In: Chemistry
Reduction Half Reaction E (V)
Ag2MoO4(s) + 2e- ---> 2 Ag(s) + MoO42-(aq) 0.4573 V
Ag+(aq) + e- ---> Ag(s) 0.7996 V
a.) Calculate the mass in grams of Ag2MoO4(s) that will dissolve in 2.0 L of water.
b.) Calcilate the cell potential of:
Ag(s) | Ag2MoO4(s) | MoO42-(aq) (0.010 M) || Ag+(aq) (0.010M) | Ag (s)
a)
Ag2MoO4(s) + 2e- ---> 2 Ag(s) + MoO42-(aq) Eo= 0.4573 V [Reduction]
2Ag(s) ----> 2Ag+(aq) +2 e- Eo=-0.7996V (reversed reaction)[oxidation]
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Add:Ag2MoO4(s)----> 2Ag+(aq) +MoO42-(aq) Eocell=Eored+Eo(ox)=0.4573-0.7996=-0.342V
Solubility reaction:Ag2MoO4(s)----> 2Ag+(aq) +MoO42-(aq) Eo=-0.342V
Ksp=Keq=equilibrium constant=solubility product
Using equation for free energy, Go=-nFEo ,n=mol of electrons exchanged,Eo=std reduction potential,
F=faraday's constant=96485 C/mol
Also,Go=-RT lnKeq
where R=Universal gas constant=8.314J/K.mol
T=temperature=298K
Keq=equilibrium constant for the reaction
Go=-RT lnKeq=-nFEo
or, ln Ksp=nFEo/RT=2 mol electrons*(96485 C/mol)*(-0.342J/C)/(8.314J/Kmol)*298K=-26.66
ksp=exp(-26.66)=2.639*10^-12
Also Ksp=[Ag+]^2 [MoO42-]
Let the solubility of Ag+ be S,so [Ag+]=S,[MoO42-]=S/2
Ksp=(S)^2*(S/2)=0.5 S^3
2.639*10^-12=0.5 S^3
S=1.741*10^-4M=solubility of Ag2MoO4(s)
So ,1.741*10^-4 mol of Ag2MoO4(s) will dissolve in 1L
2*1.741*10^-4 mol of Ag2MoO4(s) will dissolve in 2L
or ,molar mass of Ag2MoO4(s)*2*1.741*10^-4 mol Ag2MoO4(s)=mass of Ag2MoO4(s) will dissolve in 2L water
or,375.67 g/mol*2*1.741*10^-4 mol=0.131g will dissolve in 2L water
Answer:0.131g
b)Using Nerst equation,
E=Eocell-RT lnQ
Q=[Ag+]/[MoO42-(aq)]=0.01M/0.01M=1
So,E=Eocell=Eo red+Eo ox
As cathode is ,Ag+(aq) + e- ---> Ag(s) Eo(red)=0.7996V
Eo(Ox)=0.4573V
Ecell=0.7996-0.4573=0.342