Just a qn. T_T

[Starberri]

Wellsss, I came across this qn today, it's from the 2008 SAMPLE exam 2.
Multiple choice, question 13.

An electric current is passed through three celss connected in series.
The cells contain 1.0 M aqueous solutions of calcium nitrate, silver nitrate and nickel (II) nitrate.
Each cell also contains a pair of platinum electrodes.

The ratio of the amount in mole, of Ca(s), Ag(s) and Ni(s) deposited at the negative electrode in each cell under standard conditions, is:

Well I know that Ca won't be deposited..
So I'm left with two options:
         n(Ca)              n(Ag)                 n(Ni)
B:        0                    2                      1
   Or
D:        0                    1                      2

I circled D, but answer is B?
Help please?

Thanks.

[StringFever]

Wellsss, I came across this qn today, it's from the 2008 SAMPLE exam 2.
Multiple choice, question 13.

An electric current is passed through three celss connected in series.
The cells contain 1.0 M aqueous solutions of calcium nitrate, silver nitrate and nickel (II) nitrate.
Each cell also contains a pair of platinum electrodes.

The ratio of the amount in mole, of Ca(s), Ag(s) and Ni(s) deposited at the negative electrode in each cell under standard conditions, is:

Well I know that Ca won't be deposited..
So I'm left with two options:
         n(Ca)              n(Ag)                 n(Ni)
B:        0                    2                      1
   Or
D:        0                    1                      2

I circled D, but answer is B?
Help please?

Thanks.

Well, Ca won't react because it's a weaker oxidant than water.
As for Ag and Ni, they will form - but you have to consider charges.

For example
Ag --> Ag+ + e-
AND
Ni --> Ni 2+ + 2e-

So if I passed ONE FARADAY through both equations, I would get 1 mole of Ag (due to 1:1 molar ratio)
but in the Ni, because the ratio between e- and Ni is (2 e- to every 1 Ni); 1 mole of e- will result in 0.5 mole of Ni.

To clean that up, just multiply everything by 2 and you get option B

[Starberri]

Thanks a million.