Question about Galvanic cells with an inert conductor (1 Viewer)

[dbliuc]

If the experiment was like this, with an inert conductor http://community.boredofstudies.org...29198d1384568000-galvanic-cell-chem2.4.11.png

And one of the electrodes was zinc and the other graphite, and the electrolyte was NaCl (Sodium Chloride), what is getting oxidised and what is getting reduced?

Also, what would the overall redox reaction be?

 

[Queenroot]

Zinc oxidised and Sodium reduced

 

[Queenroot]

It is an electrolytic cell so the reaction would be non-spontaneous

 

[dbliuc]

It is an electrolytic cell so the reaction would be non-spontaneous

Can a non-spontaneous reaction be read off the voltmeter?

 

[Queenroot]

It would be a negative reading indicating the reaction is non-spontaneous.

 

[dbliuc]

It would be a negative reading indicating the reaction is non-spontaneous.

When we did our experiment, we got a positive reading. The graphite was connected to the positive terminal and the zinc to the negative terminal.

 

[Queenroot]

When we did our experiment, we got a positive reading. The graphite was connected to the positive terminal and the zinc to the negative terminal.

That's strange. Must have to do with the Chlorine and H2O then.

 

[dbliuc]

That's strange. Must have to do with the Chlorine and H2O then.

Is it a possibility that the Zinc was the one being oxidised and chlorine being reduced? Our teacher didn't really tell us much about this experiment

 

[HeroicPandas]

Is it a possibility that the Zinc was the one being oxidised and chlorine being reduced? Our teacher didn't really tell us much about this experiment

If that is so, then E(cell) would still be negative

Could you please give me the list of observations of this experiment? (eg. formation of metal on graphite, bubbling in anode/cathode compartment, change in concentration of anolyte/catholyte)

Was the positive voltage read mistaken to be voltage supplied for this (supposedly) non-spontaneous reaction to occur?

 

[enigma_1]

This is a shipwrecks question.
The species you have are: Zn, Na2+, Cl-, H2O

Which of the species can undergo oxidation? Look at the reduction potentials table and determine which of the above are on the RISGHT side indicating OXIDDATION: Zn, H2O, Cl-

Now Which of the species can undergo reduction? Look at the reduction potentials table and determine which of the above are on the LEFT side indicating REDUCTION: H2O, Na2+

From the OXIDATION species, let's write out the voltage for each:
Zn to oxidise requires = 0.76 (flip because it's oxidation)
H2O = -1.23
Cl- = -1.36

So which of the above is the most positive? Zn so zinc METAL oxidises. Write the eqn: Zn(s) --> Zn2+ + 2e-

From the REDUCTION species, let's write out the voltage for each:
Na2+ = -2.71
H2O = -0.83 this is the more positive one so it reduces, write the eqn: H2O + e-->0.5H2(g) + OH–

I suck at writing overall eqns lol
Someone pls help

 

[enigma_1]

That's strange. Must have to do with the Chlorine and H2O then.

Depends if solution was concentrated or not I think

 

[dbliuc]

Depends if solution was concentrated or not I think

In our prac, we also performed an experiment where we used the same metal but different concentrations of the NaCl (0.1 Mol, 1.00 Mol, 0.001 Mol), and we got higher readings the more concentrated the solution was. Would that help with anything?

 

[dbliuc]

If that is so, then E(cell) would still be negative

Could you please give me the list of observations of this experiment? (eg. formation of metal on graphite, bubbling in anode/cathode compartment, change in concentration of anolyte/catholyte)

Was the positive voltage read mistaken to be voltage supplied for this (supposedly) non-spontaneous reaction to occur? (highly unlikely because you just started Module 1 of chemistry)

The only observations we were told to take was the reading on the voltmeter. If it helps, we used different metals in the same solution, the higher reading we got was from Magnesium (considering we used Mg, Cu, Zn and Nickel)

 

[HeroicPandas]

The only observations we were told to take was the reading on the voltmeter. If it helps, we used different metals in the same solution, the higher reading we got was from Magnesium (considering we used Mg, Cu, Zn and Nickel)

Did you recall any bubbling in the cathode compartment? (links with enigma's response)

 

[dbliuc]

Did you recall any bubbling in the cathode compartment? (links with enigma's response)

Nope, we didn't notice any bubbling, or metal depositing on the graphite (but then again, we weren't really paying attention to that).

 

[AJB12]

Could someone explain how this cell works?

 

[someth1ng]

The only observations we were told to take was the reading on the voltmeter. If it helps, we used different metals in the same solution, the higher reading we got was from Magnesium (considering we used Mg, Cu, Zn and Nickel)

That's bad science, if you ask me. In future, always look at everything.

When we did our experiment, we got a positive reading. The graphite was connected to the positive terminal and the zinc to the negative terminal.

Are you going to tell us ALL of your results? Numbers/potentials, concentrations etc?

 

[dbliuc]

Just to clarify. This is the exact experiment we did. It was a prac exam, so I don't have the results with me.
http://puu.sh/d9GSa/3e3e7c3e6e.png

 

[anomalousdecay]

In regards to using a multimeter (in your experiment you should only use the voltmeter option on the multimeter), you can get a positive or negative reading depending how you connect up your multimeter to the electrodes. Black/Negative goes to anode, and Red/Positive goes to the cathode. The reading you obtain on your multimeter will be:



This is exactly what you want as the total potential of the cell is characterised by the above calculation.

 

[someth1ng]

Well, considering nobody else will answer this, here's my answer.

Basically, what happens is that some of the protons in solution (H+) gain electrons (is reduced) from the test metal (is oxidised) which produces a bit of hydrogen gas.
Reduction: 2H⁺+2e^- --> H₂
Oxidation: Metal --> Metal²⁺+2e^-

I suspect the magnitude of the potentials would be in this order (assuming all other conditions are controlled):
Cu<Ni<Zn<Mg

I don't think copper would give a reading because it has a higher reduction potential than H+ while the other test metals have lower reduction potentials.

Unsurprisingly, Mg/Zn/Ni are all very prone to dissolving in acid and Cu is much more resistant but still reacts with some acids (eg HNO3).