[newbie]

hi

i have 2 question ..which have several problems 
i was wonder if u can help me out with   

1)An aqueous solution that is .500 M in Ag+ iconis slowely added from a burette to an aqueous solution that is .01 M in CL- and .01M in I-
     A)which ion will precipitatre first?
     B)CAlcualte the concentration of each ion at max separation


2)Tha standard electrode pontenial for half cells are as follows
    a)Sn2+(aq) + 2e-  -->Sn(S)
    b)Al3+(aq)  + 3e-  --> Al(S)
    c)Ag+(aq) + 1e-  --> Ag(S)
    D)MnO4-(aq) + 8H+(aq) + 5e- --> Mn2+(aq) + 4H2O(L)

A)calculate the call voltage at 25 C of a cell based onthe folling reation
Mn2+(aq) + 4H20(L) + 5Ag(s) -->5 Ag+(aq) + MnO4-(aq) + 8H+(aq)
where the concentration are the follows : [Mn2+] = .2M , [Ag+] = .1M , [MnO4-] = .2M , and the PH of the solution is 2

Thanks guys for your help 

[Albert]

1)An aqueous solution that is .500 M in Ag+ iconis slowely added from a burette to an aqueous solution that is .01 M in CL- and .01M in I-
     A)which ion will precipitatre first?
     B)CAlcualte the concentration of each ion at max separation

Adding Ag+, you yield AgCl and AgI. These compounds have different Kps and, hence, one of them (obviously the less soluble) will begin to precipitate before the other.

for what concerns question B, i can't understand what max separation means. Maybe you have to calculate the concentration of the more soluble one, when the other has reached 10^-5M (which is generally considered a limit of detection).

[Dan]

1)An aqueous solution that is .500 M in Ag+ iconis slowely added from a burette to an aqueous solution that is .01 M in CL- and .01M in I-
     A)which ion will precipitatre first?
     B)CAlcualte the concentration of each ion at max separation

A) Which is more soluble, AgI or AgCl? (hint: which is more strongly solvated, Cl^- or I^-?)
B) Does max seperation mean total dissociation? If so this is very simple.

2)Tha standard electrode pontenial for half cells are as follows
    a)Sn2+(aq) + 2e-  -->Sn(S)
    b)Al3+(aq)  + 3e-  --> Al(S)
    c)Ag+(aq) + 1e-  --> Ag(S)
    D)MnO4-(aq) + 8H+(aq) + 5e- --> Mn2+(aq) + 4H2O(L)

A)calculate the call voltage at 25 C of a cell based onthe folling reation
Mn2+(aq) + 4H20(L) + 5Ag(s) -->5 Ag+(aq) + MnO4-(aq) + 8H+(aq)
where the concentration are the follows : [Mn2+] = .2M , [Ag+] = .1M , [MnO4-] = .2M , and the PH of the solution is 2

I feel your pain. I absolutely loathe electrochemistry. This is probably how you do it:
Construct the full cell, then use the Nernst equation.

[Albert]

B) Does max seperation mean total dissociation? If so this is very simple.

Hey, I see you are at loss too. Well, I hope Borek to help us.

[Borek]

I feel your pain. I absolutely loathe electrochemistry. This is probably how you do it:
Construct the full cell, then use the Nernst equation.

Exactly. This one is not that hard, all you have to do is to write down both halfreactions and correctly construct reaction quotients for Nernst equation. Rest is a breeze as you know all concentrations - all you have to do is to substitute values.

[newbie]

hey guys

thanks for all the help

so for the second problem i basically set it into 2 separate equation and get the E0 values and then determine which one is the oxidation and reaction equation and find E right from this formula right
and log Q is basically Log(product)/(reaction)
E = Eo -.o592/N Log(Q)

[newbie]

Adding Ag+, you yield AgCl and AgI. These compounds have different Kps and, hence, one of them (obviously the less soluble) will begin to precipitate before the other.

for what concerns question B, i can't understand what max separation means. Maybe you have to calculate the concentration of the more soluble one, when the other has reached 10^-5M (which is generally considered a limit of detection).

sorry i also for got add this to the problem

AgCl(s) <--> Ag=(aq) + Cl-(aq)   Ksp = 1.8 X 10^-10
AgI(S) <--> Ag+(aq) +I-(aq)       Ksp = 8.5 X 10^-17

i always get confused which one will precipitate first (Lowest ksp valvues right)
i thinking its 8.5 X 10-17

with the ksp values..can max separation be calculated?

[Borek]

and log Q is basically Log(product)/(reaction)
E = Eo -.o592/N Log(Q)

http://en.wikipedia.org/wiki/Reaction_quotient

In the case of Nernst equation I prefer to think in terms of

E = E₀ + RT/nF ln ([Ox]/)

+ and Ox in numerator.

[Borek]

sorry i also for got add this to the problem

AgCl(s) <--> Ag=(aq) + Cl-(aq)   Ksp = 1.8 X 10^-10
AgI(S) <--> Ag+(aq) +I-(aq)       Ksp = 8.5 X 10^-17

i always get confused which one will precipitate first
i thinking its 8.5 X 10-17

Less soluble will precipitate first.

with the ksp values..can max separation be calculated?

Define max separation.

[newbie]

for the 2nd Q

how does the ph come in use for this Q
the nearest equation doesn't require ph valves right?

[newbie]

Define max separation.

yea i have no idea wut that means also the question only states " b) calculate the concentration of each ion at max separation"

but i'm thinking i have to set equilibrum tables for each one and find the X

could that be right

[Borek]

how does the ph come in use for this Q
the nearest equation doesn't require ph valves right?

Write Nernst equation for the MnO₄^- reduction.

[Borek]

could that be right

My take is that if it is aksed - it was defined by your teacher or is defined in your book.