2.5(P2) Transition Metals Flashcards Preview

6.02 A Level Inorganic KW > 2.5(P2) Transition Metals > Flashcards

Flashcards in 2.5(P2) Transition Metals Deck (53)
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What is significant about Aluminium?

It is not a transition metal but still forms complexes
Therefore doesn’t have a colour within the complex


Why are transition metals coloured as they are?

The ion absorbs certain frequencies of white light
They have partially filled 3d sub levels
So d-d transitions can take place
So when the electrons move they often absorb energy in the visible region
This colour observed is the light that is reflected


What affects the energy difference between d orbitals other than different transition metals?

Different ligands
Different oxidation states


What is the equation relating to the colours of transition metals? Units?

ΔE = hv

ΔE - energy difference between the d orbitals - J
h - plancks constant (given) - Js
v - frequency of absorbed radiation - Hz


What is significant about light and it’s perceived colour?

They are opposites on the colour wheel

Red light = blue solution


What are optical isomers? When does this occur in transition metals?

2 isomers are non-superimposable mirror images of each other
Same molecular and structural formula but has a different spacial arrangement

When there are 2 or more bidentate ligands in a complex


Properties of optical isomers?

Have identical chemical properties

Distinguished by their effect on polarised light
One isomer rotates the plane of polarisation of polarised light clockwise and the other anticlockwise


How can we use colour to determine concentration?

By passing white light through a complementary coloured filter into two solutions
One as a test sample at a different concentration and one as the pure solvent
The light then passes through to a detector and different absorbancies will take place depending on the concentration in the samples
This will then be displayed by a meter or recorder


Why do transition metals have variable oxidation states?

They have partially filled 3d sublevels


What are Manganese’s oxidation states and colours?

Mn(7) - purple
Mn(6) -
Mn(4) - brown/black
Mn(2) - very pale pink


What are chromium’s oxidation states and colours?

Cr(7) - yellow
Dichromate(7) - orange
Cr(3) - green
Cr(2) - blue



What are vanadium’s oxidation states and colours?

V(5) - yellow
V(4) - blue
V(3) - green
V(2) - violet



What do Vanadium’s colours go in real life? (reaction with zinc)

Green (due to yellow and blue mixing)


How do you do a titration calculation?

Work out the moles (of other substance that they gave you)
Work out the ratio between the reactants by forming an overall half equation if the two
Multiply the moles by the correct ratio (this will be the smaller volume)
Multiply by something to get back to the original volume size (usually 10)

Then workout what the question wants


What is the MnO4- half equation?

MnO4- + 8H+ + 5e-
Mn2+ + 4H2O

MnO4- -> Mn2+


What is the Fe2+ equation?

Fe2+ -> Fe3+ + e-


What does C2O4 2- go to?

C2O4 2-


What is the Cr2O7 2- half equation?

Cr2O7 2- + 14H+ + 6e-
2Cr3+ + 7H2O


Why are transition metals good catalysts?

They have variable oxidation states


What kind of catalysts can transition metals act as?

Heterogeneous - the catalyst has a different state or phase to the reactants

Homogenous - the catalyst has the same state or phase to the reactants

(State: solid/liquid/gas)
(Phase includes aqueous)


What is the surface adsorption theory? Using the Haber process

Heterogenous only:
Nitrogen adsorbs onto the catalyst surface (due to lone pairs it can act as a ligand and form covalent bonds)
It speeds it up as the surface holds the molecules in place - easier to react
Nitrogen forms co-ordinate bonds to the surface which weakens N≡N so more reactive with the H2
NH4 is still held by a co-ordinate bond to the surface due to another lone pair
Desorption is the product leaving


What is adsorption?

Attaching to the surface but not absorbing in


What are some heterogeneous catalysts in processes?

Haber process: uses Iron-Fe
Contact process: uses V2O5 (makes SO3)
Manufacture of Methanol: uses Cr2O3 or Cu

All these are solids btw
And occur at the surface of a catalyst


In the contact process - what are the equations for V2O5 being regenerated (example of oxidation state)? and overall equations?

V2O5 + SO2 -> V2O4 + SO3

V2O4 + 1/2O2 -> V2O5

Overall: SO2 + 1/2O2 ⇌ SO3
Then - SO3 + H2O -> H2SO4


What reactions use homogeneous catalysts?

S2O8 2- + I-


MnO4- + C2O4 2-


What is the S2O8 and I- equation?

S2O8 2- + 2I- -> 2SO4 2- + I2
(All aqueous)


What metal catalyses S2O8 and I-? Equations?

Fe2+ and Fe3+

S2O8 2- + 2Fe2+ -> 2SO4 2- + 2Fe3+

2Fe3+ + 2I- -> 2Fe2+ + I2


In homogenous catalysts why can you add only one of the catalysts ie only Fe2+?

As when you add one the other is produced via redox to then catalyse the second half of the reaction

Eventually the original is regenerated as they continually undergo redox


Why is S2O8 2- and I- a slow reaction?

They are both negative ions so they will repel

They require a high activation energy so collisions are unlikely to react


Why is an inert medium sometimes used as a support for a heterogeneous catalyst?

Maximise the surface area

Minimise the cost


Why would a metal not work well as a heterogeneous catalyst?

Adsorbs too weakly - reactants can’t react as the bonds aren’t weak enough

Adsorbs too strongly - the products formed can’t desorb


What is the equation between MnO4- + C2O4 2- ?

2MnO4- + 5C2O4 2- + 16H+
-> 2Mn2+ + 10CO2 + 8H2O


What metal catalyses MnO4- and C2O4 2-? Equations?

Mn2+ and Mn3+

MnO4- + 4Mn2+ + 8H+ -> 5Mn3+ +4H2O

2Mn3+ + C2O4 2- -> 2CO2 + 2Mn2+


What is an autocatalysis reaction?

The products formed in a reaction then act as catalysts


What are the metal aqua ions and colours?

[Fe(H2O)6] 2+ = pale green

[Cu(H2O)6] 2+ = pale blue

[CuCl4] 2- = yellow

[Al(H2O)6] 3+ = colourless

[Fe(H2O)6] 3+ = yellow

[Cu(NH3)4(H2O)2] 2+ = deep blue


What happens to transition metal ions in an aqueous solution?

They form metal aqua complex ions


How many ligands does water normally form?

Co-ordination number of 6

Octahedral shape


Give an equation for CuSO4 in an aqueous solution?

CuSO4 + 6H2O -> [Cu(H2O)6]2+ + SO4 2-


What are the pH’s of the metal aqua ions?

2+ ion - around pH 5
3+ ion - around pH 3


What are some hydrolysis reactions? Use M

[M(H2O)6]2+ ⇌ [M(H2O)5(OH)]+ + H+

[M(H2O)6]3+ ⇌ [M(H2O)5(OH)]2+ + H+


Where does the OH ‘ligand’ come from in hydrolysis reactions?

The H+ is taken from water ligands by a water molecule (this property makes them more acidic)


Why is 3+ more acidic than 2+ metal aqua ions?

It attracts more electrons and therefore weakens the bonds more - forming more hydrogen bonds


What do the metal aqua ions turn into when NaOH is added? Colours?

Al, Fe3+, Cu, Fe2+

[Al(H2O)3(OH)3] - white ppt

[Fe(H2O)3(OH)3] - brown ppt

[Cu(H2O)4(OH)2] - pale blue ppt

[Fe(H2O)4(OH)2] - green ppt


What equation would you produce when you add a stronger base(OH-)? Use M - for 2+ and 3+

[M(H2O)6]3+ + 3OH- ⇌ [M(H2O)3(OH)3] (precipitate) + 3H2O

[M(H2O)6]2+ + 2OH- ⇌ [M(H2O)4(OH)2] (precipitate) + 2H2O

These are overall equations


What happens to the metal aqua ions when excess NaOH is added? Colours? Why?

[Al(H2O)3(OH)3 + OH- ⇌
[Al(H2O)2(OH)4] (colourless solution) + H2O

Aluminium is amphoteric and will react with an acid and a base

The rest have no change


What is significant about aluminium?

Aluminium is not a transition metal
It can form complexes
But they aren’t coloured


What happens to the metal aqua ions when they had reacted with OH- or NH3 and left to stand in the air?

[Fe(H2O)3(OH)3] - brown ppt

This is due to Fe2+ salts being unstable so they turn back into Fe3+

The rest have no change


What do the metal aqua ions turn into when NH3 is added? Colours?

Al, Fe3+, Cu, Fe2+

Exactly the same as OH-
[Al(H2O)3(OH)3] - white ppt

[Fe(H2O)3(OH)3] - brown ppt

[Cu(H2O)4(OH)2] - pale blue ppt

[Fe(H2O)4(OH)2] - green ppt


What equation would you produce when you add a a weaker base(NH3)? Use M - for 2+ and 3+

[M(H2O)6]3+ + 3NH3 ⇌ [M(H2O)3(OH)3] (precipitate) + 3NH4+

[M(H2O)6]2+ + 2NH3 ⇌ [M(H2O)4(OH)2] (precipitate) + 2NH4+

These are overall equations


What happens to the metal aqua ions when excess NH3 is added? Colours? Why?

[Cu(H2O6)]2+ + 4NH3 ⇌ [Cu(NH3)4(H2O)2]2+ + 4H2O

Colour = deep blue

The NH3 can act as a ligand with Cu
This is ligand substitution - you need an excess of the ligand (NH3)


What do 3+ metal aqua ions produce with carbonates (eg sodium carbonate)?

2[M(H2O)6]3+ 3CO3 2- ⇌ 2[M(H2O)3(OH)3] + 3CO2 + 3H2O


What do 2+ metal aqua ions produce with carbonates (eg sodium carbonate)?

M+ + (CO3)2- -> MCO3


What is the order of strength of acids?