Electrochemical Cells Hand in PreLab Coordination Complex Report

Electrochemical Cells • Hand in: Pre-Lab. Coordination Complex Report, Drop GCF • Electrochemistry – the study of the transfer of electrons • Oxidation – species loses electrons • Reduction – species gains electrons • The electromotive series – study the relative reactivity of various elements K, Na, Ba, Ca , Mg , Al, Mn, Zn, Cr, Cd, Fe, Co, Ni, Sn, Pb, H, Sb, Bi, As, Cu, Hg, Ag, Pt, Au More reactive (more likely to lose electrons) less reactive NOTE H in the series – metals to the left will lose electrons in an acidic (H+) solution Metals to the right will not lose electrons to H+, and therefore, will not readily dissolve in acids • Today • • Lab Parts A, B and C Last Lab – Check Out

Electrochemical Cells – Part A Determine the reactivity of Copper, Magnesium and Zinc using solutions of H 2 SO 4 , Mg. SO 4 , Cu. SO 4 , Na 2 SO 4 , and Zn. SO 4. STEP ONE: Use the electromotive series to predict what is going to happen STEP TWO: Set up the reactions using test plates – sets of three -use about 10 drops of the SO 4 solutions -add the metals (use small, similar sizes of Mg ribbon) -let reaction go about 10 -15 minutes – note all changes STEP THREE: Record Observations on Lab Data Sheet, page 5 STEP FOUR: Dispose of reaction solutions in containers provided – wash off metal solids and throw in garbage STEP FIVE: Write equations for those where an observed change has taken place -what could bubbles mean? -What happens to the anions? -precipitate = solid

Electrochemical Cells – Part A Solids: H 2 SO 4 Mg. SO 4 Cu. SO 4 Na 2 SO 4 Zn. SO 4 Cu Mg Zn

Electrochemical Cells – Part B and C • Parts B and C: • Each Group will make the five Voltaic Cells (as described on page 4: Standard Cells: Cell 1: Zn/Cu Standard Cell (1 M Zn soln/1 M Cu soln) Cell 2: Cu/Mg Standard Cell (1 M Cu soln/1 M Mg soln) Cell 3: Zn/Mg Standard Cell (1 M Zn Soln/1 M Mg soln) Non Standard Cells: Cell 4: Zn/Cu Cell (1 M Zn soln/ 0. 1 M Cu soln) Cell 5: Zn/Cu Cell (0. 1 M Zn soln/1 M Cu soln)

Electrochemical Cells – Part B and C A Traditional Voltaic Cell BLACK – gives e- RED – receives e-

Electrochemical Cells – Part B and C A Microcell Approach Well should be filled so solution runs down the arm and contacts the porous wall Non-reactive Salt Solution (KNO 3) (acting as the salt bridge) added prior to lab so the apparatus is conditioned. Wells for sulfate solutions for each half cell

Electrochemical Cells – Part B and C 1. Set up the Standard cells: A. Make metal strips shiny with steel wool B. Fill the Wells with the appropriate solutions C. Place the metals in the proper solutions for the standard cells 1. Zinc goes in 1 M zinc solution, 2. Mg in 1 M magnesium solution, 3. Copper goes in 1 M copper solution D. Hook up voltmeter - connect anode and cathode so that a positive number is recorded 1. Anode (black) – where oxidation occurs (loss of electrons) 2. Cathode (red) – where reduction occurs (gain of electron) 3. Get a positive Voltmeter reading E. Record Observations and Cell Potential on Data Sheet Page 6

Electrochemical Cells – Part B and C -Make sure your metals are cleaned using the steel wool -Make sure you fill the wells with the proper solutions -Be careful not to contaminate solutions including the center salt solution The Mult-EChem Half Cell Module has space for eight half-cells, each equally accessing a central salt bridge through a porous cylinder. A milled “overflow” area prevents spills and mixing of solutions. A positive voltage reading indicates that electrons are running into the black lead from the oxidation reaction and out of the red clip to the reduction reaction.

Electrochemical Cells – Part B and C 2. Set up the Non-Standard cells: A. Fill Two Wells with the appropriate solutions 1. 0. 1 M Copper Solution 2. 0. 1 M Zinc Solution B. Remove the Copper Strip, rinse it with DI water, Pat dry with kimwipe C. Place the Copper Strip in the 0. 1 M Copper Solution D. Hook up voltmeter for 0. 1 M Cu. SO 4/1 M Zn. SO 4 Cell E. Record Potential F. Repeat for the Nonstandard 0. 1 M Cu. SO 4/1 M Zn. SO 4 Cell

Effect of Concentration on Cells The Nernst Equation • The (simplified) Nernst equation at 298 K: • n is number of moles of electrons. • Q = Reaction Quotient:

Lab Report and Group Forms: Due Today or Next Week ü Title Page ü Purpose ü Results - Part A - Observations + Balanced Equations for reactions that occurred – page 5 of lab - Part B - Observations + Balanced Equations + Eo - page 6 of lab - Part C - Voltages + Explanations/Calculations – page 6 and Nernst Show work for final voltages/equation; i. e. show half-reactions with their potentials and how they add up to give overall reaction equation. ü Conclusion (Summary of results, Errors, Improvements) ü Individual Checked-Pre-labs ü LOCKER CHECK OUT TODAY

Electrochemical Cells – Final Lab – Locker Check Out – Locker Check OUT • Make sure all equipment is in drawer • NEW TAPE, tape combo to the check out sheet • All partners sign sheet • Give Sheet to TA • Leave Drawer UNLOCKED – but shut – GET SIGNATURES BEFORE YOU GO – GOOD LUCK ON FINALS