Topic 3 - Redox I Flashcards
What is meant by the term oxidation number?
The number of electrons that have been taken or gained from an element.
How do you calculate the oxidation number of elements in compounds & ions.
- Gp 1 metals = +1
- Gp 2 metals = +2
- Al = +3
- H = +1 (except in hydrides = -1 NaH)
- F = -1
- Cl, Br, I = -1 (except w/ O or F)
- O = -2 (except in peroxides H₂O₂ & w/ F = -1
What is oxidation & reduction?
Oxidation is the loss of electrons or ↑ in ox number
Reduction is the gain off electrons or ↓ in ox number
What are oxidising & reducing agents?
Ox agents are electron acceptors (gain e⁻) & are reduced in the reaction
Red agents are electron donors (loose e⁻) & are oxidised in the reaction
What is a disproportionation reaction?
When an element in a single species is simultaneously oxidised & reduced.
How can ox no. be used to classify between redox & disproportionation reactions?
If the ox no of an element is both oxidised & reduced, the reaction is disproportionate, if not then it’s redox.
How do you classify the ox no of an element in a compound or ion?
By using roman numerals. (I, II, III, IV, V, VI…)
How do you write formula given the ox no?
If you know the ox no you can figure out the ration of the elements need in the compound.
What ions do metals form?
(+ve) ions by loss of e⁻ with an ↑ in ox no
What ions do non metals form?
(-ve) ions by gain of e⁻ with a ↓ in ox no
How do you write ionic half equations?
-work out ox no
-add electrons to equal change in ox no (red = e⁻ to L/ ox = e⁻ to R)
-make sure sum of charges is equal on both sides
(if has O, balance by adding H⁺/H₂O in acidic conditions or OH⁻)
How do you combine half equations?
- multiply them to get equal no of electrons
- add them together & cancel electrons (balance H⁺ too)
