2.1.5 Redox Flashcards
What does oxidation state represent?
The degree of oxidation a particle undergoes based on the assumption that electrons are completely transferred between atoms
What does a positive oxidation number show?
That the element has been oxidised
What does a negative oxidation number show?
That the element has been reduced
What is the oxidation state of an uncombined element?
Always 0
E.g. Cl2, Fe, O2
What is the oxidation state of an ion?
Same as its charge
E.g. Ca2+ = +2
What is the oxidation state of a group 1 element?
Always +1
E.g. KCl
What is the oxidation state of a group 2 element?
Always +2
E.g. CaO
What is the oxidation state of aluminium?
Always +3
E.g. Al2O3
What is the oxidation state of hydrogen?
Usually +1 except in metal hydrides when it is -1
E.g. HF, NaH
What is the oxidation state of chlorine?
Usually -1 except in compounds when F and O when it is positive
E.g. KCl, ClF3
What is the oxidation state of fluorine?
Always -1
E.g. KF
What is the oxidation state of oxygen?
Usually -2 except in peroxides when it is -1 and in F2O when it is +2
What must the sum of oxidation states in a compound equal?
0
What do roman numerals indicate?
The magnitude of the oxidation number when an element may have compounds/ions with different oxidation numbers
E.g. Iron (II) = +2, iron (III) = +3
What is oxidation?
The loss of electrons
What is reduction?
The gain of electrons
What are reactions called which involve both oxidation and reduction?
Redox
What are reducing agents?
- Lose electrons
- Oxidised themselves
What are oxidising agents?
- Gain electrons
- Reduced themselves
How are oxidation and reduction shown through oxidation numbers?
- An increase in oxidation number (more positive) shows oxidation
- A decrease in oxidation number (more negative) shows reduction
What happens when metals react with acids?
- Oxidised
- Form hydrogen and a salt
What is the WHE method for half equations?
- Calculate oxidation states on each side of the equation
- Balance the element changing oxidation state
- Balance oxygen atoms by adding water molecules
- Balance hydrogen by adding H+ ions
- Balance the charge by adding electrons
What does the side the electrons are on tell you?
- If electrons are on the left, it is reduction
- If electrons are on the right, it is oxidation
How do you combine half equations?
- The number of reactants and products must balance
- The charges must balance
- If there is something on both sides of the equation (e.g. electrons, hydrogen), the equation can be simplified
- The number of electrons must be the same in both half equations for them to be combined
