The Foundations of Chemistry

EcellE^0 

0.0

n

592

log

 0 

0.0

2

592

log

0

1

.

.

1

0

0

0

0.030 V

As the reaction proceeds, [Cu^2 ] decreases in the more concentrated half-cell and
increases in the more dilute half-cell until the two concentrations are equal; at that point
Ecell0, and equilibrium has been reached. This equilibrium [Cu^2 ] is the same concen-
tration that would have been formed if we had just mixed the two solutions directly to obtain
a solution of intermediate concentration.

In any concentration cell, the spontaneous reaction is always from the more concen-

trated solution to the more dilute solution.

[dilute solution]



[concentrated solution]

21-20 Using Electrochemical Cells to Determine Concentrations 883

Electrochemical procedures that use the principles illustrated here provide a conve-
nient method for making many concentration measurements.

Figure 21-14 The concentration cell Cu
Cu^2 (0.10 M)

Cu^2 (1.00 M)
Cu. The overall
reaction lowers the [Cu^2 ] concentration in the more concentrated solution and increases
it in the more dilute solution.

e– e–

Salt bridge

Cu(s) → Cu2+ (0.10 M) + 2e–

Oxidation, anode

Voltmeter

0.10 M CuSO 4

Cu2+ (1.00 M) + 2e– → Cu(s)

Reduction, cathode

1.00 M CuSO 4

Cu^2 +

Cl–

Cu(s)

K+

K+ Cl–

Cu(s)

Cu^2 +

• 
  
  
  
  • e–
  
  
  
  

Copper

atom, Cu

Copper

ion, Cu2+

e–

Copper

atom, Cu

Copper

ion, Cu2+

The overall cell potential is positive;

the reaction is spontaneous as written.