chapter 24 Flashcards
special case of Chromium and Copper
- do not follow expected principal
- stability
- half filled d5 sub shell and a fully filled d10 subshell give additional stability
transition elements
d-block elements that can form an ion with a partially filled d-orbital.
Sc and Zn are d-block elements but not transition metals
common oxidation states- Ti
+2, +3 (violet), +4, +5
common oxidation states V
+2 (violet), +3 (green), +4 blue, +5 (yellow)
common oxidation states Cr
+2 (blue), +3 (green), +4, +5, +6 (red/orange)
common oxidation states Mn
+2 (pink), +3, +4 (dark pink), +5, +6 (green), +7 (violet)
common oxidation states Fe
+2 (cream), +3 (pale yellow), +4, +5, +6
common oxidation states Co
+2 (bright pink), +3 (green), +4, +5
common oxidation states Ni
+2 (green), +3, +4
Common oxidation states Cu
+1, +2 (blue), +3
Chromium
2 oxidation states in its compounds, +3 & +6
3+- green
6+- orange
transition metals as catalysts examples
- iron in the Haber process
- vanadium (V) oxide in the contact process
- Ni in hydrogenation
- manganese (IV) oxide in decomposition of hydrogen peroxide
ligand
a molecule or ion that donates a pair of electrons to a central metal ion to form a coordinate bond (dative covalent)
monodentate ligand
a ligand that is able to donate one pair of electrons to a central metal ion eg water, ammonia, chloride, cyanide & hydroxide
bidentate ligand
a ligand that can donate two lone pairs of electrons to the central metal ion, forming 2 coordinate bonds eg 1,2-diaminoethane or ethanedioate ion (oxalate)
square planar complexes
occur in complex ions of transition metals w/ 8 d-electrons in the highest energy d-subshell- Platinum (II), palladium (II) and gold (III)
cis-trans isomerism
eg square planar- in cis- isomer the 2 identical groups are adjacent to each other- 90 degrees apart, trans- isomer 2 identical groups are opposite each other- 180 degrees apart
optical isomerism in octahedral complexes
only occurs in complexes containing 2 or more bidentate ligands
optical isomers are non-superimposable mirror images of each other
trans isomers cannot form optical isomers
ligand substitution reaction
one in which one ligand in a complex ion is replaced by another ligand
aq copper (II) ions with ammonia, colours and stages
pale blue complex ion [Cu(H2O)6}2+– changes to dark blue [Cu(NH3)4(H20)2]2+, 4NH3 ligands are substituted
2 diff reactions:
1) pale blue precipitate of Cu(OH)2 formed
2) Cu(OH)2 precipitate dissolves in excess ammonia to from a dark blue solution
aq copper (II) ions w/ cl- ions
HCl used pale blue--> yellow change in shape and coordination number [Cu(H20)6]2+(aq) + 4Cl-(aq) ---> [CuCl4]2-(aq) + 6H20 octahedral--> tetrahedral
aq Chromium (III) ions w/ ammonia
[Cr(H2O)6]3+ + 6NH3 –> [Cr(NH3)6]3+ + 6H2O
violet–> purple
1) initially grey-green precipitate Cr(OH)3 formed
2) Cr(OH)3 dissolves in excess ammonia to form [Cr(NH3)6]3+
precipitation reaction
occurs when 2 aq solutions containing ions react together to form an insoluble ionic solid- precipitate
precipitation reaction w/ NaOH- Cu2+
blue solution–> blue precipitate
insoluble in excess NaOH
Cu2+ + 2OH- –> Cu(OH)2(s)
precipitation reaction w/ NaOH- Fe2+
pale green sol--> dark green precipitate turns brown in air as Fe2+ is oxidised to Fe3+ Fe2+ + 2OH- --> Fe(OH)2 in air; Fe(OH)2 --> Fe(OH)3
precipitation reaction w/ NaOH- Fe3+
pale yellow sol–> orange-brown
Fe3+ + 3OH- –> Fe(OH)3
precipitation reaction w/ NaOH- Mn2+
pale pink sol–> light brown precipitate
Mn2+ +2OH- –> Mn(OH)2
precipitation reaction w/ NaOH- Cr3+
violet sol–> green precipitate
Cr3+ + 3OH- –> Cr(OH)3 green precipitate
soluble in excess NaOH to form dark green sol
Cr(OH)3 + 3OH- –> [Cr(OH)6]3-(aq) dark green sol
precipitation w/ ammonia- Cu
Cu2+ + 2OH- –> Cu(OH)2 blue precipitate which dissolves in excess ammonia to form a deep blue solution [Cu(NH3)4(H2O)2]2+
precipitation w/ ammonia- Cr
Cr3+ + 3OH- –> Cr(OH)3 green precipitate dissolves in excess ammonia to form [Cr(NH3)6]3+ purple solution
precipitation w/ ammonia- Fe2+, Fe3+ & Mn2+
react w/ excess ammonia in the same way they react w/ aq sodium hydroxide, precipitates of Fe(OH)2, Fe(OH)3 and Mn(OH)2
no further reaction w/ aq ammonia, precipitates do not dissolve
reduction of Cr2O7 2- to Chromium (III) Cr3+
orange–> green
acidified Cr2O7 2- can be reduced to 3+ by the addition of zinc
Cr2O7 2-(aq) + 14H+(aq) + 3Zn(s)–> 2Cr3+(aq) + 7H2O + 3Zn2+(aq)
excess of Zn Cr3+ can be reduced further to Cr2+
Zn(s) + 2Cr3+(aq) –> Zn2+(aq) + 2Cr2+(aq)
green–> pale blue
Cr2O7 has more positive E value so is more likely to gain electrons, then Cr3+, then Zn
oxidation of Cr3+ to CrO42-
hydrogen peroxide is a powerful oxidising agent
3H2O2 + 2Cr3+ + 10OH- –> 2CrO4 2- + 8H2O
Cr- +3-> +6 oxidised
O- -1-> -2 reduced
Reduction of Cu2+ to Cu+
react w/ excess iodide ions - I- is oxidised to brown I2 - Cu2+ is reduced to Cu+ \+ Cu+ forms a white precipitate of copper (I) iodide 2Cu+ + 4I- --> 2CuI + I2
