20.2 – 20.4 Student
Notes
II.
Voltaic Cells
A.
Background
vocabulary
1. Electrochemical
cell –
2. Voltaic
(galvanic) cell –
3. Electrolytic
cell –
B. Construction of
Voltaic Cell
1. Half-cell –
2. Description
of a voltaic cell
3.
Salt bridge –
4.
What would happen
if the metals and solutions were in direct contact with each other?
5.
Anode –
6.
Cathode –
7.
Cell reaction –
8.
Sketching and
Labeling a Voltaic Cell
A
voltaic cell is constructed from a half-cell in which a cadmium rod dips into a
solution of cadmium nitrate, Cd(NO3)2, and another half-cell in which
a silver rod dips into a solution of silver nitrate, AgNO3. The two
half-cells are connected by a salt bridge. Silver ion is reduced during
operation of the voltaic cell. Draw a sketch of the cell. Label the anode and
cathode; showing the corresponding half-reactions at these electrodes. Indicate
the electron flow in the external circuit, the signs of the electrodes, and the
direction of the cation migration in the half-cell.
9. If you were
to construct a wet cell and decided to replace the salt bridge with a piece of
copper wire, would the cell produce a sustainable current? Explain your answer.
C. Notation for Voltaic
Cells
1. Anode
(oxidation) is always written on the left; the cathode (reduction) is written
on the right. The two electrodes are electrically connected by a salt bridge,
denoted by a ║
2. When the
half-reaction involves a gas, an inert material such as platinum serves as a
terminal and as an electrode surface on which a half-reaction occurs. Add it to
the outside of the single bar.
3. Writing the
Cell Reaction from the Cell Notation
a.
Write the cell
reaction for the voltaic cell.
Tl (s) / Tl+ (aq) ║ Sn2+ (aq)
/ Sn (s)
b.
Write the cell
reaction for the voltaic cell.
Zn (s) / Zn2+ (aq)
║ Fe3+ (aq), Fe2+ (aq) / Pt
D.
Electromotive
Force
1.
An electric
charge moves from
2.
The work needed
to move an electric charge through a conductor depends
3.
Potential
difference –
4.
Volts – V –
Electrical
work =
Joules
=
5.
Faraday constant
– F –
6.
w = - F x
potential difference
7.
Electromotive
force (emf) – cell potential – Ecell
–
8.
wmax = - nFEcell
9.
Calculating the
Quantity of Work from a Given Amount of Cell Reactant
The
emf of a particular voltaic cell with the cell
reaction
Hg22+ (aq)
+ H2 (g) ¯ 2 Hg (l) + 2 H+ (aq)
Is
0.650 V. Calculate the maximum electrical work of this cell when 0.500 g H2
is consumed.