Electrochemistry – I
Electrochemical Cells
For
GCE(O/L)
&
IGCSE
students
Redox Reactions
• Reduction
• Oxidation
- Gaining electrons
- Losing electrons
Mnenomic- “OIL RIG”
»Oxidation is Losing
»Reduction is Gaining
• The reactions in which oxidation occurs with
reduction are REDOX REACTIONS.
Need to know
• Electrode
a conductor through
which electricity enters
or leaves an object,
substance, or region.
Electrodes
• Anode
• Cathode
- Electrode at which the
oxidation half reaction occurs
- Electrode at which the
oxidation half reaction occurs
•Electrolyte
-
a substance that produces
an electrically conducting
solution when dissolved in
a polar solvent; water
Electrochemical cells
• Converts chemical energy
into electrical energy
• In a simple cell
– Two electrodes connected
by a wire
– An acidified solution as the
electrolyte
• Current passes from
cathode to anode
(from positive terminal to
negative terminal)
Electrodes of a Simple Cell
Anode
Cathode
• One electrode is the
anode
• Other electrode is the
cathode
• More reactive metal
becomes the anode
• Less reactive metal
becomes the cathode
• Oxidation half reaction
occurs at anode
• Reduction half reaction
occurs at cathode
• Negative terminal
• Positive terminal
A Simple Electrochemical Cell
Activity- 1
Materials
required
Method
• A small beaker
• Diluted sulphuric acid
• A zinc metal strip
• Add the diluted sulphuric solution to the
beaker
• Dip a part of the zinc strip into the solution
Continued..
Observations
•Zn strip dissolve
•Gas bubbles are liberated at the Zn strip
Continued..
Zn metal dissolves as electrons are leaving from the Zn atoms
Zn2+(aq) + 2e
Zn(s)
Sulphuric acid dissociates
H2SO4
2H+ + SO42-
H+ takes electrons and hydrogen gas is liberated
2H+ + 2e
H2(g)
• Oxidation half reaction
• Zn(s)
Zn2+(aq) + 2e
• Reduction half reaction
• 2H+ + 2e
H2(g)
• Balanced ionic equation
• Zn(s) + 2H+
Zn2+(aq) + H2(g)
• Completed balanced reaction
• Zn(s) + H2SO4(aq)
ZnSO4(aq) + H2(g)
Activity - 2
• Observations
•Zn strip dissolve
•Gas bubbles are liberated at the Cu strip
Cont.
• Conclusions
Zn(s)
2H+ + 2e
Zn2+(aq) + 2e
H2(g)
oxidation
reduction
• Balanced ionic equation
Zn(s) + 2H+
Zn2+(aq) + H2(g)
At anode
Oxidation
Zn
At cathode
Reduction
Cu
Negative
terminal
Positive
terminal
Activity - 3
Fe
Cuu
• Observations
•Iron strip dissolve
•Gas bubbles are liberated at the Cu strip
Cont.
• Conclusions
Fe(s)
2H+ + 2e
Fe2+(aq) + 2e
H2(g)
oxidation
reduction
• Balanced ionic equation
Fe(s) + 2H+
Fe2+(aq) + H2(g)
At anode
Oxidation
Fe
At cathode
Reduction
Cu
Negative
terminal
Positive
terminal
Activity - 4
• Observations
•Zn strip dissolve
•Gas bubbles are liberated at the Cu strip
Cont.
• Conclusions
Zn(s)
2H+ + 2e
Zn2+(aq) + 2e
H2(g)
oxidation
reduction
• Balanced ionic equation
Zn(s) + 2H+
Zn2+(aq) + H2(g)
At anode
Oxidation
Zn
At cathode
Reduction
Fe
Negative
terminal
Positive
terminal
Thank You!