Chemistry Lab/Electrochemistry

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This page refers to the 2011 and 2012 foci of Chem Lab.

Basic Information

A redox reaction, or an oxidation/reduction reaction, occurs when one reactant is oxidized, or loses electrons, and one reactant is reduced, or gains electrons. A simple way to tell the difference is OIL RIG (Oxidation Is Losing; Reducing Is Gaining) or LEO says GER (Lose Electrons - Oxidize; Gain Electrons - Reduce). The oxidizing agent is reduced, and the reducing agent is oxidized. A half-reaction is exactly what it sounds like - half a reaction. It focuses exclusively on one portion of the reaction, either oxidation or reduction.

Balancing Oxidation/Reduction Reactions

Redox reactions follow a simple set of steps to solve.

  1. Split it into 2 half-reactions, one being oxidation and the other being reduction. The reactant being oxidized loses electrons, so they start out without a charge and end up with a positive charge and an electron. The reactant being reduced gains electrons, so they start out charged and with an electron and end up uncharged. Keep in mind that the charge must be neutral on both sides; i.e., should the reducing agent lose 2 electrons, it must end up with a charge of +2 and with 2 extra electrons. Example: Cu (s) ----> Cu2+ + 2 e- An example of a reduction reaction would be 2 Ag+ (aq) + 2 e- ------> 2 Ag (s)
  2. If it's in an acidic medium...
    1. Balance all non-hydrogen or oxygen elements
    2. Balance oxygen by adding H2O to the appropriate side
    3. Balance hydrogen by adding H+ to the appropriate side
    4. Balance the charge by adding e-
  3. Multiply each reaction by an integer so that there are the same number of electrons on each side (i.e. they cancel out)
  4. Combine the half-reactions and cancel
  5. If it's in a basic medium, add OH- to each side until all H+ is gone; then, cancel again

Activity Series

One task participants may be asked to complete in this event is to construct an activity series based on what ions react with others.

Electrochemical Cells

Eelectrochemical cells results in an exchange of electrons in a redox reaction. There are two main types of electrochemical cells.

Voltaic Cells

A voltaic, or galvanic, cell is composed of two metals connected by a salt bridge. It uses the electron exchange to generate the current. It consists of two half-cells, each of which contains a metal solution with that metal submerged in it.

The cell in which oxidation occurs is called the anode, and the cell in which reduction occurs is called the cathode. You can remember this by knowing that reduction has a "c" in it, and cathode starts with a "c". Electrons flow from the anode to the cathode.

Electrolytic Cells

Electrolytic cells use a current to decompose chemical compounds.

Electron Potential