electrochemistry

Chemistry 120 with Dr. Zachary Martinez

Announcements

• Your ALEKS assignment is due Sunday at 10 pm.

• Weekly Practice Assignments (WPA) due Sunday at 10 pm.

Learning Objectives

• Define electrochemistry

• Define oxidation and reduction reactions

• Determine oxidation states for elements in molecules

• Determine oxidizing and reducing agents in a chemical reaction

• Balance a redox reaction in an acidic solution

Electrochemistry

• Definition: Electrochemistry is the study of the interchange of chemical and electrical energy.

• Concerns two processes:

  1. The generation of an electric current from a spontaneous chemical reaction

  2. The use of a current to produce chemical change

Oxidation-Reduction Reactions

• Definition: Oxidation-Reduction reactions, often referred to as "redox reactions," are reactions in which one or more electrons are transferred.

• Oxidation States: A concept that provides a means to keep track of electrons in a redox reaction according to certain rules:

  • The sum of the oxidation states equals zero for an electrically neutral compound.

  • The sum of the oxidation states of an ion equals the overall charge of the ion.

Oxidation States of Elements

• The document lists atomic numbers, symbols, and properties of various elements, highlighting groups such as alkaline earth metals, alkali metals, noble gases, etc.

Determining Oxidation States

• Examples of calculating oxidation states:

  • XeOF4

  • UO2 2+

  • Na4Fe(OH)6

  • (NH4)2Ce(SO4)3

Sample Questions on Oxidation States

• What is the oxidation state of manganese in KMnO4?

  • A. +1 B. +8 C. +7 D. +4

• What is the oxidation state of carbon in the oxalate ion, C2O4 2-?

  • A. +1 B. +4 C. -2 D. +3

• What is the oxidation state of nickel in K2Ni(CN)4?

  • A. +2 B. +1 C. -2 D. -1

Characteristics of Redox Reactions

• Oxidation: Loss of electrons, results in an increase in oxidation state

• Reduction: Gain of electrons, results in a decrease in oxidation state

• Oxidizing Agent: A reactant that accepts electrons from another reactant

• Reducing Agent: A reactant that donates electrons to another reactant

• Example Reaction:
  $2Na_{(s)} + Cl_2(g) <br>ightarrow 2NaCl_{(s)}$

Determining Reducing and Oxidizing Agents

• Example Reaction 1: $MnO_4^{-} + HSO_3^{-} ightarrow Mn^{2+} + SO_4^{2-}$

  • Question: Which element is oxidized?

  • A. Mn B. O C. S D. H

• Example Reaction 2: $BiO_3^{-} + Mn(OH)_2 ightarrow BiO(OH) + MnO_4^{-}$

  • Question: What is the oxidizing agent?

  • A. Bi B. O C. Mn D. H

Balancing Redox Reactions in Acidic Solution

Steps to Balance a Redox Reaction:

1. Write separate equations for the oxidation and reduction half-reactions.

2. For each half-reaction:
   a) Balance all elements except hydrogen and oxygen.
   b) Balance oxygen by adding H2O.
   c) Balance hydrogen by adding H+.
   d) Balance the charge by using electrons.

3. If necessary, multiply one or both half-reactions by an integer to equalize the number of electrons transferred.

4. Add the half-reactions and cancel identical species.

5. Check that the elements and charges are balanced.

Example of Balancing Redox Reactions

• Example Reaction:
  $Cr_2O_7^{2-} + Cl^{-} <br>ightarrow Cr^{3+} + Cl_2$

• Balancing Process:

  • Oxidation half-reaction:

  • Reduction half-reaction:

• Example Reaction:
  $BiO_3^{-} + Mn(OH)_2 <br>ightarrow BiO(OH) + MnO_4^{-}$

Electrons Transferred in Redox Reactions

• Question Example:
  How many electrons are transferred in the following unbalanced equation in an acidic solution?
  $MnO_4^{-} + Fe_{(s)} <br>ightarrow Fe^{2+} + Mn^{2+}$

• Answer Choices:

  • A. 5 e- B. 7 e- C. 10 e- D. 2 e-

Conclusion

• The document concludes with details on complex examples of redox reactions and their balancing in acidic solutions.

• Emphasis is placed on thorough understanding of oxidation states, redox agents, and methods of balancing equations in a systematic way.