Redox - Yr12 ✅

define oxidation state

the number of electrons lost or gained by an atom in a compound compared to the uncombined atom

what is an oxidising agent

electron acceptor

• gains electrons and is reduced

• reduction in oxidation number (gets more negative)

what is a reducing agent

electron donor

• loses electrons and is oxidised

• increase in oxidation number (gets more positive)

does an oxidising agent get reduced or oxidised

reduced- by accepting electrons

what are the 10 rules for assigning oxidation states

1. oxidation state of an uncombined element is zero

2. oxidation numbers of the elements in a compounds add up to zero

3. oxidation number of a monoatomic ion is equal to the ionic charge

4. iin a polyatomic ion the sum of the individual oxidation states of the elements adds up to the charge on the ion

5. the more electronegative element in a compound is given a negative oxidation state

6. group 1 metals= +1

7. group 2 metals = +2

8. Al always has an oxidation state of +3

9. H = +1 (except for metal hydrides when its -1 e.g.NaH)

10. F= -1

11. O = -2 (except in peroxides H₂O₂ when its -1 and in compounds with fluorine

12. Cl, Br, I = -1, expect in compounds with O and F

give the useful method which helps to write has equations

1. balance all species excluding oxygen and hydrogen

2. balance oxygen using H₂O

3. balance hydrogen using H⁺ ions

4. balance charges using e^-

see example

when combining half equations, what must you ensure?

the number of electrons is the same of both half equations

what is oxidation

loss of electrons

what is reduction

gain of electrons

more complex half equations

If the substance that is being oxidised or reduced contains a varying amount of O (eg

MnO₄^- → Mn²⁺ ) then the half equations are balanced by adding H⁺, OH^_ ions and H₂O.

method to combining half equations

1. Multiply the half equations to get equal electrons

2. Add half equations together and cancel electrons and potentially H⁺

define oxidation

• loss of electrons

• increase in oxidation state

define reduction

• gain of electrons

• decrease in oxidation state