Determining Avogadro’s Constant and Faraday’s Constant

Determining Avogadros Constant and Faradays ConstantList of ApparatusName of ApparatusQuantityUncertaintyElectronic stopwatch10.2sAmmeter10.01AWires with crocodile clips1D.C power source10.01V300cm3 Beaker3Copper slicknesss2Sand paper1Graphite rod2pH probe/ information-logger10.2Electronic weighing balance10.001DATA COLLECTIONThe electrolytic cell utilize in this investigation is illustrated in Fig 1Fig 1 Diagram of electrolytic cell used in investigationIn this investigation, a menses is passed through the outcome with strapper as the cathode and plumbago as the anode. After a set summate of time, the circuit is disconnected and the mass of the cathode is measured. Following which, calculations are made so as to determine the Avogadros and Faradays unceasing.Qualitative ObservationsWhen the D.C power source was turned on, bubbles were formed at the Graphite anode. As the reply progresses, powdery sum total gets suspended in the solution and a black solid deposits can be fo und at the bottom of the beaker and there is a visible corruption of the plumbago electrode. As the reaction progress, a pink story of hair forms on the slovenly person strip. The copper strip is originally brown in warp while the graphite electrode is black in colour. Eventually, as the graphite electrode decomposes, the graphite molecules exit turn the copper (II) sulphate solution from blue to black in colour. However, when the copper sulfate solution is filtered, it is noted that there is a decrease in the intensity of the blue colour in the filtrate after(prenominal) the electrolysis. The sign pH of the solution is 2.75, after the electrolysis is carried out, the pH decreases to 2.10.Data CollectionConstant variablesTime Interval/s(0.2)300Voltage/V4VCurrent/A(0.01)0.25CathodeTrial 1Initial mass/g ( 0.001 g)1.315Final mass/g ( 0.001 g)1.279Change in mass/g ( 0.002 g)0.036 chemic equation for reaction at the anode2H2O (l) O2 (g) + 4H+ + 4e (aq)Chemical equation for react ion at the cathodeCu2+ (aq) + 2e Cu (s)Calculations for cathodeCalculationsError PropagationChange in mass(Cu) = 0.036gMols of (Cu) = =5.7 x 10-4 molNumber of mol of negatrons-Using mol proportionalityCu2+ (aq) + 2e Cu (s)Number of mol of electrons =11.4 x 10-4Charge flowing through circuitNumber of electron charges in circut=Where is the elementary charge, the charge of one electronNumber of electron charges in circuit=Number of mol of electronsWhere L is the Avagandros constantEquating the bend of mols of electrons obtained form the copper mass data and the number of mol of electrons from the current-Faradays constant = = 67000 C% Mol of Cu =% Mol of Cu == 5.6 %% Uncertainty of number of mol of electrons=% irresolution of Mass(Cu) =5.6%% uncertainty of number of mol of electrons =5.6%% charge flowing in circuit =Percentage errorPercentage error for Faradays Constant = == 30%Percentage uncertainty of faradays constant =5.9%Percentage systematic error in Faradays constant =%e rror-%random error= 24.1%Percentage error for Avogadros Constant = = 30%Percentage uncertainty of Avogadros Constant =5.9%Percentage systematic error in Avogadros Constant =%error-%random error= 24.1%ConclusionIn conclusion, the calculated value of Faradays constant is mol-1 and Avogadros constant is.As seen above, the percentage error for both Faradays constant and Avogadros constant are both 30% and after subtracting the error due to instrumental uncertainty, the % systematic error obtained is 24.1%. This shows that the experimental values calculated differ greatly from the literature values, indicating that there has been a significant amount of systematic error, which has caused the calculated value to be much different from the literature value. As percentage error of both Faradays constant and Avogadros constant are much larger than their respective percentage uncertainties, this indicates that the sources of systematic error are significant and cannot be ignoredEvaluationTyp e of error terminus ad quemImprovementSystematicOxidation of copper occurs naturally when the copper strip is exposed to oxygen and when it is heated in the oven. Even when sand paper is used to scratch off the layer of copper oxide on the surface of the, it is difficult to completely rid of all the copper oxide. The formation of copper oxide will instill the reaction when electrolysis occurs and will affect the change in mass of the copper electrode, which is the dependent variable in this experiment. Even when the copper strip is immersed in the copper (II) sulphate solution, after a period of time, it will in timetually start to form a layer of copper (II) oxide which will not be tough in the electrolysis reaction. This will reduce the amount of copper which will undergo reaction, ca employ it to reduce the eventual calculated Faradays and Avogadros constant.It is impossible to clog the oxidation of copper from happening however, this systematic error can be minimised. Other than ensuring that the layer of copper oxide is scratched off by rubbing the copper strip excessively with sandpaper. The time for which the copper stays in the oven can be minimised or hair dryer can be used instead to electrical shock the water off.SystematicWhen the graphite electrode starts to disintegrates as the reaction progresses, fragments of graphite will be dispersed throughout the entire solution. As copper (II) ions move towards the copper strip to plate it, some of the graphite fragments may end up attached to the copper strip as well and are unable to lineage off as a layer of copper plates over the graphite fragments. This can be observed in the experiment when the copper strip is remote at the end of the experiment black fragments of graphite are observed on the copper strip.The graphite fragments would easily reach the copper strip primarily because they were quite near each other. Hence, the graphite fragments could easily move towards the copper strips and att ach to them. In order to minimise this from happening, the experiment should be conducting in a 500cm3 beaker, with the copper strip and the graphite electrode held further away from each other. Also, the graphite electrode should be positioned below the copper strip so that as the graphite electrode disintegrates, the graphite fragments will simply sink towards the bottom of the beaker, hence it will be less likely for the graphite fragments to accidentally coat onto the copper electrodeSystematicFluctuations in the current. Whenever the 2 electrodes were moved, the current of the circuit changes. Hence, whenever the copper electrode was moved in order to be weighed, the current would fluctuate, resulting in an inconsistent current throughout the experiment. If the current deviates from the express 0.25, the resulting Faradays constant and Avogadros constant will be affected as well. An profit in current will result in an increase in the Faradays constant and Avogadros constant c alculated while a decrease in current will result in a decrease in the Faradays constant and Avogadros constant calculated.In order to prevent fluctuations in the current as a result of the devious electrodes, a retort stand can be used to hold the electrodes in place and prevent them from moving. This is much more reliable than just using hands to hold the electrode, resulting in a reduction in the fluctuation of the currentA rheostat can be used and included in the circuit in order to adjust the amount of bulwark of the circuit so that the desired current can be achieved. As current is mutually proportionate to resistance according to Ohms law, the resistance of the circuit can be adjusted in order to ensure a consistent current of 0.3 throughout the experiment.SystematicAlso, another source of systematic error in this experiment would come from the fact that, the reading on the ammeter does not indicate the real electric current flowing through the electrodes and the electro lyte as this value may decrease due to power losses in the wires. That is the electrical energy would be converted to heat. However the resistance of the wires in the circuit was assumed to be negligible in this experiment for simplicity. This would lead to systematic error as we would consistently overestimate the magnitude of the current flowing through the electrolyte.This error can be avoided if the values of the resistance of the wires as well as the internal resistance of the power source were known and included in the calculations made.SystematicThe copper electrode may undergo a process called passivation1 where the metal forms a protective layer on its surface to protect it from outer factors such as water or air to prevent corrosion. Such a protective layer will result in a high resistance which will lead to a voltage delay. This process may also occur on the graphite electrode.During the reaction, in the presence of passivation, the initial rate of the increase in mass of the copper electrode will be slowed down ultimately affecting the total wee-wee in mass by the copper electrode, affecting the Faradays constant and Avogadros constant calculated.This process of passivation can be removed by allowing the reaction to progress for 5 minutes to avoid a voltage delay. 5 minutes was chosen because too short a time will be insufficient to remove the protective layer on the electrode and too long a time will result in the disintegration of the graphite electrode even before the collection of data has begun. As mentioned above, if there is too much graphite fragments in the copper (II) sulphate solution, they may come into contact with the copper electrode and affect its final mass as copper ions plate over the graphite fragments on the copper electrode.Random ErrorDue to time constrains, besides one set of data was collected. This will result in the fluctuation of the value of the Faradays and Avogadros constant.In order to reduce the error, perhaps mor e sets of data can be collected, so that a graph of metal deposited against time can be plotted and the gradient will enable the purpose of the two constants.1 Metal passivation-en.w,wikepedia.org/Passivation_(Chemistry). Accessed- 26/2/2014)