corrosion

Question 1

corrosion definition + example

Answer 1

the destruction of materials by chemical reactions with substances in the environment, rusting

Question 2

what must be present for iron to rust?

Answer 2

air and water

Question 3

rusting of iron equation

Answer 3

iron + oxygen + water —–> hydrated iron (III) oxide

Question 4

what happens in the rusting of iron?

Answer 4

iron is oxidised

Question 5

where does corrosion happen?

Answer 5

on the surface of a material, where it is exposed to air

Question 6

why does all the iron eventually corrode?

Answer 6

rust is a soft, crumbly solid that flakes off to leave more iron available to rust again

Question 7

what happens to aluminium when exposed to air?

Answer 7

-it corrodes
-however things made of Al aren’t completely destroyed
-as the aluminium oxide that forms doesn’t flake away
-instead it forms a protective layer that sticks firmly to the aluminium below and stops any further reaction taking place

Question 8

describe an experiment to show air and water are needed for iron to rust

Answer 8

1. place an iron nail in boiled distilled water and cover with a layer of oil on top
2. place an iron nail in a boiling tube with anhydrous calcium chloride powder, also place rubber bung on top of test tube,
3. place an iron nail in a boiling tube with distilled water, open to air
4. leave for several days and look for changes
5. test tube 3 will have iron covered in rust, test tube 1 and 2 will have no difference

Question 9

why is boiled distilled water used, and a layer of oil?

Answer 9

boiled: to remove dissolved air
oil: to prevent any air in test tube from dissolving
making sure it is purely just water in the test tube

Question 10

why is anhydrous calcium chloride powder used, and a bung placed on top?

Answer 10

calcium: it removes any water from the air in the test tube
bung: prevents any moist air from entering
making sure it is purely air in the test tube

Question 11

results of experiment

Answer 11

proves both water and air is needed for corrosion

Question 12

how can corrosion be prevented?

Answer 12

-electroplating
-oiling / greasing
-painting / coating with plastic
-sacrificial method

Question 13

what is electroplating?

Answer 13

process using electrolysis to reduce metal ions onto an iron electrode, coating the iron with a layer of a different metal that won’t be corroded away

Question 14

what is the sacrificial method + example?

Answer 14

placing a more reactive metal with the iron
water and air then react with the sacrificial metal instead of the iron, protecting the iron
an object can be galvanised by spraying it with a coating of zinc