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Chemistry for the Life Sciences > Redox > Flashcards

Redox Flashcards

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1
Q

WHat are redox reactions involved in?

A

involved in a variety of natural processes from the rusting of iron, the
browning of food to the respiration of animals.

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2
Q

WHen do oxidation and reduction states occur?

A

Oxidation- reduction (redox) reactions occur when electrons are transferred from the atom that becomes oxidised to the atom becomes reduced

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3
Q

Oxidation Is…

A

…Loss (of electrons) (OIL)

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4
Q

Reduction Is…

A

…Gain (of electrons) (RIG)

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5
Q

Redox has implications through out the cell such as…

A
  • Biochemical reactions
  • Biological molecule function
  • Intracellular environment
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6
Q

The transfer of electrons can have such a…

A

…profound effect where physiological and pathological states can be determined.

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7
Q

When has an atom, ion or molecule become oxidised?

A

When an atom, ion or molecule LOSES electrons and becomes more positively charged we say it has been oxidised (OIL)

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8
Q

Loss of electrons by a substance is called…

A

…OXIDATION

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9
Q

How are metal oxides formed?

A

Metals react directly with the O2
in the air to form metal oxides

Eg:
2 Ca (s) + O2 (g) –> 2CaO (s)

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10
Q

Describe the oxidation of
2 Ca (s) + O2 (g) –> 2CaO (s)

A

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

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11
Q

When one reactant loses electrons, another must…

A

…gain them

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12
Q

the oxidation of one
substance is always accompanied by the…

A

…reduction of another
REDuction & OXidation = REDOX

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13
Q

Each atom in a neutral molecule or charged species is assigned an…

A

… oxidation state

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14
Q

define oxidation state.

A

either the actual charge of the monotomic ion, or a hypothetical
charge assigned to the atom

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15
Q

Oxidation states of atoms…

A

…change in a redox reaction

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16
Q

What are the oxidation number rules?

A

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

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17
Q

What is the oxidation number of oxygen?

A

-2 (except in peroxides where it is -1)

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18
Q

What is the oxidation number of hydrogen?

A

+1 (except when bound to metals = -1)

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19
Q

What is the oxidation number of halogens?

A

Oxidation number of halogens (F, Cl, Br etc) = -1 (except when combined
with oxygen where they have positive oxidation numbers)

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20
Q

Redox reactions need to take into account…

A

…the movement of electrons

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21
Q

In acidic solutions, we can add […] and […] to balance half reactions?

A

H2O and H+

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22
Q

The energy released in a spontaneous redox reaction can be used to perform…

A

…electrical work.

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23
Q

Where is the potential energy of electrons highest in an electrical unit?

A

higher at the ANODE electrode than at the CATHODE electrode

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24
Q

What occurs at the anode?

A

(oxidation half reaction) e- loss

25
Q

What occurs at the cathode?

A

(reduction half reaction) e- gain

26
Q

The difference in the potential energy between two electrodes is called the…

A

…electromotive force (emf).

27
Q

Define electromotive force (emf)

A

The difference in the potential energy between two electrodes

28
Q

For any reaction that proceeds spontaneously the emf…

A

…must be positive

29
Q

A voltaic cell is produced when…

A

…an oxidant and reductant are separated by a salt bridge

30
Q

The cell potential is the difference between…

A

…electrode potentials

31
Q

By convention, the potential associated with each electrode is chosen to be

A

…the potential for reduction to occur at that electrode

32
Q

We can measure the potential for a particular reactant to …

A

…accept electrons (i.e. to become reduced).

33
Q

How can we measure the potential of a particular reactant to accept electrons?

A

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).

34
Q

The more positive the E^0red value for a half reaction,…

A

…the greater the tendency for the reactant of the half-reaction to be reduced, and therefore to oxidise another species

35
Q

F2 is an easily reduced species - it has the strongest tendency to remove
electrons from other species. It is therefore a…

A

… strong OXIDIZING AGENT

36
Q

Li+ is the most difficult species to reduce - it has the strongest tendency to give electrons to other species. It is therefore a …

A

…strong REDUCING AGENT

37
Q

The transfer of electrons in redox reactions is responsible (directly or indirectly) for…

A

…ALL work done by living organisms

38
Q

Electrons flow through…

A

…carriers

  • each of which has a higher affinity for the electron than the previous one
39
Q

Carriers are used to power…

A

…biological reactions

40
Q

Within a covalent bond, one of the atoms may exert a…

A

…greater attraction for the bonding electrons than the other.

41
Q

Define electronegativity

A

Electronegativity is the ability of an atom in a molecule to attract
electrons to itself

42
Q

The oxidation state gives a…

A

…measure of how oxidised an atom within a molecules is, based on electronegativity

43
Q

As the red carbon undergoes oxidation (loses electrons)…

A

…the number gets smaller and the oxidation state increases

44
Q

The cell is full of numerous…

A

redox couples, including small organic molecules as well as large macromolecules (e.g. proteins and lipids)

45
Q

Intracellular redox couples have numerous roles:

A
  • 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)
46
Q

Nernst equation calculations can…

A

… give details as to whether a redox couple is oxidising or reducing in nature

47
Q

The more oxidising the redox couple, the more…

A

…positive the (mV)

i.e. electrons will
transfer from very (-ve) to less (-ve) down an electrochemical gradient

48
Q

During oxidative stress, GSH can

A

donate electrons (removing the oxidative stress)

49
Q

Because intracellular [GSH] is so high, the ratio of GSH : GSSG is a…

A

…good indicator for cell health

50
Q

Many diseases are associated with…

A

… increased oxidative stress; cancer, cardiovascular disease, neurodegenerative disease

51
Q

GSH can be used to calculate…

A

…e the intracellular redox potential (Eh
), from the modified Nernst equation

52
Q

What is GSH?

A

glutathione

53
Q

As intracellular redox potential (Eh) becomes more (+ ve), redox couples within the cell become more…

A

…oxidised

54
Q

Many redox couples are proteins which…

A

have a role in cell growth and survival. These may be ‘switched on’ or ‘switched off’ during Ehchanges

55
Q

Altering Eh can effect…

A

…cell growth and survival

56
Q

What is Eh?

A

intracellular redox potential

57
Q

What is the mitochondria electron transport chain a set of?

A

essential set of redox reactions

58
Q

What does the mitochondria electron transport chain generate?

A

Allows 38 ATP to be generated per glucose molecule

59
Q
A

Chemistry for the Life Sciences (12 decks)

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