What are the anode and cathode for these cells? Only question 28 and 29. I\'m ha

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What are the anode and cathode for these cells?
Only question 28 and 29. I'm having trouble knowing what is the anode and cathode and how to calculate e cell for the reaction!!! I can do the rest of the calculation! Isnt is it always ecell = ecathode - eanode? But i've seen times where people added these values. Please clear this up! Thanks! #28. Determine Ecell for the following cell at 25°C:C(graphite)Sn"(aq, 0.059M) Sn2*(aq. 0.059M|IFe3 (aq. 0.150M), Fe Given: Sn4+ + 2e Sn2+ E"red= 0.154V (aq, 0.150M)|Pt Fe3+ + 2e Fe2+ E"re = 0.770V a) 0.557 V b) 0.586 V c) 0.616 v d) 0.675 v e) 0.734V #29. Determine K at 298K for the following reaction: Agl (s) Ag+ (aq) + H Given: Agl (s) + e Ag (s) + I-(aq) E"red-0.1522 V Ag+ (aq) + e Ag (s) E"red = 0.7966V a) 1.03x108 b) 7.68x1010 c) 1.06x1016 1.30x10-11 e) 9.40x10-17 #30. A silver salt AgX is dissolved in water and required 3.5A for 395.0 sec to electroplate the silver out of the salt. What mass of silver was in the salt originally? a) 0.775 g

Explanation / Answer

In an electrochemical cell, oxidation occurs at the anode and reduction occurs at the cathode.

Oxidation occurs at the anode therefore the anode is negative since e- are lost.

Reduction occurs at the cathode therefore the cathode is positive since e- are gained.

A good way to remember it is the following:

REDduction CAThode (RED CAT)

ANode OXidation (AN OX)

Eocell = Eoreduction + Eooxidation

we know, Eooxidation = - (Eoreduction) for a reaction

hence, Eocell = (Eoreduction)cathode - (Eoreduction)anode

If we have the reduction potentials of the reactions at electrodes, we subtract and if we have reduction potential and oxidation potential we add them to find electrode potential of a cell. Finally Eocell should be >0.

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