unit 2 test 2
different redox processes
combustion
decomposition
single displacement
combination
combustion
such as fuel in cars
reaction w/ oxygen
complete produces CO2
incomplete produces either CO or C (soot)
combination
two substances form a 3rd substance
decomposition
one substance becomes two
single displacement
displacing element from it (two things switch)
what is oxidation old idea
substances reacting/combining w/oxygen
what is reduction old idea
loss or removal or oxygen from a compound
redoc reactions new idea
they may not have to have oxygen
may also involve gain/loss of hydrogen
all involve combo of 2 chem reactions that occur simultaniously (reduction and oxidation)
what is the mnemonic for redox
Oxidation
Involves
Loss (of electrons)
Reduction
Involves
Gain (of electrons)
thus OILRIG
example of redox
2Mg +O2 -> 2MgO
Mg loses 2 electrons and gains oxygen (oxidation)
Oxygen gains 2 electrons (reduction)
example of half equations
2Mg + O2 -> 2MgO is full equation
one half is
Mg-> Mg^+2 + 2e- (oxidation)
other half is
O2+ 4e- -> 2O^-2 (reduction)
what are Oxidations numbers
clarify redox reactions
especially when products are molecular
determines which oxidation, which reduced
oxidation numbers rule 1
oxidation number of element is mostly 0
oxidation number rule 2
for monoatomic ions, oxidation number is charge of ion
oxidation numbers rule 2
in all compounds of hydrogen, the oxidation # of hydrogen is 1
except in metal hydrides, where the oxidation number is -1 for hydrogen
oxidation numbers rule 4
oxidation number of oxygen in compound is usually -2
except for peroxide, where its -1
and compound with flourine oxygen bond (+2) (O^+2 F2^-1)
oxidation numbers rule 5
flourine always has oxidation number of -1 (bc most electronegative)
oxidation numbers rule 6
in neutral molecule, sum of all oxidation numbers must equal 0
oxidation numbers rule 7
in polyatomic ion, sum of oxidation numbers must equal charge of the ion
wtv oxidation number is is what all adds up to
oxidation numbers rule 8
in ionic compounds, often easier to separate the compound into ions first and calulcate oxidstion number of each ion separately
oxidation numbers rule 9
in covalent when no oxygen or hydrogen, more electronegative element has the negative oxidation number
this is equal to the charge that it woukd have if it were a negative ion
Increased oxidation number means
element has been oxidised
decreased oxidation number means
element has been reduced
what to do when a half equation is uneven (incorrect amt of electrons
must double whole half equation
what is a reductant
a reducing agent
what is an oxidant
an oxidising agent
what does a reductant do
cause other substances to undergo reduction
they lose electrons and oxidise
what do oxidants do
cause other substabces to undergo oxidisation
they accept electrons and undergo reduction
what is a conjugate redox pair
a reductant and an oxidant in a redox half equation (on opposite sides)
what is a conjugate redox pair simple
the same element or molecule
what is KOHES
the opperation of transcribing redox half equations
K in KOHES
Key element
this means to balance all key atoms except hydrogen or oxygen
O in KOHES
oxygen
this means balance oxygen by adding H2O to needed side
what is H in KOHES
hydrogen
this means to balance the hydrogen by addint H+ ions to needed side
what is the E in KOHES
electrons
this means to balance the charges of each side (using oxidation #s) by adding electrons to needed side
what is the S in KOHES
states
this means include correct states throughout the question
what are the halogens (second last group) general oxidation number
usually -1
unless with oxygen, then +1
what is the general oxidation number of group 1
+1
general oxidation number of group 2
+2
general rule for hydrogen oxidation #
+1 with nonmetals
-1 with metals
rules for oxygen oxidation number
usually -2
unless O2H2 or with FO then -1
rule for Flourine oxidation #
-1