Lab 1: Determination of the Charge on an Electron by the Method of Electrolysis Introduction In this experiment we wish

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Lab 1: Determination of the Charge on an Electron by the Method of Electrolysis Introduction In this experiment we wish to use Faradays laws of electrolysis and the concept of Avogadro's number (N.) to determine the amount of electrical charge on an electron In 1833 Faraday first performed a number of experiments on the conduction of electricity by solutions. In experiments of this kind one introduces two metallic plates called electrodes into a conduction solution called an electrolyte. The combination of the two electrodes and the electrolyte is called an electrolytic cell. When current is passed through the cell, chemical reactions occur at the electrodes, and in the process positive as well as negative ions are deposited. In this experiment the electrolyte cell (shown in Figure 1) consists of two copper electrodes immersed in a solution of copper sulfate (CuSO). The solution of copper sulfate in water is strongly ionized into Curs and socions The electrodes are connected to a battery. This sets up an electric field in the solution which causes the Cr** ions to drift toward the negative electrode and the 50 ions to drift toward the positive electrode. The Cu** ions that reach the negative electrode combine with two electrons from the metal and are deposited as metallic copper in accordance with the equation: Cu +2e=Cunetul (1) The Sions, on contacting the positive electrode, give up their two electrons to the metal and combine with a Cu atom to form a molecule of Cuso, which being readily soluble, goes into solution: 50/ + Cuneta = 2e + Cuso (2) The net effect of the pair of reactions at the electrodes is the removal of a copper atom from the (+) electrode and its deposition on the (-) electrode There is no change in concentration of the Cuso, in the solution. Both electrodes are copper, since even if copper is being plated on an electrode of some other metal, the electrode becomes effectively copper as soon as the process is under way and a thin layer of copper has been deposited. Background, Theory and Application Knowledge of the mass deposited on the cathode will enable us to calculate the number of atoms which were used to obtain the mass. Realizing that the

charge (e) deposit of one atom of copper requires the transfer of two electrons from the external circuit to neutralize the positive charge of the deposited fon, we can Calculate the total charge transferred. This charge is a function of the electronic In order to derive a formula for the electronic charge (e) in terms of the quantities of the experiment we need to state Faradays Laws of electrolysis: Faradays Law 1. The mass of an element deposited at an electrode is directly proportional to the quantity of electrical charge that passes through 2. The mass of the element deposited by a given quantity of charge is directly proportional to the chemical equivalent (atomic weight divided by valence) of the element Q=the total charge through the cell me mass of each Custom and 2e = charge carried by each Ou atom Ami 02 (3) the cell Then But, the mass of an atom equals its atomic weight ( divided by Avogadro number (N.). Therefore by substituting = x/N. equation (1) becomes AMIN (4) () MO 2AV (5) But Q - It, where I current in amperes and te time in seconds. Therefore, (6) 2V Equipment Ammeter. Theostat switch, electrolytic cell power supply clock, beaker (500 to 1000 ml) and balance Experimental Procedure 1. Make the circuit shown in figure 1 and ask your instructor to check the circuit

2 Connect the terminal leads to your circuit and open the switch before plugging the leads into the power supply. With the rheostat adjusted so that the maximum resistance is in the circuit close the switch. Adjust the rheostat resistor until a suitable current is obtained. Keep the current less than about 0.25 ampere. See that the rheostat is so set that it will be possible later either to increase or decrease the current 3. After the above preliminary observation, open the switch, remove the cathode plate and clean it. Scrape off any loosely adhering granules of metal with sand paper. Rinse in clean water and carefully dry completely by twirling gently in the air. Then carefully weigh the plate. 4. Replace the plate, and at an accurately noted time, close the switch and start the current. One observer should constantly watch the ammeter and adjust the resistance so as to keep the current constant. Using a current of about 0.5 Ampere, let the current flow for about 40 minutes. This will give an evenly distributed and well-attached layer of copper on the cathode. Note carefully the time when the switch is opened 5. Remove the cathode plate, rinse it in a glass of clean water (not under direct faucet flow), and then carefully dry it completely by twirling gently in the air. Be careful not to jar off any of the loose granules of copper from the cathode. Weigh it carefully and compute the gain in mass (Am) of the cathode. 6. Determine the charge on the electron from your measurements. The experimental value of the charge on the electron is currently given as (1.60206 0.00003) x 10- coulombs Compare your result with this and discuss any discrepancy in terms of your calculated estimate of uncertainty Rh А SO4- Cu. CuSO4 Figure 1

Answer All Assigned Questions: 1. Based on equation 6, what would you predict would be the relationship between the mass change and the time. Check with your numbers from Table 2. Is this prediction verified? 2. If you had initially selected a different metal, say Nickel, or Silver, in the simulation, what do you think would change, and why?