Oxidation and reduction Flashcards
What’s oxidation
Oxidation = oxygen added, electrons lost
What’s reduction
Reduction+ Oxygen is removed, electrons gained
What do reducing agents do?
Give away electrons
What do Oxidising agents do?
Accept electrons
What do oxidation states tell us in ionic compounds?
How many electrons in compound have been lost or gained
True or false? Every element in its uncombined state has an oxidation state of zero?
True
What do positive and negative numbers mean?
\+ = oxidised as element has lost electrons - = reduced as element has gained electrons
What is the positive and negative number correlation?
more + number = more oxidised
more - number = more reduced
True or false? Numbers always have + or - sign unless they’re zero.
True
What are the rules for finding oxidation states?
- Uncombined elements have oxidation state of 0
- Some elements in all of their compounds have same oxidation states
- Sum of all oxidation states in a compound = 0
- Sum of all oxidation states of a complex ion = charge of ion
- In compounds the most electronegative element always has a negative oxidation state.
Monatomic elements?
Oxidation state is same as their charge
Hydrogen - oxidation state, E.g
+1 (except metal hydrides), HCl
Group 1 - oxidation state, E.g
+1, NaCl
Group 2 - oxidation state, E.g
+2, CaCl2
Aluminium - oxidation state, E.g
+3, AlCl3
Oxygen - oxidation state, E.g
-2, (-1 in peroxides/ =2 in components with OF2), Na2O
Flourine - oxidation state, E.g
-1, NaF
Chlorine - oxidation state, E.g
-1, (+ in compounds with F and O), NaCl
Process of working out a compounds oxidation states?
Need a periodic table to use.
- Find oxidation states of elements in compound using periodic table
- Apply oxidation state rules to a compound
- Add up pluses and minuses to find compounds oxidation state.
Example of finding oxidation state?
Ammonia (NH3)
- Hydrogen oxidation state is +1
- Nitrogen must therefore be -3 as three hydrogens makes +3 and ou need to equal zero.
- Rule 5 - Nitrogen is more electronegative than hydrogen, so hydrogen must have a positive oxidation state.
Known Oxidation states through periodic table are?
Group 1 = +1 Group 2 = +2 Group starting with Boron = +3 Group starting with carbon = +/- 4 Group starting with Nitrogen = -3 Group starting with oxygen = -2 Group starting with florune = -1 Noble gases = 0
