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Barbara Woodall

Chemistry 152 DR. Toung

In this experiment we poured Pepsi, Mt Dew and Salt water into beakers to make electrochemical cells, without a salt bridge. We selected five different metals; Aluminum, copper, zinc, magnesium, and lead. Out of the five metals we choose two, we connected these two metals to a voltmeter with the help of gator clips. Through the voltmeter we were able to read both the Current and the Voltage of the electrochemical cell. We measured the voltage from each possible metal combination in each of the electrochemical cells. There was not much of a difference between the Pepsi and the Mt. Dew. The Salt water though seemed to be a better electrolyte. When comparing the readings we recorded from our experiments to the table in our Chemistry book none of the voltages were the same or even close, though the Salt water was the closest. We tried one more type of electrochemical cell we poured half of the Pepsi into another beaker, so we had two beakers of Pepsi. We made a slat bridge and then measured the voltages from all the possible five metal combinations. Even with the salt bridge the voltages did not change much.

The following is a chart containing the results of each electrolyte and metal combination:

|Metal Combinations |Pepsi |Mt. Dew |Salt Water |Pepsi with |

| | | | |Salt Bridge |

|Al & Cu |0.51 |0.5 |0.58 |0.54 |

|Al & Zn |-0.51 |-0.5 |-0.27 |-0.36 |

|Al & Pb |0.06 |0.08 |0.26 |0.07 |

|Al & Mg |-1.33 |-1.11 |-0.94 |-1.01 |

|Cu & Zn |-1 |-0.97 |-0.82 |-0.94 |

|Cu & Pb |-0.43 |.-39 |-0.29 |-0.43 |

|Cu & Mg |-1.8 |-1.73 |-1.32 |-1.71 |

|Zn & Pb |0.56 |-0.58 |-0.55 |-0.58 |

|Zn & Mg |0.82 |-0.9 |-0.63 |-0.8 |

|Pb &Mg |1.31 |-1.43 |-1.14 |-1.34 |

Questions

2.a) What kind of experiment(s) demonstrates the necessity of the equivalent of a salt bridge (even if a physical salt bridge isn't used.

When measuring th voltage of two different metals in the same beaker filled with an electrolyte there is no need for a physical salt bridge because the electrons do not need to travel between two different beakers. The purpose of the Salt bridge is to provide electrical contact between the electrodes that make up the cell. If the electrodes are with the same electrolyte that can move somewhat freely through the solution and move towards the anode/cathode without there being a physical connection. An experiment where the anode and cathode are in the same electrolyte solution demonstrates the necessity of the equivalent of a salt bridge.

2.b) How does changing the metals in the galvanic cell change it measure voltage?

Each metal has different properties and as so different metals have different potentials for converting energy

2.c) You have some “lead” fishing sinkers. How can you tell if they are really made of lead? Devises and do another, non-electrochemical experiment to verify or refute the identity of the metal in the fishing sinkers.

You can test the fishing sinker for the properties of lead such as it is dull, nonmagnetic, and you can easily scratch the surface with a harder object. Also if you do know the voltage of the lead you can check table in the book to see if it is the same of ever close to the recorded voltage.

2.d) What is the effect of changing the electrolyte (soda)?

There was not much of a difference in the voltages of any of the metals. The biggest difference was in the change between Pepsi and Mt. Dew to Slat Water. Even with the salt bridge in the Pepsi there was not much of a difference.

3.

|Metal Combinations |Pepsi |Mt. Dew |Salt Water |Pepsi with |Table 19.1 |

| | | | |Salt Bridge | |

|Al & Cu |0.51 |0.5 |0.58 |0.54 |Al -1.66 |

|Al & Zn |-0.51 |-0.5 |-0.27 |-0.36 |Zn -.76 |

|Al & Pb |0.06 |0.08 |0.26 |0.07 |Cu .34 |

|Al & Mg |-1.33 |-1.11 |-0.94 |-1.01 |Pb -.13 |

|Cu & Zn |-1 |-0.97 |-0.82 |-0.94 |Mg -2.37 |

|Cu & Pb |-0.43 |.-39 |-0.29 |-0.43 | |

|Cu & Mg |-1.8 |-1.73 |-1.32 |-1.71 | |

|Zn & Pb |0.56 |-0.58 |-0.55 |-0.58 | |

|Zn & Mg |0.82 |-0.9 |-0.63 |-0.8 | |

|Pb &Mg |1.31 |-1.43 |-1.14 |-1.34 | |

None of our measured voltages match up with the voltages in the book. If I understand correctly the metals that were measured in table 19.1 were dissolved in the solution. We did not take correct notes to identify the cathode and the anode so I could not find E-cell.

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