Chemistry Voltaic Cell Design Lab

Abbey He Class 1 Research Question: What is the relationship between standard electrode potential and rate of electrolysis? Aim: To investigate which cathode (out of copper, zinc and iron) is the best at separating Copper (II) sulfate solution. Hypothesis: The iron cathode will have the largest increase in mass due to it having the most positive standard electrode potential out of the three. Independent Variable: Cathodes made from various metals Dependent Variable: Mass of metal deposit Control Variables:  Surface area of the electrodes  Time allowed for electrolysis to occur  Voltage of battery pack  Graphite Anode Background Information: Electrolytic cells are used to make non- spontaneous redox reactions occur by providing energy in the form of electricity from an external source-a battery pack in the case of this experiment. In an electrolytic cell electricity is passed through an electrolyte and electrical energy is converted into chemical energy. An electrolyte is a substance which does not conduct electricity when solid, but does conduct electricity when molten or in aqueous solution and is chemically decomposed in the process. The electrolyte in this experiment it Copper (II) Sulfate. The electrode which is attached to the negative pole of the battery, and which supplies electrons to the electrolyte, is called the CATHODE. Reduction takes place at the cathode. Copper cations from the Copper (II) sulfate solution will attract to the electrons at the cathode and will then form a deposit around the cathode once the electrons have been gained. Reduction reaction occurring at the cathode: Cu2+(aq) + 2e- → Cu(s) The corresponding oxidation reaction takes place at the anode. The anode, which is attached to the positive pole of the battery, attracts the sulfate and hydroxide ions. Once oxidized, the hydroxide ions will form O2 gas which can be seen as bubbles around the anode. Oxidation reaction occurring at the anode: 2H2O(l) → O2(g) + 4H+(aq) + 4eElectrodes with a more positive standard electrode potential values have a higher tendency for reduction to occur and are therefore better cathodes in electrolysis. Same theory applies for anodes-metals with lower standard electrode potentials tend to carry out oxidation. Equipment 250ml of 0.1M copper (II) sulfate solution 1x 250ml beaker

Abbey He Class 1 1x Graphite electrode 1x Copper electrode 1x Zinc electrode 1x Iron electrode 1x 6V battery pack with wires and alligator clips 1x stop watch (±0.01 sec) 1x electronic balance (±0.01g) Sand paper as needed (the electrodes should all be of of the same surface area) Health and Safety Precautions Appropriate lab attire is required. Copper (II) sulfate solution is low hazard at 0.1M concentration. Copper (II) sulfate is considered harmful if the concentration exceeds 1.0M. In case of contact with skin or eyes, rinse immediately with cold water for a prolonged period of time. 1 Method 1. Transfer roughly 250ml of copper (II) sulfate solution to a 250ml beaker 2. Polish the copper cathode the using sheet of sandpaper to ensure the ions will be attracted evenly. Alternatively, use a brand new electrode and omit this step. 3. Dip the copper cathode in solution and then pat dry with a paper towel 4. Weigh the cathode on an electronic balance and record the data on the table below. 5. Set up the battery pack by connecting positive wire to the anode and the negative wire to the cathode with alligator clips 6. Place both the copper and graphite electrode into the beaker containing copper sulfate solution, using the alligator clips to balance the electrodes against the beaker. 7. Turn on the battery pack and immediately start the timer for 5 minutes. 8. After 5 minutes take the copper cathode out of the solution and gently pat dry with a paper towel. 9. Place the cathode on the electronic balance and record the data in the raw data table below. 10. Repeat steps 3-10 with the remaining cathodes (iron and zinc), leaving the graphite anode untouched in the solution until the entire experiment has been completed. Raw Data Table 1 Cathode Zinc Iron Copper

Initial Mass (g) 22.99 23.72 1.58

Final Mass (g) 23.02 23.74 1.6

1 http://www.cdc.gov/niosh/ipcsneng/neng0751.html

Abbey He Class 1