L x e coulombs,
where L is the Avogadro constant (6.022 x 1023 mol-1) and e is the elementary charge (1.602 x
10-l0C); the resultant quantity (9.647 x 104 C mol-1 ) is termed the Faraday constant (F)
Electrical Units
6. 6
Voltaic (Galvanic) and Electrolytic Cells:
• A cell consists of two electrodes and one or more solutions in an
appropriate container. If the cell can furnish electrical energy to
an external system it is called a voltaic (or galvanic) cell.
• The chemical energy is converted more or less completely into
electrical energy, but some of the energy may be dissipated as
heat.
TERMS USED IN ELECTRO-GRAVIMETRIC ANALYSIS
• If the electrical energy is supplied from an external
source the cell through which it flows is termed an
electrolytic cell and Faraday's Laws account for the
material changes at the electrodes.
• A given cell may function at one time as a galvanic cell
and at another as an electrolytic cell: a typical example is
the lead accumulator or storage cell
Electrolytic Cell
8. 8
Cathode: The cathode is the electrode at which reduction occurs.
In an electrolytic cell it is the electrode attached to the negative terminal of the source, since
electrons leave the source and enter the electrolysis cell at that terminal.
The cathode is the positive terminal of a galvanic cell, because such a cell accepts electrons at
this terminal
Anode: The anode is the electrode at which oxidation occurs.
It is the positive terminal of an electrolysis cell or the negative terminal of a voltaic cell
Polarised electrode: An electrode is polarised if its potential deviates from the reversible or
equilibrium value.
An electrode is said to be 'depolarised ' by a substance if that substance lowers the amount of
polarisation
TERMS USED IN ELECTRO-GRAVIMETRIC ANALYSIS
9. 9
Current density: The current density is defined as the current per unit area of electrode
surface. It is generally expressed in amperes per square centimeter (or per square decimeter) of
the electrode surface.
Current efficiency: By measuring the amount of a particular substance that is deposited and
comparing this with the theoretical quantity (calculated by Faraday's Laws), the actual current
efficiency may be obtained.
Decomposition potential: If a small potential of, say, 0.5 volt is applied to two smooth
platinum electrodes immersed in a solution of 1M sulphuric acid, then an ammeter placed in
the circuit will at first show that an appreciable current is flowing, but its strength decreases
rapidly, and after a short time it becomes virtually equal to zero.
TERMS USED IN ELECTRO-GRAVIMETRIC ANALYSIS
10. 10
If the applied potential is gradually increased, there is a slight increase in the current until,
when the applied potential reaches a certain value, the current suddenly increases rapidly with
increase in the e.m.f.
TERMS USED IN ELECTRO-GRAVIMETRIC ANALYSIS
It will be observed, in general, that at the point at which
there is a sudden increase in current, bubbles of gas
commence to be freely evolved at the electrodes.
Upon plotting the current against the applied potential a
curve similar to that shown in Fig.
The point at which the current suddenly increases is
evident, and in the instance under consideration is at
about 1.7 volts
The potential at this point is termed the 'decomposition potential' and it is at this point that the
evolution of both hydrogen and oxygen in the form of bubbles is first observed
We may define the decomposition potential of an electrolyte as the minimum external potential
that must be applied in order to bring about continuous electrolysis
11. 11
If the circuit is broken after the e.m.f has been applied, it will be observed that the reading on
the voltmeter is at first fairly steady, and then decreases, more or less rapidly, to zero.
The cell is now clearly behaving as a source of current, and is said to exert a 'back' or 'counter'
or 'polarisation' e.m.f., since the latter acts in a direction opposite to that of the applied e.m.f
This back e.m.f. arises from the accumulation of oxygen and hydrogen at the anode and
cathode respectively; two gas electrodes are consequently formed, and the potential difference
between them opposes the applied e.m.f.
When the primary current from the battery is shut off, the cell produces a moderately steady
current until the gases at the electrodes are either used up or have diffused away; the voltage
then falls to zero.
This back e.m.f. is present even when the current from the battery passes through the cell and
accounts for the shape of the curve in above Fig.
The back e.m.f is usually regarded as being made up of three components:
a) the reversible back e.m.f.
b) a concentration polarisation e.m.f.; and
c) an activation overpotential
TERMS USED IN ELECTRO-GRAVIMETRIC ANALYSIS
12. 12
a) Reversible back e.m.f. : This is the e.m.f of the voltaic cell set up by the passage of the
electrolysis current. Consider the electrolysis of a molar solution * of zinc bromide between
smooth platinum electrodes.
The application of a potential will result in the deposition of zinc on the cathode (thus
producing a zinc electrode) and liberation of bromine at the anode (thus producing a bromine
electrode).
The reaction at the cathode is:
And at the cathode is:
The potential of the cathode at 25°C can be calculated from the expression
TERMS USED IN ELECTRO-GRAVIMETRIC ANALYSIS
13. 13
b) Concentration Polarisation e.m.f. (Concentration Overpotential): In the electrolysis of an
acidic solution of copper(II) sulphate between platinum electrodes, concentration changes take
place in the solution in the neighborhood of the electrodes.
• At the cathode depletion of copper ions occurs near the surface; the reversible potential of the
copper electrode therefore shifts in the negative direction.
• At the anode accumulation of hydrogen ions (2H2O O2 + 4H+ + 4e-) and perhaps of oxygen
(if the solution is not already saturated with it) causes the reversible potential of the oxygen
electrode to shift in the positive direction.
• Both effects tend to increase the back e.m.f.
• The concentration overpotential is increased by increased current density and decreased by
stirring.
c) Activation Overpotential: This is due to the effect of the potential applied to the electrode on
the activation energy of the electrode reaction
• The effect is most marked when gases are liberated at the electrode, and varies according to
the nature of the electrode material
TERMS USED IN ELECTRO-GRAVIMETRIC ANALYSIS
14. 14
• Overpotential: It has been found by experiment that the decomposition voltage of an
electrolyte varies with the nature of the electrodes employed for the electrolysis and is, in many
instances, higher than that calculated from the difference of the reversible electrode potentials.
• The excess voltage over the calculated back e.m.f is termed the overpotential.
• Overpotential may occur at the anode as well as at the cathode.
• The decomposition voltage ED is therefore:
• where Eo.c. and Eo.a. are the overpotentials at the cathode and anode respectively. The
overpotential at the anode or cathode is a function of the following variables
1. The nature and the physical state of the metal employed for the electrodes. The fact that
reactions involving gas evolution usually require less overpotential at platinised than at
polished platinum electrodes is due to the much larger effective area of the platinised electrode
and thus the smaller current density at a given electrolysis current.
2. The physical state of the substance deposited. Ifit is a metal, the overpotential is usually small;
if it is a gas, such as oxygen or hydrogen, the overpotential is relatively great.
TERMS USED IN ELECTRO-GRAVIMETRIC ANALYSIS
15. 15
3. The current density employed. For current densities up to 0.01 A cm-2, the increase in
overpotential is very rapid; above this figure the increase in overpotential continues, but less
rapidly.
4. The change in concentration, or the concentration gradient, existing in the immediate vicinity
of the electrodes; as this increases, the overpotential rises
• The overpotential of hydrogen is of great importance in electrolytic determinations and
separations.
• It is greatest with the relatively soft metals, such as bismuth (0.4 V), lead (0.4 V), tin (0.5 V),
zinc (0.7 V), cadmium (1.1 V) and mercury (1.2 V)
TERMS USED IN ELECTRO-GRAVIMETRIC ANALYSIS
16. 16
• The overvoltage values given refer to the electrolysis of 0.05M sulphuric acid with a current
density of 0.01 A em -2, and can be compared with the value (0.09 V) for a bright platinum
electrode under similar conditions.
• The existence of hydrogen overpotential renders possible the electro-gravimetric
determination of metals, such as cadmium and zinc, which otherwise would not be deposited
before the reduction of hydrogen ion.
• In alkaline solution, the hydrogen overpotential is slightly higher (0.05-0.03 volt) than in acid
solution.
• Oxygen overpotential is about 0.4-0.5 volt at a polished platinum anode in acid solution, and
is of the order of 1 volt in alkaline solution with current densities of 0.02-0.03 A em - 2.
• As a rule the overpotential associated with the deposition of metals on the cathode is quite
small (about 0.1-0.3 volt) because the depositions proceed nearly reversibly
TERMS USED IN ELECTRO-GRAVIMETRIC ANALYSIS
17. 17
• For the electrolysis of a solution to be maintained, the potential applied to the electrodes of the
cell (Eapp) must overcome the decomposition potential of the electrolyte (ED) (which as shown
above includes the back e.m.f. and also any overpotential effects), as well as the electrical
resistance of the solution.
• Thus, Eapp. must be equal to or greater than (ED + IR), where I is the electrolysis current, and
R the cell resistance.
• As electrolysis proceeds, the concentration of the cation which is being deposited decreases,
and consequently the cathode potential changes.
• If the relevant ionic concentration in the solution is ci , and the ion concerned has a charge
number of 2, then at a temperature of 25°C, the cathode potential will have a value given by:
COMPLETENESS OF DEPOSITION
18. 18
• If the ionic concentration is reduced by deposition to one ten-thousandth of its original value,
thus giving an accuracy of 0.01 per cent in the determination, the new cathode potential will
be:
• It follows that if the original solution contains two cations whose deposition potentials differ
by about 0.25 V, then the cation of higher deposition potential should be deposited without any
contamination by the ion of lower deposition potential.
• In practice, it may be necessary to take steps to ensure that the cathode potential is unable to
fall to a level where deposition of the second ion may occur
COMPLETENESS OF DEPOSITION
19. 19
• If a current is passed through a solution containing copper(II), hydrogen and cadmium(II)
ions, copper will be deposited first at the cathode.
• As the copper deposits, the electrode potential decreases, and when the potential becomes
equal to that given by the hydrogen ions, hydrogen gas will form at the cathode.
• The potential at the cathode will remain virtually constant as long as hydrogen is evolved,
which would mean as long as any water remains, and it is therefore unable to become
sufficiently negative to permit the deposition of cadmium.
• Thus, metal ions with positive reduction potentials may be separated, without external control
of the cathode potential, from metal ions having negative reduction potentials.
ELECTROLYTIC SEPARATION OF METALS
20. 20
• Silver can be readily separated from copper, even though they both have positive reduction
potentials, because the difference between the two values is large (silver, + 0.779 V; copper, +
0.337 V), but as indicated above, when the standard potentials of the two metals differ only
slightly, the electro-separation is more difficult.
• An obvious solution to this problem is to decrease the concentration of one of the ions being
discharged by incorporating it in a complex ion of large stability constant (Section 2.23).
• As an illustration of the kind of result achieved, the deposition potentials for 0.1M solutions of
ions M2+ of the following metals have the values indicated: zinc, + 0.79 V; cadmium, +0.44
V; copper, +0.34 V.
• When 0.1 mole of the corresponding cyanides are dissolved in potassium cyanide to give an
excess concentration of potassium cyanide of O.4M, the deposition potentials become: zinc, +
1.18 V; cadmium, + 0.87 V; copper, + 0.96 V
• An interesting application of these results is to the direct quantitative separation of copper and
cadmium. The copper is first deposited in acid solution; the solution is then made slightly
alkaline with pure aqueous sodium hydroxide, potassium cyanide is added until the initial
precipitate just re-dissolves, and the cadmium is deposited electrolytically
ELECTROLYTIC SEPARATION OF METALS
21. 21
• The ideal deposit for analytical purposes is adherent, dense, and smooth; in this form it is
readily washed without loss.
• Flaky, spongy, powdery, or granular deposits adhere only loosely to the electrode, and for this
and other reasons should be avoided.
• As a rule, more satisfactory deposits are obtained when the metal is deposited from a solution
in which it is present as complex ions rather than as simple ions.
• Thus silver is obtained in a more adherent form from a solution containing the [Ag(CN z )] -
ion than from silver nitrate solution.
• Nickel when deposited from solutions containing the complex ion [Ni(NH3)6] 2+ is in a very
satisfactory state for drying and weighing.
• Mechanical stirring often improves the character of the deposit, since large changes of
concentration at the electrode are reduced, i.e. concentration polarisation is brought to a
minimum
• Increased current density up to a certain critical value leads to a diminution of grain size of the
deposit
CHARACTER OF THE DEPOSIT
22. 22
• Beyond this value, which depends upon the nature of the electrolyte, the rate of stirring, and
the temperature, the deposits tend to become unsatisfactory.
• At sufficiently high values of the current density, evolution of hydrogen may occur owing to
the depletion of metal ions near the cathode.
• If appreciable evolution of hydrogen occurs, the deposit will usually become broken up and
irregular; spongy and poorly adherent deposits are generally obtained under such conditions.
• For this reason the addition of nitric acid or ammonium nitrate is often recommended in the
determination of certain metals, such as copper; bubble formation is thus considerably
reduced.
• Action of NO3
- ion at the copper cathode is represented by:
• The NO3
- ion is reduced to ammonium ion at a lower (i.e. less negative) cathode potential than
that at which hydrogen ion is discharged, and, therefore, acts to decrease hydrogen evolution.
• The nitrate ion acts as a cathodic depolariser. Raising the temperature, say to between 70 and
80°C, often improves the physical properties of the deposit. This is due to several factors,
which include the decrease in resistance of the solution, increased rate of stirring and of
• diffusion.
CHARACTER OF THE DEPOSIT