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Understanding Concentration and Redox Reactions in Electrochemistry

This chapter covers essential concepts in electrochemistry, including concentration measurements like percent composition, molarity, and molality. It explains mole fraction and the distinctions between redox reactions in both voltaic and electrolytic cells. Key principles such as oxidation states, balancing half-reactions, and the Nernst Equation are discussed for various conditions. Techniques for balancing equations in acidic and basic solutions are provided, focusing on how to handle H+ and OH- ions effectively. This guide serves as a fundamental resource for mastering electrochemical processes.

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Understanding Concentration and Redox Reactions in Electrochemistry

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  1. Chapter 4 solution basics and electrochemistry

  2. Concentration • Percent composition by mass • (Mass of wanted/ mass of solution (whole))x 100% • Molarity • M = mol of solute/ L of solution • molality • m= mol of solute/ kg of solvent • Mole Fraction • X = mole of desired / mole total

  3. Redox • Oxidation Number and normal half reactions see handout • Remember • OILRIG or LEO the lion goes GER • Red Cat • An Ox • Fat Cat

  4. Voltaic cells are spontaneous Separated into two cells Is a battery Anode is negative Cathode is positive AnOx Red Cat Fat Cat Electrolytic cells are forced to work by using a power source Single container NEEDS a battery Anode is positive Cathode is negative AnOx Red Cat Fat Cat EPA (electrolytic positive anode)

  5. Voltaic cells • E cell = E oxi + E red (all at standard condiditons) • What ever half reaction has the highest (most positive) E value on the reduction potential table is the one that is reduced, the other gets flipped to become oxidized.

  6. When cell is not at standard conditions, use Nernst Equation E = Eo – RT ln Q nF This formula is not given to you…. Or You can explain what is happening with LeChatlier’s principle

  7. Acid Redox • Write separate equations for the oxidation and reduction half-reactions. • For each half-reaction, • Balance all the elements except hydrogen and oxygen • Balance oxygen using H2O • Balance hydrogen using H+ • Balance the charge using electrons • If necessary, multiply one or both balanced half-reactions by an integer to equalize the number of electrons transferred in the two half-reactions. • Add the half-reaction, and cancel identical species • Check that the elements and charges are balanced

  8. Base Redox • Use the half-reaction method as specified for acidic solutions to obtain the final balanced equation as if H+ were present • To both sides of the equation obtained above, add a number of OH- ions that is equal to the number of H+ ions. (eliminate H+ by forming H2O) • Form H2O on the side containing both H+ and OH- ions, and eliminate the number of H2O molecules that appear on both sides of the equation. • Check that elements and charges are balanced.

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