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Electrochemistry Identifying the anode and cathode of electrochemical cells: 1. In standard reduction potential tables the species with the highest Eo value is the anode. 2. Standard reduction potential tables list metals in order of decreasing reactivity from the top down. Understanding the need for a standard half-cell for electrochemical cells: 1. The designation of the Eofor the H2 (1M)/H+ standard half-cell is not arbitrary but based on the chemistry of H+ and H2. 2. A standard half-cell is not necessary. Understanding current in an electrochemical cell: 1. Electrons enter the electrolyte at the cathode, move through the electrolyte, and emerge at the anode 2. In an electrochemical cell the anions and the cations move until their concentration in both half-cells is equal. Understanding the charge on the anode and cathode in electrochemical cells: 1. The anode is negatively charged and because of this it attracts cations. The cathode is positively charged and because of this it attracts anions. 2. The anode is positively charged because it has lost electrons. The cathode is negatively charged because it has gained electrons. Identifying the anode and cathode in electrolytic cells: 1. No reactions will occur at the surface of inert electrodes 2. Processes at the anode and cathode are reversed in electrochemical and electrolytic cells; in electrochemical cells oxidation occurs at the anode and reduction at the cathode; while in electrolytic cells oxidation occurs at the cathode and reduction at the anode. Predicting the products of electrolysis and the magnitude of the applied e.m.f.: 1. Water does not react during the electrolysis of aqueous solutions. 2. There is no association between the calculated e.m.f. of an electrolytic cell and the magnitude of the applied voltage. Electric Circuit: 1. Charge Law: a. In a cell the anions and cations attract each other and this affects the movement of ions to the electrodes. b. Electrons move through electrolytes by being attracted to positive ions in solution 2. Electric Current: a. Protons flow in metallic conductors. b. Electricity in chemistry and physics is different because the current flows in opposite directions 3. Potential Difference and e.m.f. a. A potential difference between two points is solely due to differences in the concentration of charge at the points.

b. There is a high concentration at the anode and a low concentration at the cathode. Oxidation-reduction: 1. Assigning oxidation states a. The oxidation state of an element is the same as the charge of the monatomic ion of that element. b. Oxidation numbers or states can be assigned to polyatomic molecules and/or polyatomic ions 2. Identifying Oxidation-reduction Equations Using Oxidation Numbers: a. In an equation, changes in the charges of polyatomic species can be used to identify redox equations. b. In an equation, changes in the charges of polyatomic can be used to determine the number of electrons removed from, or gained by, reacting species. 3. Using Other Definitions to Identify Oxidation-reduction Equations: a. In all chemical equations, the definitions of oxidation as the addition of oxygen, and reduction as the removal of oxygen, can be used to identify oxidation and reduction. 4. The Interdependence of Oxidation and Reduction Processes: a. Oxidation and reduction processes can occur independently.

Source: Garnett, P. J., & Treagust, D. F. (1992). Conceptual difficulties experienced by senior high school students of electrochemistry: Electrochemical (Galvanic) and electrolytic cells. Journal Of Research In Science Teaching, 29 (10), 1079-1099



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