9 redox
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what is corrosion called in the case of iron and steel
rusting
what is rust chemical formula
hydrated iron(III) oxide (Fe2O3.xH2O)
what is essential for iron to rust
water and oxygen
what increases rate of corrosion
salt and acid rain
what is sacrifical protection
an alternative method of rust prevention in which blocks of a more reactive metal are attatched to the iron surgace. these mtals are more reactive than iron and will be corroded in preference to it
what is galvanising
a layer of more reactive metal coats the object. It has the advantage over other plating methods in that the protection still works even if the zinc layer is badly scratched. The zinc layer can be applied by several different methods. These include electroplating or dipping the object into molten zinc. The bodies of cars are dipped into a bath of molten zinc to form a protective layer.
what type of reaction is a corrosion
redox, involving both oxidation and reduction
oxidation is
the loss of electrons and increase in oxidation state
reduction is
the gain of electrons and decrease in oxidation state
oxidising agent
is a species that oxidises another species
a reducing agent is
a species that redudces another species
a positive oxidation state means
it has lost electron control, and is consequerntly oxidised
a negative oxidation state means
it has gained control over electrons, and is consequently reduced
oxidation state is
a number which, with its sign, indicates the gain or loss of electron control of an atom during a reaction.
an oxidation number is
the numerical part of the oxidation state
Free elements such as O2, Cl2, N2, are assigned an oxidation state of
0
the sum of the oxidation states of all the atoms in a compound must be equal to
the net charge on the compound
The alkali metals (Li, Na, K, Rb and Cs) in compounds are always assigned an oxidation state of
+1.
Fluorine in compounds is always assigned an oxidation state of
−1.
The alkaline earth metals (Be, Mg, Ca, Sr, Ba and Ra) and Zn in compounds are always assigned an oxidation state of
+2
Hydrogen in compounds is assigned an oxidation state of X except in certain metal hydrides (e.g. NaH), where it is Y
X = +1 Y = -1
Oxygen in compounds is assigned an oxidation state of X, except in peroxides (e.g. H2O2), where it is Y, or when it is combined with fluorine.
X = -2 Y = -1
Chlorine in compounds is assigned an oxidation state of WHAT unless
-1, unless it is combined with oxygen or fluorine.
The charge on a metal ion is the same as
its oxidation state, e.g. Zn2+ has an oxidation state of +2.