Transcript Corrosion - ThinkChemistry

Corrosion
S2 Chemistry
Classifying chemicals and chemical reactions
Learning outcomes
Success criteria
Understand what is meant by
‘corrosion’.
You can define ‘corrosion’.
Understand what is meant by
‘rusting’.
You can define ‘rusting’.
Know what chemicals are required
for rusting to happen.
You can name the two chemicals.
Know how the rate of rusting can
be changed.
You can state three ways of
increasing the rate of rusting.
Know how to use an indicator to
detect rusting.
You can name the indicator used to
detect rusting.
You can state its starting and
finishing colours.
Only metals can
rust.
Do all
substances
rust?
Some metals
rust and some
don’t. It depends
on their position
in the Reactivity
Series.
Alloys don’t
rust.
When nails go
rusty they
get lighter.
When nails go
rusty they
will get
heavier.
When nails
get rusty
they stay the
same weight.
Definitions
Corrosion
“a chemical reaction which involves the
surface of a metal changing from an
element into a compound.”
Rusting
“the corrosion of iron.”
A metal corrodes when the surface atoms react
to form a compound.
An uncorroded metal is shiny in appearance.
A corroded metal is dull in appearance.
Different metals corrode at different rates:
sodium corrodes very quickly.
silver hardly corrodes at all.
Metals corrode fastest when they are exposed to
air.
Corrosion is also an example of oxidation.
LO:
I know what is meant by corrosion of a metal.
They will not
rust if they
are
completely
under water.
When nails
get wet they
go rusty.
They will not
rust if you
keep them
cold.
They will go
rusty more
quickly if
they touch
other nails.
Experiment
oil
water
nail
water
only
LO:
drying
agent
water &
oxygen
I know what causes corrosion.
oxygen
only
Result:
The iron only rusts when water and oxygen are
present.
Only the corrosion of iron is called rusting.
The rusting of iron can be speeded up by:
• Adding salt.
• Adding acid.
• Heating it up.
LO:
I know what causes corrosion.
The presence of rusting is detected using rust .
indicator:
rust
indicator
Rust indicator changes colour from yellow to blue in
the presence of rust.
LO:
I know how to test for rusting.
Preventing corrosion
S2 Chemistry
Classifying chemicals and chemical reactions
Learning outcomes
Understand how iron can be
protected from rusting.
Success criteria
You can state eight different
methods which can protect iron
from rusting.
You can explain why each method is
effective as a form of protection.
You can state which metal is used
in galvanising.
Brainstorm
• How many different ways that we use to
try and prevent rusting can you think
of?
Painting
Greasing
Plastic coating
Cathodic Protection
Electroplating
Galvanising
Tin Plating
If the iron atoms are constantly provided with
surplus electrons they can’t corrode and form ions.
• Cathodic protection:
(Iron is connected to the negative terminal (cathode)
of a power supply.)
- Car bodywork is connected to the negative terminal of
the battery.
- Oilrig platforms are connected to the negative
terminal of the electricity generator.
LO:
Understand how iron can be protected from rusting.
Experiment:
LO: Understand how iron can be protected from rusting.
• Sacrificial protection:
- A metal higher in the
electrochemical series
will give electrons to iron.
e.g. iron and magnesium
Mg
Mg2+
+
2e-
- Iron will not be able to
form ions .
- Magnesium will corrode .
instead.
LO:
Understand how iron can be protected from rusting.
HOWEVER:
- A metal lower in the
electrochemical series will
take electrons from iron.
e.g. iron and copper
Fe
Fe2+
+
2e-
- Copper will not be able
to form ions .
- Iron will corrode faster
than normal.
LO:
Understand how iron can be protected from rusting.
Learning outcomes
Understand how iron can be
protected from rusting.
Success criteria
You can state eight different
methods which can protect iron
from rusting.
You can explain why each method is
effective as a form of protection.
You can state which metal is used
in galvanising.