Edexcel 5 Question..

Help

These questions are harassing me

1.
Suggest a reducing agent which might reduce aqueous Co3+ ions to cobalt metal.. Give your reasoning.

Zn2+ + 2e- <--> Zn (-0.76)
Fe2+ + 2e- <--> Fe (-0.44)
Co2+ + 2e- <--> Co (-0.28)
Sn2+ + 2e- <--> Sn (-0.14)
O2 + 2H+ + 2e- <--> H2O2 (+0.68)
Co3+ + e- <--> Co2+ (+1.82)

<--> is my beautiful representation of a reversible reaction

2.
Suggest two factors that might prevent a reducing agent from being as effective as the electrode potentials might seem to suggest.

This is from the January 2003 paper - If anyone knows where an online mark scheme is, can they let me know.. cheers

Reply 1

charlie_1404

Now I'm confused... couldn't all of them because reversing the sign of each reducing agent in the list and adding it to +1.82 gives a positive Ecell value?

For question 2: change in temp, pressure or concentration. In each case the equilibrium position could move and this will affect the electrode potential.

Reply 2

suzzjj

ninibee

Help

These questions are harassing me

1.
Suggest a reducing agent which might reduce aqueous Co3+ ions to cobalt metal.. Give your reasoning.

Zn2+ + 2e- <--> Zn (-0.76)
Fe2+ + 2e- <--> Fe (-0.44)
Co2+ + 2e- <--> Co (-0.28)
Sn2+ + 2e- <--> Sn (-0.14)
O2 + 2H+ + 2e- <--> H2O2 (+0.68)
Co3+ + e- <--> Co2+ (+1.82)

<--> is my beautiful representation of a reversible reaction

2.
Suggest two factors that might prevent a reducing agent from being as effective as the electrode potentials might seem to suggest.

This is from the January 2003 paper - If anyone knows where an online mark scheme is, can they let me know.. cheers

answer 1..zinc metal. it will reduce the Co3+ to Co2+ because when its half equaction is reversed and added to Co3+ + e-= Co 2+, the Ecell= +0.76+ 1.82v, which is positive , so the reaction will take place. and it will reduce Co 2+ to Co, as Ecell = +0.76 + (-0.28) = +0.48 v is also positive..

answer 2.. non standard condition and higher activation energy

hope this helps
good luck

Reply 3

BabyGirl

OP, I've PM-ed you with a website for markschemes. Hope that helps!

Reply 4

ninibee

OP

Perfect.. Thanks

Reply 5

Kennychan222

a) Zn2+ ion....It reduce Co3+ into Co2+ and then Co metal

b) 1) Temperature
2) Pressure

Reply 6

Eau

15

Kennychan222

a) Zn2+ ion....It reduce Co3+ into Co2+ and then Co metal

b) 1) Temperature
2) Pressure

Uh.... no.

It's not the ion. The metal causes reduction, hence Zn. I want to point out that Fe also works.

Temperature - irrelevant here. High activation energies, and non-standard conditions (not 1 atm or not 1 mol.dm^-3)

Edexcel 5 Question..

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