What is Electrochemistry?
So in Chem 20 we looked at individual elements and
drew electron dot diagrams for them.
Non-Metal
Metal
Last we learned that when metals form compounds they lose
electrons and when non-metals form compound they gain
electrons.
The study of the transfer of electrons during chemical
reactions is known as Electrochemistry.
CHEM 30
UNIT B: ELECTROCHEMICAL CHANGE
CHAPTER 13 (P.556 – 609)
Electrochemical (Electron Transfer) reactions are the
most common type of reactions in both living and
non-living systems.
Electrochemical reactions were discovered way before
their was science to explain it.
What do you call chemical reactions before there is
science to explain them?
Magic!
No, I’m kidding…But seriously…I’m actually not.
The Alchemists main goal was to turn
Its sad,
common metals into gold and create a
but true.
magical potion so they could live
forever….
Alchemists and Early Science
So I know so far I have made the Alchemists out to be sort
of…..nut jobs, and they sort of were….
But!
Even though the alchemists and other early scientists had
somewhat…
“unusual” ideas, their contribution to our current
understanding of how things work was important. Their
empirical knowledge (things learned through
mixing things and experimenting) helped our current
understanding of chemistry.
“Technology Drove Science”
So in prehistoric times when people were learning how
to turn metal ores (mixtures of different metals) into
metals they could
make things out of, they actually
Primitive's….
discovered (by accident) the science of metallurgy.
Metallurgy is the science of extracting pure metals
from their naturally occurring compounds (ores) and
adapting these metals for Useful Purposes.
Tools
Weapons
Metallurgy
Early people learned that if they heated a pile of raw
ore (mixture of different metals) in a fire it would
reduce (get smaller) into a small amount of pure metal
when it cooled.
This is where the term
Reduction comes from.
Heated In A
Fire
Metal Ore
Pure Metal
Reduction
Early people didn’t understand that the metal ores
were reacting with something (usually gases) which
caused them to be reduced.
Carbon Monoxide
Charcoal (Carbon)
Hydrogen Gas
Understanding Oxidation and Reduction
Oxidation and Reduction were happening during early
smelting and metallurgy, the people didn’t know the science,
but that didn’t stop them from doing it.
It wasn’t until the 1700’s….more than 6500 years after the
first copper was produced…that the science was around to
explain oxygen’s role in burning and corrosion (rust).
6500 Years
Oxidation
It was only now that scientists understood that when things
interacted with oxygen they did the opposite of being reduced
to pure, useable metals.
In general scientists noticed that combustion and corrosion
were similar processes (both broke down substances, Both
reacted with oxygen)
Through experimentation scientists found other gases that
caused similar reactions. So they referred to all reactions
that caused pure metals to turn back into compounds
Oxidation.
Oxidation
Oxidizing Agent: Any substance that causes
a metal to oxidize and turn into a metal
compound.
Oxygen
Chlorine
Bromine
Oxidation and Reduction
Electron Transfer Theory
This modern theory says that all chemical reactions
can be broken in two pieces….2 ½ reactions.
When reactants combine to form products, one
reactant gains electrons and one reactant loses
electrons.
Electrons are transferred from one reactant to the
other in equal amounts.
Lets Try One.
For example, when zinc metal is dropped in
hydrochloric acid…what happens?
All those bubbles are hydrogen gas escaping.
(Hydrogen’s flammable right…….)
So lets break this reaction into two pieces…..
First, lets look at the zinc.
Zn(s)  Zn2 (aq) +2e- Oxidation
Second, look at the hydrogen.
+
2H (ag)
+
H2(g)
Reduction
Practice
Zn(s)  Zn2+(aq) + 2e-
Oxidation
Metal  Compound
Pb2+(aq)
Reduction
Compound  Metal
 Pb(s)
Its Just That Easy….
Redox Reactions Take Place In (aq)
Oxidation/Reduction(Redox) reactions take place in aqueous
(liquid) environments.
In fact most chemical reactions need water to happen…there are very few
chemical that can be put together as solids and react.
Because reactions happen in water we have to include water
in our balanced ½ reaction.
AND because water can easily be acidic or basic (just a few
ions one way or the other and water isn’t neutral anymore)
we balance the equation using the acid or basic ions.
So what is the acidic ion?
Basic Ion?
H3O+(ag)
Hydronium
OH-(aq)
Hydroxide
Balancing Half Reactions
In Acids & Bases
1
O
H+(aq) + HNO2(aq)
2 = 1
 NO(g) + H2O(l)
2
3
Balance hydrogen ions by adding (H+(aq)) to the
opposite side.
Balancing Half Reactions
In Acids & Bases
e- + H+(aq) + HNO2(aq)  NO(g) + H2O(l)
O
But what if it happened in a Basic
solution!??
AKA….add e- to the same side as you
added the H+(aq).
Balancing Half Reactions
In Acids & Bases
a basic
H+(aq) + e- + HNO2(aq)  NO(g) + H2O(l)
*** First 4 steps are exactly the same***
Balance hydrogen ions by adding (H+(aq)) to the
opposite side.
Add e- to the same side as you added the H+(aq).
Balancing Half Reactions
In Acids & Bases
a basic
/
OH-(aq) + H+(aq) + e- + HNO2(aq)  NO(g) + H2O(l)
Add OH-(aq) to both sides equal to the number of
H+(aq) you added back in step 3.
Write This Down
Practice (Acidic)
Practice (Basic)