CONTENT OBJECTIVE make qualitative or quantitative predictions about galvanic (voltaic) cells based on half-cell reactions and potentials and analyze these cells to identify properties of the underlying redox reactions. WHAT THE HECK DO I NEED TO BE ABLE TO DO? I can

Electrochemistry 1. In Pre-AP Chemistry, we deal mostly with reactions that are spontaneous— meaning, they will happen on their own if all the “ingredients” are present. Galvanic/Voltaic Cells

Electrochemistry 2. Galvanic cells use thermodynamically- favored (spontaneous) REDOX reactions to produce electrical energy via a flow of electrons (also known as Voltaic cells or batteries). a. In short: galvanic (voltaic) cells produce current!

Electrochemistry Galvanic/Voltaic Cells 3. To use that current, we need to separate the place where oxidation is occurring from the place where reduction is occurring.

Electrochemistry Galvanic/Voltaic Cells QUICK REMINDERS* 1)Oxidation is LOSS of electrons OIL (LEO) Ex: Zn (s)  Zn 2+ (aq) + 2e - 2) Reduction is GAIN of electrons RIG (GER) Ex: Cu 2+ (aq) + 2e -  Cu(s)

Electrochemistry Galvanic/Voltaic Cells B. Parts of the Galvanic Cell 1. Electron flow: ALWAYS through the wire from anode to cathode (alpha order)

Electrochemistry Galvanic/Voltaic Cells

Electrochemistry Galvanic/Voltaic Cells Electron (-) flow

Electrochemistry Galvanic/Voltaic Cells B. Parts of the Galvanic Cell Say you have 2 solutions and you’re trying to make a galvanic cell: Zinc sulfate = ZnSO 4(aq) Copper (III) sulfate Cu 2 (SO 4 ) 3 Ex: Zn (s)  Zn 2+ (aq) + 2e - Ex: Cu 2+ (aq) + 2e -  Cu(s)

Electrochemistry Galvanic/Voltaic Cells B. Parts of the Galvanic Cell 2. anode (–): the electrode where oxidation occurs (may appear smaller over time) Oxidation: Zn (s)  Zn 2+ (aq) + 2e -

Electrochemistry Galvanic/Voltaic Cells Electron (-) flow

Electrochemistry Galvanic/Voltaic Cells Electron (-) flow (oxidation) Zinc anode (electrode) Zinc sulfate solution

Electrochemistry Galvanic/Voltaic Cells B. Parts of the Galvanic Cell 3. cathode (+) : the electrode where reduction occurs (may appear larger over time) Reduction: Cu 2+ (aq) + 2e -  Cu(s)

Electrochemistry Galvanic/Voltaic Cells Electron (-) flow (oxidation) Zinc anode (electrode) Zinc sulfate solution

Electrochemistry Galvanic/Voltaic Cells Electron (-) flow (oxidation) Zinc anode (electrode) Zinc sulfate solution (reduction) Copper cathode (electrode) Copper sulfate solution

Electrochemistry Galvanic/Voltaic Cells B. Parts of the Galvanic Cell 4. Salt bridge or (disk): bridge between cells whose purpose is to provide ions to balance the charge

Electrochemistry Galvanic/Voltaic Cells Electron (-) flow (oxidation) Zinc anode (electrode) Zinc sulfate solution (reduction) Copper cathode (electrode) Copper sulfate solution

Electrochemistry Galvanic/Voltaic Cells Electron (-) flow (oxidation) Zinc anode (electrode) Zinc sulfate solution (reduction) Copper cathode (electrode) Copper sulfate solution salt bridge

Electrochemistry Galvanic/Voltaic Cells B. Parts of the Galvanic Cell 5. Voltmeter: measures the cell potential (emf or E°) in volts

Electrochemistry Galvanic/Voltaic Cells Electron (-) flow (oxidation) Zinc anode (electrode) Zinc sulfate solution (reduction) Copper cathode (electrode) Copper sulfate solution salt bridge

Electrochemistry Galvanic/Voltaic Cells Electron (-) flow (oxidation) Zinc anode (electrode) Zinc sulfate solution (reduction) Copper cathode (electrode) Copper sulfate solution salt bridge voltmeter

Electrochemistry Voltaic Cells A typical cell all labeled looks like this.

Electrochemistry C. Terms to remember through shortcuts ca + hode: the cathode is + in galvanic/voltaic cells, and so the anode is negative (-)

Electrochemistry C. Terms to remember through shortcuts AN OX: oxidation occurs at the anode (may show mass decrease) RED CAT: reduction occurs at the cathode (may show mass increase) (Combine that with remembering OIL RIG / LEO GER !) Anode = oxidation; oxidation is loss Reduction = cathode; reduction is gain

Electrochemistry C. Terms to remember through shortcuts FAT CAT: electrons in a voltaic/galvanic cell ALWAYS flow From the Anode To the CAThode  And the cat gets fat! (cathode gains mass over time)  “ANODE”-rexic! (anode loses mass over time)

Electrochemistry D. Standard Reduction Potential for a Galvanic/Voltaic Cell (E°) ° 1. In a galvanic (voltaic) cell, the metal with the greater (more positive) reduction potential will be reduced!

Electrochemistry D. Standard Reduction Potential for a Galvanic/Voltaic Cell (E°) ° 2. Because the values come from a chart of standard reduction potentials, you MUST REVERSE the sign of the E°of the oxidized species before adding to the E° of the reduced species.

Electrochemistry D. Standard Reduction Potential for a Galvanic/Voltaic Cell (E°) ° 3. How to calculate the cell potential of a galvanic cell: E o ox = - E o red and E o cell = E o oxidation + E o reduction

Electrochemistry D. Standard Reduction Potential for a Galvanic/Voltaic Cell (E°) ° 4. For a spontaneous oxidation-reduction (voltaic/galvanic cell) to occur, the overall cell potential must be positive.

Electrochemistry Example: Consider the half reactions shown below and the standard electrode reduction potentials that follow. Cu 2+ (aq) + 2 e -  Cu(s)E o = V Zn 2+ (aq) + 2 e -  Zn(s)E o = V

Electrochemistry Cu 2+ (aq) + 2 e -  Cu(s)E o = V Zn 2+ (aq) + 2 e -  Zn(s)E o = V Which one has the GREATER (more positive) reduction potential? Cu 2+ or Zn 2+ (If it has the GREATER reduction potential, E o, it has a greater desire for electrons and will be reduced!!!!)

Electrochemistry Cu 2+ (aq) + 2 e -  Cu(s)E o = V Zn 2+ (aq) + 2 e -  Zn(s)E o = V Which one has the GREATER (more positive) reduction potential? Cu 2+ or Zn 2+ (If it has the GREATER reduction potential, E o, it has a greater desire for electrons and will be reduced!!!!)

Electrochemistry Keep the equation the same since it’s being reduced: Cu 2+ (aq) + 2 e -  Cu(s) Therefore: E o red = V

Electrochemistry Zn 2+ (aq) + 2 e -  Zn(s)E o = V Zinc has the LOWER reduction potential (E o ), so it will be oxidized. (Flip the sign of the E o !) Flip the equation since it is being oxidized: Zn (s)  Zn 2+ (aq) + 2e - Therefore: E o ox = - E o red -(-0.76 V) = V

Electrochemistry Now calculate E o cell by plugging in the numbers: E o cell = E o ox + E o red = = V ****Galvanic (Voltaic) cells should ALWAYS have a positive E o cell value!!!!!!!!!!!!!****

Electrochemistry Take your half reactions, balance, and find the net ionic equation. Half reactions: Cu 2+ (aq) + 2 e -  Cu(s) Zn (s)  Zn 2+ (aq) + 2e - Net ionic equation: Cu 2+ (aq) + Zn(s)  Zn 2+ (aq) + Cu(s)