AP Chemistry Questions on Redox Titrations and Electrochemical Cells

🧪 Quick Study Guide

• ⚛️ Oxidation-Reduction (Redox) Reactions: Reactions involving the transfer of electrons. Oxidation is loss of electrons (OIL), and reduction is gain of electrons (RIG).
• 🔢 Oxidation Numbers: A number assigned to an element in a chemical combination that represents the number of electrons lost (or gained, if the number is negative) by an atom of that element in the compound.
• ⚖️ Balancing Redox Reactions: Use either the half-reaction method (splitting the reaction into oxidation and reduction half-reactions) or the oxidation number method.
• 🌡️ Redox Titrations: A laboratory method used to determine the concentration of an analyte by reacting it with a titrant in a redox reaction. A common example includes titrations involving $KMnO_4$.
• ⚡ Electrochemical Cells: Devices that convert chemical energy into electrical energy (galvanic/voltaic cells) or electrical energy into chemical energy (electrolytic cells).
• ⚗️ Galvanic (Voltaic) Cells: Spontaneous redox reactions generate electricity. The cell potential ($E_{cell}$) is positive.
• 🔋 Electrolytic Cells: Non-spontaneous redox reactions are driven by an external power source. The cell potential ($E_{cell}$) is negative.
• 📏 Nernst Equation: Relates the cell potential to the standard cell potential and the reaction quotient: $E = E^o - \frac{RT}{nF}lnQ$, where R is the gas constant, T is temperature, n is the number of moles of electrons transferred, F is Faraday's constant, and Q is the reaction quotient.
• 🔑 Standard Reduction Potential ($E^o$): The potential of a half-cell under standard conditions (298 K, 1 atm, 1 M). Used to calculate $E_{cell}$. $E_{cell}^o = E_{cathode}^o - E_{anode}^o$

Practice Quiz

1. Which of the following statements is TRUE regarding oxidation and reduction?
   1. Oxidation involves the gain of electrons.
   2. Reduction involves the loss of electrons.
   3. Oxidation is always accompanied by reduction.
   4. Oxidation and reduction are independent processes.


2. What is the oxidation number of chromium in $K_2Cr_2O_7$?
   1. +2
   2. +3
   3. +6
   4. +12


3. In a voltaic cell, where does oxidation occur?
   1. At the cathode
   2. At the anode
   3. At the salt bridge
   4. In the electrolyte solution


4. Which of the following factors does NOT affect the cell potential of an electrochemical cell?
   1. Temperature
   2. Concentration of reactants
   3. Pressure
   4. Volume of the cell


5. What is the purpose of a salt bridge in a voltaic cell?
   1. To provide electrons for the redox reaction
   2. To maintain electrical neutrality in the half-cells
   3. To prevent the oxidation reaction
   4. To increase the rate of the reaction


6. Which equation correctly relates $\Delta G$ (Gibbs Free Energy) to $E_{cell}$ (cell potential)?
   1. $\Delta G = -nFE_{cell}$
   2. $\Delta G = nFE_{cell}$
   3. $\Delta G = \frac{-nF}{E_{cell}}$
   4. $\Delta G = \frac{nF}{E_{cell}}$


7. During the titration of $Fe^{2+}$ with $KMnO_4$ in acidic solution, what is the oxidizing agent?
   1. $Fe^{2+}$
   2. $Mn^{2+}$
   3. $KMnO_4$
   4. $H^+$