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ocr a level chemistry question

chem222

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I understand how to work out the standard cell potential but how do you work out the sign of the Ni electrode?

Reply 1

NR22

Well if you can work out the electrode potentials of the cell you’ve created then you can work out the sign... basically for the standard cell electrode you take the most negative away from the most positive one, so you have therefore identified which is your positive terminal and will therefore have a + sign and which is the negative terminal and will therefore have a - sign, does that makes sense?

Reply 2

chem222

Original post by NR22

not sure but thanks a lot anyway ....

for the first one it's 0.77 -(-0.25)

why is the sign of the Ni electrode negative?

Reply 3

charco

Study Forum Helper

Original post by chem222

not sure but thanks a lot anyway ....

for the first one it's 0.77 -(-0.25)

why is the sign of the Ni electrode negative?

Because when compared to the hydrogen ion|hydrogen (SHE) electrode its equilibrium lies further towards the Left Hand Side, i.e. making negative charge

2H⁺(aq) + 2e <=> H₂(g) ........ Eº = 0.0V

Ni²⁺(aq) + 2e <=> Ni(s) ................ Eº = -0.25V

Reply 4

NR22

Original post by chem222

not sure but thanks a lot anyway ....

for the first one it's 0.77 -(-0.25)

why is the sign of the Ni electrode negative?

Yeah so you have identified bpwhen working out the potential difference of the cell that nickel is the negative electrode as you have took its cell potential away from the iron one. Therefore it is losing electrons to the iron the electrons are going from the nickel electrode to the iron electrode so you have a negative charge moving along from that electrode so nickel is the negative electrode... if it’s the negative electrode then it must be minus for negative (how do you short hand negative?? -ive remember the minus sign is for the negative electrode)