Complex ions & redox

What is a complex ion?

ion formed by a central metal ion surrounded by ligands forming coordinate bonds

What is a ligand?

an atom or ion or molecule that can form a coordinate bond with a metal ion

What is a coordinate bond?

a bond formed when both electrons shared come from the same species

What are the 3 types of shapes formed in a complex ion?

Octahedral, tetrahedral, rare square planar

What is this?

Octahedral complex ion

What is this?

Tetrahedral complex ion

What is this?

Square planar complex ion

When does a octahedral complex ion become a tetarhedral ion?

When there’s more than 2 Cl- ligands as its too big for the octahedral

What are monodentates?

complex ions with 1 lone pair

Give examples of common monodentates:

H2O, CN-1, NH3, Cl-1, OH-1, ScN-1

What are bidentates?

complex ions with 2 lone pairs

Give common examples of bidentates:

What are the interconversion equations between Fe3+ and Fe2+?

• oxidation of Fe2+ → Fe3+ by Mn(VII) ions in acid solution

• reduction of Fe3+ → Fe2+ by Iodide ions in solution

What are the interconversion equations between Cr3+ and Cr2O72-?

• oxidation of Cr3+ to dichromate (VI) Cr2O72- using hydrogen peroxide

  • reduction of Cr2O72- to Cr3+ by acidified zinc

Give the reduction, oxoidation equations for oxidation of Cr3+ to dichromate Cr2O72- using hydrogen peroxide:

Reduction:

H2O2 +2e- → 2OH-

Oxidation:

2Cr(OH)6 3- + 4OH- → 2CrO4 2- + 8H2O + 6e-

Overall equation:

3H2O2 + 2Cr(OH)6 3- +4OH- → 6OH- + 2CrO4 2-+ 8H2O

Add acid:

CrO4 2- + 2H+ →Cr2O7 2- + H2O

What is the colour change when Cu2+ → Cu1+?

pale blue → colourless