5.3 transition metals Flashcards by Kamile Garuolyte

define transition element

a d-block element that has an incomplete d-subshell as a stable ion

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what are some chemical properties of transition elements

they can have different oxidation states
form coloured compounds
often catalyse chemical reactions

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What elements have the maximum oxidation states

Manganese + 7
chromium +6

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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

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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

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what transition metal catalyses the Haber process

iron

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what transition metal catalyses the contact process

2SO2 + O2 = 2SO3
vanadium oxide + 5 oxidation state

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what transition metal catalyses the hydrogenation of alkenes

nickel - lowers temperature and pressure required

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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

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Define complex ion

transition metal ion bonded to one or more ligands by coordinate bond

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define ligand

molecule or ion that can donate a pair of electrons to the transition metal by coordination bond

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Define coordination number

number of coordinate bonds formed between a central metal ion and its ligands

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What are the ligands acting as

lewis bases
electron pair donor

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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

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Are all ligands charged

no e.g. water

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describe a monodentate ligand

donates just one pair of electrons to the central metal ion to form a coordinate bond e.g. water

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Why is water a monodentate ligand even though it has 2 lone pairs

they are too close together

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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

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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

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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

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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

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What is the shape of a complex ion with four-fold coordination

tetrahedral

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Why do chlorine ligands form a tetrahedral

they are so large that only four chlorines can fit around a transition metal ion

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What is the shape and bond angles of a six-fold coordination

octahedral
90

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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