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