Topic 5 - Separate Chemistry 1 Flashcards
Where are transition metals located?
In the middle of the periodic table between group 2 and group 3
What do all transition metals have common?
All have typical properties if metals.
Describe the properties of transition metals
- Hard, strong and malleable materials that conduct electricity and heat well.
- High melting point (except mercury which is liquid at room temperature)
- High densities
- They form colourful compounds
- They make good catalysts - Iron catalyst for Haber process.
What does the oxidation of metals cause?
Corrosion
How can the rusting of iron be prevented?
- Removing contact with oxygen
- Removing contact with water
- Create physical barriers such as paint or grease to stop the rust.
- Sacrificial protection
What is electroplating?
Electroplating involves using electrolysis to put a thin layer of a metal on the object:
- the cathode (negatively charged electrode) is the iron or steel object
- the anode (positively charged electrode) is the plating metal
- the electrolyte contains ions of the plating metal
Why is electroplating useful?
Electroplating improves the corrosion resistance of metal objects. It also improves their appearance and may be used to produce gold-plated jewellery.
What is sacrificial protection?
Iron can be protected from rusting if it is in contact with a more reactive metal, such as zinc. The more reactive metal oxidises more readily than iron, so it ‘sacrifices’ itself while the iron does not rust. Once the sacrificial metal has corroded away, it can simply be replaced.
What is Galvanising?
When iron is coated in zinc, the process is called galvanising. The zinc layer stops oxygen and water reaching the iron. Zinc is more reactive than iron, so it also acts as a sacrificial metal. This protection works, even if the zinc layer is scratched.
What are alloys?
An alloy is a mixture of two or more elements, where at least one element is a metal. Many alloys are mixtures of two or more metals.
Why are alloys stronger than pure metals?
Solid metals have a regular lattice structure. When a force is applied to a metal, layers of atoms can move past each other. The more difficult it is for the layers to move, the more force is needed and the stronger the metal.
Copper and zinc atoms have different sizes. This changes the regular lattice structure in brass, so layers of atoms cannot slide over each other so easily. This makes brass stronger than copper or zinc alone.
How are alloy steels made?
Iron with other metals
Why is iron paired with different metals to make alloy steels?
To suit a specific use due to their different properties. For example:
> Mild Steel - Iron + Carbon - Malleable, Ductile - Car body parts
> Tool Steel - Iron + Tungsten - Hard, Resistant to high tempereatures - Drill bits
> Stainless steel - Iron + Chromium - Hard, Resistant to rusting - Dishwasher and Washing machines.
How is the properties of aluminium related to its use?
Aluminium foil is used to wrap food and store it because it doesn’t react to the substances in the food. It is malleable so it can be wrapped around the food.
How is the properties of magnalium related to its use?
Has low density, is strong and is malleable so it is used for aircraft parts.
How is the properties of copper and brass related to its use?
Copper and brass resist corrosion and are good electrical conductors. Copper is a better conductor than brass, and it is used in electrical wiring. Brass is stronger than copper, so it is used for the pins in electrical plugs.