Chemistry - Corrosion And Rusting

Front 1

WHAT HAPPENS TO THE METAL WHEN

EXPOSED TO AIR?

Back 1

IT FORMS A DULL SURFACE COATING, WHICH

IS A COMPOUND.

EXAMPLE: MAGNESIUM WITH OXYGEN

FORMS A COATING OF MAGNESIUM OXIDE.

THIS CHEMICAL REACTION IS CALLED

CORROSION.

Front 2

HOW DOES OXIDE LAYER HELP THE METAL?

Back 2

THE OXIDE LAYER PREVENTS THE OXYGEN

GETTING AT THE METAL UNDERNEATH.

THIS MEANS THAT THE METAL IS PROTECTED

FROM FURTHER CORROSION.

SCRATCHING THE METAL WILL REVEAL

THE SHINY METAL.

Front 3

WHAT IS THE SPEED OF CORROSION?

Back 3

CORROSION IS GENERALLY A SLOW REACTION,

BUT THE MORE REACTIVE METALS TEND TO

CORRODE FASTER.

GOLD AND PLATINUM DO NOT CORRODE

AT ALL.

Front 4

WHAT IS RUSTING?

Back 4

RUSTING IS A SPECIAL NAME GIVEN TO

CORROSION OF IRON AND STEEL. SINCE IRON

AND STEEL ARE THE MOST WIDELY USED

METALS IN THE WORLD, RUSTING IS

A COMMON PROBLEM.

Front 5

WHEN DO IRON AND STEEL RUST?

Back 5

BOTH AIR AND WATER NEED TO BE PRESENT

FOR IRON TO RUST.

THE PRESENCE OF SALT OR ACID SPEEDS UP

THE RUSTING OF IRON.

Front 6

WHEN DOES IRON NAIL NOT RUST

IN THE TEST TUBE EXPERIMENT?

Back 6

1. WHEN IRON NAIL IS PLACED IN A TUBE

WITH DRY AIR AND CALCIUM CHLORIDE

AT THE BOTTOM (TO ABSORB WATER).

2. WHEN IRON NAIL IS PLACED IN WITH

FRESHLY BOILED WATER (NO AIR PRESENT)

AND OIL.

Front 7

WHEN DOES IRON NAIL RUST

IN THE TEST TUBE EXPERIMENT?

Back 7

1. WHEN IRON NAIL IS PLACED IN WATER

WITH AIR ACCESS.

2. WHEN IT IS PLACED IN SODIUM CHLORIDE

SOLUTION (SALT) WITH AIR ACCESS.

3. WHEN IRON IS PLACED IN DILUTE ACID

SOLUTION WITH AIR ACCESS.

Front 8

HOW DO WE SHOW THAT IRON COMBINES

WITH OXYGEN IN THE AIR?

Back 8

WHEN THE STEEL WOOL IS PLACED IN

THE TEST TUBE, WHICH IS PLACED UPSIDE

DOWN INTO THE GLASS OF WATER. AFTER

A FEW DAYS, THE STEEL WOOL HAS RUSTED

AND WATER IN THE TEST TUBE RISES ABOUT

ONE-FIFTH OF THE WAY UP, WHICH MEANS

ABOUT 20% OF THE AIR HAS BEEN USED.

Front 9

WHAT IS RUST?

Back 9

RUST IS HYDRATED IRON OXIDE, FORMED FROM

THE REACTION OF IRON WITH OXYGEN AND

WATER. THE WORD EQUATION IS:

IRON+OXYGEN+WATER=HYDRATED IRON OXIDE

(RUST).

Front 10

WHAT IS THE RUSTING LEVEL OF THE TANKS

LEFT IN THE DESERT SINCE THE END OF

WW2?

Back 10

THE TANKS HARDLY SHOW ANY SIGNS OF

RUSTING BECAUSE THE DESERT

ATMOSPHERE CONTAINS LITTLE OR

NO WATER.

Front 11

WHAT IS THE RUSTING LEVEL OF THE SHIPS

THAT HAVE SUNK IN THE DEEP AREAS OF

THE OCEANS?

Back 11

THE SHIPS HARDLY RUST AT ALL, BECAUSE

THERE IS VERY LITTLE AIR DISSOLVED IN

THE WATER OF THE DEEPEST PARTS OF

THE OCEAN.

Front 12

WHAT IS THE RUSTING LEVEL OF IRON AND

STEEL STRUCTURES BUILT IN OR NEAR

TO THE SEA?

Back 12

THEY RUST VERY QUICKLY DUE TO THE SALT

DISSOLVED IN THE SEA WATER, WHICH SPEEDS

UP THE RUSTING.

Front 13

WHAT IS THE RUSTING LEVEL OF CARS AND

OTHER IRON OBJECTS EXPOSED TO ACID RAIN?

Back 13

THEY CORRODE MORE IN AREAS WHERE

THERE IS ACID RAIN.

Front 14

HOW DOES THE CORROSION OF IRON AND

STEEL HAPPEN?

Back 14

THE BROWN FLAKES OF RUST, WHICH FORM

DURING THE CORROSION, ARE BRITTLE

AND WEAK. THIS CAUSES THEM TO CRUMBLE

AND BREAK AWAY, EXPOSING THE IRON

UNDERNEATH. THE IRON RUSTS FURTHER

UNTIL IT HAS ALL CORRODED AWAY.

Front 15

WHY IS THE CORROSION OF IRON AND STEEL

A MAJOR PROBLEM?

Back 15

RUST CAN DESTROY ANY OBJECT MADE OF

IRON, AND RUSTED MACHINERY, CARS,

BRIDGES, ETC. WILL HAVE TO BE REPLACED.

THIS COSTS THE COUNTRY MILLIONS OF

POUNDS EACH YEAR IN REPLACEMENT PARTS

AND LOST PRODUCTION.

Front 16

WHAT ARE THE MAIN WAYS OF PROTECTING

THE IRON AND STEEL FROM CORROSION?

Back 16

THERE ARE TWO MAIN WAYS:

1. USING A PHYSICAL BARRIER TO KEEP OUT

THE AIR AND WATER.

2. SACRIFICIAL PROTECTION INVOLVES ATTACHING A MORE REACTIVE METAL TO

THE IRON.

Front 17

DESCRIBE THE OPTIONS OF PHYSICAL

BARRIER PROTECTION.

Back 17

1. Painting-cheap and easily applied. Used

to protect cars, bikes, bridges, etc.

2. Oil and grease-good flexible coatings, suitable for coating of tools and machinery.

3. Plastic coatings-more expensive, but strong

and long lasting (used for wire netting).

Front 18

WHAT IS CORROSION?

Back 18

CORROSION IS THE FORMATION OF

COMPOUNDS ON THE SURFACE OF THE METAL

Front 19

DESCRIBE THE OPTIONS OF PHYSICAL

BARRIER PROTECTION (CONTINUED).

Back 19

4. Tin plating - making a sheet metal for

'tin' cans. It is strong and non-poisonous.

Suitable for food containers.

5. Electroplating-uses electricity to put a thin

coating of expensive metal onto iron. Chromium and nickel can be used for

electroplating. They form hard, shiny

protective coating (cutlery and taps).

Front 20

MAIN DISADVANTAGE OF USING

PHYSICAL BARRIER.

Back 20

IN THE PHYSICAL BARRIER, THE COATING HAS

TO BE MAINTAINED. IF THE COATING GETS

SCRATCHED OR BROKEN, THEN THE AIR AND

WATER WILL GET IN TO THE IRON, AND IT

WILL RUST.

Front 21

WHAT IS SACRIFICIAL PROTECTION?

Back 21

IT IS WHERE A MORE REACTIVE METAL, LIKE

MAGNESIUM OR ZINC, IS ATTACHED TO

THE IRON AND CORRODES INSTEAD OF

THE IRON. FOR EXAMPLE, BAGS OF

MAGNESIUM ARE ATTACHED TO

THE RAILWAY LINES AT REGULAR INTERVALS.

Front 22

WHY IS IT CALLED "SACRIFICIAL PROTECTION"?

Back 22

BECAUSE THE MORE REACTIVE METAL IS

"SACRIFICED" TO PROTECT THE IRON

FROM RUSTING.

Front 23

OTHER EXAMPLES OF SACRIFICIAL PROTECTION

Back 23

1. BLOCKS OF MAGNESIUM METAL IS

ATTACHED TO THE OIL RIGS IN

THE NORTH SEA.

2. BLOCKS OF ZINC BOLTED TO THE HULLS

OF IRON SHIPS.

3. BAGS OF SCRAP MAGNESIUM METAL

ATTACHED TO UNDERGROUND OIL AND GAS

PIPES.

Front 24

WHAT IS THE MAIN DISADVANTAGE OF

SACRIFICIAL PROTECTION?

Back 24

THE MORE REACTIVE METAL, USED TO

PROTECT THE IRON, WILL BE USED UP IN TIME.

THE PROTECTING METALS HAVE TO BE

REPLACED REGULARLY, OTHERWISE THE IRON

WILL START TO RUST.

Front 25

WHAT IS GALVANISING?

Back 25

IT IS THE PROTECTION OF IRON AND STEEL

BY COATING IT WITH ZINC. IT IS USUALLY

APPLIED BY DIPPING THE IRON IN MOLTEN

ZINC.

Front 26

WHY IS GALVANISING A DOUBLE" PROTECTION?

Back 26

BECAUSE IT INVOLVES BOTH A PHYSICAL

BARRIER AND SACRIFICIAL PROTECTION.

THE ZINC COATING KEEPS OUT AIR AND

WATER, AND IF THE COATING GETS

SCRATCHED OR BROKEN, THE IRON WILL

STILL BE PROTECTED BECAUSE ZINC IS

A MORE REACTIVE METAL.

Front 27

GIVE EXAMPLES WHERE GALVANISING

IS USED.

Back 27

1. GIRDERS FOR BRIDGES AND BUILDINGS.

2. SOME CAR BODY PANELS.

3. MOTORWAY CRASH BARRIERS.

4. BUCKETS AND ROOFING NAILS.

Front 28

GIVE TWO WAYS IN WHICH MANUFACTURERS

PROTECT CARS AGAINST RUSTING.

Back 28

1. CAR BODIES ARE ATTACHED TO

THE NEGATIVE TERMINAL OF THE BATTERY.

IT PROTECTS SOME METAL STRUCTURES,

SUCH AS OIL RIGS.

2. SOME CAR BODY PANELS ARE PROTECTED

BY GALVANISING.

Front 29

WHY ARE RAILWAY LINES CAN NOT BE PAINTED?

Back 29

BECAUSE THE PAINTING WOULD WEAR OFF

VERY FAST DUE TO FREQUENT FRICTION OF

HEAVY TRAIN WHEELS ON THE IRON.

Front 30

WHY DO OLD RAILWAY TRACKS, WHICH ARE

NO LONGER USED, START TO RUST?

Back 30

BECAUSE THE IRON IS THEN EXPOSED TO AIR

AND WATER (RAIN), OR ACID (ACID RAIN)