13 - Transition Metals, Alloys & Corrosion Flashcards
Describe the location of transition metals in the periodic table
Between groups 2 & 3
What are the physical properties of transition metals?
- Malleable
- Ductile
- Good conductors of electricity
- Shiny when polished
- High densities
- High Mp & Bps
- Shows Catalytic activity
Suggest a reason that explains why catalytic converters usually contain iron or platinum?
Transition metals & their compounds show catalytic activity
What does the oxidation of metals result in?
Corrosion
What is Tarnish?
A thin layer that forms on a metal due to oxidation
What is the purpose of tarnish on metals?
Stops further oxidation by stopping oxygen reaching the metal
When do metals oxidise in terms of electronic configurations?
When they lose electrons
What is sacrificial protection?
Using a more reactive metal to protect iron from rusting
What is corrosion?
When a metal continues to oxidise and so the metal becomes weaker over time
What is Rusting?
The corrosion of iron or steel
Explain how iron rusts
Iron rusts when it reacts w/ water or o2
Rust flakes off rusty iron, which exposes more metal to the air & water
—> Therefore, Iron continues to corrode & weaken
What are the different methods to prevent rusting of Iron?
- Exclusion of oxygen
- Exclusion of water
- Sacrificial protection
How can the rusting of Iron be prevented by Exclusion of air?
Storing metal in an unreactive atmosphere of nitrogen or argon
—> Prevents o2 in air reacting with the Iron
How can the rusting of Iron be prevented by Exclusion of water?
E.g. Using a desiccant powder that absorbs water vapour
—> Prevents water reacting with the Iron - causes rusting
How can the rusting of Iron be prevented by Sacrificial protection?
Using another more reactive metal will oxidise more easily than Iron - o2 reacts with them rather with the Iron or steel object
What metals are commonly used for Sacrificial protection?
- Magnesium
- Zinc
Why does Zinc & Magnesium react more easily than Iron?
The more reactive a metal is, the more easily it loses electrons
Zinc & Magnesium loses electrons more easily than Iron does - more easily oxidised
Give an example of an unreactive metal?
Gold
What is electroplating?
Coats the surface of one metal with a thin layer of another metal
Explain how electroplating is used to improve the appearance of metals
Silver & Gold can be electroplated onto cheaper ‘base metals’
—> Produces cheap, attractive jewellery that is cheaper than solid gold or silver
Explain how electroplating is used to improve a metals ability to resist corrosion
A thin layer of metal that resists corrosion can be electroplated onto vehicle & boat parts to stop air & water reaching the steel below
—> Prevents rusting
What objects do you need to electroplate a metal object?
- An Anode - Made from the plating metal
- A Cathode - Metal object itself
- An Electrolyte - A solution containing ions of the plating metal
What is galvanising?
Coating iron & steel objects with Zinc
How does galvanising improve the corrosion resistance?
By stopping water reaching the iron or steel by acting as a sacrificial metal
—> Sacrificial protection can continue even if the Zinc layer is damaged
How can galvanising be carried out?
- Using electroplating
- Dipping the object in molten zinc
Describe why you shouldn’t buy damaged food tins
- Food cans are made from steel
- Inner surfacing is protected from rusting by electroplating with tin
- Steel will rust faster if tin layer is damaged. Iron is more reactive than tin - acts as a sacrificial metal to protect the tin
What is an alloy?
A mixture of a metal element with one or more other elements, usually metals
How are alloy steels made?
By deliberately adding other elements to iron
Explain why pure metals aren’t as strong as alloys
Pure metals - same size atoms & regularly arranged. Layers move past each other if enough force is applied
Alloys - atoms of other elements present is other sizes. This distorts the regular structure, makes it more difficult for the layers to slide past each other
What does the uses of a metal or alloy depend on?
- Chemical properties
- Physical properties
What are the properties of aluminium?
- Resists corrosion
- Can’t conduct electricity
- Strong
- Less dense
- Cheap
