CHEM 126 Lecture Notes - Lecture 10: Ammonium Chloride, Lead, Reagent

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violetcamel580

9 Aug 2020

School

Simon Fraser University

Department

Chemistry

Course

CHEM 126

Professor

Jenny Wong

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Document Summary

What is the purpose of polishing the electrodes prior to using them in the cell, the purpose of polishing the electrodes for approximately 30 seconds with. Scotch brite pad prior to using them in the cell is to remove the thin outer oxide layer. The purpose of a salt bridge is to minimize the junction potential between the solution interface of the two half cells. It is important to put ionic species into the salt bridge that will not be reduced or oxidized in either of the half cells such as alkali cations and halide anions. Also, it is important the charge balance in each half cells facilitated by the ions in the salt bridge occurs at the same rates. The ideal species for a salt bridge depends on their mobility which means its size. Small ions have a higher mobility than larger ions.

Related Questions

What are the similarities and differences between Figure 20.3 and Figure 20.4? (b) Why are Na⁺ ions drawn into the cathode half-cell as the voltaic cell shown in Figure 20.5 operates?

One Class Solution:-

Figure 20.3 shows spontaneous reaction when a strip of zinc is placed in contact with a Cu²⁺ solution. Cu²⁺(aq) ions fades and copper metal deposits on the zinc. At the same time, the zinc begins to dissolve.

Same redox reaction: Cu²⁺_(aq) +Zn → Cu +Zn²_(aq)⁺ is occurs in both cases (Figure 20.3 and 20.4). The significant difference between Figure 20.3 and 20.4 is that in the voltaic cell the Zn metal and Cu²⁺(aq) are not in direct contact with each other. Zn metal is in contact with Zn²⁺(aq) in one compartment, and Cu metal is in contact with Cu²⁺(aq) in the other compartment. Cu²⁺(aq) reduction can occur only by the flow of electrons through an external circuit, namely, a wire connecting the Zn and Cu strips. Electrons flowing through a wire and ions moving in solution both constitute an electrical current.

In Figure 20.5, a salt bridge serves this purpose. The salt bridge consists of a U-shaped tube containing NaNO₃(aq), whose ions will not react with other ions in the voltaic cell or with the electrodes. The electrolyte is often incorporated into a paste or gel so that the electrolyte solution does not pour out when the U-tube is inverted. As oxidation and reduction proceed at the electrodes, ions from the salt bridge migrate into the two half-cells—cations migrating to the cathode half-cell and anions migrating to the anode half-cell—to neutralize charge in the half-cell solutions. Whichever device is used to allow ions to migrate between half-cells, anions always migrate toward the anode and cations toward the cathode.

harlequinguinea-pig268

Hello,

Here are some conceptquestions that come from a review for an exam, having some troubleplease help me!!! I know there are multiple questions, Sorry! Ihope someone will help me! be brief but I still want to be able toknow why its that answer! Thanks!

1. What is the purpose of the salt bridge in a galvanic cell? Couldyou have a galvanic cell without it?

2. If a redox reaction involves no net destruction or production ofelectrons, how do we obtain âhalf cell potentials?â

3. Is E0 positive or negative for an electrolytic cell? For agalvanic cell?

4. A battery is made of two half cells that have a combined E0 of1.8 volts. Is the voltage constant through the life of the battery?Explain why or why not.

5. A galvanic cell is made from a Zn rod in a solution of 1.0 MZnSO4 and a Cu rod in a solution of 1.0 M CuSO4Â¬. The two cells areconnected with a salt bridge and used to run a small motor. What isthe voltage produced from this cell and which electrodes getsheavier (due to plating of metal) and which electrodes becomeslighter via corrosion. Which electrode is the anode, which is thecathode? You can assume that both half cell reactions involve 2e-.

6. What is the voltage of the cell above if instead, a 0.10 Msolution of ZnSO4 is used? What is the voltage when equilibrium isreached?

7. Using the galvanic system in #7 above, show what happens to thecell voltage as the battery is used. Show what happens withchemical equations and calculate the voltage with the Nernstequation.

8. Explain in detail one of the commercially electrochemicalprocesses described in class. Show the redox equations, explain thetype of electrochem process and explain why this process isindustrially important.

I hope you can HELP!Thanks!

tanmammoth274

CHEM 126 Lecture Notes - Lecture 10: Ammonium Chloride, Lead, Reagent

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