Topic 15: Transition Metals Flashcards
What is the colour of [Cu(H20)6]^2+
Light blue
Describe Cu(H20)4(OH)2 (s) in solution
Bright blue gelatinous precipitate
What is the colour of [CuCl4]^2-
Bright yellow
Why does the reaction of copper sulfate + HCl produce a green solution?
The [CuCl4]^2- is bright yellow but the [Cu(H20)6]^2+ is blue. The reaction is in equilirium so the yellow colour is made green by the presence of the remaining [Cu(H20)6]^2+
Why does the reaction of copper sulfate + NH3 produce a darker blue solution when excess NH3 is added?
Cu(H20)4(OH)2 (s) is a bright blue precipitate, but when excess ammonia is added, [Cu(H2O)2(NH3)4]^2+ is formed in a ligand substitution reaction and appears dark blue in solution.
What is the product of the reaction between copper sulfate and KI?
This is a redox reaction where a white precipitate and a dark brown I2 (iodine) solution is formed. The white precipitate is copper iodide.
Why is copper iodide white?
Copper iodide has a complete d subshell and so does not produce the colours that other transition metal compounds which arises from having an incomplete d subshell.
What type of reaction occurs between copper sulfate and solid zinc?
Displacement - the Zn (s) is replaced by Cu (s) which is an orangey colour.
What colour change accompanies the reaction between copper sulfate and solid zinc?
Blue to colourless solution.
What colour is chromium (III) in solution?
[Cr(H20)6]^3+ is violet/green in solution
What is formed from the reaction of CrCl3 with NaOH? What happens if you add excess NaOH?
A green gelatinous precipitate of Cr(OH)3(H2O)3. This dissolves in excess NaOH to form a green solution which is a mixture of [Cr(OH)6]^3-, [Cr(OH)5(H2O)]^2-, and [Cr(OH)4(H2O)2]^-.
What is formed from the reaction of CrCl3 with NH3?
Green gelatinous precipiate of Cr(H2O)(OH)3 (s) in an acid-base or precipitate reaction
What happens when the product of the reaction of CrCl3 with NH3 is dissolved in excess NH3?
A ligand subsitution reaction happens which forms a dark green solution containing [Cr(NH3)6]^3+
What colour is Cr2O7^2- (dichromate ions)?
Orange
What colour is CrO4^2- (chromate ions)?
Yellow
What is happening in a dichromate solution?
Equilibrium reaction:
dichromate + water <–> 2chromate + 2H+
What happens to a dichromate solution when NaOH is added?
Orange –> Yellow
What happens to a dichromate solution when HCl is added?
Yellow –> Orange
What is a transition metal
A d-block metal which forms stable ions with partially filled d-orbitals
Why do transition metals form ions variable oxidation states
Transition metals exhibit variable oxidation states by losing or gaining electrons to form ions with different charges. This is because transition metals have very similar successive ionisation energies so the increase is small (gradual increase in successive ionisation energies).
What is a ligand
Something which has a lone pair of electrons and forms a coordinate bond with a central metal ion
What is a complex ion
A central metal ion surrounded by ligands
How does the colour of complex ions arise
Splitting of the d-orbitals by ligands
Why does Cu+ not have colour
It has a fully filled d-subshell
Why might changes of the colour of a transition metal ions arise
Changes in:
oxidation number
ligand
coordination number
What is the coordination number of a complex ion
The number of coordinate bonds surrounding the central metal ion
Why might a transition metal from a tetrahedral complex with some ligands
The ligand is too large to form an octahedral complex, such as Cl-
What is an example of a square planar complex?
Cis-Platin
What metal ions are more likely to form square planar complexes
Nickel
Palladium
Platinum
What shapes of complex ions can display cis/trans isomerism
square planar
octahedral
What must be true for a complex ion to display cis/trans isomerism
They must have 2 identical ligands
What is the relationship between the difference in energy levels and frequency of light absorbed
proportional
If the energy gap increases, what happens to the frequency of light absorbed?
higher frequency of light
Higher frequencies of light are closer to which end of the visible light spectrum?
Blue end
What equation links the difference in energy and wavelength?
ΔE=hc/λ
where c = speed of light
λ = wavelength
h = planck’s constant
What equation links the difference in energy and frequency?
ΔE=hv
where h = planck’s constant
v = frequency of light
Ions with higher oxidation states tend to absorb ______ frequencies of light
Higher
But we can’t use this as a rule because there are other factors at play because some complexes absorb multiple frequencies of light
Order these ligands in terms of how much they cause d-orbital splitting, starting with the smallest difference:
water, hydroxide, ammonia, cyanide, chloride
chloride, hydroxide, water, ammonia, cyanide
What is the relationship between coordination number and d-orbital splitting?
The higher the coordination number, the greater the d-orbital splitting
How do you find the concentration of a solution using colorimetry?
Find the absorbance (of the complementary colour to the solution) using a colorimeter. Plot the percentage absorbance on a calibration curve (percentage absorbance against concentration). Find the absorbance of the unknown solution and compare with the calibration curve to find the concentration.
Why should sample containers of the same size and material be used when doing colorimetry.
Absorbance is proportional to the distance the light travels through the solution as well as the concentration of the solution, so using the same size and material container ensures the distance the light travels through the solution remains constant.
What does en represent
Ethane-1,2-diamine
How many coordinate bonds can en form?
2
What is ethanedioate also known as?
Oxalate
What is the structural formula and charge of ethanedioate?
-OOCCOO-
2- charge
What is the structural formula and charge of ethane-1,2-diamine
NH2(CH2)2NH2
Neutral/No charge
Which lone pairs does oxalate form coordinate bonds with? Where is the negative charge?
The negative charge is on the oxygen with a single bond to the carbon (used to be OH)
The lone pair on the negative oxygen is used to form coordinate bonds
What is the chelate effect?
Whenever bidentate or multidentate ligands substitute monodentate ligands, the entropy of the system increases drastically, driving the reaction
Why does entropy increase when a multidentate ligand substitutes a monodentate ligand
There are more moles of particles in the products than in the reactants
How many coordinate bonds can EDTA form
6
What is the charge on EDTA
4-
Why is EDTA an effective treatment for heavy metal poisoning
There is a massive increase in entropy when EDTA substitutes 6 ligands surrounding a transition metal ion in a complex, so the EDTA stays holding onto the metal ion, preventing further poisoning
How many coordinate bonds can haem form?
4
Which ligands form unstable coordinate bonds with haemoglobin?
Oxygen, water, and carbon dioxide
What ligand forms very stable bonds with haemoglobin
carbon monoxide
Colour of cobalt (II) solution
Pale pink slution due to [Co(H2O)6]2+
Cobalt (II) + NaOH
Pale blue precipitate of Co(H2O)4(OH)2 which is insoluble in excess
Cobalt (II) + HCl
Formation of blue [CoCl4]2- in eqm with pink [Co(H2O)6]2+ -> purple solution
Cobalt (II) + NH3
Pale blue precipitate of Co(H2O)4(OH)2 with dilute;
conc NH3 gives yellow-brown solution of [Co(NH3)6]2+ which darkens to red-brown due to oxidation to cobalt (III)
If oxidation completed with peroxide, effervescence due to base-catalysed decomposition of peroxide to water and oxygen
Cobalt (II) + Na2CO3
Pink precipitate of CoCO3
2+ hexaaqua ions not acidic enough to have hydrogen ion removed by carbonate so double displacement reaction occurs
hexaaquacobalt + carbonate -> cobalt carbonate + water
Colour of iron (II) solution
Palge green but on standing turns yellow-brown due to oxidation of Fe (II) to Fe (III)
Fe (II) + Mg
Light green/yellow solution gets lighter in colour.
Fe (II) reduced to Fe metal
Effervescence of hydrogen gas
Mg + Fe2+ -> Fe + Mg2+
Mg + 2H+ -> Mg2+ + H2
Fe (II) + H2O2
Pale Green solution turns brown due to oxidation of Fe (II) to Fe (III)
Fe (II) + NaOH
Green precipitate Fe(H2O)4(OH)2 which oxidises to brown Fe(H2O)3(OH)3 (s)
Insolube in excess
Acid base reaction
Fe (II) + NH3
Green precipitate Fe(H2O)4(OH)2 which oxidises to brown Fe(H2O)3(OH)3 (s)
Insoluble in excess
Acid-base reaction
Fe(II) + [Fe(CN)6]3-
Pale blue precipitate
Turnbull’s blue - Prussian blue
Fe (II) + SCN-
No reaction
Darkening of solution is due to oxidation of Fe (II) to Fe (III)
Colour of Fe (III) in solution
Brown solution
pH of Fe(III) solution
pH 4
Hydrated Fe (III) undergoes deprotonation
Fe (III) + Mg
Effervescence and decolourisation of brown solution
Fe (III) reduced to Fe metal
Fe (III) salts are acidic to some bubbles of H2 observed
2Fe3+ + 3Mg -> 3Mg2+ + 2Fe
Mg + 2H+ -> Mg2+ + H2
Fe (III) + NaOH
Yellow-brown gelatinous precipitate of Fe(H2O)3(OH)3
Insoluble in excess
Acid-base reaction
Fe (III) + NH3
Yellow-brown gelatinous precipitate of Fe(H2O)3(OH)3
Insoluble in excess
Acid-base reaction
Fe (III) + [Fe(CN)6]3-
Dark blue precipitate forms
This is turnbell’s blue (also called Prussian blue)
KFe(II)[Fe(II)(CN)6] or Fe4[Fe(CN)6]3 or iron (III) hexacyanoferrate (II)
Fe (III) + SCN-
Blood red solution formed due to formation of [Fe(SCN)(H2O)5]2+
Also contains Fe(SCN)3 and [Fe(SCN)4]-
Ligand exchange reaction
What is the colour of VO2^+ in solution?
Yellow
What is the colour of VO^2+ in solution?
Blue
What is the colour of V^3+ in solution?
Green
What is the colour of V^2+ in solution?
Purple
What does NH4VO3 form in acidic conditions?
ammonium trioxovanadate (V) is a soluble vanadium compund. In acidic consitions, it forms the dioxovanadium (V) ion, VO2^+
How can you reduce VO2^+ to vanadium (II)?
Zinc with sulfuric or hydrocholoric acid.
What colour change accompanies the reduction of VO2^+ to vanadium (II)?
- yellow to blue (+5 to +4)
- blue to green (+4 to +3)
- green to purple (+3 to +2)
What is the half equation for the reduction VO2^+ to VO^2+
VO2^+ + 2H+ + e- –> VO^2+ + H2O
What is the half equation for the reduction of VO^2+ to V^3+?
VO^2+ + 2H+ + e- –> V^3+ + H2O
What is the half equation for the reduction of V^3+ to V^2+?
V3+ + e- –> V2+
Give the equations for the catalysed reaction between iodide and peroxidisulphate ions
2Fe2+ + 2(S2O8)^2- -> 2Fe^3+ + 2(SO4)^2-
2Fe^3+ + 2I- -> 2Fe^2+ + I2
DONT THINK THIS IS RIGHT - need to edit
How could you track the reaction between iodide and peroxidisulphate ions
Add starch which would cause solution to get darker OR
Using a clocking reagent such as thiosulfate and measure time taken for (S2O3)^2- (thiosulfate ions) to run out.
Give the equations for the catalysed reaciton between ethandioate ions and manganate (VII) ions
4Mn2+ + MnO4- + 8H+ -> 5Mn^3+ + 4H2O
2Mn3+ + C2O4^2- -> 2Mn^2+ + 2CO2
Give the overall equation for the reaction between ethandioate ions and manganate (VII) ions
2MnO4^- + 5C2O4^2- + 16H+ -> 2Mn^2+ +8H2O + 10CO2
What is interesting about the reaction between ethandioate ions and manganate (VII) ions
One of the products is the catalyst for the reaction
How could you monitor the reaction between ethandioate ions and manganate (VII) ions
Colorimetry to measure the disappearance of the deep purple/pink colour ( from the MnO4^- ions)
What is the reaction and purpose for the Contact Process
SO2 (g) + 1/2 O2(g) <=> SO3(g)
used in the manufacture of sulfuric acid
What is the catalyst for the contact process and give the accompanying reactions
V2O5 is the heterogeneous catalyst
SO2 (g) + V2O5 (s) <=> SO3 (g) + V2O4 (s)
V2O4 (s) + 1/2 O2 (g) <=> V2O5 (s)
During catalysis, V undergoes reversible chaneg in oxidation state
Importance of Specificity for heterogeneous catalysts
Catalysts selected so that the space between active sites matches the bond length of the bond being broken
Importance of adsorption strength for heterogeneous catalysts
If too strong:
* reactants cannot move around on the surface of the catalyst
* products cannot leave AKA desorb
If too weak:
* reactants won’t adsorb
What is the trend in strength of adsorption of transition metals across a period?
Increasing strength of adsorption moving left along transition metals
What is the poisoning of catalysts?
Some substances can block active sites on catalysts, ruining the catalyst.
For example: S in the Haber process
or Pb in catalytic converters
Why is the honeycomb structure used in a car exhaust system?
Increased surface area of heterogenous catalyst and honeycomb structure allows gases to flow through
