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Author Topic: Lab: Galvanic Cells - How to calculate standard cell potential  (Read 3163 times)

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sallyhansen

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Calculate the standard cell potentials listed below
1. Zn│Zn2+(1 M)║ Cu2+(1 M)│Cu
2. Zn│Zn2+(1 M)║ Ni2+(1 M)│Ni
3. Zn│Zn2+(1 M)║ Fe2+(1 M)│Fe
4. Zn│Zn2+(1 M)║ Ag+(1 M)│Ag

So the ones above are the ones I found for the cell notation
Voltmeter readings
1.05 V
0.42 V
0.31 V
0.42 V

Also how does the accuracy of each result (in terms of a percentage difference) need to be calculated for each one?

Would the equation just be this
% difference = Ka Experimental/ Ka Given * 100
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sallyhansen

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Re: Lab: Galvanic Cells - How to calculate standard cell potential
« Reply #1 on: May 04, 2013, 08:31:58 AM »

Anyone please  ???
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Borek

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Re: Lab: Galvanic Cells - How to calculate standard cell potential
« Reply #2 on: May 04, 2013, 09:54:15 AM »

I guess you won't get any help as your original post is confusing to the point where it is impossible to give any meaningful answer. You failed to explain what is given, what is calculated, what is measured and what you are doing.
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sallyhansen

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Re: Lab: Galvanic Cells - How to calculate standard cell potential
« Reply #3 on: May 04, 2013, 12:24:09 PM »

I guess you won't get any help as your original post is confusing to the point where it is impossible to give any meaningful answer. You failed to explain what is given, what is calculated, what is measured and what you are doing.
Purpose:  The purpose of this activity is to demonstrate the design and operation of a galvanic cell used in scientific research and to compare the measured potential difference of that cell to the calculated potential difference using a standard table.

Materials:
waste beaker      zinc electrode      zinc nitrate solution (1.00 M)
beaker         copper electrode   copper (II) nitrate solution (1.00 M)
Voltmeter      nickel electrode      nickel (II) nitrate solution (1.00 M)
wire leads (x2)          iron electrode      iron (II) nitrate solution (1.00 M)
porous cup      silver electrode      silver nitrate solution (1.00 M)

Procedure:
1.   Place the zinc nitrate solution into a beaker and connect the zinc electrode so that it is partially submerged in the solution.
2.   Place copper (II) nitrate solution into the porous cup and connect a copper electrode so that it is partially submerged in the solution.
3.   Connect each electrode up to the voltmeter.  If the needle moves left, change the connection so that the needle moves right.  Record your observations.
4.   Remove the copper electrode and porous cup.  Pour out the solution from the porous cup and thoroughly rinse and dry the porous cup.
5.   Repeat steps 2 to 4 using nickel/nickel (II) nitrate and zinc/zinc nitrate.
6.   Repeat steps 2 to 4 using iron/iron (II) nitrate and zinc/zinc nitrate.
7.   Repeat steps 2 to 4 using silver/silver nitrate and zinc/zinc nitrate.
8.   Remove the porous cup and pour out the contents of the beaker.
9.   Place the porous cup back into the beaker and use iron/iron (II) nitrate.
10.   Repeat steps 8-9 using nickel/nickel (II) nitrate in the beaker and silver/silver nitrate.

Analysis:
Prepare a table to record your observations. The table should include a column for the following:  the cell notation of the cell constructed, the voltmeter reading, and the calculated cell potential.  Include a column for expressing the accuracy of each result (in terms of a percentage difference).

The chart I have constructed

   Cell notation of the cell constructed   Voltmeter readings   Calculated cell potential   Percentage difference
Zinc nitrate/copper (II) nitrate   Zn│Zn2+(1 M)║ Cu2+(1 M)│Cu
1.05 V      
Nickel (II) nitrate/Zinc nitrate   Zn│Zn2+(1 M)║ Ni2+(1 M)│Ni
0.42 V      
Iron (II) nitrate/Zinc nitrate   Zn│Zn2+(1 M)║ Fe2+(1 M)│Fe
0.31 V      
Silver nitrate/Zinc nitrate   Zn│Zn2+(1 M)║ Ag+(1 M)│Ag
0.42 V      
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sallyhansen

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Re: Lab: Galvanic Cells - How to calculate standard cell potential
« Reply #4 on: May 05, 2013, 04:52:56 AM »

Anyone please my assignment is due Thursday of this week???
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Borek

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Re: Lab: Galvanic Cells - How to calculate standard cell potential
« Reply #5 on: May 05, 2013, 07:51:27 AM »

What are standard potentials of all half electrodes you constructed in the experiment?
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sallyhansen

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Re: Lab: Galvanic Cells - How to calculate standard cell potential
« Reply #6 on: May 05, 2013, 10:23:23 AM »


Half electrodes                Standard Potential
Zn2+(aq) + 2e- -> Zn(s)            -0.76
Cu2+(aq) + e- -> Cu+(aq)            0.16
Fe2+(aq) + 2e- -> Fe(s)            -0.41
Ag+(aq) + e- -> Ag(s)                    0.80
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sallyhansen

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Re: Lab: Galvanic Cells - How to calculate standard cell potential
« Reply #7 on: May 06, 2013, 04:04:31 AM »

What are standard potentials of all half electrodes you constructed in the experiment?
Half electrodes                Standard Potential
Zn2+(aq) + 2e- -> Zn(s)            -0.76
Cu2+(aq) + e- -> Cu+(aq)            0.16
Fe2+(aq) + 2e- -> Fe(s)            -0.41
Ag+(aq) + e- -> Ag(s)                    0.80
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Borek

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Re: Lab: Galvanic Cells - How to calculate standard cell potential
« Reply #8 on: May 06, 2013, 04:17:55 AM »

Cu2+(aq) + e- -> Cu+(aq)            0.16

That's definitely not the right one.
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sallyhansen

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Re: Lab: Galvanic Cells - How to calculate standard cell potential
« Reply #9 on: May 06, 2013, 07:42:41 AM »

Cu2+(aq) + e- -> Cu+(aq)            0.16

That's definitely not the right one.
As you can see the Cu2+(aq) + e- -> Cu+(aq) is 0.16 on this website
http://hyperphysics.phy-astr.gsu.edu/hbase/tables/electpot.html
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kriggy

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Re: Lab: Galvanic Cells - How to calculate standard cell potential
« Reply #10 on: May 06, 2013, 07:46:24 AM »

We have this one in our book at my UNI:
Cu2+(aq) + 2e- -> Cu(s) 0.337V
0,16 goes for Cu+ + e- -> Cu


ok basicaly you calculate standart cell potential for each of your cells and then compare it with value found in book and then calculate mistake or inaccuracy
The cell potential can be calculated by Nernst equation and inaccuracy is calculated like
[(potential calculated - potential in book)/potential in book]*100.
btw did you do more measurements? Or just one?
« Last Edit: May 06, 2013, 08:14:16 AM by kriggy »
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sallyhansen

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Re: Lab: Galvanic Cells - How to calculate standard cell potential
« Reply #11 on: May 06, 2013, 09:21:50 AM »

We have this one in our book at my UNI:
Cu2+(aq) + 2e- -> Cu(s) 0.337V
0,16 goes for Cu+ + e- -> Cu


ok basicaly you calculate standart cell potential for each of your cells and then compare it with value found in book and then calculate mistake or inaccuracy
The cell potential can be calculated by Nernst equation and inaccuracy is calculated like
[(potential calculated - potential in book)/potential in book]*100.
btw did you do more measurements? Or just one?
what do you mean by more measurements?
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kriggy

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Re: Lab: Galvanic Cells - How to calculate standard cell potential
« Reply #12 on: May 06, 2013, 09:36:39 AM »

I mean if you measure each cell only once or more.
For example when we did titrations at school, we did it 3-5 times and used average number. It gets more accurate results.
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sallyhansen

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Re: Lab: Galvanic Cells - How to calculate standard cell potential
« Reply #13 on: May 07, 2013, 03:29:02 AM »

I mean if you measure each cell only once or more.
For example when we did titrations at school, we did it 3-5 times and used average number. It gets more accurate results.
I only did it once for each reaction. And my chemistry class is online so the results will always show up the same.
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sallyhansen

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Re: Lab: Galvanic Cells - How to calculate standard cell potential
« Reply #14 on: May 07, 2013, 01:06:55 PM »

What would the anode and cathode of each reaction be?
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