Redox Flashcards
WHat are redox reactions involved in?
involved in a variety of natural processes from the rusting of iron, the
browning of food to the respiration of animals.
WHen do oxidation and reduction states occur?
Oxidation- reduction (redox) reactions occur when electrons are transferred from the atom that becomes oxidised to the atom becomes reduced
Oxidation Is…
…Loss (of electrons) (OIL)
Reduction Is…
…Gain (of electrons) (RIG)
Redox has implications through out the cell such as…
- Biochemical reactions
- Biological molecule function
- Intracellular environment
The transfer of electrons can have such a…
…profound effect where physiological and pathological states can be determined.
When has an atom, ion or molecule become oxidised?
When an atom, ion or molecule LOSES electrons and becomes more positively charged we say it has been oxidised (OIL)
Loss of electrons by a substance is called…
…OXIDATION
How are metal oxides formed?
Metals react directly with the O2
in the air to form metal oxides
Eg:
2 Ca (s) + O2 (g) –> 2CaO (s)
Describe the oxidation of
2 Ca (s) + O2 (g) –> 2CaO (s)
Ca is oxidised to CaO. Ca has lost two electrons and O has gained two electrons.
Ca is now more positively charged and O is now more negatively charged: REDUCED
When one reactant loses electrons, another must…
…gain them
the oxidation of one
substance is always accompanied by the…
…reduction of another
REDuction & OXidation = REDOX
Each atom in a neutral molecule or charged species is assigned an…
… oxidation state
define oxidation state.
either the actual charge of the monotomic ion, or a hypothetical
charge assigned to the atom
Oxidation states of atoms…
…change in a redox reaction
What are the oxidation number rules?
1 – For an atom in its elemental form, the oxidation number is 0
2 – For any monotomic ion (e.g. Na+
), the oxidation number is the equal to the charge on the ion.
3 – Nonmetals usually have negative oxidation numbers
4 – The sum of the oxidation numbers in a neutral compound is 0
5 – The sum of the oxidation numbers of all atoms in a polyatomic ion equals the charge on the ion
What is the oxidation number of oxygen?
-2 (except in peroxides where it is -1)
What is the oxidation number of hydrogen?
+1 (except when bound to metals = -1)
What is the oxidation number of halogens?
Oxidation number of halogens (F, Cl, Br etc) = -1 (except when combined
with oxygen where they have positive oxidation numbers)
Redox reactions need to take into account…
…the movement of electrons
In acidic solutions, we can add […] and […] to balance half reactions?
H2O and H+
The energy released in a spontaneous redox reaction can be used to perform…
…electrical work.
Where is the potential energy of electrons highest in an electrical unit?
higher at the ANODE electrode than at the CATHODE electrode
What occurs at the anode?
(oxidation half reaction) e- loss
What occurs at the cathode?
(reduction half reaction) e- gain
The difference in the potential energy between two electrodes is called the…
…electromotive force (emf).
Define electromotive force (emf)
The difference in the potential energy between two electrodes
For any reaction that proceeds spontaneously the emf…
…must be positive
A voltaic cell is produced when…
…an oxidant and reductant are separated by a salt bridge
The cell potential is the difference between…
…electrode potentials
By convention, the potential associated with each electrode is chosen to be
…the potential for reduction to occur at that electrode
We can measure the potential for a particular reactant to …
…accept electrons (i.e. to become reduced).
How can we measure the potential of a particular reactant to accept electrons?
by the standard reduction potential where the more positive the value, the greater the tendency for the reactant to accept electrons and become reduced (an OXIDIZING AGENT).
The more positive the E^0red value for a half reaction,…
…the greater the tendency for the reactant of the half-reaction to be reduced, and therefore to oxidise another species
F2 is an easily reduced species - it has the strongest tendency to remove
electrons from other species. It is therefore a…
… strong OXIDIZING AGENT
Li+ is the most difficult species to reduce - it has the strongest tendency to give electrons to other species. It is therefore a …
…strong REDUCING AGENT
The transfer of electrons in redox reactions is responsible (directly or indirectly) for…
…ALL work done by living organisms
Electrons flow through…
…carriers
- each of which has a higher affinity for the electron than the previous one
Carriers are used to power…
…biological reactions
Within a covalent bond, one of the atoms may exert a…
…greater attraction for the bonding electrons than the other.
Define electronegativity
Electronegativity is the ability of an atom in a molecule to attract
electrons to itself
The oxidation state gives a…
…measure of how oxidised an atom within a molecules is, based on electronegativity
As the red carbon undergoes oxidation (loses electrons)…
…the number gets smaller and the oxidation state increases
The cell is full of numerous…
redox couples, including small organic molecules as well as large macromolecules (e.g. proteins and lipids)
Intracellular redox couples have numerous roles:
- Oxidising redox couples such as; protein disulphide isomerase (PDI) – involved with intramolecular disulphide bond formation (correct protein folding)
- Reducing redox couples such as; thioredoxin (TrX) – involved with breaking intermolecular disulphide bonds (protein-protein aggregates)
Nernst equation calculations can…
… give details as to whether a redox couple is oxidising or reducing in nature
The more oxidising the redox couple, the more…
…positive the (mV)
i.e. electrons will
transfer from very (-ve) to less (-ve) down an electrochemical gradient
During oxidative stress, GSH can
donate electrons (removing the oxidative stress)
Because intracellular [GSH] is so high, the ratio of GSH : GSSG is a…
…good indicator for cell health
Many diseases are associated with…
… increased oxidative stress; cancer, cardiovascular disease, neurodegenerative disease
GSH can be used to calculate…
…e the intracellular redox potential (Eh
), from the modified Nernst equation
What is GSH?
glutathione
As intracellular redox potential (Eh) becomes more (+ ve), redox couples within the cell become more…
…oxidised
Many redox couples are proteins which…
have a role in cell growth and survival. These may be ‘switched on’ or ‘switched off’ during Ehchanges
Altering Eh can effect…
…cell growth and survival
What is Eh?
intracellular redox potential
What is the mitochondria electron transport chain a set of?
essential set of redox reactions
What does the mitochondria electron transport chain generate?
Allows 38 ATP to be generated per glucose molecule
