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Describe how aluminium can rust, and how it’s different to rusting iron (use the information found in the “Iron and Aluminium” worksheet)
Aluminum is very, but is usually covered by a thin “skin” of oxide, which protects the metal underneath from attack by oxygen, water, or acids.
Iron is less active, but its oxide skin is porous in water. It doesn’t protect the metal underneath from oxygen in wet conditions, and the whole of the metal eventually reacts to form the oxide.
Rusting Aluminium?
Aluminum is actually very prone to corrosion. However, aluminum corrosion is aluminum oxide, a very hard material that actually protects the aluminum from further corrosion. Aluminum oxide corrosion also looks a lot more like aluminum, so it isn't as easy to notice as rusted iron.
“How to prevent rusting” sheet
Each table group read through and summarize one method of preventing rust. Then report to back to the class – report should contain:What is this method?How does it work?
Method How it works Where it’s used
Painting The paint stops oxygen and water from reaching the iron beneath.
Cars, roofs
Greasing The paint stops oxygen and water from reaching the iron beneath.
Machinery
Electroplating
A coating of a metal like tin or chromium stops oxygen and water reaching the iron.
Car and bike parts
Galvanising A coating of zinc stops oxygen and water reaching the iron and also corrodes before the iron.
Roofs, sheds
Alloying Combining the iron with chromium or nickel to make stainless steel slows down rusting.
Kitchen surfaces
Questions about rusting
1. Iron oxide
2. Iron, water, oxygen
3. Iron + oxygen iron oxide
4. Brass (Cu + Zn) does not rust. Steel (99% Fe) rusts
5. Painting provides a barrier to water and oxygen, preventing them from reacting with iron
6. Two sacrificial metals: magnesium and zinc
7. Hull of ship or drilling platform, hot water heater
8. Copper – the steel/Fe will become the sacrificial metal
9. Zinc10. Zinc prevents water or oxygen
from reaching iron. Also acts as sacrificial metal (will corrode before iron)
1. Give one example of the use of metals relating to each of the different physical properties.
a) Ductileb) Sonorousc) Malleabled) High melting pointe) Lustrousf) High electrical conductance
Gold - earringsBrass – cow bells
Steel – car bodiesCooking pots - steel
Silver - mirror
Copper – electrical wires
Quiz
2. Name the elements represented by the following symbols.
Al Fe Sn Pb Na Au S I He Cu
3. Draw the atom diagram for
Electron:
Proton:
Neutron:
Al27
13131327 – 13 = 14
13p14n
Rusting
1. Only one metal rusts. Which one is it?2. What is the chemical name for rust?3. What conditions are needed for rusting
to occur?4. Give at least four different methods of
preventing rusting and explain how each one works.
5. Give an example of a situation in which each of these methods is used.
Method How it works Where it’s used
Painting The paint stops oxygen and water from reaching the iron beneath.
Cars, roofs
Greasing The paint stops oxygen and water from reaching the iron beneath.
Machinery
Electroplating
A coating of a metal like tin or chromium stops oxygen and water reaching the iron.
Car and bike parts
Galvanising A coating of zinc stops oxygen and water reaching the iron and also corrodes before the iron.
Roofs, sheds
Alloying Combining the iron with chromium or nickel to make stainless steel slows down rusting.
Kitchen surfaces
The reaction of metals with water
1. What is the general word equation for the reaction of metal with water?
Metal + water metal hydroxide + hydrogen
2. Write the word equation for the reaction of calcium with water.
Calcium + water calcium hydroxide + hydrogen
2. How do you test for the gas produced in the reaction in Q3?
Pop test – put flame near collected gas, if hydrogen was present, a squeaky pop should be heard.
The reaction of metals with acid
1. What is the general word equation for the reaction of metal with acid?
metal + acid salt + hydrogen2. Write the word equation for the reaction
of zinc with hydrochloric acid.Zinc + hydrochloric acid Zinc chloride + hydrogen
1. Write the general word equation for the reaction of metals with oxygen.
Metal + oxygen metal oxide
2. Write the word equation for the reaction of magnesium with oxygen.
Magnesium + oxygen Magnesium oxide
The reaction of metals with oxygen
Magnesium reacts slowly with hot water and doesn’t react with cold water. Calcium reacts rapidly with hot water and slowly with cold water. Sodium explodes in hot water and reacts rapidly with cold water.
Which of these three metals is the most active chemically?
Which metal is the least active?
Sodium
Magnesium
Think about it…
1. How could you make zinc sulfate from zinc metal?
2. Could you make copper sulfate in the same way? Explain your answer.
3. Why would it not be a good idea to store vinegar (dilute acetic acid) in aluminium cans?
4. Car batteries contain dilute sulphuric acid. Why are battery cases made of plastic rather than steel?
By reacting Zn with dilute sulfuric acid
No
Acid in vinegar would react with Al and make holes in can
As above