Transition metals and reactions of aqueous ions

What to memorise

Definition of transition metal

Element that has an incomplete d -sub shell in either its atoms or one of its common ions.

What are the four properties of transition metals

• variable oxidation state

• form metal complexes

• coloured compounds

• catalytic action

What is a ligand?

Particle with lone pair of electrons that bond to metals by co-ordinate bone

What is a complex?

Metal ion with co-ordinately bonded ligands

Lewis base

lone pair donor

Lewis acid

lone pair acceptor

What is the Chellating effect?

multidentate ligands substitue mono dentate or bidentate ligands and increase entropy of products so has a very right-shifted equilibrium.

What is the ion change in tollens test?

Ag 1+ in (Ag(NH3)2)+ become Ag 0 element

What is the ion change in Fehling’s solution?

• blue Cu2+ → Cu+ in Cu2O (brick-red precipitate)

What is the ion change in Acidified potassium dichromate?

• from K2Cr2O7

• Cr2O72- reduced to Cr 3+ orange to green

What is the effect of pH and ligand?

• alkaline = easier to oxidise transition metal

• acidic = easier to reduce transition metal

some ligand have different redox potentials

What are the equations and colours for reduction of Vanadium ions (include zinc below)

5+ (VO2 +) + 2H+ + e -→ (VO 2+) + H2O yellow to blue

4+ (VO 2+) + 2H+ + e —→ V3+ + H2O blue to green

3+ V3+ + e —> V2+ green to violet

Zn —> Zn2+ + 2e

mnemonic is You Better Get Vanadium

Redox titrations with MnO4 -. What acid should you use with these ions and why not others

• not ethanoic acid as too weak

• not con sulfuric or nitric as oxidising agents themselves so affect MnO4 - required

• not HCl because MnO4 - will oxidise Cl- affecting volume required

Red is side reactions

What is MnO4- in reactions?

oxidising agent

What are the redox titration ratios and equation advice

Fe 2+ and MnO4-

→ 5:1

forms water Mn 2+ and Fe 3+, remember acidic conditions

C2O4 2- and MnO4-

—> 2.5:1

forms CO2 and Mn2+ and water remember acidic conditions

Mn2+ acts as an autocatalyst here reacting MnO4- to become Mn 3+

then Mn3+ with C2O4 2- to form Co2 and Mn 2+ again

What is your autcatalysis example?

MnO4 - + C2O4 2- → CO 2 + H2O + Mn2+

Mn2+ acts as an autocatalyst here reacting MnO4- and H+ to become Mn 3+and water

then Mn3+ with C2O4 2- to form CO2 and Mn 2+ again

What are the catalysts and their process you need to know? heterogenous

heterogeneous

= Vanadium Oxide (V2O5) in The contact process

to produce H2SO4 by making SO3

=Platinum in catalytic converters

= Fe 2+ in Haber process to produce ammonia

What are the catalysts and their process you need to know?

Homogeneous

Fe 2+ with S2O82- and I - to form I2 and SO42-

Fe2+ + S2O82- → Fe3+ + SO42-

Fe 3+ + I- → I2 + Fe2+

(not balanced here)

Autocatalysis

MnO4- + C2O42- → Mn2+ + H2O + CO2

H+ + Mn2+ + MnO4- → Mn3+ + H2O

Mn3+ + C2O42- → Mn2+ + CO2

not balanced

What is the general rule for reacting metal complex with OH-

• form precipitate (M(OH)(H2O)4) in 2+ metals

• form precipitate (M(OH)3(H2O)3 in 3+ metals

colour change of

Cu is blue sol to blue pp

Fe is green sol to green pp

Fe is lilac/orange to brown pp

Al is colourless to white pp

What is the exception for OH- reactions with metal complexes?

Al3+(H2O) reacts with excess OH- to form (Al(OH)6)3- and form colourless solution again

What is the general rule for NH3 reactions with metal complexes?

• form precipitate (M(OH)(H2O)4) in 2+ metals

• form precipitate (M(OH)3(H2O)3 in 3+ metals

Cu goes blue sol to blue pp

Fe goes green sol to green pp

Fe goes lilac/orange to brown pp

Al goes colourless to white pp

this occurs because NH3 reacts with H2O to form NH4+ and OH-

What is the exception for NH3 and metal complex ions?

• (Cu(OH)2(H2O)4) blue pp reacts with excess NH3 to form (Cu(NH3)4(H2O)2)2+ which is a deep blue sol

by ligand substitution

What is the general trend of Na2CO3 with M2+ complexes?

• form carbonates by precipitation

• both green precipitates

What is the general trend of Na2Co3 with M3+ complexes

• complex acidic enough for acid base reaction by hydrolysis

• 2(Fe(H2O)6)3+ + 3CO2- → 2(Fe(OH)3(H20)3) + 3 CO2 + 3 H2O

colour changes

Fe is lilac/orange to brown pp

Al is colourless sol to white pp

What is general trend of adding XS acid to metal ion precipitates?

reform metal original complexes

Fe(OH)2(H2O)4 + 2H+ —> (Fe(H2O)6)2+

reverse colour changes

What is general trend for aqueous metal ions with excess Cl-?

Cl substitutes to form negative square planar ion

Fe(H20)6 2+ + 4Cl- → (FeCl4)2- + 6H2O

Colour changes

Cu is blue sol to green sol

Fe is green sol to yellow sol

Fe is orange/lilac to yellow sol

Al is colourless to colourless

What is the unexpected for aqueous metal ions with Cl-?

Colour changes

Cu is blue sol to green sol

All rest form yellow sol except Al (colourless