Experiment 1

EXPERIMENT 1 : GALVANIC CELL

OBJECTIVES a) To measure measure the relative reduction reduction potentials for a number of half cell (redox) (redox) couples in galvanic cell b) To develop and understanding understanding of the movement of electrons, anions anions and cations in galvanic cell c) To study factors factors aecting aecting cells cells potentials potentials d) To estim estimate ate the concen concentra tratio tion n of ions ions in soluti solution on using using the Nernst Nernst Equation

INTRODUCTION

PROCEDURE A. Galvanic cell – C#!(le$

Re!c"i#n

P#"en"ial$ #%

Seve&al

Re#'

1. C#llec" ")e Elec"&#e$* S#l!"i#n$ an E+!i(,en" Four small beaers are obtained and are !lled "ith dierent 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 beaers$ 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 maing 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 dierences 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 =unno"n> copper ion concentration are obtained and a galvanic cell is set up$ The unno"n copper ion concentration in the solution is determined through the graph$

CALCULATIONS

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 aecting 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 eect of dierent concentration on cell potential and 9rocedure ' apply the Nernst equation and determine the unno"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 dierence of measured and calculated reduction potential$ For redox couple bet"een 'u7Fe, the reduction potential dierences bet"een measured and calculated are not as big as n7Fe and 'u7n$ 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 'u7n 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 dierent forms that can>t be dierentiate by naed 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 mae 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 unno"n is #$% &$  There are some precaution steps that can be taen 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$6B comes from 'u7n redox couple$ 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 unno"n copper is identi!ed and it is #$% &$ RE5ERENCES