Transition metals Flashcards by Annabelle Clark

4 characteristics of transition metals

Can form complex ions
Variable oxidation states
Form coloured compounds
Can act as catalysts

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Why is Zn not a transition metal

It can only form Zn2+ ions which have a complete d orbital

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What is a complex ion

central metal atom surrounded by ligands

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Ligand definition

Atom, ion or molecule that can donate a lone electron pair

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Co-ordination number

number of co-ordinate bonds around the central atom

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3 examples of monodentate ligands

Cl-, NH3, H2O

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2 examples of bidentate ligands

NH2CH2CH2NH2, C2O4^2-

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example of multidentate ligand

EDTA-

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Why can H2O and NH3 ligands exchange without a change in coordination number

they are uncharged and a similar size

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Reaction of [Cu(H2O)6]^2+ and NH3

Incomplete substitution
Forms [Cu(NH3)4(H2O)2]^2+
dark blue colour

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Why can compunds with NH3 or H2O ligands undergo a ligand substitution with Cl-

Cl- is larger and charged

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[CuCl4]^2- colour

yellow/green solution

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[CoCl4]^2- colour

blue solution

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What is the change in coordination number when H2O/ NH3 is replaced with Cl- ligands

6 to 4

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When would the [Cu(Cl)4]^2- complex not form

if the solid copper chloride is dissolved in water
[Cu(H2O)6]^2+ forms

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when might partial substitution of ethanedioate ligands form

if a dilute aqueous solution of ethanedioate ions is added to a solution containing aqueous copper (II) ions
only 4 water molecules are replaced

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Example of an iron (II) complex with a multidentate ligand

Haem

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How is oxygen transported in the blood

oxygen forms a coordinate bond to Fe(II)

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Why is CO toxic to humans

CO can from a strong
coordinate bond with haemoglobin. This is a
stronger bond than that made with oxygen and so it
replaces the oxygen attaching to the haemoglobin.

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What is the chelate effect

The substitution of monodentate ligand with a bidentate or a multidentate ligand leading to a more stable complex

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How does entropy explain the chelate effect

There are more moles of products than reactants
Enthalpy change is small as there are similar numbers of bonds in both complexes

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Why is the stability of EDTA- complexes useful

it is not toxic so can be added to rivers to remove heavy metal ions
Can be added to shampoo to remove calcium ions to help with lathering

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Shape of transition metal complexes with small monodentate ligands

octahedral

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Shape of transition metal complexes with larger monodentate ligands

tetrahedral

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What shape is cisplatin

square planar

What is cisplatin

NH3NH3PtClCl

what shape complexes does Ag+ form

linear

What is tollen's reagent

[NH3AgNH3]^+

what kind of isomerism is present in square planar complexes

cis-trans

What kind of isomerism is present in octahedral complexes

cis-trans (monodentate ligands) optical (bidentade ligands)

when can colour change occur in transition metal complexes

from a change of: 1. oxidation state, 2. co-ordination number 3. ligand

How does colour arise in transition metal complexes

d-d transitions so electrons become excited so can absorb wavelengths of visible light Light that is transmitted produces the colour

which equation links frequency of light absorbed and energy of d orbitals

(change)E = hv E= J v= frequency of light absorbed in Hz or S^-1 h- Plank's constant in J s

why does changing a ligand change the colour of complexes

it changes the split of energy between d orbitals changing E

why do some transition metal ions not have a colour

full d orbital

How can spectrophotometry show the concentration of the absorbing species

concentration is propotional to amount of light absorbed

method for spectrophotometry

Add an appropriate ligand to intensify colour Make up solutions of known concentration Measure absorption or transmission Plot graph of absorption vs concentration Measure absorption of unknown and compare

How is the coloured filter chosen in spectrophotometry

The colour of the filter is chosen to allow the wavelengths of light through that would be most strongly absorbed by the coloured solution

what are compunds with high oxidation states best as

oxidising agents

colour of VO2+ Oxidation state +5

yellow solution

colour of VO^2+ Oxidation state + 4

blue solution

colour of V^3+ Oxidation state + 3

green solution

colour of V^2+ Oxidation state + 2

violet solution

what is the redox potential of an ion changing oxidation state influenced by

pH and the ligand

how is vanadium reduced down to different oxidation states

adding zinc to V in acidic solution

How does tollen's reagent show the presence of aldehydes

they reduce tollens reagent to form silver

disadvantage of the manganate redox titration

the purple colour can make it hard to see the meniscus in the burette

equation for manganate and Fe titration

MnO4-(aq) + 8H+(aq) + 5Fe^2+(aq)---> Mn^2+ (aq) + 4H2O (l) + 5Fe^3+ (aq) purple to colourless

which acid can be used for manganate titration

dilute sulfuric acid

what happens if insufficient acid is provided for manganate redox titration

solution is not acidic enough and MnO2 will be produced instead of Mn^2+

what happens if MnO2 is produced in the manganate redox titration

brown MnO2 will mask the colour change and lead to a greater (inaccurate) volume of Manganate being used in the titration

Why can't HCl be used in manganate titration

Cl- would be oxidised to Cl2 which is poisonous

Why can't nitric acid be used for the manganate titration

it is an oxidising agent so oxidises Fe^2+ to Fe^3+ so a smaller volume of manganate would be used

heterogenous vs homogeneous catalysts

heterogeneous- different phase than reactants homogeneous- same phase as reactants

describe the process of heterogeneous catalysis

Adsorption of reactants at active sites on the surface bonds within the reactant molecules become weaker or higher concentration of reactants at the solid surface so leading to a higher collision frequency New bonds form between the reactants held close together on catalyst surface. This weakens bonds between product and catalyst and product desorbs

why are Ni and Pt useful catalysts

Ni and Pt have about the right strength too strong adsorption- products don't desorb too weak- don't adsorb in high enough concentration

what is used as a catalyst in the contact process

V2O5

equations for contact process

Overall equation : 2SO2 + O2 -> 2SO3 step 1 SO2 + V2O5 -> SO3 + V2O4 step 2 2V2O4 + O2 -> 2V2O5

what catalyst is used in the production of methanol

Cr2O3

what is methanol manufactured from

carbon monoxide and hydrogen

what is used as a catalyst in the Haber process

iron

what can decrease a catalyst's efficiency

if poisons adsorb to the active site and don't desorb so block it

what catalyses the reaction between iodide and persulphate ions

Fe2+ or Fe3+ ions

why is the reaction between I- and S2O8^2- usually slow

like charges repel

equations for iodide and persulphate reaction

overall S2O8^2- + 2I^- -> 2SO4^2- + I2 stage 1 S2O8^2- + 2Fe^2+ -> 2SO4^2- + 2Fe^3+ stage2 2I^- + 2Fe^3+ -> 2Fe^2+ + I2

why can both Fe2+ and Fe3+ catalyse the iodide and persulphate reaction

they are both produced in the reaction so the stages just switch round depending on which is added first

example of an autocatalytic reaction

reaction between ethanedioate and manganate ions

2 MnO4^- + 5 C2O4^2- + 16H+ -> 2Mn^2+ + 10 CO2 + 8 H2O Step 1 4Mn^2+ + MnO4^- + 8 H+ -> 5Mn^3+ + 4 H2O Step 2 2Mn^3+ + C2O4^2- -> 2Mn^2+ + 2 CO2

how to determine the reaction rate of manganate and ethanedioate ions

colorimetry- this is faster and does not disrupt the reaction mixture

how to construct a catalysed mechanism reaction

write 2 half equations make the redox equations of the catalyst combine reduction of catalyst with oxidation of reactants and vice versa check they add up

what complexes does silver commonly form

linear, colourless e.g [Ag(H2O)2]+

how is silver similar to transition metals

form complexes and can show catalytic behaviour

how is silver different from transition metals

does not form coloured compounds and does not have variable oxidation states

oxidation state of silver in complexes

+1 with 4d10 full subshell

how can silver nitrate be used to work out formulae of chloride containing complexes

silver nitrate will only form the silver chloride precipitate with the free chloride ions outside of the complex