24. Transition Elements
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Define a transition metal
a d-block element that forms at least one stable ion with a partially filled d-orbital
What are the 3 main properties of transition metals?
form compounds in which the transition element has different oxidation states form coloured compounds elements and their compounds can act as catalysts
Why are transition metals good catalysts?
adsorb other substances onto the surface, as a partially filled d orbital can be used to form bonds to adsorb reactants
Write an equation for the Haber process. What is the catalyst?
N2(g) + 3H2(g) => 2NH3(g) Fe
Write equations for the reaction catalysed by Fe2+
(S2O8)2- + Fe2+ => 2(SO4)2- + Fe3+ 2Fe3+ + 2I- => I2 + 2Fe2+ thiosulphate ions + iodide ions
Write an equation for the reaction catalysed by nickel. What type of reaction is it and what are the other conditions?
C2H4 + H2 => C2H6 + Ni + 150 C hydrogenation produces margarine
Write an equation for the reaction catalysed by Cu2+
Zn + H2SO4 => ZnSO4 + H2
Write an equation for the Contact Process. What is the catalyst? What does it manufacture?
2SO2(g) + O2(g) => 2SO3(g) V2O5 catalyst manufactures sulphuric acid
Define a ligand
a molecule or ion that donates a pair of e- to a central metal ion to form a co-ordinate/dative bond (AKA a nucleophile)
Define co-ordination number
number of co-ordinate bonds attached to a central metal ion
What are the 2 important bidentate ligands?
1,2-diaminoethane (H2NCH2CH2NH2) ethandioate (C2O4)2-
How does a complex ion form in water from a transition metal compound?
water molecules are attracted to the positive metal ion and surround it transition metals have small size and high charge density therefore they strongly attract ligands like water and NH3
Why is there a change in co-ordination number when water ligands are substituted for chloride ions?
chloride ions are too large to fit 6 around a relatively small transition metal ion therefore only 4 bond
Name the 4 shapes of complexes, and give an example.
octahedral: most complexes: [Cu(H2O)6]2+ tetrahedral: [CuCl4]2- square planar: Pt(NH3)2Cl2 (cis-platin) linear: [Ag(NH3)2]+
How do ethandioate ions and 1,2-diaminoethane ions work in complexes?
have an octahedral shape: 3 bidentate ligands each forming 2 co-ordinate bonds: co-ord number = 6
What is the colour change (i.e. colour of precipitate) when NaOH (or NH3) is added to Cu2+ (aq)?
blue => blue ppt
What is the colour change (i.e. colour of precipitate) when NaOH (or NH3) is added to Fe2+ (aq)?
pale green => dark green ppt oxidises to orange-brown in the air
What is the colour change (i.e. colour of precipitate) when NaOH (or NH3) is added to Fe3+ (aq)?
pale yellow => orange-brown ppt
What is the colour change (i.e. colour of precipitate) when NaOH (or NH3) is added to Mn2+ (aq)?
pale pink => light brown ppt
What is the colour change (i.e. colour of precipitate) when NaOH (or NH3) is added to Cr3+ (aq)?
violet => grey-green
What is the colour change when EXCESS NaOH is added to Cr3+ (aq)? What is the formula of the solution formed?
green ppt dissolves to a dark green solution [Cr(OH)6]3- (aq)
What is the colour change when EXCESS NH3 is added to Cu2+ (aq)? What is the formula of the solution?
(pale) blue => deep blue [Cu(NH3)4(H2O)2]2+ (aq)
What is the colour change when EXCESS NH3 is added to Cr3+ (aq)? What is the formula of the solution?
violet => purple [Cr(NH3)6]3+ (aq)
What colour is a solution of Cr3+ if SO4 2- ions are also present?
green