transition elements Flashcards
Fe2+ -> Fe3+
use MnO4 2-
purple to colourless
Fe3+ -> Fe2+
use I-
orange to green
Cr3+ -> Cr2O7 2-
use hot alkaline H2O2
green to orange
Cr2O7 2- -> Cr3+
use Zn
orange to green
Cr3+ -> Cr2+
use Zn
green to blue
Cu2+ -> Cu+
use I-
pale blue solution to brown solution with white precipitate
Cu+ -> Cu2+
use acid
white precipitate to brown precipitate in pale blue solution
Cu2+ with dropwise NaOH
blue solution to blue precipitate
Cu2+ (aq) + 2OH- (aq) -> Cu(OH)2 (s)
Cu2+ with excess NH3
dark blue solution
[Cu(H2O)6] 2+ + 4NH3 -> [Cu(H2O)2(NH3)4] 2+ + 4 H2O
Fe2+ with dropwise NaOH
pale green solution to green precipitate
Fe2+ (aq) + 2OH- (aq) -> Fe(OH)2 (s)
Fe3+ with dropwise NaOH
yellow solution to rust-brown precipitate
Fe3+ (aq) + 3OH- (aq) -> Fe(OH)3 (s)
Mn2+ with dropwise NaOH
pink solution to pale-brown precipitate
Mn2+ (aq) + 2OH- (aq) -> Mn(OH)2 (s)
Cr3+ with dropwise NaOH
violet solution to grey-green precipitate
Cr3+ (aq) + 3OH- (aq) -> Cr(OH)3 (s)
Cr3+ with excess NH3
purple solution
[Cr(H2O)6] 3+ + 6NH3 -> [Cr(NH3)6] 3+ + 6H2O
Cu2+ with excess HCl
blue solution to yellow solution
[Cu(H2O)6] 2+ + 4Cl- -> [CuCl4] 2- + 6H2O
what is a transition element?
a d-block element that forms an ion with an incomplete d sub-shell
which d-block elements aren’t transition elements?
Zn forms Zn2+ which has a complete d sub-shell
Sc forms Sc3+ which has an empty d sub-shell
ligand
a compound/ion that donates a pair of electrons to a central transition metal ion to form a coordinate bond
types of ligand
monodentate = donates one pair of electrons
bidentate = donates two pairs of electrons
multidentate = donates multiple pairs of electrons
common monodentate ligands
H2O
NH3
Cl-
OH-
SCN-
CN-
common bidentate ligands
[(COO)2] 2-
NH2CH2CH2NH2
square planar
coordination number of 4
bond angle 90
eg cis-platin [PtCl2(NH3)2]
what are optical isomers?
stereoisomers that are a pair of non-superimposable mirror images of each other
stereoisomerism
stereoisomers are compounds that have the same structural formula but different arrangement of atoms in space
cis isomer = groups next to each other
trans isomer = groups opposite each other
what is ligand substitution?
a reaction in which one ligand in a complex ion is replaced by another
haemoglobin and ligand substitution
at the centre of each haem complex is an Fe2+ ion
the Fe2+ ion binds reversibly with oxygen (O2) by accepting a lone pair from the O2 molecule to form a coordinate bond
CO binds irreversibly with haemoglobin so oxygen can’t be transported
properties of transition elements
variable oxidation states
formation of coloured ions
effective catalysts
what is cis-platin used for?
binds to the DNA in fast-growing cancer cells
this alters the DNA structure in the cancerous cells, preventing cell division
what is a racemic mixture?
a mixture containing equal amounts of the two optical isomers
this has no effect on plane polarised light, as the rotations cancel each other out
how do we distinguish between optical isomers?
using a polarimeter
optical isomers rotate plane-polarised light differently
