Electrochemical Cells
By, Marvin Lu and Riley Corr
Purpose

To determine the effects of changing
the concentrations of solutions and the
identities of the solutions themselves
on the voltage in an electrochemical
cell.
CHEMICAL CHANGE --->
ELECTRIC CURRENT
Mg metal
Cu2+ ions
Electrons are
transferred from Mg to
Cu2+, but there is no
useful electric current.
Oxidation: Mg(s)---> Mg2+(aq)+2eReduction: Cu2+(aq)+2e- --->Cu(s)
----------------------------------------Cu2+(aq)+Mg(s)--->Mg2+(aq)+Cu(s)
CHEMICAL CHANGE --->
voltmeter
ELECTRIC CURRENT
To
obtain a useful
current, we separated
the oxidizing and
reducing agents so
that electron transfer
occurred thru a volt
meter.
l
Mg
salt
bridge
Mg2+ ions
This is accomplished in a GALVANIC or
VOLTAIC cell.
A group of such cells is called a battery.
Cu
Cu2+ ions
Mg --> Mg2+ + 2e-
Cu2+ + 2e- --> Cu
wire
Oxidation
Anode
Negative
Mg
salt
bridge
Cu
Reduction
Cathode
Positive
<--Anions
Cations-->
Mg2+ ions
Cu2+ ions
•Electrons travel thru the voltmeter.
Salt bridge allows anions and cations to
move between electrode compartments.
Procedure








Obtain Goggles
Obtain a 3”x5” piece of copper sheet and a 3”
long magnesium ribbon
Obtain .5M, .1M, and .01M Mg(NO3)2 solutions
Obtain .5M, .1M, and .01M Cu(NO3)2 solutions
Obtain a .1M CuSO4 solution
Obtain filter paper and .1M KNO3 solution for salt
bridge. To make salt bridge, roll filter paper and
soak in solution.
Obtain a voltmeter, set it to 40V.
Obtain two 50mL beakers, and two 50mL
graduated cylinders.
Procedure (Continued)
• Set up electrochemical cells as follows:
- Measure out 30mL of each solution to be used, pour into
separate beakers.
- Make a salt bridge and place an end into each beaker.
- Place the copper into the solution containing the copper ion.
- Place the magnesium into the solution containing the
magnesium ion.
- Connect the voltmeter to the electrodes, the red wire should
attach to the Copper, the black to the Magnesium.
• Repeat the procedure for all combinations of solutions below.
Trial:
1
2
3
4
5
Trial:
6
[Mg(NO3)2] .1
(mol/L)
.01
.5
.1
.1
[Mg(NO3)2] .1
(mol/L)
[Cu(NO3)2] .1
(mol/L)
.1
.1
.01
.5
[CuSO4]
(mol/L)
.1
Electrochemical Cell
Voltmeter
Mg
Mg 2+ ions
Anode
Salt Bridge KNO3
Cu
Cu
2+
ions
Cathode
Observations







Copper solutions had blue color, the higher the
concentration, the darker the color.
Magnesium ribbon was coated in a white oxide, it
was scraped off with a scoopula before use.
Magnesium solution was clear.
Solutions were prepared from solid salts: Cu(NO3)2
• 3H2O, Mg(NO3)2 • 6H2O, KNO3
The CuSO4 solution was prepared from a .4M
solution of unknown quality.
BK Precision Voltmeter
Voltage readings required some time to stabilize.
Data
Trial:
1
2
Voltage 1.47 1.76
(V)
3
4
5
6
1.55
1.66
1.67 1.54
Discussion
In this lab, Mg(NO3)2 and Cu(NO3)2 were used
as solutions in a voltaic cell. Concentrations
of both were varied and the differences in
voltage were negligible.
In trial 6, the source of Cu2+ ions was
changed from Cu(NO3)2 to CuSO4. Once
again, there was a negligible change in
voltage.
Trial:
1
2
3
4
5
[Mg(NO3)2]
(mol/L)
.1
.01
.5
.1
.1
[Cu(NO3)2] (mol/L) .1
.1
.1
.01
.5
Voltage (V)
1.76
1.55
1.66
1.67
1.47
Trial:
6
[Mg(NO3)2] (mol/L)
.1
[CuSO4] (mol/L)
.1
Voltage (V)
1.54
Error



The CuSO4 solution was prepared from
a .4M solution of unknown quality.
The Cu(NO3)2 solution was a hydrate
but the exact chemical formula was
unknown. It was assumed to be
Cu(NO3)2 • 3H2O based on the Flinn
Scientific chemical and biological
catalog reference manual 2001
Not all of the impurities of the
magnesium ribbon were removed.
Bibliography
http://bkprecision.com/www/np_searchmodel7.asp?lf=
Dual+Display+RS%2D232+Interface+Multimeters
http://www.brookscole.com/cgi-
Brookscole/course_products_bc.pl?fid=M63&product_isb
n_issn=003033604X&chapter_number=20&resource_id
=21&altname=PowerPoints
www.ivygreen.ctc.edu/knutsen/chem160/vltaicll.html