CORROSION

TOPICS COVERED

INTRODUCTION

01

DAMAGES
CAUSED

02

PREVENTIVE
MEASURES

03

QUIZ TIME

04

01

Corrosion : When a metal chemically reacts with a substance around
it such as moisture, acid etc. It is said to corrode and the process is
corrosion.

Corrosion causes:-

●

Black coating on silver ,

●

Green coating on copper

●

and Brown coating on iron .

Corrosion in the case of iron is called rusting.

Corrosion of

copper

Corrosion of silver

Rusting of Iron

OXIDISING REACTION

From above slides we got to know
that when metal reacts with oxygen
and moisture , it forms metal oxide.
Basically the metal in the reactants
get oxidised in the reaction with
oxygen .
Therefore ,
Oxygen is the oxidizing agent in any
formation of metal oxide.

Metal+Oxide→Metal Oxide

02

Silver articles become black after
some time when exposed to air.

This is because it reacts with sulphur
in the air to form a coating of silver
sulphide.

Copper reacts with moist carbon
dioxide in the air and slowly loses its
shiny brown surface and gains a
green coat.

This green substance is basic copper
carbonate.

Iron when exposed to moist air for a
long time acquires a coating of a
brown flaky substance called rust.

Damage caused by
corrosion

Corrosion is an extremely dangerous
and costly problem, because it
causes damage to car bodies, iron
railing, ships and to all object made
of metals, specially those of iron.

Every year an enormous amount of
money is spent to replace damaged
iron .

03

Methods for prevention of corrosion
The rusting of iron can be prevented by greasing, painting,
galvanizing, anodizing, or oiling the surface. These methods can be
classified into the following categories:

1.Galvanization: Galvanized metal is coated with a thin layer of
zinc to protect it against corrosion. The zinc oxidizes when it is
exposed to air creating a protective coating on the metal
surface.

2.Alloying: It is the method of improving the properties of a
metal by mixing the metal with another metal or nonmetal.
When iron is alloyed with chromium and nickel in stainless
steel is obtained. Stainless steel does not rust at all.

3.Painting: Rusting of iron can be easily prevented by coating
the surface with paint which protects iron from air and
moisture.

4.Greasing/Oiling: When some grease oil is applied to the
surface of an iron object, then air and moisture cannot come
in contact with it, and hence rusting is prevented.

What is the anodizing

process?

Anodizing is a process that thickens the
natural oxide layer on a metal part's surface
into an anodic oxide film.
This extra thickness protects the part's
surface and improves aesthetics.
Aluminum and titanium are the most
commonly anodized metals, but other
nonferrous metals can also undergo the
process.

Lets see how much you understood from

our PPT

Q-What is the chemical name for rust?

Ans.Ferric Oxide is the chemical
name of rust.

Q-What is the chemical name for
rust?

Q-Which conditions must be present for
iron to rust?

The presence of air (oxygen) and
moisture (Water) are the essential
conditions for rusting to occur.

When an object made of iron is exposed
to moist air and water for a long time, it
gets corroded and leads to the formation
of a compound called ferric oxide or iron
oxide also called rust.

Q-Which conditions must be present for iron
to rust?

Q-Which method of protection is likely to be
used to prevent an iron bucket from rusting?

Two ways to prevent the rusting of iron are:

●Oiling, greasing, or painting: By applying
oil, grease, or paint, the surface gets a
waterproof coating and the moisture and
oxygen cannot come into direct contact
with the iron article. Hence, rusting is
prevented.

●Galvanization: An iron article is coated
with a layer of molten zinc metal that
prevents the iron article to come in contact
with oxygen and moisture. Hence, rusting
is prevented.

Q-Which method of protection is likely to be used to
prevent an iron bucket from rusting?

Q-Which metal is used in the process of
galvanising iron?

Ans.Zinc metal is used in the process of
galvanising Iron

Q-Which metal is used in the process of
galvanising iron?

GAME TIME!

INSTRUCTION:

●

On the basis of rows, the class shall
be divided into 4 groups.

●

Each group would be asked 3
questions each.

●

There will be a time limit, and points
will be awarded on the basis of
answering speed.

●

The timer will start as soon as the
question is displayed on the screen

15 seconds : 2 points

10 seconds : 3 points

5 seconds : 4 points

<5 seconds: 5 points

Q-Which element reacts with metals in
corrosion?

a)Hydrogen

b)Oxygen

c)Water

d)Both b and c

Q-What is the chemical name for rust?

a)Hydrated iron(III) oxide

b)Iron(III) hydroxide

c)Iron(III) oxide

Q-Which chemical process does iron undergo
when it rusts?

a)Neutralisation

b)Oxidation

c)Reduction

Q-Which method of protection is likely to be
used to prevent an iron bucket from rusting?

a)Galvanising

b)Greasing

c)Painting

Q-Which of these would be a suitable
electrolyte for electroplating steel knives to
prevent them from corrosion?

a)Potassium nitrate solution

b)Iron nitrate solution

c)Silver nitrate solution

Q-Why is painting often used to protect
bridges from rusting?

a)It is cheaper than other methods of
protection

b)Oil would not stick to the bridge

c)Bridges would be weaker if they

were galvanised

1.Balance the following equation for the corrosion of iron in the presence of oxygen and
water:

Fe + O2 + H2O → Fe(OH)3

2.Balance the following equation for the corrosion of aluminum in the presence of
hydrochloric acid:

Al + HCl → AlCl3 + H2

3.Balance the following equation for the corrosion of copper in the presence of sulfuric acid:

Cu + H2SO4 → CuSO4 + SO2 + H2O

4.Balance the following equation for the corrosion of silver in the presence of nitric acid:

Ag + HNO3 → AgNO3 + NO + H2O

5.Balance the following equation for the corrosion of magnesium in the presence of
hydrochloric acid:

Mg + HCl → MgCl2 + H2

NOTE: THERE IS NO TIME LIMIT IN
THESE QUESTIONS.
Correct ANSWER = 1 point

Balance the following equation for the corrosion of silver in the presence of sulfur dioxide:

1.Ag + SO2 + H2O + O2 → Ag2SO4 + H2SO4

Balance the following equation for the corrosion of copper in the presence of oxygen and
water:

2.Cu + O2 + H2O → Cu(OH)2

Balance the following equation for the corrosion of aluminum in the presence of
hydrochloric acid:

3.Al + HCl → AlCl3 + H2

Efforts by:- Aryan,Akshat,Aryaan,Afiza,
(Afiya)