5.3 transition metals Flashcards
define transition element
a d-block element that has an incomplete d-subshell as a stable ion
what are some chemical properties of transition elements
they can have different oxidation states
form coloured compounds
often catalyse chemical reactions
What elements have the maximum oxidation states
Manganese + 7
chromium +6
Describe how transition metal compounds produce a coloured compound
When white light passes through a solution containing a transition metal ions some of the visible wavelengths of light are absorbed
the colour we see is a mixture f wavelengths that have not been absorbed
Describe 2 ways in which transition metals act as catalysts
they provide a surface on which a reaction can take place, reactants are adsorbed on the surface and held in place while the reaction occurs and then desorbed whilst the metal remains unchanged
they bind to reactants forming intermediates as part of a chemical pathway often with a lower activation energy
what transition metal catalyses the Haber process
iron
what transition metal catalyses the contact process
2SO2 + O2 = 2SO3
vanadium oxide + 5 oxidation state
what transition metal catalyses the hydrogenation of alkenes
nickel - lowers temperature and pressure required
what transition metal catalyses hydrogen production
zinc granules will react with dilute4 sulfuric acid to form zinc sulfate and hydrogen
the metal ion acts as the catalyst
Define complex ion
transition metal ion bonded to one or more ligands by coordinate bond
define ligand
molecule or ion that can donate a pair of electrons to the transition metal by coordination bond
Define coordination number
number of coordinate bonds formed between a central metal ion and its ligands
What are the ligands acting as
lewis bases
electron pair donor
How would you write the formula of a complex ion
square brackets group the species together making up the complex ion
overall charge is shown on the outside of the brackets
Are all ligands charged
no e.g. water
describe a monodentate ligand
donates just one pair of electrons to the central metal ion to form a coordinate bond e.g. water
Why is water a monodentate ligand even though it has 2 lone pairs
they are too close together
Describe bidentate ligands
have two pairs of electrons from different atoms to donate to the central atom and form 2 coordinate bonds- ethane-1,2-diamine
NH2CH2CH2NH2 - en
each nitrogen donates a pair of electrons
Describe and give an example of a multidentate ligand
hexadentate ligand has 6 lone pairs available to form coordinate bonds e.g. ethylenediaminetetraacetic acid or EDTA
it is a chelating agent meaning it decreases the concentration of metal ions in solutions by binde=ing them to a complex
define chelating agent
it is a chelating agent meaning it decreases the concentration of metal ions in solutions by binde=ing them to a complex
What are some of the uses of EDTA
detergents - binds to Ca and Mg to reduce hardness of water
foods
medical applications - added to blood samples to prevent clotting
What is the shape of a complex ion with four-fold coordination
tetrahedral
Why do chlorine ligands form a tetrahedral
they are so large that only four chlorines can fit around a transition metal ion
What is the shape and bond angles of a six-fold coordination
octahedral
90
give an example of a bidentate
ethanedioate
C2O4 2-
Define stereoisomer
a species with the same structural formula but differing arrangement of atoms in space
What ae the two types of stereoisomers in transition element chemistry
cis-trans
optical
What do cis isomers look like
ligands are at adjacent corners of the octahedron 90 apart
what do trans isomers look like
opposite corners of the octahedron or square
180 apart
Describe how transition metal complexes are used in chemistry
cis-platin is one of the most effective drugs used to treat cancer cis[PtCl2(NH3)2]
it acts by binding to the DNA of fast growing cancer cells and prevents cell division and activation of repair mechanism eventually leads to death of the cancer cells
Describe the ethandioate ion
can com from ethandioic acid and when put into water will partially dissociate one proton at a time to form a bidentate ligand in an equilibrium
What are the requirements for optical isomers
complex with three molecules or ions of a bidentate ligand
complex with two bidentate ligands and two monodentate ligands
a complex with a hexadentate ligand
Define optical isomer
non-super-imposable mirror images which refract polarised light in different directions and have similar chemical properties but different biological properties
what is the colour of a Fe2+ ion
green
what is the colour of a Fe3+ ion
yellow
what is the colour of a Cu2+ ion
blue
what is the colour of a Cu2- ion
yellow
what is the colour of a Cr2- ion
orange
what is the colour of a Cr3+ ion
violet
what is the colour of a Mn2+ ion
pale pink
what is the colour of a MnO4 - ion
purple
define ligand substitution
reaction in which one ligand in a complex ion is replaced by another ligand
what kind of substitution occurs between copper ions and ammonia
partial substitution
Give the complex ion equation for the rection between copper ions and ammonia and the colour change
[Cu(H2O)6]2+ + NH3 = [Cu(NH3)4(H2O)2]2+ + 4H2O pale blue to dark blue
Describe what occurs when ammonia is added dropwise to copper ions
a pale blue Cu(OH)2 precipitate forms because ammonia acts as an alkali
Give the complex ion equation and colour change between copper ions and hydrochloric acid
[Cu(H2O)6]2+ +4Cl- = [CuCl4]2- + 6H2O pale blue to yellow
Give the complex ion equation of the intermediate formed between chromium and ammonia
[Cr(H2O)6] 3+ + 3NH3 = [Cr(H2O)(OH)3] +3NH4 and a green precipitate is formed
Give the complex ion equation and colour change for the reaction between chromium and ammonia
[Cr(H2O)6]3+ +6NH3 == [Cr(NH3)6]3+ +6H2O grey green to dark green
give the equation and observation between copper and NaOH
Cu2+ +2OH- == Cu(OH)2 blue gelatinous precipitate formed
give the equation and observation between Fe2+ and NaOH
Fe2+ +2OH- ==Fe(OH)2 pale green solution forms a green precipitate turning a rusty brown at its surface
give the equation and observation between Fe3+ and NaOH
Fe3+ + NaOH == Fe(OH)3 pale yellow solution forms a rusty brown precipitate
give the equation and observation between Mn2+ and NaOH
Mn2+ + 2OH- == Mn(OH)2 brown precipitate forms and it darkens
give the equation and observation between Cr3+ and NaOH
[Cr(H2O)6]3+ + 3OH- = [Cr(OH)3(H2O)3] + 3H2O green precipitate
[Cr(OH)3(H2O)3] + 3OH- = [Cr(OH)6]3- + 3H2O
give the equation and observation between Fe2+ and ammonia
[Fe(H2O)6] 2+ + 2NH3 = [Fe(OH)3(H2O)3] +NH4- dark green precipitate formed
give the equation and observation between Fe3+ and ammonia
[Fe(H2O)6]3+ +3NH3 = [Fe(OH)3(H2O)3] + NH4- rusty brown precipitate formed
give the equation and observation between Mn2+ and ammonia
[Mn(H2O)6]2+ + 2NH3 == [Mn(OH)2(H2O)4] + 2NH4- brown precipitate which darkens
give the equation and observation between Cr3+ and ammonia
[Cr(H2O)6] + 3NH3 = [Cr(OH)3(H2O)3] + 3NH4- green precipitate forms
if excess ammonia is added then it re-dissolves
[Cr(OH)3(H2O)3] +6NH3 = [Cr(NH3)6]3+ + 3H2O + 3OH-
describe haemoglobin and its function
contains 4 non-protein haem groups Fe2+ in it’s centre which can bind reversibly to oxygen
describe the coordinate bonds formed around the Fe2+ions in a haem group
4 coordinate bonds between the Fe2+ ions and nitrogen atoms in the haem structure
further coordinate bond is formed to the protein globin
final coordinate bond can be formed to the oxygen molecule and be transported
describe why carbon monoxide is described as the silent killer
it can bind more strongly to haemoglobin leaving fewer haemoglobin molecules to bind to oxygen molecules and this reaction is not reversible, this is an example of ligand substitution
define precipitation reaction
one in which soluble ions in separate solutions are mixed together to produce an insoluble compound
