5 Steps to a 5 AP Chemistry 2019

246 ❯ STEP 4. Review the Knowledge You Need to Score High

a current of 1.10 V would be measured. This galvanic cell shown in Figure 16.1 is com-

monly called a Daniell cell.

In the Daniell cell shown in Figure 16.1, note that the compartment with the oxidation

half-reaction is on the left and the compartment undergoing reduction is on the right. This

is a convention that you will have to follow. The AP graders look for this. The electrode at

which oxidation is taking place is called the anode, and the electrolyte solution in which

it is immersed is called the anode compartment. The electrode at which reduction takes

place is called the cathode, and its solution is the cathode compartment. The anode is

labeled with a negative sign (-), while the cathode has a positive sign (+). The electrons

flow from the anode to the cathode.

Remember: Oxidation is an anode process.

Sometimes the half-reaction(s) involved in the cell lack a solid conductive part to act as

the electrode, so an inert (inactive) electrode, a solid conducting electrode that does not

take part in the redox reaction, is used. Graphite and platinum are commonly used as inert

electrodes.

Note: The electrode must be a conductor onto which a wire may be attached. It can

never be an ion in solution.

Cell Notation

Cell notation is a shorthand notation representing a galvanic cell. To write the cell nota-

tion in Figure 16.1:

1. Write the chemical formula of the anode: Zn(s)


2. Draw a single vertical line to represent the phase boundary between the solid anode and
   the solution: Zn(s)|


3. Write the reactive part of the anode compartment with its initial concentration (if known)
   in parentheses (assume 1 M in this case): Zn(s)Zn(2+1)M


4. Draw a double vertical line to represent the salt bridge connecting the two electrode
   compartments: Zn(s)Zn(2+ 1)M


5. Write the reactive part of the cathode compartment with its initial concentration (if known)
   shown in parentheses: Zn(s)Zn(1)2+ MMCu (1 )2+


6. Draw a single vertical line representing the phase boundary between the solution
   and the solid cathode: Zn(s)Zn(1)2+ MMCu (1 )2+


7. Finally, write the chemical formula of the cathode: Zn(s)Zn(1)2+ MMCu (1 )C2+ u(s)

If an inert electrode is used because one or both redox half-reactions do not have a

suitable conducting electrode material associated with the reaction, the inert electrode is

shown with its phase boundary. If the electrode components are in the same phase, they

are separated by commas; if not, a vertical phase boundary line. For example, consider the

following redox reaction:

Ag(++aq)F+→+e(^23 aq)Fe(+aq)Ag(s)

The oxidation of the ferrous ion to ferric doesn’t involve a suitable electrode material,

so an inert electrode, such as platinum, would be used. The cell notation would then be:

Pt(s)|Fe^23 ++(aq),Fe(aq)Ag(+aq)Ag(s)

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