Chapter 15 (Chemistry only) Flashcards
What is an alloy?
An alloy is a combination of metals or of a metal and another element. Alloys are defined by a metallic bonding character.
How does the structure of an alloy affect its properties?
E.g.
Stronger -The regular layered packing structure of a pure metal is disrupted. The layers can no longer slide over each other.
Higher Melting point - a stronger force of attraction (metallic bonds) between the different atoms in the alloy
What is rusting?
Iron and steel rust when they come into contact with water and oxygen. Both water and oxygen are needed for rusting to occur
What is a sacrificial metal?
A sacrificial metal is a metal that corrodes to prevent a primary metal from corrosion or rusting
What is galvanising?
Galvanisation is the process of zinc-plating other metals to protect them from corrosion
What is carbon steel?
Steel in which the main alloying element is carbon
What is stainless steel?
A form of steel containing chromium, resistant to tarnishing and rust
What is the Haber process?
The manufacture of ammonia (NH3 )
N2 + 3H2 —>2NH3
What conditions are used in the Haber process?
450oC
200 atmospheric pressure
What is ammonia used for?
Fertilisers
To make nitric acid
Why are fertilisers important?
Thye help to replenish the nitrogen in the soil and increase crop yield especially in areas of intensive farming or poor soil
Why is the low yield in the Haber process acceptable?
The unreacted nitrogen an hydrogen can be recycled
What is meant by compromise conditions in the Haber process?
A compromise between the pressure and temperature of the process
- A higher temperature would speed up the rate of reaction but in this case, also decreases the yield
- A high pressure would increase the yield but is costly and needs specialist equipment
Why is an iron catalyst used in the Haber process?
To speed up the reaction
How are fertilisers made?
A neutralisation reaction between an acid and ammonia
e.g. ammonia + nitric acid —-> ammonium nitrate
Why does a high-pressure increase the yield in the Haber process?
The Haber process is a reversible reaction so according to Le Chataliers principle, the reaction will move to the side with fewer moles of gas i.e, in this case, the forward direction, so more product is made
Why does increasing the temperature decrease the yield in the Haber process?
The Haber process is a reversible reaction, as the reaction is exothermic increasing the temperature pushes the reaction in the backward direction, to make more reactants
te of reaction
What is a composite?
Composite materials are made from two or more different types of material.
For example, MDF is made from wood fibres and glue, and fibreglass is made from a mesh of glass fibres set in a tough polymer
These products have specially engineered properties such as higher strength
What are ceramics?
Ceramic materials are solids made by baking a starting material in a very hot oven or kiln. For example, clay to make tiles. They are hard, resistant and have high melting points but they are also brittle
Ceramics have orderly giant structures (crystalline)
What is a thermoset plastic (thermosetting)?
Thermosetting polymers once moulded do not soften when heated and they cannot be reshaped. Vulcanised rubber is a thermoset used to make tyres. Strong covalent crosslinks form between the polymer chains
What is thermosoftening plastic?
Thermosoftening polymers soften when heated and can be shaped when hot. The shape will harden when it is cooled but can be reshaped when heated up again
What is glass?
A hard, brittle substance, typically transparent or translucent, made by fusing sand with soda and lime and cooling rapidly. It is used to make windows, drinking containers, and other articles
Glass has a disorderly giant structure (amorphous structure)
What is HDPE?
The polymer molecules line up regularly to give a crystalline structure. This means that:
the material has a higher density than LDPE
the forces of attraction between polymer molecules are strong
the material is stronger, and has a higher melting point, than LDPE
e.g. uses plastic bottles
What is LDPE?
The side branches stop the polymer molecules from lining up regularly. Its structure is not crystalline.
This means that:
the material has a lower density than HDPE
the forces of attraction between polymer molecules are weakened
the material is less strong, and has a lower melting point, than HDPE
e.g. used for plastic bags
What other ways can iron be protected from rusting?
Paint, plastic, oil and grease
What is steel?
Alloys of iron with carbon or other elements. By carefully changing the amounts of carbon or other elements added to the iron, the properties of the steel can be changed
