transition metaks Flashcards
What are transition metals?
= these have incomplete d-subshells
= d subshells can hold up to 10 electrons, 5 orbitals
What are the main characteristics of transition metals?
= form coloured compounds
= complex ions
= variable oxidation states
= hetergenous and homogenous catalysts
why is zinc not a trannsition metal?
= has a complete d-subshell
What is a complex?
= metal ion surrounded by ligands
examples: [Ag(Nh3)2]+
=
What is a ligand?
= these are atoms, compounds and molecules with a lone pair of electron that can forma dative covalent bond wth a central metal ion
= donates lone pair of electron
What is the coordination number?
= no of dative covalent bonds formed to a central metal ion
What are examples of monodentate ligabds?
= Nh3
= H2O
= :Cl
What are examples of bidentate ligands?
= ethandioate
= ethane-1-2-diame
=
what are multidetate ligabds?
= EDTA4-
What are subsitution reactions?
= these can happen with ligands of the same size, different size and different strength
What is the normal reaction of colbalt with ammonia?
[CO(H2O)6]2+ + 6Nh3 => [Co(Nh3)6]2+ + 6H2O
= the charge remains unchanged- with ligands of the same size, and the coordination number is the same (number of dative covalent bonds)
= therefore this would still be an octahedral shape
What are examples of octahedral shape if needed to be drawn?
= copper or colbalt with 6 water or 6 ammonias
What is the partial subsitution of copper and ammonia?
[Cu(H2O)6]2+ + 4Nh3 => [Cu(Nh3)4(H2o)2]2+
= 4H2O
= this is only partial
= the coordiation number however remains the same and the number of dative covalent bonds so the charge remains the same
What happens with the reaction with chloride ions?
= these are a different shaped ligand- and only react with 4Cl-, therefore the shape changes as the coordination nuber changes and the no of datibe covalent bonds
= with copper the charge goes from +2 to 2- and with colbalt
= with iron it goes from 3+ to -
= replaces the water to form 4 chlorine and them produces 6 water
What is the colour of [CuCl4]2- ?
= yellow/green solution
= tetrahedral shape
What is the colour of [CoCl4]-
= this is a blue solution
= tetrahedral shape
What example do we use for tetrahedral shapes?
= [cucl4]2-
= this is a tetrahedral
109.5 degrees
=
What example do we use for square planar?
= cis platin
90 degrees
What example do we use for a linear shape?
= tollens reagant
= 180 degrees
What examples can we use for cis trans isomerism?
[cr(H2o)4cl2]+
How do colour changes arise?
= changes in oxidation state
= coordination number
= ligands
How does colour formed?
= electron transitions from the ground state to the excited state, creates a gap in energy and a split in the d-orbital into 2 orbitals, sub-shells, this creates an energy gap
= a portion of visibke light is absorbed and this causes this split, light not absorbed and transmitted displays the colour
What is the first equation to find the difference in energy between split orbitals?
= plancks constant
x
= frequency of light absorbed
What is the second wquation to find the difference in energy split between orbitals?
= plancks consyant x speed of light/ wavelength of light
Why are so compounds colourless and are white?
= empty
= full subshell
= so cannot split the d-orbital- so no transmission of electrons from ground state to excied state
= there is not an energy transfer equal to that of visible light
What do compounds with high oxidation states tend to be?
= oxidising agents
What do compounds with low oxidation states tend to be?
reducing agents
What oxidation state does Vo2+ have?
= +5
= yellow solution
What oxidation state and colour does VO 2+ have?
= +4
= blue solution
What oxidation state does v3+ have?
= +3
= green solution
What oxidation state does v2+ have?
= violet colour
= +2
How can we reduce vanadium?
= using zinc in acidic solution
= the equations have 2 moles of the vanadoum compound
= 4H+ on LHS
Zn2+ on rhs
= and 2 water
= we do not have water and 4H+ on the last one
What do catalysts do?
= speed up rate of reaction without being used up- reducing the activation energy
= transition metals can act as heterogenous or homogenous catalysts
What is the simple concept for heterogenous catalysts?
= different phase from the reactants
What are the general concept for homogenous catalysts?
= samephase as the reactants
what are heterogenous catalysts?
= = usually solids, whilst the reactahts are gaseous in a solution, reaction occurs at surface of catalyst
= different phase from the reactants
How do these catalysts work? heterogenous
= reactants form bonds with atoms at active sites on the surface of the catalyst
= as a result, bonds in the reactants are weakened and break
= new bonds form between the reactants held close on the catalytic surface
= weakens the bonds between product and catalyst and product leaves
= ADSORPTION
What are the strengths of adsorption?
= determine effectibvness
= some metals are too strong adsorption, producys cannot be released
= somemetals are too werak adosorption, and do not adsorb in high enough concetration
= ni and platinium have the right ebogh catalyst
What catalust is used in the comtact process?
= = V2O5 is the catalyst- remember these are never used up
= 2SO2 + O2 => 2SO3
What is step 1 od rhe contact process?
[= = SO2 + V2O5 => SO3 + V2O4
What is step 2 of the contact process?
= = 2V2O4 + O2 => 2V2O5
How are catalysts posioned?
= = catalysts can be posioned by impurities and reduces efficiency and may need to be replaced
= less product is made
= increaes cost of chemical proceses
=
What are homogenous catalysts?
= when catalysts and reactants are the same state, the reaction uses an in intermediate that reacts to form producy and regenerates the catalyst
What will the interediate tends to have?
= different oxidation states to the oriignal transition metal
Why do transition metals make good homogemous catalysts?
= form various oxidation states, able to donate and recieve electrons
What ar are the reactions between I- and S2O82- ?
S2O8 2- + 2I- => 2So4 2- + I2
What are the 3 reactions that need to be leart?
S2O8 + 2e- => 2So4 2-
Fe3+ + e- => Fe2+
I2 + 2e- => 2I-
Why is the uncatalustsed reaction vert slow?
= reaction needs a collision between 2 negative ions repulsiomeans there is a high activation energy
What is the catalysed alternative route?
= S2O8 + 2Fe2+ -> 2So42- + 2Fe3+
= 2I- + 2Fe3+ => 2Fe2+ + I2
What is an autocatalytic reaction?
= = where one of the products, of the reaction can catalyse the reaction
= the catalyst is not used up and is reformed
What makes a reaction have a high activation energy?
= = if there are 2 negative ions repel eachother and this causes a high activation energy
How do autocatalysts work?
= product acts as a catalyst, so after slow start the reaction begins to speed up, as they provide an alternate route with lower activation energy
= the reaction slows down as the catalyst product drops
What is the reaction with Mn2+ ions as the catalyst and reacting C2O4 2- and MnO4 -?
2MnO4 - + 5C2O4 2- + 16H+
=>
2Mn2+ + 10CO2 + 8H2O
What are the 2 steps involved?
4Mn2+ + MnO4- + 8H+ => 5Mn3+ + 4H2O
2Mn3+ + C2O4- => 2Mn2+ + 2Co2
How do we use the calorimeter?
= add appropriate ligand to intensify colour
= make up solutions of known concentrations
= measure absorption or transmission
= plot graph of absorption against concentratio
= measure absoroption of unknown and compare
What does the coloured filter do?
= allow wavelengths of light that are most likely to be absorbed by the coloured solution
What is the colour of [Co(H2O)6]2 +
=pink
What is the reaction of [Co(Nh3)6]2+ when adding o2?
[Co(Nh3)6]3+ +e-
= goes from yellow to brown
What is the reaction when [Co(H2O)6]2+ and 6 moles of ammonia?
= [Co(Nh3)6]2+ and 6 water
What are some metal complexes more stable than others?
= entropy has increased- there is more disorder,
= more moles on the product side, so more stable
What is the colour of [Co(Nh3)6]2+?
= yellow
What is the colour of [Co(Nh3)6]3+?
= brown
What kind of curve is the autocatalyst curve?
= s shaped
[MnO4-] and time
For monodentate ligands how many moles do we use?
= the moles of 6 but, if it is partial only 4, such as copper complexes with ammonia
For bidentate ligands how many moles do we us?
6/2 3, as bidentate ligands can each form 2 dative covalen bonds as there are 2 lone pairs of electrons
What is the side effect of cis platin?
= may attach to healthy DNA cells, and kill them, medical side effects
What impurties posion the iron catalyst in the haber process?
= sulfur impurities
How does spectphotometry work?
= visile light of increasing frequency passes through a sample of coloured complex ion, some light is absorbed
= amount of light absorbed is porportional to concentration of absorbing species and distance travelled throug solution
So there is not an energy transfer equal to
that of visible light.
= some complexes have pale solutions
What happens with the redox tritratio between fe2+ ions and mno4- ions?
= titration is self indicating, significant colour change from reactant to product
What is the equation for the redox tritration?
= Mno4- + 8h+ + 5Fe2+ forms
Mn2+ + 4H2O + 5fe3+
What is the problem with the colour of the magnate?
= purple colour of magnate can make it difficult to see bottom of miniscus
= if magnate is in birutte, end point of tritration will be first permanent pink colour- colourless to pink
What does copper aqeous react with ammonia general points?
= blue precipitate
= dissolves to form deep blue solution
Why can magnate ion be detected?
= coloured ions
What factors affecy the heterogenous catalysts?
= adsorption
= surface area
= impurities.
