Inorganic - Transition Metals

Question 1

What are the general physical properties of transition metals?

Answer 1

The elements from titanium to copper lie within the d-block elements.

Across a period, electrons are being added to a d-sub-level (3d in the case of titanium to copper). The elements from titanium to copper are metals. They are good conductors of heat and electricity. They are hard, strong, and shiny, and have high melting and boiling points.

These physical properties, together with fairly low chemical reactivity, make these metals extremely useful. Examples include iron (and its alloy steel) for vehicle bodies and to reinforce concrete, copper for water pipes, and titanium for jet engine parts that must withstand high temperatures.

Question 2

What are the electronic configurations in the d-block elements?

Answer 2

In general, there are two outer 4s electrons and as you go across the period, electrons are added to the inner 3d sub-level. This explains the overall similarity of these elements.

These arrangements of chromium and copper do not quite fit the pattern. The d-sub-level is full in copper and half full in chromium and there is only one electron in the 4s outer level. It is believed that a half-full d-level makes the atoms more stable in the same way as a full outer main level makes the noble gas atoms stable.

Question 3

When transition metal ions are formed, which electrons are lost first?

Answer 3

With all transition elements, the 4s electrons are lost first when ions are formed.

Question 4

What is the definition of a transition element?

Answer 4

A transition metal is an element that has an incomplete d sub-shell in one of its common, stable ions (excluding Scandium).

Question 5

What are the four main features that are common to all the transition metals?

Answer 5

• variable oxidation states
• coloured compounds
• catalysis
• formation of complexes

Question 6

Why are variable oxidation states a chemical property of transition metals?

Answer 6

Transition metals have more than one oxidation state in their compounds, e.g. Cu(I) and Cu(II). They can therefore take part in many redox reactions.

Question 7

Why is colour a chemical property of transition metals?

Answer 7

The majority of transition metal ions are coloured, e.g. Cu 2+ is blue.

Question 8

Why is catalysis a chemical property of transition metals?

Answer 8

Catalysts affect the rate of reaction without being used up or chemically changed themselves. Many transition metals, and their compounds, show catalytic activity.

E.g. iron is the catalyst in the Haber process, vanadium oxide in the Contact process and manganese oxide in the decomposition of hydrogen peroxide.

Question 9

Why is complex formation a chemical property of transition metals?

Answer 9

Transition elements form complex ions. A complex ion is formed when a transition metal ion is surrounded by ions or other molecules, collectively called ligands, which are bonded to it by co-ordinate bonds.

E.g. [Cu(H2O)6]2+ is a complex ion that is formed when copper sulphate dissolves in water.

Question 10

What are ligands?

Answer 10

All transition metal ions can form co-ordinate bonds by accepting electron pairs from other ions or molecules. The bonds that are formed are co-ordinate (dative) bonds.

An ion or molecule with a lone pair of electrons that forms a co-ordinate bond with a transition metal is called a ligand. Some ligands are neutral and others have a negative charge.

Question 11

What is a complex ion?

Answer 11

In some cases, two, four, or six ligands bond to a single transition metal ion. The resulting species is called a complex ion. They may have a positive charge or a negative charge.

Question 12

What is the co-ordination number?

Answer 12

The number of co-ordinate bonds from ligands to the metal ion (determines the shape of the molecules).

Question 13

How does the co-ordination number affect the shape of the complex ion?

Answer 13

• Ions with co-ordination number six are usually octahedral.
• Ions with co-ordination number four are usually tetrahedral.
• Some ions with co-ordination number four are square planar.

Question 14

What are aqua ions?

Answer 14

If you dissolve the salt of a transition metal in water, e.g. copper sulphate, the positively charged metal ion becomes surrounded by water molecules acting as ligands. Normally there are six water molecules in an octahedral arrangement. Such species are called aqua ions.

Question 15

What are uni/bi/multidentate ligands?

Answer 15

Unidentate: ligands that form one co-ordinate bond to a metal ion (e.g. :Cl-)
Bidentate: ligands that form two co-ordinate bonds to a metal ion (e.g. en)
Multidentate: ligands that form more than two co-ordinate bonds to a metal ion (e.g. porphyrin)

Multidentate ligands form complexes that are more stable than monodentate ligands.

Question 16

Give examples of bidentate ligands (form two co-ordinate bonds).

Answer 16

• ethane-1,2-diamine, or 1,2-diaminoethane
• ethanedioate (oxalate) ion
• benzene-1,2-diol, or 1,2-dihydroxybenzene

Question 17

What is EDTA 4-?

Answer 17

An important multidentate ligand is the ion ethylenediaminetetracetate, called EDTA 4-.

This can act as a hexadentate ligand using lone pairs on four oxygen and both nitrogen atoms.

Question 18

What are chelates?

Answer 18

Complex ions with polydentate ligands are called chelates. Chelates can be used to effectively remove d-block metal ions from solution.

Question 19

What is the chelate effect?

Answer 19

If you add a hexadentate ligand such as EDTA to a solution of a transition metal salt, the EDTA will replace all six water ligands in the aqua ion [Cu(H2O)6]2+ as shown:

[Cu(H2O)6]2+(aq) + EDTA 4-(aq) -> [CuEDTA]2-(aq) + 6H2O(l)

In this equation, two species are replaced by seven. This increase in the number of particles causes a significant increase in entropy which drives the reaction to the right. For this reason, chelate complexes with polydentate ligands are favoured over complexes with monodentate ligands and is called the chelate effect.

Question 20

What do both ligand sites of bidentate ligands do?

Answer 20

Both ligand sites of bidentate ligands usually bond to the same metal forming a ring. However, they can act as bridges between two metal ions.

Question 21

What are the shapes of complex ions?

Answer 21

• 6 ligands, octahedral, 90 degrees, most complexes with small ligands
• 4 ligands, tetrahedral, 109.5 degrees, with larger ligands (when ligands are too big for 6 to fit)
• 4 ligands, square planar, 90 degrees, Pt2+ and Ni2+ complexes (e.g. anti-cancer drug cis-platin)
• 2 ligands, linear, 180 degrees, Ag+ complexes (e.g. [Ag(NH3)2]+)

Question 22

What complex ion does Tollen’s reagent contain?

Answer 22

[Ag(NH3)2]+ is a linear complex. A solution containing this complex ion is called Tollen’s reagent and is used in organic chemistry to distinguish aldehydes from ketones.

Aldehydes reduce the [Ag(NH3)2]+ to Ag (metallic silver), while ketones do not. The silver forms a mirror on the surface of the test tube.

Question 23

What isomers can transition metal complexes form?

Answer 23

Isomers are compounds with the same molecular formula but with different arrangements of their atoms in space. Transition metal complexes can form both geometrical isomers (cis-trans, E-Z) and optical isomers.

Question 24

How do transition metal complexes form geometrical isomers?

Answer 24

Here ligands differ in their position in space relative to one another.

This type of isomerism occurs in octahedral and square planar complexes. Ligands can be next to each other, or on opposite sides of the central ion.

A pair of geometrical isomers will have different chemical properties.

Question 25

How do transition metal complexes form optical isomers?

Answer 25

Here the two isomers are non-superimposable mirror images of each other.

In transition metal complexes this occurs when there are two or more bidentate ligands in a complex.

Optical isomers are said to be chiral. They have identical chemical properties but can be distinguished by their effect on polarised light. One isomer will rotate the plane of polarisation of polarised light clockwise and the other anticlockwise.

Question 26

What is ionisation isomerism?

Answer 26

This is a third form of isomerism found in transition metal chemistry.

Consider the compound of formula CrCl3 [H2O)6. Both chloride ions and water molecules can act as ligands. This compound can exist as three different isomers depending on how many of the chloride ions are bound to the chromium atom as ligands and how many are free as negative ions.

Question 27

What is the colour of transition metal compounds caused by?

Answer 27

The colour is caused by compounds absorbing energy that corresponds to light in the visible region of the spectrum. If a solution of a substance looks purple. it is because it absorbs all the light from a beam of white light shone at it except red and blue. The red and blue light passes through and the solution appears purple.

Question 28

Why are transition metal complexes coloured?

Answer 28

• It is possible for electrons to move from one d-orbital to another because transition metal compounds have part-filled d-orbitals.
• In an isolated transition metal atom, all the d-orbitals are of exactly the same energy, but in a compounds, the presence of other atoms nearby makes the d-orbitals have slightly different energies.
• When electrons become excited and move from one d-orbital to another of a higher energy level, they often absorb energy in the visible region of the spectrum equal to the difference in energy between levels.
• This colour is therefore missing from the spectrum and you see the combination of the colours that are not absorbed.

Question 29

How is the frequency of the light related to the energy difference?

Answer 29

change in energy = Planck’s constant (6.63 x 10-34) x frequency

The frequency is related to the colour of light. Violet is of high energy and therefore high frequency and red is of low energy and low frequency.

Question 30

How is the wavelength of light related to the energy difference?

Answer 30

energy change = (Planck’s constant (6.63 x 10-34) x velocity of light) / wavelength

Question 31

What does the colour of a transition metal complex depend on?

Answer 31

• the energy gap
• the charges in the metal
• the oxidation state of the metal
• the co-ordination number
• the ligands (and therefore the shape of the complex ion)

So different compounds of the same metal will have different colours.

Question 32

How does a colorimeter work?

Answer 32

A simple colorimeter uses a light source and a detector to measure the amount of light of a particular wavelength that passes through a coloured solution. The colours we see are complements of the colours absorbed by the solution.

The more concentrated the solution, the less light transmitted through the solution. A colorimeter is used, with a suitable calibration graph to measure the concentration of solutions of coloured transition metal compounds.

Question 33

How can you make the colorimetry experiment more sensitive?

Answer 33

Usually the experiment is made more sensitive by using a coloured filter in the colorimeter. The filter is chosen by finding out the colour of light that the red solution absorbs most. Red absorbs light in the blue region of the visible spectrum, so a blue filter is used, so that only blue light passes into the sample tube.

Question 34

How can you find the formula of a transition metal complex using colorimetry?

Answer 34

A colorimeter can be used to find the ratio of metal ions to ligands in a complex, which gives us the formula of the complex. Two solutions are mixed together, one containing the metal ion and one the ligand, in different proportions. When they are mixed in the same ratio as they are in the complex, there is a maximum concentration of complex in the solution. So, the solution will absorb most light.

Question 35

How many oxidation states to transition metals in compounds have?

Answer 35

Group 1 metals lose their outer electron to form only +1 ions and Group 2 lose their outer two electrons to form only +2 ions in their compounds. A typical transition metal can use its 3d-electrons as well as its 4s-electrons in bonding, and this means that it can have a greater variety of oxidation states in different compounds.

Question 36

Which transition metals exist as simple ions?

Answer 36

Only the lower oxidation states of transition metals actually exist as simple ions.

Question 37

What reactions do transition metal compounds typically undergo?

Answer 37

Many of the reactions of transition metal compounds are redox reactions, in which the metals are either oxidised or reduced. Oxidation is loss of electrons, reduction is gain of electrons.

Question 38

How do you measure the concentration of an oxidising or a reducing agent?

Answer 38

One way is to do a redox titration. An example is the analysis of iron tablets for quality control purposes. Iron tablets contain iron (II) sulphate and may be taken by patients whose diet is short of iron for some reason.

Fe2+(aq) reacts with manganate ions (in potassium manganate(VII)) in the ratio 5:1. The reaction does not need an indicator, because the colour of the mixture changes as the reaction proceeds.

Using a burette, you gradually add potassium manganate(VII) solution (which contains the MnO4 -(aq) ions) to a solution containing Fe 2+(aq) ions, acidified with excess dilute sulphuric acid. The purple colour disappears as the MnO4 - ions are converted to pale pink Mn 2+(aq) ions to leave a virtually colourless solution. Once just enough MnO4 -(aq) ions have been added to react with all the Fe 2+(aq) ions, one more drop of MnO4 -(aq) ions will turn the solution purple. This is the end point of the titration.

Question 39

Why can’t you use hydrochloric acid as an alternative to sulphuric acid?

Answer 39

You cannot use hydrochloric acid, as an alternative to sulphuric acid, to supply the H+(aq) ions in the reaction between potassium manganate(VII) and Fe 2+(aq). You can see why this is the case by using E values.

Hydrochloric acid contains Cl- ions. These are oxidised by MnO4 - ions, as shown by the calculations of emf for the reaction below. This would affect the titration, because the manganate(VII) ions must be used only to oxidise Fe 2+ ions. Manganate(VII) ions do not oxidise sulphate ions.

This reaction is feasible, so MnO4 - ions will oxidise Cl- ions and hydrochloric is not suitable for this titration.

Question 40

Why does the oxidation of transition metal ions occur in alkaline solutions?

Answer 40

A high oxidation state of a metal and Cr are reduced in acidic conditions.

Oxidation of lower oxidation states of transition metal ions tend to happen in alkaline solution. This is because in alkaline solution there is a tendency to form negative ions. Since oxidation is electron loss, this is easier from negatively charged species than positively charged or neutral ones.

Typical transition metal species, where M represents a transition metal:

• Acid solution: M(H2O)6 2+ positively charged.
• Neutral solution: M(H2O)4(OH)2 neutral.
• Alkaline solution: M(H2O)2(OH)4 2- negatively charged.

Low oxidation states of transition metals, such as Fe2+ are often stabilised against oxidation by air by keeping them in acid solution.

To oxidise a transition metal to a high a oxidation state, an alkali is often added, followed by an oxidising agent.

Question 41

What cobalt chemistry?

Answer 41

Many M2+ ions will be oxidised to M3+ in alkaline solutions, for example cobalt(II) to cobalt (III).

In ammoniacal solution, Co2+ ions can be oxidised by oxygen in the air. If you add an excess of ammonia solution to an aqueous solution containing cobalt(II) ions, you get a brownish complex ion formed, [Co(NH3)6]2+, containing cobalt(II) ions.

The reactions are as follows:
1. First a precipitate is formed by reaction with OH- ions from the ammonia solution, which is alkaline:
[Co(H2O)6]2+ + 2OH- –> Co(H2O)4(OH)2(s) + 2H2O(l)
2. Then the precipitate dissolves in excess ammonia:
Co(H2O)4(OH)2(s) + 6NH3(aq) –> [Co(NH3)6]2+ + 2OH-(aq) + 4H2O(l)
3. The resulting complex ion is oxidised by oxygen in air (or rapidly by hydrogen peroxide solution) to the yellow(III) ion, [Co(NH3)6]3+.

Question 42

What are catalysts?

Answer 42

Catalysts affect the rate of a reaction without being chemically changed themselves at the end of the reaction. Catalysts play an important part in industry because they allow reactions to proceed at lower temperatures and pressures thus saving valuable resources.

Question 43

What are catalytic converters?

Answer 43

Modern cars have a catalytic converter in the exhaust system which is based on platinum and rhodium. This catalyses the conversion of carbon monoxide, nitrogen oxides, and unburnt petrol to carbon dioxide, nitrogen, and water.

Question 44

What groups can catalysts be divided into?

Answer 44

Many catalysts used in industry are transition metals or their compounds. Catalysts can be divided into two groups:

• heterogeneous
• homogeneous

Question 45

What are heterogeneous catalysts?

Answer 45

Heterogenous catalysts are present in a reaction in a different phase (solid, liquid, or gas) than the reactants. They are usually present as solids, whilst the reactants may be gases or liquids. Their catalytic action occurs on the solid surface. The reactants pass over the catalyst surface, which remains in place so the catalyst is not lost and does not need to to be separated from the products.

Question 46

How can you make heterogenous catalysts more efficient?

Answer 46

Catalysts are often expensive, so the more efficiently they work, the more the costs can be minimised. Since their activity takes place on the surface you can:

• Increase their surface (the larger the surface area, the better the efficiency).
• Spread the catalyst onto an inert support medium, or even impregnate it into one. This increases the surface-to-mass ratio so that a little goes a long way. The more expensive catalysts are often used in this way. For example, the catalytic converter in a car, has finely divided rhodium and platinum on a ceramic material.

Question 47

Why do catalysts not last forever?

Answer 47

• Over time, the surfaces may become covered with unwanted impurities. This is called poisoning. The catalytic converters in cars gradually become poisoned by substances used in fuel additives. Until a few years ago, lead-based additives were used in petrol. The lead poisoned the catalysts and so leaded fuel could not be used in cars with converters.
• The finely divided catalyst may gradually be lost from the support medium.

Question 48

How do transition metals act as catalysts?

Answer 48

Transition metals have partly full d-orbitals which can be used to form weak chemical bonds with the reactants. This has two effects - weakening bonds within the reactant and holding the reactants close together on the metal surface in the correct orientation for reaction.

Question 49

What are some importance examples of heterogeneous catalysts?

Answer 49

• the Haber process

- the Contact process

Question 50

What is the Haber process?

Answer 50

In the Haber process, ammonia is made by the reaction of nitrogen with hydrogen. The catalyst for the process is iron - present as pea-sized lumps to increase the surface area:

N2(g) + 3H2 –>(iron catalyst)

Question 51

What is the Contact process?

Answer 51

The Contact process produces sulphuric acid - a vital industrial chemical. Around two million tonnes are produced each year in the UK and it is involved in the manufacture of many goods.

It is made from sulphur, oxygen, and water, the key step being:
2SO2 + O2 -> SO3 + V2O4

The vanadium (IV) oxide is then oxidised back to vanadium(V) oxide by oxygen@
2V2O4 + O2 -> 2V2O5

The vanadium(V) oxide is regenerated unchanged. Each of the two steps has a lower activation energy than the uncatalysed single step and therefore the reaction goes faster.

This is a good example of how the variability of oxidation states of a transition metal is useful in catalysts.

Question 52

How is methanol manufactured?

Answer 52

Synthesis gas is made from methane, present in natural gas and steam:
CH4(g) + H2O(g) -> CO + 3H2(g)

It is a mixture of carbon monoxide and hydrogen and is used to make methanol:
CO(g) + 2H2(g) -> CH3OH(g)

This reaction may be catalysed by chromium oxide, Cr2O3. Today, the most widely used catalyst is a mixture of copper, zinc oxide, and aluminium oxide.

Methanol is an important industrial chemical (over 30 million tonnes are made each year world wide) and is used mainly as a starting material for the production of plastics such as Bakelite, Terylene, and Perspex.

Question 53

What are homogeneous catalysts?

Answer 53

When the catalyst is in the same phase as the reactant, an intermediate species is formed. For example in the gas phase chlorine free radicals act as catalysts to destroy the ozone layer. The intermediate here is the ClO* free radical.

Question 54

What is homogeneous catalysis by transition metals?

Answer 54

Peroxodisulphate ions, S2O8 2-, oxidise iodide ions to iodine. This reaction is catalysed by Fe2+. The overall reaction is:

S2O8 2-(aq) + 2I-(aq) -> 2SO4 2-(aq) + I2(aq)

The catalysed reaction takes place in two steps. First the peroxodisulphate ions oxidise iron(II) to iron(III):

S2O8 2-(aq) + 2Fe 2+(aq) -> 2SO4 2-(aq) + 2Fe 3+(aq)

The Fe3+ then oxidises the I- to I2, regenerating the Fe2+ ions so that none are used up in the reaction:

2Fe3+(aq) + 2I-(aq) -> 2Fe2+(aq) + I2(aq)

So iron first gives an electron to the peroxodisulphate and later takes one back from the iodide ions.

The uncatalysed reaction takes place between two ions of the same charge (both negative), which repel, therefore giving a high activation energy. Both steps of the catalysed reaction involve reaction between pairs of oppositely charged ions. This helps to explain the increase in rate.

Question 55

What is autocatalysis?

Answer 55

An interesting example of catalysis occurs when one of the products of the reaction is a catalyst for the reaction. Such a reaction starts slowly at the uncatalysed rate. As the concentration of the product that is also the catalyst builds up, the reaction speeds up the catalysed rate. From then on it behaves like a normal reaction, gradually slowing down as the reactants are used up. This leads to an odd-looking rate curve.

Question 56

What is the oxidation of ethanedioic acid by manganate(VII) ions?

Answer 56

One example of an autocatalysed reaction is that between a solution of ethanedioic acid (oxalic acid) and an acidified solution of potassium manganate(VII). It is used as a titration to find the concentration of potassium manganate(VII) solution.

2MnO4 -(aq) + 16H+(aq) + 5C2O4 2-(aq) -> 2Mn2+(aq) + 8H2O(l) + 10CO2(g)

The catalyst, Mn2- ions, is not present at the beginning of the reaction. Once a little Mn2+ has formed, it can react with MnO4 - ions to form Mn3+ as an intermediate species, which then reacts with C2O4 2- ions to reform Mn2+:

4Mn2+(aq) + MnO4 -(aq) + 8H+(aq) -> 5Mn3+(aq) + 4H2O(l)

2Mn3+(aq) + C2O4 2-(aq) -> 2CO2(g) + 2Mn2+(aq)

The reaction can easily be followed using a colorimeter to measure the concentration of MnO4 -, which is purple.

Question 57

How do variable oxidation states help transition metals to catalyse reactions?

Answer 57

Variable oxidation states help transition metals to catalyse reactions by providing an alternative reaction pathway with a lower activation energy.

Question 58

Why is copper sulphate solution blue?

Answer 58

• Once the Cu 2+ ion hits the water, a complex is formed, [Cu(H2O)6]2+.
• There is a repulsion between the electrons on the water ligands and the 3d orbitals of the Cu 2+ ion.
• This causes the 3d orbitals to split into two energy levels.
• Energy is absorbed from a certain frequency of light, and an electron is promoted from the lower energy d orbitals to the higher energy d orbitals.
• The colour we see corresponds to the remaining wavelengths of light that are transmitted.

Question 59

What is a Lewis base?

Answer 59

lone pair donor

Question 60

What is a Lewis acid?

Answer 60

lone pair acceptor

Question 61

How do ligands and metal ions act as Lewis bases and Lewis acids?

Answer 61

Ligands are acting as Lewis bases when they bond to transition metals as they donate a lone pair to form a co-ordinate bond. The metal ion acts as a Lewis acid as it accepts lone pairs.

Question 62

What is the complex of haemoglobin?

Answer 62

Haemoglobin is the red pigment in blood, responsible for carrying oxygen from the lungs to the cells of the body.

The molecule consists of an Fe 2+ ion with a co-ordination number of six. Four of the co-ordination sites (nitrogen) are taken up by a ring system called a porphyrin which acts as a tetradentate ligand. This complex is called haem. One of the other two sites (nitrogen) is bonded to the rest of the haemoglobin structure (globin protein) leaving one site bonded to a water ligand.

Question 63

Why are carbon monoxide and cyanide compounds toxic?

Answer 63

Oxygen is carried around the body in the blood bonded to the iron in haemoglobin. It easily separates from the iron when it’s needed to transfer to cells for respiration.

Cyanide ions (CN-) and carbon monoxide (CO) are better ligands than oxygen (O2) and so will bond to haemoglobin in preference to oxygen and are not readily replaced. This is why carbon monoxide and cyanide compounds are toxic as they prevent the transfer of oxygen around the body.

Question 64

What is cis-trans isomerism?

Answer 64

This is a special case of E-Z isomerism (two different groups, alkenes, can’t rotate around double bond). It can occur in octahedral and square planar complexes where there are two ligands of one type different to the other ligands.

Question 65

What is optical isomerism?

Answer 65

Non-superimposable mirror images. This occurs in an octahedral complex with three bidentate ligands.

Question 66

What are the variable oxidation states and the coloured ions that are formed in solution of vanadium?

Answer 66

V 2+: violet
V 3+: green
VO 2+: blue
VO2 +: yellow

Question 67

What are the variable oxidation states and the coloured ions that are formed in solution of chromium?

Answer 67

Cr 3+: normally green when substituted but violet when surrounded by 6H2O
Cr2O7 2-: orange

Question 68

What are the variable oxidation states and the coloured ions that are formed in solution of manganese?

Answer 68

Mn 2+: pale pink

MnO4 -: purple

Question 69

What are the variable oxidation states and the coloured ions that are formed in solution of iron?

Answer 69

Fe 2+: pale green

Fe 3+: yellow

Question 70

What are the variable oxidation states and the coloured ions that are formed in solution of cobalt?

Answer 70

Co 2+: pink

Question 71

What are the variable oxidation states and the coloured ions that are formed in solution of nickel?

Answer 71

Ni 2+: green

Question 72

What are the variable oxidation states and the coloured ions that are formed in solution of copper?

Answer 72

Cu 2+: blue

Question 73

Give examples of unidentate ligands.

Answer 73

H2O: (smaller, 6)
\:NH3 (smaller, 6)
\:Cl- (larger, 4)
\:CN-
\:OH-

Question 74

Give examples of bidentate ligands.

Answer 74

C2O4 2-: ethanedioate (3)

NH2CH2CH2NH2: ethane-1,2-diamine (3)

Question 75

Give examples of polydentate ligands.

Answer 75

haem

EDTA 4-

Question 76

How does haemoglobin transport oxygen around the body?

Answer 76

Oxygen substitutes the water ligand in the lungs where oxygen concentration is high to form oxyhaemoglobin. This is transported around the body. The water is expelled from the body as water vapour.

Oxyhaemoglobin gives up oxygen to a place where it is needed. Water takes the place and haemoglobin returns back to the lungs to start the process again.

Question 77

Which complexes show optical isomerism?

Answer 77

octahedral complexes with 3 bidentate ligands

Question 78

When will you get a cis isomer?

Answer 78

if the two different isomers are adjacent each other

Question 79

When will you get a trans isomer?

Answer 79

if the two different isomers are opposite each other

Question 80

What is cisplatin?

Answer 80

[Pt(NH3)2Cl2]

Cisplatin is a chemotherapy medication used to treat a number of cancers. The cis isomer is effective, but the trans isomer is not.

Question 81

What is d-orbital splitting?

Answer 81

The d-subshell is split into 2 when ligands bond with the central metal ion. Orbitals gain energy when a ligand is attached. This is why transition metals have to have a partially filled 3d sublevel.

Question 82

What does the frequency absorbed by a transition metal complex dependent on?

Answer 82

Some frequencies of visible light are absorbed by transition metal complexes. The frequencies absorbed depends on the size of the energy gap between the sublevels.

The larger the energy gap, the higher the frequency of light absorbed.

Any frequencies which are not absorbed are reflected or transmitted. The combination of all these frequencies create a complementary colour that we observe with some complexes.

Question 83

What colour are complexes with a full or empty 3d sublevel?

Answer 83

No electrons can migrate to the higher energy level, so we see these complexes as colourless or white.

Question 84

What happens in ligand substitution when the coordination number stays the same?

Answer 84

The coordination number is the same and so is the shape, but the colour of the complex will change.

Question 85

What happens in ligand substitution when the coordination number changes?

Answer 85

The coordination number changes and so does the shape. This normally happens when a small ligand is substituted by a larger ligand. The colour of the complex will also change.

Question 86

What happens when only the oxidation state changes?

Answer 86

When the oxidation state changes, but the ligands and coordination numbers are the same, the shape of the complex stays the same. The colour, however, changes.

Question 87

How is colorimetry used to analyse transition metal complexes?

Answer 87

The combination of all the frequencies absorbed creates a complementary colour that we observe. If we mix the complementary colour and the absorbed colour, we get white light.

Question 88

How is colorimetry used to measure the concentration of transition metal ions in solution?

Answer 88

A colorimeter measures the absorbance of light by a coloured sample. The more concentrated a sample is, the darker it’s colour and hence the more light absorbed.

Question 89

How can vanadium (V) ions be reduced?

Answer 89

Vanadium ions (VO2 +) can be reduced using zinc in an acidic solution all the way to Vanadium ions (V 2+).

Question 90

What are redox potentials?

Answer 90

Redox potentials tell us how easily an ion is reduced, which is the same as electrode potentials.

The least stable ions have the largest redox potential and are more likely to be reduced.

Question 91

Why might there be a difference in redox potential to the standard values seen in a data book?

Answer 91

it is dependent on the environment the ions are in

Question 92

How do ligands affect the size of redox potentials?

Answer 92

Standard electrode potentials are always measured in aqueous solutions. The metal ion is surrounded by water molecules.

However, ligands other than water can form stronger bonds to the metal ions with particular oxidation states. This means the redox potential can be higher or lower than the standard value.

Question 93

How does pH affect the size of redox potentials?

Answer 93

The pH of the solution affects the size of redox potentials with some reactions.

Generally, the more acidic the solution the larger the electrode potential. This means the ion is more easily reduced.