Module 3

Question 1

What is oxidation in terms of the transfer of electrons?

Answer 1

Oxidation is a loss of electrons (more positive).

Question 2

What is reduction in terms of the transfer of electrons?

Answer 2

Reduction is a gain of electrons (more negative).

Question 3

What is redox?

Answer 3

A reaction involving the transfer of electrons from one species to another.

Question 4

What is the oxidant?

Answer 4

The thing that is getting reduced.

Question 5

What is the reductant?

Answer 5

The thing that is getting oxidised.

Question 6

What is the concept of oxidation numbers?

Answer 6

The oxidation number is the charge that the atoms in molecules would possess IF all molecules were ionic compounds.

Question 7

What is the sum of the oxidation numbers of the atoms in a molecule equal to?

Answer 7

0.

Question 8

What is the oxidation number of Oxygen (O2), and what is the exception in which it is different.

Answer 8

Usually the oxidation number of Oxygen is -2, except in hydrogen peroxide (H2O2), where is it -1.

Question 9

What does an increase in the oxidation number indicate?

Answer 9

Loss of electrons (oxidation number is more positive) - Oxidation.

Question 10

What does a decrease in the oxidation number indicate?

Answer 10

Gain of electrons (oxidation number is more negative) - Reduction.

Question 11

In balancing redox equations, what do you balance first and how?

Answer 11

First you balance the oxygens on each side by adding H2O on the side in need of Oxygen, you then balance the hydrogens on the side needing it by adding Hydrogen ions, then balance the number of electrons, by adding them to the side needing them.

Question 12

What must exist if electron transfer occurs?

Answer 12

A driving force or potential difference (units - J C-1 energy per unit charge).

Question 13

What do we use to determine the magnitude of the potential difference?

Answer 13

Galvanic cell.

Question 14

For the cell diagram: Ag | Ag+(aq, co)||Cu 2+(aq, co) | Cu

What does l & ll represent?

Answer 14

l - represents the state change

ll - represents the salt bridge.

Question 15

What does a positive value of the potentiometer indicate?

Answer 15

That the reduction is occurring on the right hand side. (oxidation on left)

Question 16

What does a negative value of the potentiometer indicate?

Answer 16

That the oxidation is occurring on the right hand side. (reduction on left)

Question 17

What does Ecell measure and how is it calculated?

Answer 17

Difference between how much each slide wants to gain electrons - i.e. how much the oxidant in each half of the equations wants to be reduced.
So Ecell = E RHS – E LHS

Question 18

What occurs at the cathode?

Answer 18

Reduction.

Question 19

What occurs at the anode?

Answer 19

Oxidation.

Question 20

What is the purpose of the cell bridge?

Answer 20

Allows for the ions to flow from the 2 different solutions.

Question 21

What happens in a galvanic cell?

Answer 21

Electrons flow from the anode (as the electrons of the solid metal are lost to form ions in solution) to the cathode, allowing for the ions at the cathode to turn be reduced and form metal.

Question 22

What is a Standard Hydrogen Electrode (SHE)?

Answer 22

A half cell that has a standard reduction potential of zero. (so it can act as either an anode or a cathode). Which acts as a reference electrode.

Question 23

For the predicting the spontaneity (direction) of electron transfer we use the equations
ΔG = -n x F x Ecell

and

                     RT
  Ecell =     ---------  x lnK
                   n x F

What do each of the letters mean?

Answer 23

n = the number of electrons transferred 
F = Faradays constant 

R = constant

The signs of ΔG and Ecell helps determine the direction the reaction proceeds under standard conditions.

And the magnitude of K determines the relative amounts of reactants and products in an equilibrium. (very large number = the products).

Question 24

How can you tell which reaction is the oxidation reaction and which reaction is the reduction reaction just by looking at the Ecell?

Answer 24

The reaction that wants to get reduced (gain electrons - reduction), will have the lower Ecell, therefore the other reaction is the oxidation reaction.

Question 25

What is the Nernst equation used for?

Answer 25

To calculate the E of a redox reaction, under non-standard conditions.

Question 26

What is the following equation and what do the letters represent?
RT
E = Eo - ——– x ln Q
n x F

Answer 26

The Nernst equation where;

n = the number of electrons transferred 
F = Faradays constant 

R = constant

Question 27

What is a concentration cell?

Answer 27

A galvanic cell where the same species are on both sides, but at differing concentrations.
Such a system can be described as a concentration gradient.

So Eo = E rhs - E lhs = 0.
However there is still a flow of electrons.
The E must be calculated with the Nernst equation.

Question 28

Describe a membrane potential, and give an example.

Answer 28

When a biological membrane separates two solutions of an ion (e.g. H+). Resulting in a concentration gradient, which generates a membrane potential, which can be harnessed by biological systems to do work. (e.g. ATP synthesis in mitochondria).

Question 29

Most oxidants require low pH, are toxic, and unselective, hence cannot be used within a biological system, list oxidants biological systems use.

Answer 29

• Coenzyme Q
• Flavine adenine dinucleotide FAD
• Nicotinamide adenine dinucleotide NADH

Question 30

What are the oxidants of biological systems called?

Answer 30

Coenzymes.

Question 31

What must occur to the coenzymes in order for the reactions to occur at the required rate?

Answer 31

They must be catalysed by an enzyme.

Question 32

What are transition metal and what are they used for?

Answer 32

Compounds in which transition metal cation has bound has a number of ligands bonded to it.

Question 33

What is a ligand?

Answer 33

The ligand contains one or more donor atoms, which have a lone pair of electrons which can be used to form the bond to the transition metal ion.

Question 34

What is a coordinate covalent bond?

Answer 34

The transition metal ion contributes no electrons to the bond with the ligand, while the ligand contributes both of its lone pairs to the bond.

Question 35

Why are ligands classified as lewis bases?

Answer 35

Because they donate both their lone pairs to the transition metal ion.

Question 36

Why are transition metal ions classified as lewis acids

Answer 36

Because it accepts both electrons from the ligands.

Question 37

Ligands are always charged ….. (negatively or positively or neutral)?

Answer 37

Ligands are always charged either negatively or neutral.

Question 38

Transition metal ions are always…. (anion or cation)?

Answer 38

The transition metal ions is always a cations.

Question 39

What does the denticity of a ligand refer to and what are the types of denticity bonds?

Answer 39

The number of donor atoms it has, hence the number bonds it can make to the transition metal ion.

Monodentate - 1 donor atom
Bidentate - 2 donor atoms
Tridentate - 3 donor atoms

Question 40

What are Bidentate and Tridentate lagands also referred to as?

Answer 40

Chelating - as they form chelate rings.

Question 41

What is a transition metal ion often described as?

Answer 41

A transition metal ion is often described as one with an electron configuration which finishes with a partially filled d shell.

Question 42

How can iron (Fe) form 2 cations?

Answer 42

For Fe2+ the first two 4s orbital electrons are lost.
For Fe3+ an electron is then lost from the 3d orbital.

Electron configuration of Fe:
1s2 2s2 2p6 3s2 3p6 4s2 3d6

Electron configuration of Fe2+:
1s2 2s2 2p6 3s2 3p6 4s0 3d6

Electron configuration of Fe3+:
1s2 2s2 2p6 3s2 3p6 4s0 3d5

Question 43

The common biological transition metals are..?

Answer 43

Mn, Fe, Co, Ni, Cu and Zn.

Question 44

What is the coordination number?

Answer 44

The number of ligands that can bond to the transition metal ion. Most common coordination number is 6 (but 5 and 4 are also relatively common).

Question 45

What is the coordination geometry (shape) of a metal ion with a coordination number of 6?

Answer 45

Octahedral.

Question 46

What is the coordination geometry (shape) of a metal ion with a coordination number of 5?

Answer 46

Can be either a square pyramidal or trigonal bipyramidal coordination geometry.

Question 47

What is the coordination geometry (shape) of a metal ion with a coordination number of 4?

Answer 47

Can either be a square planar or tetrahedral coordination geometry.

Question 48

How do you write the formula for a transitional metal? (explain the formula of [Ni(H2O)6]Cl2 and what it is telling us.

Answer 48

[ ] - encloses the transition metal ion and all of the ligands attached to it.

Ions outside of the [ ] are called counterions, and are present to counter the charge on the complex ion, hence making the molecule a neutral overall. (the Cl2 are 2 Cl- ions) and the charge of these ions in total (-2) can tell us what the charge of the complex ion must be (+2).

hence, [Ni(H2O)6]2+

Question 49

How would you figure out the charge of the transition metal ion? (e.g. Ni in [Ni(H2O)6]2+)

Answer 49

(charge on the metal ion) + (charges of the ligands) = (charge of the metal complex ion)

So in order to get the charge of the transition metal, we need to minus the charge of the H2O ligands, so:

Charge on nickel + (6x0) = +2

H2O has no charge, so the charge of the transition metal ion, Ni, is +2.

Question 50

What would the coordination number of be for the transition metal complex [Ni(H2O)6]2+ , and hence the coordination geometry?

Answer 50

6 ligands (H2O) each donation

Question 51

What are the common types of ligands in biological systems?

Answer 51

• Water (H2O)

- Amino acids

Question 52

What is the most abundant ligand in a biological system?

Answer 52

Water (H2O).

Question 53

What happens to amino acids in high pH levels, and how does this affect its ability to be a ligand?

Answer 53

At high pH levels, the COOH group is deprotonated, turning into COO-. This allows for amino acids to act as a bidentate ligand.

Question 54

Can amino acids still act as a ligand when in a peptide form of a protein?

Answer 54

Yes, depending the the R group present.

Question 55

How can a protein generate large multidendate ligand for the metal ion?

Answer 55

The folding of the protein in a 3-D shape can bring the amino acids close together, generating a huge multidendate ligands.

Question 56

What is a heme-based ligand?

Answer 56

A heme unit is a cyclic tetradentate ligand with four nitrogen donor atoms.

Question 57

What is ligand activation?

Answer 57

When a bonding of a ligand to a transition metal can sometimes lead to the ligand being more susceptible to chemical reactions.

Question 58

Give an example of ligand activation with the example of H2O as a ligand.

Answer 58

Sometimes the transition metal’s positive charge can attract the electrons from the O-H bond to it, hence breaking the O-H bond completely in the H2O molecule, and leaving it to be a neutral OH ion, with the transition metal gaining a negative charge.

Question 59

Explain how the complex ion can be considered a weak acid, due to the ligand activation with H2O.

Answer 59

The H+ that came off from the breaking of the O-H bond in H2O, is then donated to H2O, forming H3O+. Making the complex ion essentially a weak acid, as it donated a proton (H+).

Question 60

Are enzyme reactions faster or slower with the OH - (neutral) ligand reactant.

Answer 60

Faster, compared to the H2O ligand.

Question 61

When ligands bond to a transition metal, they can change the reduction potential value of the mental due to differences in electronegativity, explain how.

Answer 61

If the ligands have a higher electronegativity than the metal, they will pull electrons away from the metal, hence increasing the need for electrons by the metal, hence increasing the reduction potential value.

If the ligands were to have a lower electronegativity compared to the metal, the metal will have electrons more closer to it compared to the ligands, decreasing its need to electrons and hence decreasing the reduction potential value.

Question 62

Explain how the changing the structure of the ligands can change the reduction potential of transition metals, and what this is called.

Answer 62

Small changes to the structure of the ligand can change the reduction potential of the transition metal, this is called tuning, and is done often in biological systems.