Question

Part 4: Electrolysis Check out a conductivity kit from the stockroom window (includes well-plate and well-charged 9V battery). You will make observations on three solutions. Fill the oblong well with distilled water for rinsing the electrodes. First well: Fill the well 2/3 full with 0.1 M Na SO, +one drop of phenolphthalcin. Place the electrodes into the solution. Look carefully around cach cloctrode. You may see the appearance of color or the disappearance of color, as well as bubbles. Make a table showing the two polari- ties for your headings and record these observations under the appropriate column in your lab notebook table. Which is the anode? the cathode? Rinse the electrode with distilled water. Electrochemistry 76 Second well: Use a solution of 0.1 M KI + one drop of phenolphthalein. Follow the same procedure outlined for the first well. Additionally, fill an adjacent well with the 0.1 M KI, this time without any phenolphthalein. Place the clectrodes in the solution for several minutes. Note any observations. Third well: Use a 0.1 M solution of CuCl + one drop of phenolphthalein. Follow the same pro- cedure as outlined for the first well. Based on your observations, write the half reactions at the anode and cathode for each of the above wells and write the overall reaction. Make a schematic sketch of the cell you set up in Well #1. What is the purpose of the phenolphthalein in each well?

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Answer 1

128 Caa) (g) Electedytic all +) desteode is known Anode and oxidation takes place at Anode Negative - electrode is knoron as cathode Reduction takes place at cathode. Phenolphthaleen is a Pink colour in basic solution and Colour less in acidic solution. teoll - I electrolysis of No,304 solution. In this tydedysis of water takes place. Nat and sour Tous does not undergoes Redox reaction due to Reduction potential. Anode reaction 2o 4+ + Q1 +46 cathode le reaction 240 +26 → H,1 + 20H bubbles due to g) can) at anode a gas liberate and at cathode Hagos liberated color dueto & At cathode reaction off con forms this leads to basic condition caueses Phenolphthalien to Pink colour at cathode (-ue electrode). well Electedlysis of KI solution. cridation Icons and Reduction of H₂O takes place. It is due to standoed Reduction potential of kties KE° = -2.93 v, HT E=0.00 I5 E 0.544, OK t= 0.400. -> I, Inaal 2 Howe 9) bubbles due to. At cathode He gas liberated. color dueto At Anode formation Is causes violet ① yellow colove. At cathode pink colour formation takes place to basic condition due to frohnation of cons as shown above. well 3: Electedlysis of cache solution. oridation of el cons at anode and Reduction of cations takes place at cathode Anode a reaction 2 Ioan + ze Cathode le reaction +2e Hb t + 2040 ar)

cate cus) Arrode half reaction achary clog, the cathode half reaction; +2€ @9) bubbles due to: At Anode cle 303 firmation takes place It smells like bleach Color due - At cathode reduction cat2 cons takes place this caveses Colour of Riddish brown at calliode. this is due to fuimation @ deposition of coppee at calliode