C15 Using our resources Flashcards
Rusting
the corrosion of iron caused when iron is exposed to water AND oxygen for a long period.
Methods to prevent rusting:
- barrier methods (paint/oil/ plastic/electroplating)
- sacrificial methods (galvanising)
Word equation for rusting:
Iron + water + oxygen → hydrated iron oxide (rust) (Fe₂O₃)
Describe an experiment to prove the conditions required for rusting:
- prepare 3 test tubes
- in one, add an iron nail to boiled water with a layer of oil on the top. (Boiled water contains no oxygen and the oil prevents any oxygen from entering)
- in another, add an iron nail to calcium chloride (calcium chloride removes any water vapour from the air)
- in another, add the nail to water (it is exposed to both water and oxygen)
- close the test tubes of the boiled water and the calcium chloride.
- over time observe the changes, seeing if rust will form (we would see that the third test tube only would form rust)
galvanising
both a barrier and sacrificial method of preventing rusting which coats the iron in a layer of zinc. it creates a physical barrier that stops oxygen or water from contacting the iron whilst also reacting with the surrounding oxygen to form a layer of zinc oxide instead of the iron reacting, even when the barrier is breached.
Explain the sacrificial method of preventing rusting:
To prevent iron from rusting we can add a more reactive metal than iron to the iron as it would be a stronger reducing agent, meaning that it can be oxidised easier than iron, therefore would stop the iron from rusting as it gets corroded itself.
Copper alloys:
- Bronze = copper and tin, strong and resists corrosion (propellers)
- Brass = copper and zinc, easily malleable but stronger than copper (instruments)
What is steel?
Iron with adjusted amounts of carbon in it, the amounts of carbon determine its properties. there are two types of steel alloy (varying amounts of carbon, by mixing other metals in)
High carbon vs. Low carbon steel
High carbon steel is hard and brittle whereas low carbon steel is soft and more malleable hence is less likely to shatter.
Polymer:
A molecule made up of repeating monomers.
Difference between low and high density polyethenes:
(this shows how polymer properties can differ depending on their manufacturing conditions)
Low density (LD) polyethenes are made under higher pressures and with the presence of oxygen causing the polymer chains to become randomly branched and not able to be compressed together. High density (HD) are formed using a catalyst at 50ºC at a lower pressure, causing the polymer chains to be lines up and able to be packed closely together.
HD has a higher softening temperature and is harder than LD polyethene.
What impact the properties of polymers?
- type of monomer its made from
- conditions in its manufacturing
Thermosetting vs. Thermosoftening polymers:
thermosoftening polymers are polymers where the polymer chains are individual strands that are tangled together, when heated they soften and set in place.
thermosetting polymers are when polymer strands are fixed together by strong covalent bonds (cross-linking). this means they burn not melt under heat.
Thermosoftening polymers:
Polymers whose polymer chains are weakly bonded through intermolecular forces, when heated, these forces break allowing the polymer to become soft before cooling and reshaping.
Thermosetting polymers:
Polymers whose polymer chains are bonded together because their monomers form covalent bonds between the chains (cross-linking). these covalent bonds are very strong preventing the polymer from melting under heat.
Define the Haber process:
a process which produces ammonia from nitrogen and hydrogen as a starting chemical for nitrogen-based fertilisers using an iron catalyst.
N₂ + 3H₂ ⇌ 2NH₃
Where do we source the reactants for the Haber process?
nitrogen - the air
hydrogen - reacting methane (from crude oil) with steam
Explain the Haber process:
- the raw materials (nitrogen and hydrogen) are passed through a compressor, pressurising the gasses at 200 atm
- they are then pressurised into the converter, this container a hot iron catalyst at around 350ºC.
- some of the nitrogen and hydrogen react, producing ammonia.
- the gas mixture (of nitrogen, hydrogen and ammonia) are fed into a condenser, which cools the gas. since ammonia has a lower boiling point it condenses into a liquid much earlier than the other gasses, so is collected.
- the remaining nitrogen and hydrogen gas is passed back to the compressor and it reused.
What minerals are in NPK fertilisers?
- nitrogen
- phosphorous
- potassium
What are NPK fertilisers?
A soluble formulation with varying ratios of nitrogen, potassium and phosphorous that farmers use to replace the mineral ions taken up from the soil into the crops.
Why must NPK be soluble?
so that the fertiliser can be absorbed (osmosis) through the plant’s root hair cells.
What are soluble sources of nitrogen, phosphorous and potassium?
