Re: Need help with concentration cell problem.

On Wed, 27 Apr 2005 17:41:58 +0200, "Michael Andersen"
<man052@xxxxxxxxxxxxxx> wrote:

>I'd be enourmously grateful if someone could help me with the following
>problem:
>
>We have two containers 1 and 2. In 1 we have a 0.01 M Cu++ solution, and in
>2 we have an unknown concentration of Cu++.
>
>Furthermore we have a container 3, which is divided in two by a
>semipermeable membrane (let's call the two parts 3a and 3b). In 3a there is
>a 0.01 M solution of K+, and in 3b there is a 0.1 M solution of K+. The
>membrane is permeable to K+, but not to the anions in the solutions. This
>gives a difference in potential that is easily calculated with Nernst's
>equation (59 mV, where 3a has higher potential).
>
>Now we dip a copper electrode in 1, and connect this to a calomel electrode
>which is dipped into 3a. Then another copper electrode is dipped into 2, and
>this one is connected to a calomel electrode which is dipped into 3b. The
>circuit is completed by a salt bridge between 1 and 2.
>
>The question is, what is the concentration of Cu++ in 2, if there is no
>current flowing in the circuit?
>
>The answer is either 1 M or 0.0001 M,


Well, that simplifies the immediate issue. This is a fairly complex
problem, and hard to discuss without a good picture in front of us.
But with the constraint you suggest above, we don't need to do any
calculations, just think about what is happening.

What do you think is the condition for "no current"?

How do you think that is achieved? That is, what terms contribute?

Be careful with signs. It is probably better to try to describe the
situation in words.

bob



>but I cannot agree with my teacher who
>claimed the answer has 0.0001 M in a lecture today. Can someone check if
>this is correct, and if it is explain why?
>
>Sincerely,
>Michael
>

.

Relevant Pages

  • Need help with concentration cell problem.
    ... we have an unknown concentration of Cu++. ... Now we dip a copper electrode in 1, and connect this to a calomel electrode ... circuit is completed by a salt bridge between 1 and 2. ...
    (sci.chem)
  • Re: Need help with concentration cell problem.
    ... Bob wrote: ... >>Furthermore we have a container 3, which is divided in two by a ... >>Now we dip a copper electrode in 1, and connect this to a calomel ... >>this one is connected to a calomel electrode which is dipped into ...
    (sci.chem)