Electrochemistry experimen Essay

insane asylum Redox responses are reactions where the oxidation states of the atoms change. The atoms are either oxidized or reduced, depending if they lose or gain electrons. Electrochemical jail cells are devices that cause a current from redox reactions. It is set up so that electrons lost from whiz of the reagents rear end travel to another reagent. This creates a voltage, which is also known as the electric electromotive force difference. This voltage can be read if a high-resistance voltmeter or multimeter is connected to the circuit.Salt twain is used to allow migration of ions amidst two electric cells to maintain neutrality of effects. It is usually made up of a filter paper mois cristaled with an torpid solution or an inert solution/gelatine coarseness bridge to prevent oxidation of certain(p) ions. This experiment is divided into 2 sort outs segmentation A and part B. Part A Objective To investigate the effect of change in lead(II) ion concentration on the po tentiality of the Pb2+(aq) Pb(s) electrode Introduction This experiment investigates the e. m. f. of the cell Cu(s) Cu2+(aq) Pb2+(aq)Pb(s). property the ion concentration in the copper electrode system aeonian(1M) and varying the ion concentration in the lead electrode system, the effect of change in lead(II) ion concentration on the potential of electrode as well as the Kc of the higher up reaction can be found. Chemicals Copper foil x1, lead foil x1, 1M Cu2+ solution, 0. 1M Pb2+ solution, saturated kibibyte nitrate solution Apparatus 250 cm3 beakers, 50cm3 beakers multimeter, distilled irrigate bottle, filter papers, electric wires with electrode holders, forceps, 100ml volumetric flask,10ml pipette x2, dropper Procedure 1. The 0. 1M, 0.01M, 0. 001M, 0. 0001M Pb2+ solutions were hustling from 0. 1M Pb2+ solution by dilution(1 share solution plus 10 portions water). 2. The copper and lead electrodes were cleaned with a gumption paper. 3. The circuit was connected as the di agram below. 4. The e. m. f. was recorded when the data shown was stable. 5. The preceding(prenominal) steps(2-4) were repeated with 0. 01M, 0. 001M and 0. 0001M Pb2+ solutions. Safety precaution Potassium nitrate solution accomplish with combustible material whitethorn lead to fire 1M Copper(II) sulphate solution harmful and irritating to eyes and skin. Safety goggles should be worn.Experimental set-up Results Pb2+/M logPb2+ E/V 0. 1 -1 0. 482 0. 01 -2 0. 502 0. 001 -3 0. 521 0. 0001 -4 0. 545 Graph of E against log Pb2+ heading shown Given the ion concentration in the copper electrode system constant, it is found that the potential of the cell drops as the lead(II) ion concentration increment. The electrode potential is inversely proportional to the ten folds of ion concentrations. Calculation When the reaction Cu2+(aq) + Pb(s) Pb2+(aq) + Cu(s) achieves symmetricalness, the net e. m. f. of the cell=0 volt. The equilibrium aspect of this reaction isKc= Pb2+(aq) Cu(s) /Cu2+( aq) Pb(s) The effective concentration of Pb(s)/ Cu(s) are independent of its issue forth present and can be considered as constant. This reduces the expression to Kc= Pb2+(aq) /Cu2+(aq) = 11021 Conclusion The potential of the cell decreases ad the ion concentration of Pb2+ increases. Further outline Using the Nernst equation E=E? -0. 059/n logox/red, Take Pb2+=0. 1 M as an example, E=0. 47-0. 059/2 log(0. 1/1)=0. 4405(V) Pb2+/M logPb2+ E/V(calculated) E/V(measured) %difference 0. 1 -1 0. 4405 0. 482 9. 42% 0. 01 -2 0. 529 0. 502 5. 10%.0. 001 -3 0. 5585 0. 521 6. 71% 0. 0001 -4 0. 588 0. 545 7. 31% It is shown that difference is present between the calculated value and measured value.This whitethorn be because of different conditions, resistance of the multimeter or misconducts in preparation of versatile concentrations of solutions. Part B Objective To find out the equilibrium constant by e. m. f. measurement Introduction The equilibrium constant for the below reaction is foun d out Ag+(aq) + Fe2+(aq) Fe3+ (aq) + Ag(s) By e. m. f. measurement on the cell Pt Fe2+(aq), Fe3+(aq)Ag+(aq)Ag(s) Chemicals 0. 1 M Fe3+ solution, 0.2 M iron(II)sulphate, 0. 2M barium nitrate, 0. 4M silver grey nitrate, platinum electrode, silver electrode Apparatus gelatine salt bridge, 250 cm3 beakers, 50cm3 beakers ,multimeter, distilled water bottle, electrical wires with electrode holders, forceps, 10ml pipette x2 Procedure 1. Equal volumes of 0. 2M FeSO4 and 0. 2M Ba(NO3)2 were mixed and the precipitate was allowed to rout without disturbance. 2. Equal volumes of 0. 1M iron(II) nitrate solution obtained and the iron(III)nitrate solution were mixed. This was the Fe2+(aq)/Fe2+(aq) half-cell. 3.The 0. 4M, 0. 2M, 0. 1M, 0. 05M, 0.025M silver nitrate solutions were prepared from 0. 4M silver nitrate solution by dilution. 4. The silver electrode was cleaned with a gumption paper. 5. The circuit was connected as the diagram below. 6. The e. m. f. was recorded when the data shown was stable. 7. The above steps (4-6) were repeated with 0. 2M, 0. 1M, 0. 05M, 0. 025M silver nitrate solutions. Safety Precaution capital nitrate harmful and oxidizing 1) Poisonous if swallowed or inhaled 2) Skin contact with silver nitrate solid or solutions is likely to leave silver stains on the skin. Barium nitrate is poisonous and really harmful if swallowed.It is also a strong oxidizer, so may be hazardous if mixed with inflammable materials. Experimental Set-upResults Ag+/M logAg+ E/V 0. 4 -0. 398 0. 023 0. 2 -0. 699 0. 005 0. 1 -1 -0. 030 0. 05 -1. 301 -0. 050 0. 025 -0. 025 -0. 053 Graph of E against logAg+(aq) Calculation When the reaction reaches equilibrium, both forward and cacuminal reactions proceed to the same extent. This means that both the half cell reactions would soak up the same potential to proceed, so that the net e. m. f of the cell =0 volt at equilibrium.From the graph, the x-intercept is logAg+(aq)=-0.72, hence,Ag+(aq)eqm=0. 1905 Ag+(aq) + Fe2+(aq) Fe3+ ( aq) + Ag(s) KC= Fe3+ (aq)/ Ag+(aq) Fe2+(aq) =0. 1/ (0. 1905X0. 1) =5. 2493(mol2dm-6) 5. 25(mol2dm-6) Conclusion The equilibrium constant for the reaction between Fe2+/Fe3+ and Ag+ is 5. 25 mol2dm-6. Discussion(for both parts) 1. accomplishable Errors -The electrodes (Cu(s),Pb(s),Ag(s)) were not cleaned very well with a sand paper so that they are not conducting electricity in all parts. The e. m. f. measured may hence be underestimated. -The same ammonium nitrate/gelatine salt bridge was used several times in part II of experiment.Ions of previous measurement may remain in the salt bridge and change the concentration of ions in the next measurement. -The apparatus including pipettes, beakers and volumetric flask may not be washed to be very clean. The error in concentration may be enormous when handling very dilute solutions (e. g. 0. 001M, 0. 0001M, 0. 025M) -The electrode touched the salt bridge once so that the trueness of measurement of e. m. f. was affected. The solution is no t exactly passed. -Air gap may be present in the ammonium nitrate/ gelatine salt bridge, increase the resistance of ion migration. 2.Difference in effect of ion concentration on electrical potential of cell -In part A, the cell e. m. f. increases as Pb2+(aq) decreases. However, in part B, the e. m. f. drops as Ag+(aq). This suggests that when the species is a stronger oxidizing agent in the reaction and undergoes drop-off, the presence of its ions tends to increase the e. m. f. whereas the one which undergoes oxidation tends to reduce the e. m. f. The species with more positive standard reduction potential has a positive effect but the one with less(prenominal) positive potential has a negative effect.Reference Physical alchemy II by TM Leung and CC Lee( p. 295-298 &299-301).