Metal aq ions

• Metal aqua complexes?

  Formed when a transition metal is added to water.

  6 water molecules form coordinate bonds with the ion.

  A lone pair on the oxygen allows this bond to form.

  eg [Cu(H2O)6]2+(aq)
• Acidic metal aqua complexes?

  Metal aqua ions are acidic when in solution. The ion charge affects how acidic it is.

  Hydrolysis reaction.

  eg [Fe(H2O)6]2+ + H2O > [Fe(H2O)5(OH)]+ + H3O+

  H+ ions are produced to make H3O+ which makes the solution acidic.
• Why are 3+ complex ions more acidic?

  They have a higher charge density as they are smaller.

  They are more polarising and attract the O-H bond electrons in water more strongly.

  This means H+ ions are more likely to be released, so its more acidic.
• Further hydrolysis of metal aqua ions?

  We can hydrolyse further using OH- ions for make insoluble metal hydroxides.

  eg [Al(H2O)6]3+ + H2O > [Al(H2O)5(OH)]2+(aq) + H3O+

  [Al(H2O)5(OH)]2+ + H2O > [Al(H2O)4(OH)2]+(aq) + H3O+

  [Al(H2O)4(OH)2]+ + H2O > [Al(H2O)3(OH)3](s) + H3O+
• Define amphoteric?

  Can act as an acid or a base.
• Amphoteric metal aqua ions?

  We can hydrolyse metal aqua ions to form an insoluble metal hydroxides by adding a base.

  We can reverse this by adding an acid to the metal hydroxide ppt to dissolve it. It does this by accepting a H+.
• Aluminium hydroxide?

  (Al(H2O)3(OH)3] is amphoteric.

  When we add a base it donates H+ to react with the OH- ions and dissolve.

  Al(H2O)3(OH)(s) + OH- > [AL(H2O)2(OH)4]-(aq) + H2O

  When we add an acid it accepts H+ ions to form H3O+

  Al(H2O)3(OH)3(s) + 3H3O+ > [Al(H2O)6]3+(aq) + 3H2O
• Metal aqua ions and ammonia?

  By adding small amounts of NH3, it produces the same metal hydroxide when adding a base.

  eg NH3 + H2O > NH4+ + OH-

  When excess NH3 is added we get a partial ligand substitution.

  eg Cu(H2O)4(OH)2 + 4NH3 > [Cu(NH3)4(H2O)2]2+ + 2OH- + 2H2O
• Metal aqua ions and carbonates?

  2+ metal ions form insoluble metal carbonates.

  eg [Fe(H2O)6]2+(aq) + CO32- > FeCO3(S) + 6H2O

  3+ ions are more acidic so carbonate ions react with the free H3O+ ions. This remove the H3O+ in solution and moves equilibrium right.

  eg 2[Fe(H2O)6]3+(aq) + 3CO32- > 2Fe(OH)3(H2O)3(s) + 3CO2 + 3H2O
• Identifying metal ion sol with sodium hydroxide, ammonia and sodium carbonate?

  1: Add sample of unknown metal ion solution into 3 test tubes.

  2: Drop by drop add NaOH to tube 1. Add excess. Record observations.

  3: Repeat step 2 in tube 2 using NH3 instead.

  4: Add Na2CO3 into tube 3 and record observations.

  Safety= Wear goggles and gloves as chemicals cause irritants. NH3 gives off fumes so use fume cupboard.
• Fe2+, Fe3+, Cu2+, Al3+ test tube reactions?

  All react with NaOH to give ppt.

  Only Al(OH)3 ppt dissolves in excess NaOH as its amphoteric.

  All react with NH3 to give ppt.

  Only Cu(OH)2 ppt dissolves in excess NH3 as there is ligand substitution.

  All react with Na2CO3 to give ppt.

  Al3+ and Fe3+ form ppt and CO2 effervescence.

  Cu2+ and Fe2+ form ppt ONLY.

  (Fe2+ oxidises readily to form Fe3+ so solutions need to be made fresh)
• Cu2+

  In aq sol= [Cu(H2O)6]2+ Blue

  Add NaOH or NH3 to aq sol= Cu(OH)2(H2O)4(s) Pale blue ppt.

  Add excess OH- to ppt= No change.

  Add excess NH3 to ppt= [Cu(NH3)4(H2O)2]2+(aq) Dark blue sol

  Add Na2CO3= CuCO3(s) Green ppt
• Fe2+

  In aq sol= [Fe(H2O)6]2+ Pale green

  Add NH3 or Oh- to sol= [Fe(H2O)4(OH)2]2+ Green ppt.

  Add excess OH- to ppt= No change.

  Add excess NH3 to ppt= No change.

  Add Na2CO3= FeCO3(s) Green ppt
• Fe3+

  In aq sol= [Fe(H2O)6]3+ Yellow

  Add NH3 or OH- to sol= Fe(H2O)3(OH)3](s) Orange ppt.

  Add excess OH- to ppt= No change.

  Add excess NH3 to ppt= No change.

  Add Na2CO3= Fe(OH)3(H2O)3(s) Brown ppt
• Al3+

  In aq sol= [Al(H2O)6]3+ Colourless

  Add NH3 or OH- to sol= Al(OH)3(H2O)3)(s) White ppt

  Add excess OH- to ppt= [Al(OH)4(H2O)2(aq) Colourless sol

  Add excess NH3 to ppt= No change

  Add Na2CO3= Al(OH)3(H2O)3(s) White ppt
• Explain how the electron pair repulsion theory can be used to deduce the shape of, and the bond angle in, PF3?

  P has 5 outer electrons. 3 electrons from the 3 fluorine.

  There is 3 bond pairs and 1 lone pair.

  This is a trigonal pyramidal shape with 107 degree bond angle.

  Electron pair repulsion theory states electrons repel as far as possible and lone pairs repel more than bonding, so 109.5 decreased to 107.
• Suggest one reason why electron pair repulsion theory cannot be used to predict the shape of the [CoCl4] 2− ion?

  Too many electrons in d subshell
• An acidified solution of NH4VO3 reacts with zinc. Explain how observations from this reaction show that vanadium exists in at least two different oxidation states?

  2 different colours are absorbed due to Vanadiums different oxidation states.
• A co-ordinate bond is formed when a transition metal ion reacts with a ligand. Explain how this co-ordinate bond is formed?

  An electron pair on the ligand Is donated to the central metal ion
• Describe what you would observe when dilute aqueous ammonia is added dropwise, to excess, to an aqueous solution containing copper(II) ions?

  Blue precipitate Dissolves to give a dark blue solution

  [Cu(H2O)6] 2+ + 2NH3 > Cu(H2O)4(OH)2 + 2NH4+

  Cu(H2O)4(OH)2 + 4NH3 > [Cu(NH3)4(H2O)2]2+ + 2OH– + 2H2O
• When the complex ion [Cu(NH3)4(H2O)2] 2+ reacts with 1,2-diaminoethane, the ammonia molecules but not the water molecules are replaced?

  [Cu(NH3)4(H2O)2]2+ + 2H2NCH2CH2NH2 > [Cu(H2NCH2CH2NH2)2(H2O)2]2+ + 4NH3
• Why would a reactions enthalpy change be approx 0?

  Bonds formed have similar enthalpy And the same number of bonds broken and made.
• Explain why a reaction occurs despite having an enthalpy change that is approximately zero?

  Disorder increases as more particles form so free energy change is negative.
• Write an equation for the reaction between iron(II) ions and manganate(VII) ions?

  MnO4− + 8H+ + 5Fe2+ > Mn2+ + 4H2O + 5Fe3+
• The redox reaction aq MnO4- and sodium ethanedioate is autocatalysed. Write an equation for the reaction. Identify the species that acts as the catalyst. Explain how the properties of the species allow it to catalyse.

  2MnO4− + 16H+ + 5C2O4 2− > 2Mn2+ + 8H2O + 10CO2

  Mn2+ is the catalyst.

  Mn can exist in variable oxidation states. Ea lowered because oppositely charged ions attract.

  Mn3+ to Mn2+ by C2O42−.

  Mn2+ to Mn3+ by MnO4-
• Suggest why it is important that a container for dif samples has the same dimensions?

  Absorption depends on path length.
• Why is a colour filter used in a calorimeter?

  To select the colour absorbed by the sample.
• Suggest one reason why a colorimetric method might be chosen in preference to titration?

  Quicker to analyse extracted samples than by titration and uses smaller volumes of solution.
• When cisplatin is ingested, an initial reaction involves one of the chloride ligands being replaced by water. Write an equation for this reaction?

  (NH3)2PtCl2 + H2O > [(NH3)2PtCl(H2O)]+ + Cl-
• How can the risk of using cis-platin by minismised?

  Use in smaller amounts.
• Explain, with the aid of equations, how and why vanadium(V) oxide is used in the Contact Process?

  V2O5 + SO2 > V2O4 + SO3

  V2O4 + 1/2O2 > V2O5

  Acts as a catalyst and speeds up the rate of reaction.
• Explain why the reaction between I– ions and S2O82– ions is slow?

  Negative ions repel eachother.
• Why are Fe2+ ions good catalysts?

  Positive ions attract negative ions in catalysed processes.
• Why might electron transition cause a solution containing the transition metal ion to be coloured?

  Light is absorbed and The remaining colour is transmitted.
• State 3 different features of transition metal complexes that cause a change in the value of ΔE?

  Identity of metal

  Charge on the metal

  Identity of ligands

  Co-ordination number
• Write an equation for the reaction between iron(II) sulfate and sodium ethanedioate?

  FeSO4 + Na2C2O4 > FeC2O4 + Na2SO4
• Explain how the precipitate in the desiccator becomes dry?

  Water in the gaseous state from the precipitate absorbed by drying agent
• Explain how you could use results to determine the initial rate of this reaction?

  Plot a graph of ‘volume of gas against ‘time’.

  Determine the slope gradient at the beginning
• State the general property of transition metals that allows the vanadium in vanadium(V) oxide to act as a catalyst in the Contact Process?

  Variable oxidation states.
• Give the meaning of the term heterogeneous?

  In a different state from reactants