PG electrolyets ppt_Debanjali Sarkar-4.pptx

Electrochemistry PPT for M. Tech

1. ELECTROCHEMISTRY Presented by Debanjali Sarkar M. Tech. (Dairy Chemistry) 1 st Semester Faculty of Dairy Technology West Bengal University of Animal & Fishery Sciences Mohanpur , Nadia-741252 2024

2. I N D E X Electrolytes & Non-electrolytes Non-Electrolytes Electrolytic Dissociation Arrhenius Equation The Theory of Electrolytic Dissociation Ionic Mobility Ionic Activity Ionic Strength Dissociation Constant Acids and Bases Dissociation Constants for an Acid Dissociation Constants for a Base Ionic Strength Effect on Dissociation Constant Electrode 11/28/2024 2 DC-511: Electrochemistry

3. I N D E X Electrode Potential Nernst Equation Le Chatelier's Principle Buffer Henderson– hasselbalch Equation Buffer-capacity Buffer Index Constituents Contributing to the Buffering Capacity of Milk Redox Reaction in Milk Photo- Oxidation of Milk Conclusion References 11/28/2024 3 DC-511: Electrochemistry

4. ELECTROLYTES AND NON-ELECTROLYTES 11/28/2024 DC-511: Electrochemistry 4

5. ELECTROLYTES & NON-ELECTROLYTES Electrolytes Substances which cause increase in electrical conductivity in solutions (Sharma, 2019). Electrolytes dissociate in the process of conducting the electric current (Sharma, 2019). In other words, electrolyte is an electrical conductor (Sharma, 2019). Electrolytes conduct current by ions rather than by free electrons (as in a metal ) (Sharma, 2019). 11/28/2024 5 DC-511: Electrochemistry

6. NON- ELECTROLYTES A non-electrolyte is a compound that does not conduct electricity when molten or in aqueous solutions (Sharma, 2019). Non-electrolytes give the expected result to osmotic pressure, freezing point and boiling point (Sharma, 2019). They do not significantly increase the electrical conductivity (Sharma, 2019). 11/28/2024 6 DC-511: Electrochemistry

7. ELECTROLYTIC DISSOCIATION To understand electrolytic dissociation, first we have to know about Arrhenius Theory According to this theory, molecules of an electrolyte on going into solution dissociate into ions (Sharma, 2019). The ions are dissimilar as to the elements or elements represented in them and as to the electrical charge which they carry (Sharma, 2019). In each case there are ions that carry positive charge and ions that carry negative charges (Sharma, 2019). The positive and negative charges ions are present in such a number that two types just compensate each other (Sharma, 2019). So, the resulted solution is electrically neutral or balanced (Sharma, 2019) . 11/28/2024 7 DC-511: Electrochemistry

8. ARRHENIUS EQUATION In physical chemistry, the Arrhenius equation is a formula for the temperature dependence of reaction rates. The Arrhenius equation describes the exponential dependence of the rate constant of a chemical reaction on the absolute temperature as k = Ae -Ea/RT Where, k is the rate constant (frequency of collisions resulting in a reaction), T is the absolute temperature, A is the pre-exponential factor or Arrhenius factor or frequency factor. Ea is the molar activation energy for the reaction, R is the universal gas constant. 11/28/2024 8 DC-511: Electrochemistry

9. ARRHENIUS EQUATION Alternatively, the equation may be expressed as k = Ae -Ea/ k B T Where, Ea is the activation energy for the reaction (in the same unit as  kBT ), kB  is the Boltzmann constant. (Arrhenius, S. A.1889) 11/28/2024 9 DC-511: Electrochemistry

10. THE THEORY OF ELECTROLYTIC DISSOCIATION The theory of electrolyte dissociation explains The abnormal behaviors of electrolytes with respect to osmotic pressure, freezing point and boiling point (Sharma, 2019). The electrical conductivity of solutions (Sharma, 2019). The facts of electrolysis (Sharma, 2019). 11/28/2024 10 DC-511: Electrochemistry

11. IONIC MOBILITY In the absence of external electrical field, the ions of a solution are in random motion since all directions are equivalent (Sharma, 2019). When an external electrical field is applied although the randomness of motion will basically remain, one of the directions (Sharma, 2019). The velocity of an ion is the value of this preferential migration towards one of the electrode expressed in cm/s (Sharma, 2019). Ionic mobility = Ionic conductance/ 96500 11/28/2024 11 DC-511: Electrochemistry

12. IONIC ACTIVITY Ionic activity is a measure of how active individual ions are in a solution.  It's a parameter that's related to the number density of ions, but it more realistically expresses the interactions between ions than molar concentration. Ionic activity is related to concentration by the equation 𝑎 i =𝛾 i 𝑐 i , where 𝛾 i is the activity coefficient. The activity coefficient can take different forms depending on how concentration is expressed, such as molarity , molality , or mole fraction ( Pobelov , 2018). 11/28/2024 12 DC-511: Electrochemistry

13. IONIC STRENGTH Ionic strength is a unit less quantity that measures the concentration of ions in a solution, and the total charge of those ions. It's calculated using the formula I=1/2∑c i z i 2 , where c i is the molar concentration of each ion and z i is the charge of each ion.  Ionic strength is important because it affects the properties of a solution, such as the solubility of salts and the dissociation constant. (Solomon & Theodros , 2001). 11/28/2024 13 DC-511: Electrochemistry

14. DISSOCIATION CONSTANT 11/28/2024 DC-511: Electrochemistry 14

15. DISSOCIATION CONSTANT A general example is the dissociation of the compound AB into A+B which can be written as AB A + B (Sharma, 2019). when a solution is prepared by adding AB, it is possible to calculate from the dissociation how much of the material added is in the form of AB, A and B which are constant (Sharma, 2019) . However, before calculation it is important to know that dissociation of AB into A and B is a reversible process (Sharma, 2019) . A and B can assemble back to AB (Sharma, 2019) . The dissociation constant can be written as Ka = {[A] x [B]}/ [AB] (Sharma, 2019). 11/28/2024 15 DC-511: Electrochemistry

16. ACIDS AND BASES What is acid? Arrhenius has proposed that acids are the substances that produce protons H+ in aqueous solutions (Sharma, 2019) . What is Base? According to Arrhenius, bases are the substances which produce OH - (Sharma, 2019) . the behavior of some acids and bases in aqueous solutions was different (Sharma, 2019) . A cids was that the compounds of which are capable of donating protons. Similarly bases are the substance which accepts protons (Sharma, 2019) . 11/28/2024 16 DC-511: Electrochemistry

17. DISSOCIATION CONSTANTS FOR AN ACID The acid dissociation constant (Ka) is an equilibrium constant that measure the strength of acids in solution (Sharma, 2019). The dissociation constant of an acid is used to study the dissociation of weak or strong acids (Sharma, 2019). Dissociation constants are often denoted as Ka-values (Sharma, 2019). A simple example on how to use Ka-values is given here Consider ammonium (NH 4 + ) dissociating reversibly into ammonia (NH 3 ) (Sharma, 2019). NH 4 + NH 3 + H + 11/28/2024 17 DC-511: Electrochemistry

18. DISSOCIATION CONSTANTS FOR A BASE The base dissociation constant (Kb) is a equilibrium constants that measure the strength of bases in solution (Sharma, 2019). Acid dissociation constants (𝐾 a ) and base dissociation constants (𝐾 b ) are equilibrium constants for the reactions of acids and bases with water (Sharma, 2019). The greater the value of an acid's 𝐾 a , the stronger the acid (Sharma, 2019). The greater the value of a base's 𝐾 b , the stronger the base (Sharma, 2019).  [H 3 O + ] [A - ] Acid Dissociation Constant, K a = [HA] Dissociation Constant [BH + ] [OH - ] Acid and Base Formula Base Dissociation Constant, K b = [HB] 11/28/2024 18 DC-511: Electrochemistry

19. IONIC STRENGTH EFFECT ON DISSOCIATION CONSTANT The dissociation constant of a solution increases as the ionic strength of the solution increases. This is because more ions diffuse into the ionic atmosphere. For the reaction of an acid HA with water is shown in the diagram. The equation shows that the acids which dissociate to a greater extent will have larger value of K a are stronger acids while those which have a smaller values of K a are weaker acids. ( Khouri , 2015) HA( aq ) + H 2 O(l) A + ( aq ) + H 3 O + ( aq ) [A + ] [H 3 O + ] K aq [H 2 O] = K a = [HA] 11/28/2024 19 DC-511: Electrochemistry

20. IONIC STRENGTH EFFECT ON DISSOCIATION CONSTANT Similarly for bases Kb with the equation is shown in the diagram (Sharma, 2019) . Higher equilibrium constant of a base indicates that it is a strong base (higher ionic strength) while the smaller value a weak base (lower ionic strength) (Sharma, 2019) . B( aq ) + H 2 O (l) BH + ( aq ) + OH + ( aq ) [BH + ] [ OH + ] K eq [H 2 O] = K b = [B] 11/28/2024 20 DC-511: Electrochemistry

21. ELECTRODE 11/28/2024 DC-511: Electrochemistry 21

22. ELECTRODE An electrode is an electrical conductor used to make contact with a nonmetallic part of a circuit (e.g. a semiconductor, an electrolyte, a vacuum or air). Electrodes are essential parts of batteries that can consist of a variety of materials (chemicals) depending on the type of battery. Michael Faraday coined the term " electrode" in 1833; the word recalls the Greek ἤλεκτρον ( ḗlektron , "amber") and ὁδός ( hodós , "path, way"). The  electrophore , invented by Johan Wilcke  in 1762, was an early version of an electrode used to study static electricity. ( Whitaker & Harry ,2007).  11/28/2024 22 DC-511: Electrochemistry

23. ELECTRODE POTENTIAL In electrochemistry, electrode potential is the voltage of a galvanic cell built from a standard reference electrode and another electrode to be characterized.   By convention, the reference electrode is the standard hydrogen electrode (SHE). It is defined to have a potential of zero volts. It may also be defined as the potential difference between the charged metallic rods and salt solution. The electrode potential has its origin in the potential difference developed at the interface between the electrode and the electrolyte. It is common, for instance, to speak of the electrode potential of the M + /M  redox couple. (Hamel, 1964) 11/28/2024 23 DC-511: Electrochemistry

24. Standard Electrode Potential of Zinc Electrode 11/28/2024 DC-511: Electrochemistry 24

25. ELECTRODE POTENTIAL The measurement is generally conducted using a three-electrode setup working electrode, counter electrode, reference electrode (standard hydrogen electrode or an equivalent). Historically, two conventions for sign for the electrode potential have formed convention "Nernst–Lewis–Latimer" (sometimes referred to as "American"), convention "Gibbs–Ostwald–Stockholm" (sometimes referred to as "European") 11/28/2024 25 DC-511: Electrochemistry

26. Three-electrode setup for measurement of electrode potential 11/28/2024 DC-511: Electrochemistry 26

27. NERNST EQUATION The Nernst equation has a physiological application when used to calculate the potential of an ion of charge z across a membrane. ( Orna et al ., 1989) This potential is determined using the concentration of the ion both inside and outside the cell RT [ion outside cell] RT ion outside cell E = ln = 2.3026 log 10 ZF [ion inside cell] ZF ion inside cell 11/28/2024 27 DC-511: Electrochemistry

28. LE-CHATELIER’S PRINCIPLE 11/28/2024 DC-511: Electrochemistry 28

29. LE CHATELIER'S PRINCIPLE In chemistry, Le Chatelier's principle is a principle used to predict the effect of a change in conditions on chemical equilibrium.  Other names include  Chatelier's principle, Braun–Le Chatelier principle, Le Chatelier –Braun principle or the equilibrium law. The principle is named after French chemist Henry Louis Le Chatelier  who enunciated the principle in 1884 by extending the reasoning from the Van 't Hoff relation of how temperature variations changes the equilibrium to the variations of pressure and what's now called chemical potential, and sometimes also credited to Karl Ferdinand Braun, who discovered it independently in 1887. ( Helmenstine & Anne Marie,2020) 11/28/2024 29 DC-511: Electrochemistry

30. LE CHATELIER'S PRINCIPLE It can be defined as: If the equilibrium of a system is disturbed by a change in one or more of the determining factors (as temperature, pressure, or concentration) the system tends to adjust itself to a new equilibrium by counteracting as far as possible the effect of the change  - Le Chatelier's principle, Merriam-Webster Dictionary In scenarios outside thermodynamic equilibrium, there can arise phenomena in contradiction to an over-general statement of Le Chatelier's principle. Le Chatelier's principle is sometimes alluded to in discussions of topics other than thermodynamics. ( Helmenstine & Anne Marie,2020) 11/28/2024 30 DC-511: Electrochemistry

31. BUFFER 11/28/2024 DC-511: Electrochemistry 31

32. BUFFER Solutions with stable hydrogen ion concentration and therefore usually with no change in pH (Sharma, 2019) . which is almost independent of dilution and changing very little with small additions of a strong acid or alkali (Sharma, 2019) . In simple terms it can also be defined as a solution which resists any change of pH when a small amount of a strong acid or a strong base is added to it, is called a buffer solution or simply as a buffer (Sharma, 2019) . buffers have acidity and reserve alkalinity (Sharma, 2019) . 11/28/2024 32 DC-511: Electrochemistry

33. BUFFER There are two types of buffers, acid buffer and basic buffer. A buffer solution containing large amounts of a weak acid, and its salt with a strong base, is termed as an acid buffer. Acid buffer solutions have pH on the acidic side i.e., pH is less than 7 at 298 K. The pH of an acid buffer is given by the equation in the diagram. CH3COOH and CH3COONa Where K a is the acid dissociation constant of the weak acid [salt] pH = pK a + ln [acid] 11/28/2024 33 DC-511: Electrochemistry

34. BUFFER A buffer solution containing relatively large amounts of a weak base and its salt with a strong acid is termed as a basic buffer. Such buffers have pH on the alkaline side i.e., pH is higher than 7 at 298 K. e.g.: NH 4 OH and NH 4 Cl The pH of a basic buffer is given by the equation in the diagram. Where K b is the base dissociation constant of the weak base. These equations are called Henderson Hasselbalch equations. [salt] pOH = pK b + ln [base] 11/28/2024 34 DC-511: Electrochemistry

35. HENDERSON–HASSELBALCH EQUATION In chemistry and biochemistry, the Henderson– Hasselbalch equation [Base] pH = pK a + log 10 [Acid] relates the pH of a chemical solution of a weak acid to the numerical value of the acid dissociation constant, Ka, of acid and the ratio of the concentrations, [Base]/[Acid] of the acid and its conjugate base in an equilibrium (Sharma, 2019) . 11/28/2024 35 DC-511: Electrochemistry

36. GOOD'S BUFFER Good's buffers (also Good buffers) are twenty buffering agents for biochemical and biological research selected and described by Norman Good and colleagues during 1966–1980. Most of the buffers were new  zwitterionic  compounds prepared and tested by Good and coworkers for the first time, though some (MES, ADA, BES,  Bicine ) were known compounds previously overlooked by biologists. Before Good's work, few hydrogen ion buffers between pH 6 and 8 had been accessible to biologists, and very inappropriate, toxic, reactive and inefficient buffers had often been used. Many Good's buffers became and remain crucial tools in modern biological laboratories. Because most biological reactions take place near-neutral pH between 6 and 8, ideal buffers would have  p K a  values in this region to provide maximum buffering capacity there (Good et al .,1966). 11/28/2024 36 DC-511: Electrochemistry

37. BUFFER-CAPACITY The effectiveness of any buffer is described in terms of its buffer capacity. It is defined as, 'the number of equivalents of a strong acid (or a strong base) required to change the pH of one litre of a buffer solution by one unit, keeping the total amount of the acid and the salt in the buffer constant. The buffer capacity of a buffer is maximum when acid to salt or base to salt ratio is equal to 1 i.e., it contains equal number of moles of acid (or base) and the salt (Sharma, 2019). 11/28/2024 37 DC-511: Electrochemistry

38. BUFFER INDEX This can be defined as the differential ratio of the increase in the amount of strong acid or strong base added, to pH variation (Sharma, 2019). The number of gram equivalents of acid or base that must be added to one liter of a buffer solution to change its pH by one unit. β = dB/ dpH , where 𝛽 is the buffer index, 𝑑𝐵 is the number of gram equivalents of acid or base added to one liter of buffer solution, and 𝑑 (𝑝𝐻 ) is the change in pH after the addition of acid or base. The field of application of both notions is different: the buffer capacity is used in the quantitative chemical analysis and the buffer index in studying biological systems. 11/28/2024 38 DC-511: Electrochemistry

39. CONSTITUENTS CONTRIBUTING TO THE BUFFERING CAPACITY OF MILK Milk contains many acidic and basic groups. These groups have a buffering action. The buffering capacity of solution can be expressed as which is the molar quantity of acid or base needed to change the pH of 1 litre of solution by one unit. Where n is number of equivalents of added strong base. Note that addition of dn moles of acid will change pH by exactly the same value but in opposite direction. β = d n / dpH 11/28/2024 39 DC-511: Electrochemistry

40. CONSTITUENTS CONTRIBUTING TO THE BUFFERING CAPACITY OF MILK The ionizable groups of the proteins, the phosphates, and the citrates mainly determine the acidity and the buffering capacity of milk. There will be variation in the titration curves due to the considerable variation in the concentration of these substances. Ionizable groups of the whey proteins and casein molecules are not exposed. 11/28/2024 40 DC-511: Electrochemistry

41. CONSTITUENTS CONTRIBUTING TO THE BUFFERING CAPACITY OF MILK Test Samples Buffering Capacity (%) Lactogen 15.29 Nestogen 9.21 Nan 11.92 Farex 18.56 Lactodex 20.13 Amul Spray 18.48 Positive Control 0.05 Negative Control 0.08 11/28/2024 41 DC-511: Electrochemistry

42. CONSTITUENTS CONTRIBUTING TO THE BUFFERING CAPACITY OF MILK The presence of Ca 2+ ions strongly modifies the ionization of di and triprotic acids such as phosphoric acid and citric acid. Lowering of the pH of milk will make calcium phosphate soluble because it is not soluble in normal pH of milk whereas colloidal phosphate will increase when the pH is increased. The Magnesium citrate and protein affect the composition and quantity of colloidal phosphate (Sharma, 2019). 11/28/2024 42 DC-511: Electrochemistry

43. CONSTITUENTS CONTRIBUTING TO THE BUFFERING CAPACITY OF MILK 11/28/2024 DC-511: Electrochemistry 43

44. REDOX REACTIONS IN MILK 11/28/2024 DC-511: Electrochemistry 44

45. REDOX REACTION IN MILK The oxidation reduction reactions involve transfer of electrons between atoms or molecules. Transfer of oxygen (O) or hydrogen (H) or both also may occur. Oxidation is loss of electrons while reduction is the gain of electrons. In a redox system when half of the system is having oxidation reaction and the other half is having a reduction reaction, there will be no flow of electrons either in to the system or go out of the system. In normal milk there are several complicated biological systems with varying composition and concentration. In addition to this microorganism gaining entry in to milk contribute certain redox systems to it depending upon the type of the organisms. 11/28/2024 45 DC-511: Electrochemistry

46. REDOX REACTION IN MILK Methylene blue is reduced by freshly drawn milk when it is drawn from udder anaerobically indicating a more negative potential than methylene blue system. Apart from this the chief oxidation and reduction systems present in milk are Ascorbate , lactate and riboflavin. 11/28/2024 46 DC-511: Electrochemistry

47. REDOX REACTION IN MILK The ascorbic content of fresh milk is about 0.25 meq litre-1. the milk is drawn from the udder, all the ascorbate present in milk will be in its reduced form but reversible oxidation to dehydro ascorbate occurs at rates dependent on temperature, copper (Cu) and oxygen (O2) concentration. Preventing the contamination with copper (Cu) and by deaeration the ascorbate content can be preserved. 11/28/2024 47 DC-511: Electrochemistry

48. REDOX REACTION IN MILK The redox potential E of milk and standard potential E of some important systems in milk are plotted against pH is presented in the Fig. Individual milk samples in equilibrium with air generally have E h ’s in the range of +0.25 to +0.35 V at 25℃ at their normal pH of milk i.e 6.6 to 6.7. Fresh raw whole milk will reduce 0.6 to 0.8 m mol of ferricyanide to ferrocyanide per liter at 50 ℃ for 20 min. 11/28/2024 48 DC-511: Electrochemistry

49. REDOX REACTION IN MILK Concentration of lactate- pyruvate system in milk is negligible. Enzymatic activation of this system would influence the redox system. At higher pH the aldehyde group of lactose is oxidizable to carboxyl group, but this reaction is not a reversible and hence it will not influence the Eh at pH of 6.6. Redox reactions in milk systems are influenced by heat treatment, by concentration of O 2 and metal ions such as Cu 2+ , by exposure to light and by oxido redcutases of milk and or micro organisms (Sharma, 2019). 11/28/2024 49 DC-511: Electrochemistry

50. PHOTO-OXIDATION OF MILK 11/28/2024 DC-511: Electrochemistry 50

51. PHOTO- OXIDATION OF MILK Photo-oxidation is a process that occurs in milk when it is exposed to light, which can degrade the milk's proteins, lipids, and vitamins.  This can lead to a loss of nutritional value and sensory characteristics, and can make the milk taste and smell off.   Photo-oxidation can occur during storage, transportation, and display in grocery stores.  Milk and other lipid containing products are susceptible to oxidative deterioration. Light from either natural or artificial sources catalyzes certain chemical reactions, resulting in the development of off‐flavors and the breakdown of pigments and vitamins. 11/28/2024 51 DC-511: Electrochemistry

52. PHOTO- OXIDATION OF MILK 11/28/2024 DC-511: Electrochemistry 52

53. CONCLUSION In a nutshell, it can be concluded that electrochemistry deals with the facts like electrolytes, non-electrolytes, dissociation of electrolytes, ionic mobility, ionic strength, ionic activity, acids, bases, dissociation constant of acids and bases, buffers, redox reaction in milk, photo-oxidation of milk etc.  Electrochemical techniques are used to analyze milk for a variety of substances, including antioxidants, heavy metals, and endocrine disruptors. For some electro analytical procedures, it is also necessary to employ milk pretreatment processes before running the electrochemical test. These pre-treatment steps can be comprised of acid digestion, centrifugation, filtration, etc., and finally dilution with a buffer or electrolyte.  11/28/2024 53 DC-511: Electrochemistry

54. REFERENCES Sharma. K. P, 2019,Physical chemistry of milk Whitaker, Harry (2007). Brain, Mind and Medicine: Essays in eighteenth-century neuroscience. New York, NY: Springer. p. 140. ISBN 978-0387709673. Orna , M. V., Stock , John (1989). Electrochemistry, past and present. Columbus, OH: American Chemical Society. ISBN 978-0-8412-1572-6. OCLC 19124885 Arrhenius, S. A. (1889). "Über die Dissociationswärme und den Einfluß der Temperatur auf den Dissociationsgrad der Elektrolyte". Z. Phys. Chem. 4: 96–116. doi:10.1515/zpch-1889-0408 Abbas , Z. & Ahlberg , E. 2019. Activity Coefficients of Concentrated Salt Solutions: A Monte Carlo Investigation, Journal of Solution Chemistry, 48(17), pp. 1222-1243. 11/28/2024 54 DC-511: Electrochemistry

55. REFERENCES Petrucci , R., H ., Harwood., William, S ., Herring, F. Geoffrey (2002). General Chemistry (8th ed.). Prentice Hall. p. 718. ISBN 0-13-014329-4 . Good, N. E ., Izawa, Seikichi (1972). Hydrogen ion buffers. Methods Enzymol . Vol. 24. pp. 53–68. doi:10.1016/0076-6879(72)24054-x. ISBN 978-0-12-181887-6. PMID  4206745 Anson, F. C .; "Common sources of confusion; Electrode Sign Conventions," J. Chem. Educ., 1959, 36, p. 394 . Atkins, P.W. (1993). The Elements of Physical Chemistry (3rd ed.). Oxford University Press . Münster , A. (1970), Classical Thermodynamics, translated by E.S. Halberstadt , Wiley– Interscience , London, ISBN 0-471-62430-6. 11/28/2024 55 DC-511: Electrochemistry

56. T H A N K Y O U 11/28/2024 56 DC-511: Electrochemistry