C15 Flashcards
what is the equation for rust
iron + oxygen + water = hydrated iron (111) oxide
what 2 things are needed for iron to rust
air and water
what 5 things are used to coat iron or steel to prevent rust
paint (with added rust inhibitors) oil or grease plastic less reactive metal more reactive metal
what does it mean to galvanise iron
coat it in a more reactive metal eg zinc
zinc is a strogner reducing agent than the iron so has a stronger tendency to form positive ions by giving away ions
as zinc atoms lose electrons they become oxidised so any water or oxygen reacts with the zinc rather than the iron
what is sacrificial protection
for example in glavanising, the zinc is being sacrificed to protect the iron
what 3 things can be used to sacrificially protect iron
zinc, magnesium, aluminium
why are pure metals usually soft and easily shaped
their regular layers of positive ions in their giant lattices can slide over each other easily when forces are applied to the metal
why are alloys harder than pure metals
differently sized metal ions make it harder for the layers to slip
what is bronze an alloy of and what is it used for
copper and tin
statues, decorative items and ship propellors due to its toughness and resistance to corrosion
what is brass an alloy of and what is it used for
copper and zinc
brass instruments, door fittings and taps as it is hard but can be hammered into sheets and intricate shapes
why is gold alloyed with copper
in jewellery as pure gold wears away more easily than its copper alloy
what is steel
an alloy of iron with carbon and/ or other elements
how can properties of steel be changed
by controlling the amounts of carbon and other elements
property of high carbon steel
strong but brittle
property of low carbon steel
soft, easily shaped not as strong as high carbon steel but less likely to shatter on impact
what is chromium nickel steel
stainless steel- combines hardness and strength with great resistance to corrosion and they do not rust making them good for cutlery and kitchen utensils
what do the properties of a polymer depend on
the monomers used to make it
the conditions chosen to carry out the reaction
what are the differences between the conditions used to form LD poly(ethene) and HD poly(ethene)
LD: high pressures and a trace of oxygen- polymer chains are randomly branched and cannot pack closely together
HD: catalyst, 50c, slightly rasied pressure- straighter poly(ethene) chains that can pack closer together than LD chains. stronger than LD
what is a thermosoftening polymer
softens quite easily and then re sets when cooled. made up of individual polymer chains that are tangled together
what is a thermosetting polymer
do not melt when heated as they have strong covalent bonds forming cross links between their polymer chains
explain the forces between polymer chains in thermosoftening polymers
weak intermolecular forces that break when heated causing the polymer to soften. when the molecule cools the intermolecular forces bring the polymer molecules back together so the polymer hardens again
explain the forces between polymer chains in thermosetting polymers
monomers make covalent bonds between polymer chains when first heated in order to shape them. the covalent bonds are strong and stop them from softening or separating. polymer will not soften but may char at a high enough temperature
what is the most common type of glass (soda lime glass) made of
mainly sand but also silicone dioxide, limestone and sodium carbonate
how is glass formed
the raw materials are heated to 1500c where they melt and react to form molten glass. as it cools it solidifes but the particles do not form a regular pattern
