EXPERIMENT 1 : GALVANIC CELL EXPERIMENT 1 : GALVANIC CELL
OBJECTIVES OBJECTIVES
a)
a) TTo measuro measure the relative re the relative reduction potentials for a eduction potentials for a number of half cellnumber of half cell (redo
(redox) couples in x) couples in galvanic cellgalvanic cell b)
b) TTo develop and uno develop and understanding of the derstanding of the movement of movement of electrons, aelectrons, anionsnions and cations in galvanic cell
and cations in galvanic cell c)
c) TTo study facto study factors aeors aecting celcting cells potenls potentialstials d)
d) TTo o estestimimate the ate the conconcencentratratiotion n of of ionions s in in solsolutiution on usiusing ng the Nerthe Nernstnst Equation
Equation
INTRODUCTION INTRODUCTION
PROCEDURE
A. Galvanic cell – Re!c"i#n P#"en"ial$ #% Seve&al Re#' C#!(le$
1. C#llec" ")e Elec"&#e$* S#l!"i#n$ an E+!i(,en"
Four small beaers are obtained and are !lled "ith dierent solutions "ith same concentration, "hich is #$% & 'opper Nitrate, inc Nitrate, ron *ulphate and &agnesium *ulphate solutions$ The strips of copper, +inc and iron metal are polished "ith sand paper and rinsed them "ith deioni+ed "ater$ The polished metals are used as electrodes and are immersed them in their respective solutions$ The voltmeter is connected to the electrodes by using crocodile clips$
-. Se" U( ")e C#((e&/inc Cell
copper strip is placed in the copper () nitrate solution and a +inc strips is placed in the +inc () nitrate solution$ piece of !lter paper is rolled and -attens$ Then, the rolled !lter paper is immersed in the potassium chloride until it is "et$ This "et !lter paper is acted as salt bridge$ The end of salt bridge is inserted bet"een t"o beaers$
0. De"e&,ine ")e C#((e&/inc Cell P#"en"ial
The potential at the voltmeter is read and recorded$ The metal strips that is served as the cathode and the anode are identi!ed$ . Re(ea" %#& ")e Re,ainin2 Cell$
The cell potentials for all possible galvanic cells that can be constructed from the other redox couples are determined$ ne" salt bridge is prepared for each galvanic cell$
3. De"e&,ine ")e Rela"ive Re!c"i#n P#"en"ial$
The reduction of the n./ (#$% &) 0 n redoc couple is 1 #$23 4 is
assumed$ Then, the reduction potentials of all other redox couples are determined$ ll the calculations and data results are presented together in this report$
B. E4ec" #% C#ncen"&a"i#n C)an2e$ #n Cell P#"en"ial 1. E4ec" #% Di4e&en" M#la& C#ncen"&a"i#n$
The galvanic cell is set up using % & copper sulphateand #$##% & copper sulphate solutions$ polished copper electrode is
immersed in each solution$ salt bridge is prepared to connect the t"o redox couples$ The cell potential is measured$ The anode and cathode are determined$
-. E4ec" #% C#,(lec 5#&,a"i#n
5 ml of 6 & of ammonia solution is added to the #$##% & copper sulphate, until all precipitate is redissolved$ The changes in the half7cell and the cell potential are observed$
C. T)e Ne&n$" E+!a"i#n an an Un6n#7n C#ncen"&a"i#n 1. P&e(a&e ")e Dil!"e S#l!"i#n$
*olution % through 8 as outlined are prepared using % ml pipette and %## ml volumetric -as$ The apparatus that are used are rinsed "ith more concentrated solution before maing the transfer$ The deioni+ed "ater is used for dilution to the calibration mar in the volumetric -as$ The molar concentration of each solution is calculated$
-. Mea$!&e an Calc!la"e ")e Cell P#"en"ial %#& S#l!"i#n
The n./ 0 n redox couple is used as the reference half7cell for
this part of the experiment$ The t"o half7cells are connected "ith a ne" salt bridge$ The electrodes are connected to the potentiometer and the potential dierences are recorded$ The theoretical cell potential is calculated$
0. Mea$!&e an Calc!la"e ")e Cell P#"en"ial$ %#& S#l!"i#n 0 an
-9art '. is repeated "ith solution : and . respectively$ freshly prepared salt bridge is required for each cell$
. Pl#" ")e Da"a
Ecell(measured) and Ecell(calculated) vs log ;'u./< is plotted on a graph paper
for the four concentrations of copper() nitrate solutions$ 3. De"e&,ine ")e c#ncen"&a"i#n #% ")e Un6n#7n
copper () nitrated solution "ith and =unno"n> copper ion concentration are obtained and a galvanic cell is set up$ The unno"n copper ion concentration in the solution is determined through the graph$
DISCUSSION
n this experiment, a galvanic cell is conducted to measure the relative reduction potentials for a number of half7cell couples in a galvanic cells, to develop and understanding of the movement of electrons, anions and cations in galvanic cell, to study factors aecting cells potentials and to estimate the concentration of ions in solution using the Nernst Equation$
There are three segments of procedures, "hich are for 9rocedure , it>s all about the reduction potentials of several redox couples$ For 9rocedure ?, this experiment the eect of dierent concentration on cell potential and 9rocedure ' apply the Nernst equation and determine the unno"n concentration of copper ion through a graph$
?ased on the data and the result that are sho"ed in the previous pages, for Experiment %, it can be concluded that there are big dierence of measured and calculated reduction potential$ For redox couple bet"een 'u7Fe, the reduction potential dierences bet"een measured and calculated are not as big as n7Fe and 'u7n$ The percentage error for 'u7 Fe redox couple @ust :5$AB$ Co"ever, for a redox couples that are used +inc (n) electrodes indicates a huge percentage error$ For n7Fe redox couples, the percentage error is %A5$2%B and 'u7n gives 35$6B$ These percentage error are quite high due to several error "hile conducting these experiments$
The !rst error is "hile polishing the strips, probably it is not "ell7 polished$ &oreover, it can be said that the +inc strips are having problem as there are several +inc stripes in dierent forms that can>t be dierentiate by naed eyes$
For Experiment ., the cell potential of =concentration cell> is #$#8 4 and the cell potential from complex formation gives #$% 4$ The colour change of copper sulphate solution in half7cell is recorded$ The colour change from pale blue to blue after 5 ml of 6 & of ammonia solution is added into #$##% & copper sulphate solution$ Furthermore, the cell potential is changed after the addition of 6& of ammonia solution$ This 6 & ammonia is high enough to mae the potential increases$
For Experiment :, there are some errors "hile conducting this experiment$ Firstly, "hile diluting the copper solution, probably "hile pipetting the % ml of this solution is not accurate$ Furthermore, "hile diluting copper solution to the calibration mar, the eye level is not parallel to the meniscus$ ?ased on the result, the molar concentration of 'u./ in the unno"n is #$% &$
There are some precaution steps that can be taen for further preferences$ Firstly, "hile conducting the experiment, it has to be sure to "ear gloves "hile pouring the chemicals into the apparatus$ *econdly, all the apparatus have to be clean up "ith deioni+ed "ater or "ith more concentrated chemicals before using them$ Thirdly, the strips should be identi!ed and being polished as clean as possible$
CONCLUSION
The relative reduction potentials for a number of half7cell couples in a galvanic cell are measured$ For 'u7Fe redox couple, the percentage error is :5$AB, n7Fe gives 25$6B and the highest percentage error is 35$6B comes from 'u7n redox couple$ For Experiment ?, the cell potential of =concentration cell> is #$#8 4 and cell potential from complex formation gives #$% 4$ these increasing in potentials happen after the addition of 6 & of ammonia, NC: into copper sulphate solution$ Next, Experiment ' the
molar concentration of the unno"n copper is identi!ed and it is #$% &$ RE5ERENCES
