transition Flashcards
Why do transition elements have cloured ion solutions?
The transitional property of colour depends on the metal ion having a partially filled d-subshell.
When light passes through a coloured substance, specific wavelengths are absorbed. We see a mixture of what is left over.
Transition metal ions absorb energy from visible light to PROMOTE ELECTRONS from lower energy levels to higher ones.
However this means that there must be d electrons in the ion to promote, and that there must be spaces in the orbitals to promote the electrons into.
What are the colours of:
- Fe 2+ or [Fe(H2O)6]2+
- Fe 3+ or [Fe(H2O)6]3+
- Fe(OH)2 (s)
- Fe(OH)3 (s)
- pale green
- yellow
- pale green
- orange-brown
What are the colours of
- Cu 2+ or [Cu(H2O)6]2+
- [Cu(NH3)4(H20)2]2+
- [CuCl4]2-
- Cu(OH)2 (s)
- pale blue
- dark blue
- yellow
- pale blue
What are the colours of chromium ions:
- Cr 3+ or [Cu(H2O)6]3+
- [Cr(H2O)5SO4]+ (when H2SO4 is present)
- Cr 2+ or [Cr(H2O)6]2+
- [Cr(NH3)6]3+
- [Cr(OH)6]3-
- Cr(OH)3 (s)
- Cr2O7^2-
- violet
- green
- blue
- purple
- dark green
- grey-green
- orange
What are the colours of manganese ions:
- Mn2+
- MnO4 -
- Mn(OH)2 (s)
- pale pink
- purple
- light brown
Why do transition elements make good heterogeneous catalysts?
They can easily adsorb (attach to the surface of) reactants, weakening bonds within the reactants.
What are examples of processes which use transition element catalysts?
The Haber process ( Iron )
The Contact process ( Vanadium oxide)
Hydrogenation of vegetable oil ( Nickel)
Decomposition of hydrogen peroxide ( MnO2)
The reaction between iodate and peroxidisulfate ions ( Fe2+ ions)
Redox reaction of Fe2+ to Fe3+ and colour change
Fe2+ is oxidized with H+/MnO4-
Fe3+ is reduced with I-
Redox reaction of Cr3+ to Cr2O7^2-
Cr3+ is oxidized with H2O2/OH-
Cr2O7^2- is reduced with I-
What are manganite (VII) titrations used to analyse?
reducing agents
- Fe (II) ions
- ethanedioic acid (COOH)2
What can be used instead of KMnO4 in titrations?
H+/Cr2O7^2-
acidified dichromate ions
What are the basic techniques and procedures used when carrying out a redox titration with Fe2+/MnO4-? What is the end point?
Measure the meniscus from the top
Add the KMnO4 to the burette
Add sulfuric acid to the solution to be analysed to provide the H+ ions
The endpoint is when the first permanent pink colour arises.
(if MnO4- is in the conical flask, it will be when the pink/purple disappears)
what are the colours of manganate (VII) and Mn2+ ions?
dark purple and nearly colourless, respectively
What are iodine/thiosulfate titrations used to analyse?
Oxidising agents e.g.
ClO- in bleach
Cu2+ in copper (ii) compounds
Cu in copper alloys
What is the test for sulfate ions?
Barium nitrate
if a white ppt forms (barium sulfate)
What is the test for CO3- ions?
Add nitric acid
A white ppt forms in limewater (due to CO2)
What is the test for NH4+ ions?
Add NaOH and heat
If damp red litmus paper turns blue, then ammonia is present
What happens when excess ammonia is added to Cu2+ ions? What is the formula of the product?
A deep blue soln forms
[Cu(NH3)4(H2O)2]2+ (aq)
What is the equation for when NaOH is added to Cu2+ ions?
Cu2+ + 2OH- –> Cu(OH)2
What happens when NaOH is added to Fe2+ ions?
Pale green soln reacts to form a gelatinous green ppt of Fe(OH)2 which is insoluble in excess NaOH but turns brown at the surface on standing in air (iron ii is oxidized to iron iii)
What happens when NaOH is added to Fe3+ ions?
Pale yellow son reacts to form an orange-brown ppt of Fe(OH)3 which is insoluble in excess NaOH
What happens when NaOH is added to Mn2+ ions?
Pale pink soln reacts to form an orange-brown ppt of Mg(OH)2 which darkens on standing in air
It is insoluble in excess NaOH
What happens when NaOH is added to Cr3+ ions?
Violet soln reacts to form a grey-green ppt of Cr(OH)3 which is SOLUBLE in excess NaOH, forming a dark green soln
Define complex ion
The species formed when a central metal ion is bonded to one or more ligands by coordinate bonds
