Determining Avogadro’s Constant and Faraday’s Constant

determine Avogadros constant quantity and Faradays ConstantList of Apparatus be of ApparatusQuantityUncertaintyElectronic Stopwatch10.2sAmmeter10.01AWires with crocodile clips1D.C power source10.01V300cm3 Beaker3Copper scavenges2Sand paper1Graphite rod2pH probe/selective information-logger10.2Electronic weighing balance10.001 data COLLECTIONThe electrolytic carrel employ in this investigation is illustrated in Fig 1Fig 1 Diagram of electrolytic cell used in investigationIn this investigation, a on-line(prenominal) is passed through the solution with slob as the cathode and black lead as the anode. After a set make sense of duration, the roundabout is disconnected and the chaw of the cathode is measured. Following which, calculations argon made so as to determine the Avogadros and Faradays constant.qualitative ObservationsWhen the D.C power source was upseted on, bubbles were formed at the Graphite anode. As the reply progresses, powdery substance gets suspended in the sol ution and a black solid deposits shag be found at the tail of the beaker and there is a visible decomposition of the black lead electrode. As the answer progress, a pink story of bulls eye forms on the crap strip. The hog strip is originally brown in colour while the black lead electrode is black in colour. Eventually, as the black lead electrode decomposes, the graphite groinecules leave turn the hog (II) sulphate solution from blue to black in colour. However, when the slovenly person sulfate solution is filtered, it is noted that there is a decrease in the intensity of the blue colour in the filtrate after the electrolysis. The initial 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)0.25Cathode run 1Initial the great unwashed/g ( 0.001 g)1.315Final mass/g ( 0.001 g)1.279Change in mass/g ( 0.002 g)0.036Chemical equation for reaction at the anod e2H2O (l) O2 (g) + 4H+ + 4e (aq)Chemical equation for reaction at the cathodeCu2+ (aq) + 2e Cu (s)Calculations for cathodeCalculations misunderstanding PropagationChange in mass(Cu) = 0.036gMols of (Cu) = =5.7 x 10-4 break body of waterNumber of seawall of electrons-Using mol ratioCu2+ (aq) + 2e Cu (s)Number of mol of electrons =11.4 x 10-4Charge streamlined through circuitNumber of electron charges in circut=Where is the elementary charge, the charge of superstar electronNumber of electron charges in circuit=Number of mol of electronsWhere L is the Avagandros constant equivalence the number of mols of electrons obtained form the slovenly person 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=% uncertainty of Mass(Cu) =5.6%% uncertainty of number of mol of electrons =5.6%% charge flowing in circuit = part misunderstanding section error for Faradays Constan t = == 30%Percentage uncertainty of faradays constant =5.9%Percentage taxonomical error in Faradays constant =%error-%random error= 24.1%Percentage error for Avogadros Constant = = 30%Percentage uncertainty of Avogadros Constant =5.9%Percentage authoritative error in Avogadros Constant =%error-%random error= 24.1%ConclusionIn conclusion, the figure cheer of Faradays constant is mol-1 and Avogadros constant is.As seen above, the percentage error for both Faradays constant and Avogadros constant atomic number 18 both 30% and after subtracting the error due to instrumental uncertainty, the % systematic error obtained is 24.1%. This shows that the experimental abide bys mensural differ greatly from the books determines, indicating that there has been a epoch-making amount of systematic error, which has caused the compute value to be ofttimes different from the literature value. As percentage error of both Faradays constant and Avogadros constant are very much larger than their respective percentage uncertainties, this intimates that the sources of systematic error are significant and cannot be ignoredEvaluationType of errorLimitation receiptsSystematicOxidation of copper occurs naturally when the copper strip is receptive 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 approach of the, it is demanding to completely rid of all the copper oxide. The formation of copper oxide giveing affect 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 eventually start to form a layer of copper (II) oxide which will not be involved in the electrolysis reaction. This will reduce the amount of copper which will undergo reaction, causing it to reduce the eventual calculated Faradays a nd Avogadros constant.It is impossible to prevent the oxidation of copper from incident however, this systematic error can be belittled. 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 h telephone circuitsbreadth dryer can be used instead to blow 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 unavailing to fall off as a layer of copper plates over the graphite fragments. This can be observed in the experiment when the copper strip is upstage at the end of the experiment black fragments of graphite are observed on the copper strip.The graphite fragments would easil y happen upon the copper strip mainly because they were quite near each other. Hence, the graphite fragments could easily move towards the copper strips and attach 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 exactly sink towards the bottom of the beaker, hence it will be less apparent 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, takingsing in an inconsistent current throughout the experiment. If the current deviates from the give tongue to 0.25, the expirationing Faradays constant and Avogadros constant will be stirred as well. An increase in current will issuance in an increase in the Faradays constant and Avogadros constant calculated 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 shifting electrodes, a retort stand can be used to hold the electrodes in place and prevent them from moving. This is much much 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 resistance of the circuit so that the in demand(p) current can be achieved. As current is inversely 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 s ource of systematic error in this experiment would come from the fact that, the reading on the ammeter does not indicate the actual electric current flowing through the electrodes and the electrolyte as this value may decrease due to power losses in the wires. That is the galvanising 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 cognise and included in the calculations made.SystematicThe copper electrode may undergo a process called passivation1 where the alloy 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 h igh 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 hit gain 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 last-place mass as copper ions plate over the graphite fragments on the copper electrode.Ran dom ErrorDue to time constrains, only 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 more sets of data can be collected, so that a graph of metal deposited against time can be plotted and the gradient will enable the determination of the two constants.1 Metal passivation-en.w,wikepedia.org/Passivation_(Chemistry). Accessed- 26/2/2014)