Electrochemical CellsElectrochemical 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

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+) solutionMetals 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

K, Na, Ba, Ca ,Mg ,Al, Mn, Zn, Cr, Cd, Fe, Co, Ni, Sn, Pb, H, Sb, Bi, As, Cu, Hg, Ag, Pt, Au

Electrochemical Cells – Part AElectrochemical Cells – Part A

Determine the reactivity of Copper, Magnesium and Zinc using solutions of H2SO4 , MgSO4 , CuSO4 , Na2SO4 , and ZnSO4 .

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 SO4 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 5STEP FOUR: Dispose of reaction solutions in containers provided –

wash off metal solids and throw in garbageSTEP FIVE: Write equations for those where an observed change has taken place

- what could bubbles mean?- What happens to the anions?- precipitate = solid

H2SO4

MgSO4

CuSO4

Na2SO4

ZnSO4

Solids: Cu Mg Zn

Electrochemical Cells – Part AElectrochemical Cells – Part A

• Parts B and C: • Each Group will make the five Voltaic Cells (as

described on page 4:

Electrochemical Cells – Part B and CElectrochemical Cells – Part B and C

Standard Cells:

Cell 1: Zn/Cu Standard Cell (1M Zn soln/1M Cu soln)Cell 2: Cu/Mg Standard Cell (1 M Cu soln/1M Mg soln)Cell 3: Zn/Mg Standard Cell (1 M Zn Soln/1M Mg soln)

Non Standard Cells:

Cell 4: Zn/Cu Cell (1 M Zn soln/ 0.1 M Cu soln)Cell 5: Zn/Cu Cell (0.1M Zn soln/1 M Cu soln)

RED – receives e-

BLACK – gives e-

Electrochemical Cells – Part B and CA Traditional Voltaic Cell

Electrochemical Cells – Part B and CA Traditional Voltaic Cell

Electrochemical Cells – Part B and CA Microcell Approach

Electrochemical Cells – Part B and CA Microcell Approach

Well should be filled so solution runs down the arm and contacts the porous wall

Non-reactive Salt Solution (KNO3) (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 CElectrochemical Cells – Part B and C

1.Set up the Standard cells:

A. Make metal strips shiny with steel woolB. Fill the Wells with the appropriate solutionsC. Place the metals in the proper solutions for the standard cells

1.Zinc goes in 1M zinc solution, 2.Mg in 1M magnesium solution, 3.Copper goes in 1M copper solution

D. Hook up voltmeter - connect anode and cathode so that a positive number is recorded

4.Anode (black) – where oxidation occurs (loss of electrons)5.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

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 CElectrochemical 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

Electrochemical Cells – Part B and CElectrochemical Cells – Part B and C

2. Set up the Non-Standard cells:

A. Fill Two Wells with the appropriate solutions1. 0.1M Copper Solution2. 0.1M Zinc Solution

B. Remove the Copper Strip, rinse it with DI water, Pat dry with kimwipeC. Place the Copper Strip in the 0.1M Copper SolutionD. Hook up voltmeter for 0.1M CuSO4/1M ZnSO4 CellE. Record PotentialF. Repeat for the Nonstandard 0.1M CuSO4/1M ZnSO4 Cell

) V 2.37- ( Mg(s) - 2e )(Mg -2 aq

The Nernst Equation• The (simplified) Nernst equation at 298 K:

• n is number of moles of electrons.

• Q = Reaction Quotient:

Effect of Concentration on CellsEffect of Concentration on Cells

QlogV0592.0

nEE

i

iQcoeffstoich

coeffstoich

Ion]Reactant [

Ion]Product [

Lab Report and Group Forms: Due Today or Next Week Lab Report and Group Forms: Due Today or Next Week

Title Page

Purpose

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.

Conclusion (Summary of results, Errors, Improvements)

Individual Checked-Pre-labs

LOCKER CHECK OUT TODAY

– 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 – 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

Electrochemical Cells – Final Lab – Locker Check Out

Electrochemical Cells – Final Lab – Locker Check Out