Rusting and its prevention.
Watch the video to the right ⇒
- What must be present for iron to rust?
- Is salt required for iron to rust?
- Does this experiment establish which gas in air is used in rusting?
- Can you suggest a further experiment that would give us more information about the factors causing iron to rust.
- What is rust? Write a word equation and chemical equation for the formation of rust.
[Click here for the answers.]
QUESTION.
(a) A student used this apparatus to find the percentage by volume
of oxygen in a sample of air.
She used this method.
♦ place some wet iron wool in the bottom of a test tube
♦ invert the test tube in a beaker containing water
♦ measure the height of the column of air in the test tube
♦ leave the test tube for one week
♦ measure the new height of the column of air
The table shows her results.
(i) Some of the iron turned into rust.
Write a word equation for this reaction.
(ii) Use the student’s results to calculate the percentage of oxygen in this
sample of air.
(b) The student left the apparatus for another week and measured the height of the
column of air again.
From this measurement, how could she tell whether all of the oxygen in the test tube
had been used up in the first week?
ANSWERS. Highlight the space below to reveal the answers.
(a) (i) iron + oxygen + water → (hydrated) iron (III) oxide
(ii) M1 volume of oxygen = (80 – 63 / 17 (cm 3 )
M2 percentage = (17/80 x 100 ) / 21
= 78.75/78.8/78.7
(b) whether the measurement is the same as before
IGNORE references to iron had stopped rusting
Rust prevention techniques.
Preventing rusting is important in various industries, including construction, automotive, and manufacturing, to maintain the integrity and longevity of iron-based structures and components. Here are the main methods used to prevent rusting of iron:
Barrier Protection: This method involves creating a physical barrier between the iron surface and the surrounding environment to prevent exposure to moisture and oxygen. Common barrier protection methods include:
Painting: Applying a layer of paint acts as a barrier that prevents direct contact between iron and moisture.
High-quality paints with rust-inhibiting properties provide better protection (e.g. hammerite metal paint).- Galvanizing: This process involves coating iron with a layer of zinc through hot-dip galvanizing.
Protection even continues when the zinc coating is scratched to uncover the iron beneath.
This is known as “sacrificial protection”, where a more reactive metal reacts in place of a less reactive one.
Alloying: Alloying iron with other metals or elements can alter its properties, including its susceptibility to rusting.
Stainless steel, for example, contains chromium, which forms a unreactive oxide layer on the surface, protecting the underlying iron from corrosion.- Oiling: Iron-made object that are designed to move freely (e.g. a bicycle chain) can be oiled regularly.
The oil facilitates free movement and prevents air and water coming into contact with the chain. - Greasing: Again, used for moving parts made of iron. Gate hinges would be one example and heavy springs would be another.
Each of these methods has its advantages and limitations, and the choice of method depends on factors such as the environment, cost, durability requirements, and specific application of the iron structure or component. Combining multiple methods may provide enhanced protection against rusting.
In advanced studies, a method called “cathodic protection” will be considered – used to protect the steel hulls of ships and underground iron pipes.
Question.This question is about rusting.
(a) A simplified formula for rust is Fe2O3
(i) Name the two substances needed for iron to rust.
(ii) Give the chemical name for rust.
(iii) What type of reaction occurs in the rusting of iron?
A. combustion B. neutralisation C. oxidation D. thermal decomposition
(b) Some iron objects are coated with a layer of zinc to prevent rusting.
(i) Name this type of rust prevention.
(ii) Explain how this type of rust prevention continues to protect iron
when the layer of zinc is damaged.
(iii) Give two other methods used to prevent iron from rusting.
Answer.
(a) (i) M1 oxygen / air 2
M2 water
(ii) (hydrated) iron(III) oxide
(iii) C.
C. is the correct answer because rusting involves the oxidation of iron.
A. is not the correct answer because the rusting of iron is not combustion.
B. is not the correct answer because the rusting of iron is not neutralisation.
D. is not the correct answer because the rusting of iron is not
thermal decomposition.
(b) (i) galvanising
(ii) M1 zinc is more reactive (than iron)
M2 zinc reacts / oxidises / corrodes before / instead of iron
iii) Any two from:
painting; plastic coating; oiling / greasing; chromium plating;
sacrificial protection; cathodic protection/ air ACCEPT O2
M2 water
Question. Answer ⇒
A student investigates the rusting of iron.
(a) She places an iron nail in a test tube of water and leaves it for
several days.
(i) Predict the appearance of the iron nail after several days.
(ii) Name the main compound in rust.
(b) The student then sets up two more test tubes containing iron nails.
Explain why the iron nail in tube 1 and the iron nail in tube 2
do not rust.
Answer.
(a) (i) red-brown (coating on nail)
(ii) (hydrated) iron(III) oxide/ferric oxide
(b) An explanation that links 4 of the following 5 points tube 1
M1 air/oxygen is needed for rusting
M2 boiled water does not contain air/oxygen
M3 oil keeps air/oxygen out tube 2
M4 water/moisture is needed for rusting
M5 drying agent keeps water/moisture out