1.6 redox Flashcards
(11 cards)
What are redox reactions?
Oxidation is loss of electrons. Reduction is a gain in electrons - OIL RIG
Reduction and oxidation happen simultaneously - hence the term “redox”
reaction.
oxidising / reducing agent
An oxidising agent accepts electrons and gets reduced.
A reducing agent donates electrons and gets oxidised
Oxidation states
The oxidation state / oxidation number of an element tells you the total number of electrons it has donated or accepted. There are lots of rules for working out oxidation states.
Oxidation states rules - elements
Uncombined elements have an oxidation state of 0.
Elements just bonded to identical atoms also have an oxidation state of 0.
The oxidation state of a simple monatomic ion is the same as its charge.
Oxidation states rules - compounds
In compounds or compound ions, each of the constituent atoms has an oxidation state of its own and the sum of the oxidation states equals the overall oxidation state which is equal to the overall charge on the ion.
Within a compound ion, the most electronegative element has a negative oxidation state (equal to its ionic charge). Other elements have more positive oxidation states.
Oxidation states rules - oxygen & hydrogen
Combined oxygen is nearly always -2, except in peroxides, where it’s -1 (see Figure 6). Combined hydrogen is +1, except in metal hydrides where it is -1 (see Figure 7) and H2, where it’s 0.
Finding oxidation states e.g. Find the oxidation state of Zn in Zn(OH)2.
Finding oxidation states of elements with multiple
If an element can have multiple oxidation states (or isn’t in its ‘normal’ oxidation state) its oxidation state is sometimes shown using Roman numerals,
e.g. (I) = +1, (II) = +2, (III) = +3 and so on. The Roman numerals are written
after the name of the element they correspond to.
Examples
* In iron(II) sulfate, iron has an oxidation state of +2. Formula = FeSO4
* In iron(III) sulfate, iron has an oxidation state of +3. Formula = Fe2(SO4)3
This is particularly useful when looking at -ate ions. lons with names ending in -ate (e.g. sulfate, nitrate, carbonate) contain oxygen, as well as another element. For example, sulfates contain sulfur and oxygen, nitrates contain nitrogen and oxygen … and so on. But sometimes the ‘other’ element in the ion can exist with different oxidation states, and so form different ‘-ate ions’. You can use the systematic name to work out the formula of the ion.
Examples
* In sulfate(VI) ions the sulfur has oxidation state +6. This is the SO 2- ion.
* In sulfate(IV) ions, the sulfur has oxidation state +4. This is the SO32- ion.
* In nitrate(III), nitrogen has an oxidation state of +3. This is the NO,- ion.
Half-equations and redox equations
lonic half-equations show oxidation or reduction (see Figure 1). The electrons
are shown in a half-equation so that the charges balance.
Magnesium burns in oxygen to form magnesium oxide:
2Mg + O2-> 2MgO
Write half-equations for the oxidation and reduction reactions
that are part of this process.
complicated Half-equations and redox equations
