unit 11 - redox Flashcards
what are redox reactions caused by
caused by competition of atoms for electrons
redox is an abbreviation for
Reduction/Oxidation Reactions
oxidation
- The LOSS of electrons.
- Charge becomes more positive
reduction
- The GAIN of electrons.
- Charge becomes more negative
ATOMS are neutral but in a bond there is
shuffling of electrons (sharing, transferring) which ultimately gives them an “apparent” charge.
- this apparent charge is the Oxidation Number
Oxidation Number
The ”apparent charge” on an atom in a compound, due to difference in electronegativity and bonding
Ion
Charge an atom becomes when it gains or loses electron(s).
Redox: Rule 1
all neutral compounds must sum to the total charge of ZERO
Redox: Rule 2
polyatomic ions have a sum of charges equal to the ion’s charge
Redox: Rule 3
Any atom uncombined has an oxidation of zero, because atoms are neutral
Redox: Rule 4
Charge on a mono-atomic ion equals the charge of the ion
Redox: Rule 5
In Binary Compounds the MORE electronegative element is assigned FIRST (it’s the oxidation number is the name charge as an ion)
Redox: Rule 6
Elements in groups 1, 2, & aluminum have oxidation states ALWAYS +1, +2, and +3 respectively
Redox: Rule 8
oxygen is always -2 unless its combined with fluorine (OF2), then its +2, or in a peroxide (H2O2) then its -1
Redox: Rule 7
- Fluorine is the MOST ELECTRONEGATIVE ELEMENT so it takes precedence over ANY
- fluorine will always have a -1 oxidation #
Redox: Rule 9
hydrogen is +1; unless it combines with a metal then its -1 because thats a hydride
redox is a reaction defined by
the transfer of electrons
LEO the Lion says GER
Lose Electrons Oxidize
Gain Electrons Reduction
redox reaction can be broken into two parts that happen…
simultaneously!!
- oxidation and reduction
what typa reaction is never redox?
double replacement
hint to identify redox!!
- if theres a free guy and hes a compound on the otherside, yk it’s a redox
oxidizing agent
The substance that makes
something else undergo oxidation.
- Takes away the electrons (it gains electrons)
- Oxidizing Agent is also Reduced
reducing agent
Any substance that makes
something else gain electrons.
- Supplies Electrons (it loses electrons)
- Reducing Agent is also Oxidized
what gets oxidized is the ____ agent
reducing agent
what gets reduced is the ____ agent
oxidizing agent
in redox reactions, electrons shift from
one atom/species to another SIMULTANEOUSLY!!
half reaction
an equation which shows only a reduction OR oxidation
half reactions show conservations of what? exceptions?
**show conservation of Mass, Charge, and Energy
- except for Nuclear Reactions
Redox reactions like all chemical reactions MUST be balanced to show conservation of
mass, charge, and energy
shortcut for balancing redox
the difference in charge is the coefficient of the opposite
- does not work if you have diatomics
when a redox reaction takes place in an acidic solution,
it has excess H+ ion concentration as opposed to neutral conditions
redox in acidic: what are we adding
We will now add Water molecules and H+ ions to balance the Oxygens & Hydrogens under acidic conditions.
voltaic cells
- are electrochemical cells (batteries)
- involve a spontaneous redox reaction
- chemical energy is converted into electrical energy
voltaic cells setup: two electrodes
are the site of oxidation/reduction
voltaic cells setup: salt bridge
connects the two containers and produces the path for a flow of ions
voltaic cells setup: the wires of voltmeter
connect the 2 half cells and electrons travel through them
voltaic cell: table j
- most active metals lose electrons easily
- top: atom oxidized
- bottom: ion reduced
voltaic cell: anode
Anode is the site of oxidation
voltaic cell: cathode
cathode is site of reduction
voltaic cell: electrons move from…
anode to cathode through the wire
voltaic cell: anode mass/size
anode decreases in mass/size
voltaic cell: cathode mass/size
cathode increases in mass/size
voltaic cell: ions move through
Ions (+/-) move through salt bridge in the direction of electrode with same charge to maintain neutrality.
voltaic cell: battery
battery will die and voltage will read zero (state of equilibrium)
maximum battery voltage or cell potential
- based reduction potential chart
- cell potential (v) = reduction potential (v) - oxidation potential (v)
if cell potential (+)
reaction is spontaneous
if cell potential (-)
reaction is nonspontaneous
predicting spontaneous reactions
- one metal must be neutral ex. Mg (s) or Al (s) these can be oxidized (lose electrons)
- the other must be an ion ex. Mg^+2 or Al^+3 these can be reduced (gain electrons)
predicting spontaneous reactions: table j
the metal atom being oxidized (the neutral one) must be higher on the table J than the ion being reduced
electrolysis
- is a non spontaneous reaction
- requires electricity (battery)
electrolytic cells:
- electrolysis
- requires electricity
- need an electric generator (battery) placed into the circuit to force electrons to flow from the anode (+) to the cathode (-)
- electrical energy drives a chemical (redox rxn)
electroplating
used to plate expensive metal on top of cheaper metals
electrolytic: anode
● (+)
● always the expensive metal
● site of oxidation
electrolytic: cathode
● (-)
● site of reduction
electrolytic cells are used to
retrieve very active metals (group 1 & 2) from salts that contain them
