Inorganic - Transition Metals Flashcards
What are the general physical properties of transition metals?
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.
What are the electronic configurations in the d-block elements?
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.
When transition metal ions are formed, which electrons are lost first?
With all transition elements, the 4s electrons are lost first when ions are formed.
What is the definition of a transition element?
A transition metal is an element that has an incomplete d sub-shell in one of its common, stable ions (excluding Scandium).
What are the four main features that are common to all the transition metals?
- variable oxidation states
- coloured compounds
- catalysis
- formation of complexes
Why are variable oxidation states a chemical property of transition metals?
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.
Why is colour a chemical property of transition metals?
The majority of transition metal ions are coloured, e.g. Cu 2+ is blue.
Why is catalysis a chemical property of transition metals?
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.
Why is complex formation a chemical property of transition metals?
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.
What are ligands?
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.
What is a complex ion?
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.
What is the co-ordination number?
The number of co-ordinate bonds from ligands to the metal ion (determines the shape of the molecules).
How does the co-ordination number affect the shape of the complex ion?
- 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.
What are aqua ions?
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.
What are uni/bi/multidentate ligands?
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.
Give examples of bidentate ligands (form two co-ordinate bonds).
- ethane-1,2-diamine, or 1,2-diaminoethane
- ethanedioate (oxalate) ion
- benzene-1,2-diol, or 1,2-dihydroxybenzene
What is EDTA 4-?
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.
What are chelates?
Complex ions with polydentate ligands are called chelates. Chelates can be used to effectively remove d-block metal ions from solution.
What is the chelate effect?
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.
What do both ligand sites of bidentate ligands do?
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.
What are the shapes of complex ions?
- 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]+)
What complex ion does Tollen’s reagent contain?
[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.
What isomers can transition metal complexes form?
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.
How do transition metal complexes form geometrical isomers?
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.
How do transition metal complexes form optical isomers?
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.
What is ionisation isomerism?
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.
What is the colour of transition metal compounds caused by?
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.
Why are transition metal complexes coloured?
- 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.
How is the frequency of the light related to the energy difference?
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.
How is the wavelength of light related to the energy difference?
energy change = (Planck’s constant (6.63 x 10-34) x velocity of light) / wavelength
What does the colour of a transition metal complex depend on?
- 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.
How does a colorimeter work?
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.
How can you make the colorimetry experiment more sensitive?
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.
How can you find the formula of a transition metal complex using colorimetry?
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.
How many oxidation states to transition metals in compounds have?
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.
Which transition metals exist as simple ions?
Only the lower oxidation states of transition metals actually exist as simple ions.
What reactions do transition metal compounds typically undergo?
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.
How do you measure the concentration of an oxidising or a reducing agent?
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.
Why can’t you use hydrochloric acid as an alternative to sulphuric acid?
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.
Why does the oxidation of transition metal ions occur in alkaline solutions?
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.
What cobalt chemistry?
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+.
What are catalysts?
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.
What are catalytic converters?
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.
What groups can catalysts be divided into?
Many catalysts used in industry are transition metals or their compounds. Catalysts can be divided into two groups:
- heterogeneous
- homogeneous
What are heterogeneous catalysts?
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.
How can you make heterogenous catalysts more efficient?
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.
Why do catalysts not last forever?
- 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.
How do transition metals act as catalysts?
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.
What are some importance examples of heterogeneous catalysts?
- the Haber process
- the Contact process
What is the Haber process?
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)
What is the Contact process?
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.
How is methanol manufactured?
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.
What are homogeneous catalysts?
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.
What is homogeneous catalysis by transition metals?
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.
What is autocatalysis?
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.
What is the oxidation of ethanedioic acid by manganate(VII) ions?
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.
How do variable oxidation states help transition metals to catalyse reactions?
Variable oxidation states help transition metals to catalyse reactions by providing an alternative reaction pathway with a lower activation energy.
Why is copper sulphate solution blue?
- 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.
What is a Lewis base?
lone pair donor
What is a Lewis acid?
lone pair acceptor
How do ligands and metal ions act as Lewis bases and Lewis acids?
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.
What is the complex of haemoglobin?
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.
Why are carbon monoxide and cyanide compounds toxic?
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.
What is cis-trans isomerism?
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.
What is optical isomerism?
Non-superimposable mirror images. This occurs in an octahedral complex with three bidentate ligands.
What are the variable oxidation states and the coloured ions that are formed in solution of vanadium?
V 2+: violet
V 3+: green
VO 2+: blue
VO2 +: yellow
What are the variable oxidation states and the coloured ions that are formed in solution of chromium?
Cr 3+: normally green when substituted but violet when surrounded by 6H2O
Cr2O7 2-: orange
What are the variable oxidation states and the coloured ions that are formed in solution of manganese?
Mn 2+: pale pink
MnO4 -: purple
What are the variable oxidation states and the coloured ions that are formed in solution of iron?
Fe 2+: pale green
Fe 3+: yellow
What are the variable oxidation states and the coloured ions that are formed in solution of cobalt?
Co 2+: pink
What are the variable oxidation states and the coloured ions that are formed in solution of nickel?
Ni 2+: green
What are the variable oxidation states and the coloured ions that are formed in solution of copper?
Cu 2+: blue
Give examples of unidentate ligands.
H2O: (smaller, 6) \:NH3 (smaller, 6) \:Cl- (larger, 4) \:CN- \:OH-
Give examples of bidentate ligands.
C2O4 2-: ethanedioate (3)
NH2CH2CH2NH2: ethane-1,2-diamine (3)
Give examples of polydentate ligands.
haem
EDTA 4-
How does haemoglobin transport oxygen around the body?
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.
Which complexes show optical isomerism?
octahedral complexes with 3 bidentate ligands
When will you get a cis isomer?
if the two different isomers are adjacent each other
When will you get a trans isomer?
if the two different isomers are opposite each other
What is cisplatin?
[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.
What is d-orbital splitting?
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.
What does the frequency absorbed by a transition metal complex dependent on?
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.
What colour are complexes with a full or empty 3d sublevel?
No electrons can migrate to the higher energy level, so we see these complexes as colourless or white.
What happens in ligand substitution when the coordination number stays the same?
The coordination number is the same and so is the shape, but the colour of the complex will change.
What happens in ligand substitution when the coordination number changes?
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.
What happens when only the oxidation state changes?
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.
How is colorimetry used to analyse transition metal complexes?
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.
How is colorimetry used to measure the concentration of transition metal ions in solution?
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.
How can vanadium (V) ions be reduced?
Vanadium ions (VO2 +) can be reduced using zinc in an acidic solution all the way to Vanadium ions (V 2+).
What are redox potentials?
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.
Why might there be a difference in redox potential to the standard values seen in a data book?
it is dependent on the environment the ions are in
How do ligands affect the size of redox potentials?
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.
How does pH affect the size of redox potentials?
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.
