sc13, transition metals, alloys, corrosion (paper 1) Flashcards
(37 cards)
in what groups are transition metals found in
between 2 and 3
give properties of transition metals
- high melting points (except mercury)
- high density
- stronger + harder than group 1 and 2, so they are more suitable as construction metals
- form coloured compounds
transition metals have catalytic activity, what does this mean
- increase the rate of a chemical reaction
- without altering the products of a reaction
- without changing chemically
- without changing in mass at the end of reaction
suggest two reasons why a metal object may be electropated
- improve it’s appearance
- improve its resistance to corrosion
what happens in the process of electropating a metal object
- a thin layer of an unreactive metal is deposited on the surface of the metal object
- (e.g silver, nickel, gold)
- keeping air and water out
how can you prevent rusting from oxygen and water
- painting
- using oil or grease
- coating with plastic or another metal
what is name given to the process of coating a metal with another metal
galvanising
what is galvanising
coating a metal with another metal
what happens during galvanising
- the metal is dipped in molten metal or electropated with it
what are the conditions for the chosen metal in galvanising
- more reactive thn iron
- reacts slowly with water
- so it corrodes before the iron/steel
- and prevents air and water reaching the iron beneath (acts as a sacraficial protector)
how can you keep oxygen away from an object
store it in a vacuum cleaner
how can you keep water away from an object
store it in a container with a desiccant
what is a desiccant
absorbs water vapour
what is an alloy
a mixture of a metal with one or more other elements (usually another metal or carbon0
what metal is mixed with pure iron to form an alloy called steel
carbon and other metals
why is pure iron often mixed with other elements
it’s too soft for most purposes
what is the most common steel
carbon steels
what are the two main properties of carbon steels
- consist of iron with up to 2% carbon
- are harder and stronger than iron alone
suggest why copper and gold is a good alloy for jewellery
- both unreactive
- similar in colour
what is stainless steel
an iron alloy that resists corrosion fused to make items
suggest why stainless steel is used in cutlery, washine machine, dishwashers etc.
- contain an invisible thin layer of chromium oxide on the surface of the steel
- it stops air and water reaching the iron
- the layer quickly reforms if it’s scratched
why are alloys stronger than their pure metals
- in their pure metals, layers of atoms can slide over each other easily
- the metal mixed in atoms disrupts the layers so they cannot slide over each other easily
what is the carbon steel alloy made of
iron mixed with carbon
what is the magnalium alloy made of
aluminium mixed with magnesium
