galvanic cell question help please (2 Viewers)

[kr73114]

http://www.ed.gov.nl.ca/edu/k12/evaluation/chem3202/chem3202_aug07.pdf
qu.54(b)
pg18.

 

[kr73114]

http://www.boardofstudies.nsw.edu.au/hsc_exams/hsc2000exams/hsc00_chemistry/00chemistry2U.pdf

It's also in the 2000 HSC chemistry exam.
33e) ii) and iv)

Can't anyone help? pls

 

[jamesfirst]

Is 54 b) a galvanic cell question ???


For 33 e) ii) I don't know what Pt is and it's not on the standard potential table so I don't know if Cu is more reactive than Pt... But the colour change is due to the redox reaction taking place. The displacement reaction will cause the electron to move from anode to cathode which means that the ions from the solution will leech onto the cathode and metal of anode will be oxidised producing more of its ion in the solution. Hence the colour of the solution changes.. (I think !!!! Don't call me dumb if I'm wrong )

iii) Magnesium is more reactive (from the potential table) hence it acts as anode and will oxidise (donate its electron).

Ox: Mg -> Mg^+2 + 2e- = 2.36 V
Red: 2Ag^+1 + 2e- -> 2Ag = 0.80 V

Net Potential difference = 2.36 + 0.80 = 3.16 V


I don't know if it's right.. Can anyone else confirm ?

 

[FCB]

James youre correct for the 33e) (iii)

For the 33e(ii) the copper solution would go darker as platinum is chemically inert (i think it is anyway) and thus it would receive the electrons from the copper. Ions from the copper will go into solution making the solution a darker blue (the Cu2+ will make it bluer) and the solution containing the Fe3+ and the Fe2+ will become a lighter colour until the copper electrode goes into solution.

I think this is the answer and if not then im sorry, but i cant help you.

p.s The paper looks so long and it would probably take ages to complete.

 

[hscishard]

54b) That paper doesn't look like it's made in Australia. I got 0.3A. I'm not confident with the answer because I had to use physics to solve this one..

33ii) I'd say the left solution will become more green(pale) and the right cell will become
darker blue.
iv) I don't know much on this but it's caused by the changing concentrations the electrolytes in the half cells

these questions seem harder than the few hsc questions i've done

 

[danjw]

I'm almost certain what 54b is asking is not in the syllabus, I've never seen anything like it.

 

[jamesfirst]

Same. I doubt they'll ask it. And is platinum (Pt) used in HSC anymore ? Because it's not on the standard potential table.


Oh wait. My teacher said something about platinum being chemically inert. But I don't know what that means. Can anyone explain ????

 

[hscishard]

Pt is a "perfect" conductor

.ca seems to be california...hmm
If the syllabus has or had a dot point on 1A= 1C/s, then this question is doable.

 

[FCB]

54b) That paper doesn't look like it's made in Australia. I got 0.3A. I'm not confident with the answer because I had to use physics to solve this one..

33ii) I'd say the left solution will become more green(pale) and the right cell will become
darker blue.
iv) I don't know much on this but it's caused by the changing concentrations the electrolytes in the half cells

these questions seem harder than the few hsc questions i've done

Wouldnt it become less green as the Fe2+ is more easily reduced.??

 

[FCB]

Same. I doubt they'll ask it. And is platinum (Pt) used in HSC anymore ? Because it's not on the standard potential table.


Oh wait. My teacher said something about platinum being chemically inert. But I don't know what that means. Can anyone explain ????

Yes platinum is still used. In fact, its often used when something is getting bubbled into solution (Cl2) as it doesnt take part in the reaction.

Chemically inert means it will not take part in the reaction. The electrolyte contains ions and these will just build up on the Pt electrode

 

[jamesfirst]

Fe2+ isn't been reduced ???

It's the electrodes that undergo redox reaction and the solutions just leech onto the cathode. So I think if Pt was reduced, then the green solutions of Fe2+ will fade.

Same point as FCB

 

[hscishard]

I dunno tbh. I just saw fe3+ is more more reducible, so I just went less orange and therefore more green.

Inert = unreactive

 

[FCB]

Fe2+ isn't been reduced ???

It's the electrodes that undergo redox reaction and the solutions just leech onto the cathode. So I think if Pt was reduced, then the green solutions of Fe2+ will fade.

Same point as FCB


now someone explain to me what chemically inert means!!!

Wait, In a way, i dont understand your reply.

But according the the standard table to reduction thing the Fe2+ is more easily reduced and thus the Fe2+ will come out of solution and thus it will become 'Less' pale.

 

[jamesfirst]

But Fe+2 is a solution ?

I thought it was the electrodes that undergo redox reaction


so by saying Fe+2 is reduced, wouldn't it be incorrect ?

 

[hscishard]

Ok...if fe2+ is more reducible then wouldn't it be still orange? I thought fe3+ was more reducible

 

[FCB]

But Fe+2 is a solution ?

I thought it was the electrodes that undergo redox reaction


so by saying Fe+2 is reduced, wouldn't it be incorrect ?

But the Fe is displaced out of solution and thus it has to gain electrons which means its getting reduced.

Ok...if fe2+ is more reducible then wouldn't it be still orange? I thought fe3+ was more reducible

Now i am confused. Fe2+ has higher reducing power.

 

[hscishard]

Now i am confused. Fe2+ has higher reducing power.

you sure? Fe(3+) + e- ---> Fe(2+) is 0.77V. As you go down the table, the stuff are more reducible.

 

[FCB]

At the Hydrogen one and down the oxidising power increases.

 

[FCB]

you sure? Fe(3+) + e- ---> Fe(2+) is 0.77V. As you go down the table, the stuff are more reducible.

That means you have to pump in 0.77v for it to happen spontaneously whilst that not the case with Fe2+

 

[hscishard]

That means you have to pump in 0.77v for it to happen spontaneously whilst that not the case with Fe2+

Okay...i'm just thinking of which one is more easily reduced which I think is Fe3+ to fe2+

we need some1 else