[3.1.7] Oxidation, Reduction & REDOX Equations Flashcards
What is oxidation?
- Oxidation is the process of electron loss.
- It involves an increase in oxidation number.
What is reduction?
- Oxidation is the process of electron gain.
- It involves an decrease in oxidation number.
What are the rules for assigning oxidation numbers?
- All uncombined elements have an oxidation number of 0.
- e.g. Zn, Cl₂, O₂ and Ar all have oxidation numbers of 0.
- The oxidation numbers of the elements in a compound add up to 0.
- e.g. NaCl -> Na = +1 Cl = -1 -> Sum = +1 -1 = 0
- The oxidation number of a monoatomic ion is equal to the ionic charge.
- e.g. Zn²⁺ = +2 & Cl⁻ = -1
- In a polyatomic ion, the sum of the individual oxidation numbers of the elements adds up to the charge on the ion.
- e.g. in CO₃ ²⁻… C = +4 & O = -2… so… Sum = +4 + (4 x -2) = -2
- Several elements have invariable oxidation numbers in their compounds:
- Group 1 metals = +1
- Group 2 metals - +2
- Al = +3
- H = +1 (except in metal hydrides where it is -1 e.g. NaH)
- Cl, Br, I = -1 (except in compounds with oxygen and fluorine)
- O = -2 (except in perioxides e.g. H₂O₂ where it is -1 and in compounds with fluorine).
What is the oxidation number of Fe in FeCl₃?
- Cl has an oxidation number of -1.
- The oxidation numbers of the elements must add up to 0.
- Fe must have an oxidation number of +3 in order to cancel out 3 x -1 = -3 of the Cl’s.
What is an oxidising agent?
- An oxidising agent is the species that causes another element to oxidise.
- It itself is reduced in the reaction and is an electron acceptor.
What is a reducing agent?
- A reducing agent is the species that causes another element to reduce.
- It itself is oxidised in the reaction and is an electron donor.
In a reduction half equation, which side are the electrons on?
In an oxidation half equation, which side are the electrons on?
- The electrons are on the left in a reduction half equation.
- The electrons are on the right in an oxidation half equation.
Describe how you write a half equation.
- Work out oxidation numbers for element being oxidised/reduced.
- Add electrons equal to the change in oxidation number.
- For reduction, add electrons to reactants.
- For oxidation, add elections to products.
- Check to see that the sum of the charges on the reactant side equals the sum of charges on the product side.
Write a half equation for this reaction.
If a substance that is being oxidised or reduced contains varying amounts of oxygen, how do you balance its half equations?
The half equations are balanced by adding H₂O to balance the oxygen and H⁺ to balance the hydrogen in the water molecule(s).
How do you combine two half equations?
To combine two half equations, there must be equal numbers of electrons in the two half equations so that the electrons cancel out.
Combine the two half equations below.
Combine the two half equations below.
