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Posted: Wed Feb 21, 2018 7:59 pm
by ClaireHW
Determine the unknown quantity in each of the following cells:
a) Pt(s) I Hg2 (1.0 bar) I H+ (pH=?) II Cl- (aq, 1.0 M) I Hg2Cl2(s) I Hg(l), E=0.33V
b) C(gr) I Cl2(g, 1 bar) I Cl- (aq, ?) II MnO4- (aq, 0.010 M), H+ (pH=4.0), Mn2+ (aq, 0.10 M) I Pt(s), E=-0.30

I'm specifically confused about part b and the order the products and reactants are organized with in the equation and how to tell which are which in the cell diagram.


(Claire Woolson Dis 1K)

Re: 14.39  [ENDORSED]

Posted: Thu Feb 22, 2018 8:42 am
by Chem_Mod
Looking at part b, we knows the leftmost compartment (to the left of the salt bridge) is where the oxidation takes place (anode) and the rightmost where reduction takes place (cathode).

So we need to look up a half-reaction in Appendix 2B that matches the oxidation on the left. The reaction we are interested in is 2Cl- --> Cl2 + 2e- (written as an oxidation here, it will be written as a reduction in the appendix). None of the components are conductive, so we have to place a conductive electrode in there. We choose graphitic carbon over platinum to avoid it's oxidation and potential reaction with the Cl2.