Transition metals, alloys and corrosion Flashcards
where are the transition metals placed?
placed in the central part of the periodic table.
properties of transition metals? (4)
high melting points
high densities
they form coloured compounds
they (and their compounds) can act as catalysts
what coloured compounds do metals or non metals often form?
white or colourless compounds
how is Iron an exception? (4)
-it has the typical properties of transition metals
-high melting and boiling point + high density
-pale green
-used as a catalyst in the haber process
what do metals do in air?
oxidise
what do very unreactive metals NOT do?
oxidise at all
what is corrosion?
-what does it eventually become?
when a metal continues to oxidise and becomes weaker over time
-metal oxide
when does rusting occur?
-how could you prevent this?
when iron or steel reacts with oxygen and water
-keeping them away from water and oxygen
Explain whether iron is oxidised or reduced when it forms rust.
Iron is oxidised because it gains oxygen during rusting.
how can rusting from oxygen and water be prevented (specific)? (2)
oxygen : storing the metal in an atmosphere of unreactive nitrogen or argon
water : storing the metal with a desiccant
what is a dessicant?
a substance that absorbs water vapour, so it keeps the metal dry.
state some physical barriers to prevent water and oxygen from causing rusting: (3)
painting
oiling and greasing
coating with plastic or a metal (electroplating)
Explain why a bike chain is protected from rusting by oiling it, rather than by painting it. (2)
oil lubricates the chain, helping it to move smoothly.
-paint flakes off when bike is ridden, exposing steel chain to air and water again.
what does electroplating involve?
using electrolysis to put a thin layer of a metal on an object
describe the components in the electroplating process: (3)
-cathode (negatively charged electrode) is the iron or steel object
-anode (positively charged electrode) is the plating metal
-electrolyte contains ions of the plating metal
what does electroplating improve? (2)
-corrosion resistance of metal object
-appearance
how can iron also be protected? (sacrificial protection)
if it is in contact with a more reactive metal
how does the process of sacrificial protection work?
-why is it useful?(2)
-more reactive metal oxidises more readily than iron, so it ‘sacrifices’ itself while the iron does not rust.
-once metal has corroded away, it can simply be replaced.
what is galvanising? (1)
-how does it work? (2)
when iron is coated in zinc
-since zinc is more reactive then iron, it acts as a sacrificial method
-stops oxygen and air reaching iron, even if it is scratched
The inside of a steel food can is electroplated with tin, a less reactive metal than iron. It provides a physical barrier to oxygen and water, stopping the can rusting. Explain why the inside of the can rusts very quickly if the layer of tin is broken. (3)
-Oxygen and water can reach the steel when the layer is broken.
-Iron is more reactive than tin, so it oxidises more readily than tin.
-The damaged can rusts faster than if the tin was not there at all.
what is an alloy?
a mixture of two or more elements, where at least one element is a metal
why is converting pure metals into alloys often convenient?
it increases the strength of the product
what do solid metals have in terms of composition?
and what happens when a force is applied to a metal?
-a regular lattice structure.
-layers of atoms can move past each other.
what happens when it is more difficult to move through the regular lattice structure of solid metals?
The more difficult it is for the layers to move, the more force is needed and the stronger the metal.
explain why alloys have a higher tensile strength compared to their (separate) metal counterparts? (4)
what does this make brass?
-atoms of different elements have different sizes.
-this distorts 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.
what are alloy steels?
Alloy produced by mixing iron with one or more other metals.
what are the properties of mild, tool and stainless steel?
mild = Malleable, ductile
tool = Hard, resistant to high temperatures
stainless = Hard, resistant to rusting
what is mild steel useful for making?
what is a problem which occurs because of this and how could it be fixed?
car body parts because it is easily pressed into shape.
mild steel rusts, however it can be protected by galvanising and painting
what is tool steel used for?
and why?
Tool steel is useful for making drill bits.
These do not easily become damaged by the heating caused by friction during drilling.
Explain why stainless steel is used to make washing machines and dishwashers. (2)
Washing machines and dishwashers contain water.
This would cause other steels to rust, but stainless steel does not rust.
what is the equation for the reaction of iron, oxygen and water?
Iron + oxygen + water → hydrated iron(III) oxide
what does Hydrated iron(III) oxide (rust) look like?
orange-brown substance seen on the surface of rusty objects.
