🟢 TOPIC 3: Redox 1 Flashcards
Define oxidation number:
The total number of electrons that an atom either gains or loses in order to form a chemical bond with another atom
Define redox reaction:
A reaction in which both oxidation and reduction occur - there is no net gain/loss of electrons
Define oxidation:
- loss of electrons
- oxidation number goes up
Define reduction:
- gain of electrons
- oxidation number goes down
What is the oxidation number of uncombined elements?
0
What is the sum of oxidation numbers in compounds?
0
What is the oxidation number of monotomic ions?
The charge on the ion
What is the sum of oxidation numbers in polyatomic/ molecular ions?
The charge on the ion
What is the oxidation numbers of group 1 and group 2 elements?
+1 and +2 (respectively)
What is the oxidation number of aluminium (and usually iron)?
+3
What is usually the oxidation number of lead?
+2
What is the oxidation number of hydrogen?
Always +1, except when in metal hydrides (eg. NaH), when it’s -1
What is the oxidation number of oxygen?
-2, except in peroxides when its -1 (eg. H2O2) or when with F, where it will be +ve
What is the oxidation number of group 7 elements?
-1, except when combined with a more electronegative element, where it will be +ve
Define reducing agent:
A substance that causes another substance to be reduced as it donates electrons easily. It is oxidised itself
Define oxidising agent:
A substance that causes another substance to be oxidised as it accepts electrons easily. It is itself reduced.
Define disproportionation reaction:
Both oxidation and reduction have taken place with the SAME element
(Eg. 2H2O2 —> 2H2O + O2)
[If a reaction is NOT disproportionation then there is not one SPECIES that is being oxidised and reduced - don’t be specific]
In the reaction, NaBr + Cl2 —> NaCl + Br2, which element is being oxidised, and which is being reduced?
ANSWER IN THIS FORMAT
- the oxidation number of sodium has not changed from +1, so sodium has neither been oxidised or reduced
- the oxidation number of bromine has increased from -1 to 0, so bromine has been oxidised
- the oxidation number of chlorine has decreased from 0 to -1, so chlorine has been reduced
How do you write an ionic half equation?
- Work out before and after oxidation states and identify the species that is being oxidised or reduced
- Write a balanced equation for the species that is being oxidised or reduced (other atoms can remain unbalanced)
- Balance oxidation states with e- (remember if there are multiple of the atom, there will have to be multiple e-)
- Work out the new charges (NOT oxidation states) - remember to count ALL electrons
- If charges don’t balance, add H+ ions to one side to balance
- If atoms don’t balance, add enough H2O so it balanaces
(7. If still doesn’t balance, may have to add O2)
Write the half equation for H2O2 to O2
H2O2 —> O2 + 2e- + 2H+
What does in acidic/ basic/alkali conditions mean?
In the prescence of H+ / OH- ions (respectively)
How do you combine half equations?
- Write the two half equations (one oxidation, one reduction) - (for the two separate species)
- Multiply equations so number of electrons in each is the same
- Add the two equations and cancel out electrons and any other species which appear on both sides
What does the roman numeral number indicate in a systematic name?
The oxidation number of the element it comes after (usually a transition metal as they can have multiple oxidation states)
What is the systematic name of NaClO3?
Sodium chlorate (V)
What is the systematic name of VO^2+?
Vanadate (IV)
-ite and -ate endings are both used for when an element is bonded with oxygen, but what is the difference between them?
-ite indicates a low oxidation state of the element bonded with oxygen (eg. III)
-ate indicates a high oxidation state of the element bonded with oxygen (eg. IV)
(may only apply for when oxygen and ONE other element is bonded/ for ions)
What are the systematic names for V2O5 and VO2^+?
Vanadium (V) oxide and Vanadate (V) respectively
What is the formula of copper (II) oxide?
CuO
What is the formula of chromium (III) sulfate (VI)?
Cr2(SO4)3
What is the formula of cobalt (III) nitrate (V)?
Co(NO3)3
