29. In corrosion, the metal is oxidised by loss of electrons to oxygen and formation of oxides. The products of electrolysis of molten sodium chloride are sodium metal and chlorine gas. which corrodes itself but saves the other object. A. Inert electrodes do not participate in the reaction but provide their surface for oxidation or reduction reactions and for the conduction of electrons. During the electrolysis of aqueous sodium chloride, oxidation of chloride ion is preferred at anode due to over-potential of oxygen. The cell potential is measured in volts. Assertion : Λ m for weak electrolytes shows a sharp increase when the electrolytic solution is diluted. The change in molar conductivity for weak electrolytes with dilution is due to increase in degree of dissociation. Michael Faraday was the first scientist who described the quantitative aspects of electrolysis. Zinc is used for galvanization because it is more reactive than iron and will consequently sacrifice itself, leaving the iron untouched by rust. The electrode potential for any given concentration of Zn2+ ions is given as E(Zn2+/Zn) = Eo(Zn2+/Zn) -RT/2Fln1/[Zn2+(aq)]. The competing reduction reaction at the cathode during the electrolysis of aqueous sodium chloride is H+ (aq) + e– → ½ H2 (g). At 298 K, Eom (KCl) - Eom (NaCl) = Eom (KBr) - Eom (NaBr) = Eom (KI) - Eom (NaI) ≈ 23.4 S cm2 mol–1 Kohlrausch observed certain regularities for a number of strong electrolytes. Weak electrolytes have lower degree of dissociation at higher concentrations and hence for such electrolytes, the change in Λm with dilution is due to increase in the degree of dissociation and consequently the number of ions in total volume of solution that contains 1 mol of electrolyte. Acetic acid is an example of a weak electrolyte. Tin is less reactive than iron, while sodium is highly reactive and catches fire when subjected to air and moisture. The corrosion of metal is prevented by covering the surface with chemical like bisphenol. An electrochemical method is to provide a sacrificial electrode of another metal (like Mg, Zn, etc.) The conductance of electricity by ions present in the solutions is called electrolytic or ionic conductance. Pure water has small amounts of hydrogen and hydroxyl ions (~10–7M) which lend it very low conductivity (3.5 × 10–5 S m–1). The copper electrode of the Daniell cell is called as reduction half cell and the zinc electrode is called as oxidation half cell, where the respective reactions take place. The reaction with higher value of E0 is preferred. Besides Na+ and Cl– ions, we also have H+ and OH– ions along with the solvent molecules, H2O in aqueous sodium chloride solution electrolyses to give the products NaOH, Cl2 and H2. Corrosion is an electrochemical phenomenon. Bisphenol is commonly used to prevent corrosion in the cans used for storage of food and beverages. The reaction at anode with lower value of Eo is preferred and therefore, water should get oxidised in preference to Cl– (aq). The magnitude of conductivity depends on nature of the material and the temperature at which the measurements are made. In Daniel cell of Cu2+ and Zn2+ ions, E(cell) increases with increase in the concentration of Cu2+ ions and decreases with increase in the concentration of Zn2+ ions. Thus, the degree of dissociation can be calculated at any concentration as, where is the degree of dissociation, is the molar conductance at concentration C … Log in. Assertion: Am for weak electrolytes shows a sharp increase when the electrolytic solution is diluted. Platinum is used as inert electrode. The amount of chemical reaction which occurs at any electrode during electrolysis by a current is proportional to the quantity of electricity passed through the electrolyte. The two different portions of the Daniell cell on which the two half reactions occurs are called as half-cells. However, on account of over-potential of oxygen, reaction Cl- (aq) → 1/2Cl2 (g) + e- is preferred. The limiting value of molar conductance corresponds to degree of dissociation equal to 1 i.e., the whole of the electrolyte dissociates. Thus, there exists a potential difference between the electrodes. E(cell) depends on the concentration of both Cu2+ and Zn2+ ions. Magnesium is used as a sacrificial electrode to prevent corrosion. This is Faraday's first law of electrolysis. This is obtained by applying Nernst equation. The charge on 1g of Mn4+ ion is 3.85 × 105 C. Charge on one ion of Mn4+ = 4 × 1.6 × 10-19 C Thus, charge on one g ion of Mn4- = 4 × 1.6 10-19 × 6.02 × 1023 = 3.85 × 105 C. The cell potential is the difference between the electrode potentials of the cathode and anode and is called the cell electromotive force of the cell, when no current is drawn through the cell. Faraday published his results during 1833-34 in the form of Faraday’s two laws of electrolysis. electrochemistry; cbse; class-12; Share It On Facebook Twitter Email. Free PDF Download of CBSE Chemistry Multiple Choice Questions for Class 12 with Answers Chapter 3 Electrochemistry. Weak electrolytes have lower degree of dissociation at higher concentrations and hence for such electrolytes, the change in Λm with dilution is due to increase in the degree of dissociation and consequently the number of ions in total volume of solution that contains 1 mol of electrolyte. It cannot be unity. In an electrochemical cell, the decrease of free energy (-ΔG0)provides a measure of electrical work done (E0cell). Since corrosion involves redox reaction with release of energy used for non-spontaneous chemical reaction, it is an electrochemical phenomenon. The cell potential is given by Eo = EoR - EoL As EoL for standard hydrogen electrode is zero, Eo = EoR – 0 = EoR. The number of mole of electrons required for the reduction of one mole of Mg2+ ions are 2e-. Solution : In weak electrolyte the degree of dissociation is very small. The molar conductivity of a weak electrolyte remains approximately constant as the concentration increases. The standard electrode potential of Li+/Li at 298 K is -3.05 V. Lithium has the lowest electrode potential indicating that lithium ion is the weakest oxidising agent, while lithium metal is the most powerful reducing agent in an aqueous solution. The cation Na+ is reduced at the cathode Na+ + e– → Na and one anion Cl– is oxidised at the anode Cl–→ ½Cl2+e– to give sodium metal and chlorine gas. Standard hydrogen potential is zero at all temperatures. The degree of dissociation of week electrolyte increases as_____? Class 12th Chemistry - 3 Electrochemistry MCQs, https://shikshahouse.com/wp-content/uploads/2018/12/17-Electrochemistry.jpg, https://shikshahouse.com/wp-content/uploads/2018/09/Logo-png-150x109.png, COPYRIGHT © 2018 - Shiksha House. Electrical conductance through metals is called metallic or electronic conductance and is due to the movement of electrons.

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