3. Redox I Flashcards
What is oxidation, in terms of electrons and oxidation numbers?
. electron loss
. increase in oxidation number
What is reduction, in terms of electrons and oxidation numbers?
. electron gain
. decrease in oxidation number
What is the oxidation number for uncombined elements?
zero
What do oxidation numbers of the elements in a compound add up to?
zero
The oxidation number of a monoatomic ion is equal to what? (e.g Zn2+ = ?)
the ionic charge
In a polyatomic ion (CO3 2-) the sum of the individual oxidation numbers of the elements add up to what?
the charge on the ion
What is the oxidation number of H in metal hydrides? (e.g. NaH)
-1
When do Cl, Br, and I oxidation numbers not equal -1?
in compound with oxygen and fluorine
When is O oxidation number not -2? What is it instead?
. in peroxides (H2O2) = -1
. and in compounds with fluorine
When does an element in a compound be given roman numerals when writing its name?
if the element has various oxidation numbers
(e.g. FeCl2 : Iron (II) chloride
FeCl3 : Iron (III) chloride)
What are reducing agents, in terms of electrons?
electron donors
What are oxidising agents, in terms of electrons?
electron acceptors
What does a reduction half equation show?
. only shows the parts of a chemical equation involved in reduction
. the electrons are on the left
What does a oxidation half equation show?
. only shows the parts of a chemical equation involved in oxidation
. the electrons are on the right
What do oxidising agents do in a reaction? (to itself and other elements)
. is the species that causes another element to oxidise (lose electrons)
. itself reduces in the reaction
What do reducing agents do in a reaction? (to itself and other elements)
. it’s the species that causes another element to reduce (gain electrons)
. itself oxidises in the reaction
How do metals generally form ions? (electrons, O.N. and +/-)
. by losing electrons
. with an increase in O.N
. to form positive ions
How do non-metals generally form ions? (electrons, O.N. and +/-)
. by gaining electrons
. with a decrease in O.N.
. to form negative ions
ACID + METAL ——-> ?
SALT + HYDROGEN
What is a disproportionation reaction?
when an element in a single species simultaneously oxidises and reduces
How do you balance redox equations?
- work out O.N. for the element being oxidised/ reduced
- add electrons to the change in O.N. (reduction = add e’s to reactants, oxidation = add e’s to products
- IF NEEDED, add H2O to balance O’s
- add H+ to balance H’s
Write the half equation for the change MnO4
- —–> Mn2+
- Mn changes from +7 to +2, add 5 electrons to reactants
- MnO4 - + 5e- —–> Mn2+ - add H2O to balance O’s in MnO4-
- MnO4- + 5e- ——> Mn2+ +4H2O - add H+ in reactants to balance H’s in H2O
- MnO4- + 5e- + 8H+ ——> Mn2+ + 4H2O
