Corrosion and its Prevention Video Lecture - Class 10

let's think about cars for a moment the
car that you've had in mind was likely
painted with your favorite color the
paint is not only there to make your car
look pretty but it has a more important
purpose to prevent rusting when iron and
steel are exposed to oxygen and moisture
rusting will occur rusting describes the
corrosion of iron and steel the term
corrosion is used to describe the
breakdown of a metal when exposed to the
environment when we say a metal corrodes
we mean that it has reacted with water
and oxygen from the environment to form
their respective oxides we can
demonstrate this using a simple
experiment place an iron nail in four
test tubes fill one with regular tap
water until the nail is submerged fill
another with regular tap water and add
half a spoonful of sodium chloride
regular table salt shake from side to
side to ensure that sodium chloride
fully dissolves fill the third test tube
with recently boiled water and add a
thin layer of oil when we boil the water
we remove any dissolved oxygen and the
layer of oil prevents any oxygen from
further dissolving in the last test tube
add a spoonful of calcium chloride
calcium chloride removes moisture or
water so in the first test tube the nail
is exposed to oxygen and moisture in the
second test tube the nail is exposed to
oxygen moisture and salt so in the third
test tube the nail is only exposed to
water in the fourth test tube the nail
is exposed only to oxygen stop her all
four test tubes with a rubber bung and
let stand for a couple of days you will
find the
the nails in the first and second test
tubes have rusted in particular the nail
in the second test tube has rusted more
than the nail in the first test tube and
the rust has likely flaked off you may
see a reddish-brown precipitate at the
bottom of these tubes the nails in the
third and fourth test tubes have not
rusted so what has happened here the
iron has undergone an oxidation reaction
forming hydrated iron 3 oxide or rust
salt and acid act as a catalyst for this
reaction which is why the nail in the
second test tube formed more rust than
the nail in the first test tube rusting
can be very costly if we have to
constantly replace these items made of
iron and steel rust can be prevented if
we paint the areas exposed to oxygen and
moisture this is done on many bicycles
and cars another method to prevent rust
is by placing a layer of oil or grease
this is done on many bicycle chains it
helps lubricate the moving parts which
reduces friction and slows down the
rusting process another way to prevent
rusting is a sacrificial protection
method called galvanizing have a look at
this reactivity table zinc is more
reactive than iron when exposed to
oxygen and moisture a zinc will corrode
faster than iron so if we put them
together
zinc protects iron but is sacrificing
itself hence the term sacrificial
protection this method is applied to
prevent rusting on ships in the
oxidation of zinc can be described using
this following equation so besides
preventing rusting there is another
advantage to this galvanizing process
the formed is zinc oxide layer can be
removed and the freshly exposed the zinc
can corrode once again thereby further
protecting the iron or steel hull
you