Different types of reaction (Iron And Copper)

Question 1

Amphoteric behaviour refers to

Answer 1

the ability of a species to react with both acids and bases

Question 2

the four main types of reaction that can occur and produce a visible colour change are:

Answer 2

→redox: the oxidation number of the transition metal ion changes
→acid-base: one or more of the ligands gains of loses a hydrogen ion (H+)
→ligand exchange: one or more of the ligands on the transition metal ion is replaced by a different ligand
→coordination number change: the number of ligands changes

Question 3

a ligand exchange reaction is when:

Answer 3

one or more of the ligands on the transition metal ion is replaced by a different ligand

Question 4

an acid-base reaction is when:

Answer 4

one or more of the ligands gains of loses a hydrogen ion (H+)

Question 5

an aqueous solution of Fe2+ is …………….. in colour

Answer 5

pale green

Question 6

when Fe2+(aq) is exposed to air, it gradually turns …………… because

Answer 6

turns from pale green to yellow or brown
the oxidation number of Fe increases from 2+ to 3+
the number or type of ligand does not change, so the change is:
[Fe(H2O)6]2+ → [Fe(H2O)6]3+

Question 7

the equation, colour change and type of reaction for the reaction between aqueous NaOH and copper(II) sulfate is:

Answer 7

[Cu(H2O)6]2+ +2OH- → [Cu(H2O)4(OH)2] + 2H2O

pale blue solution → blue precipitate

acid-base reaction: two OH- ions have removed H+ ions from two H2O molecules and converted to H2O molecules themselves while the two H2O ligands are now OH- ligands.

this reaction is amphoteric because of its reversible nature. when an acid is added, the H+ ions from the acid re-convert the OH- ligands into H2O molecules, so the blue precipitate is converted back into a pale blue solution

Question 8

the equation, colour change and type of reaction for the reaction between copper(II) sulfate and aqueous ammonia is:

Answer 8

[Cu(H2O)6]2+ + 2NH3 → [Cu(H2O)4(OH)2] + 2NH4+
pale blue solution → blue precipitate
acid-base reaction

when more NH3 is added:
[Cu(H2O)4(OH)2] + 3NH3 → [Cu(NH3)4(H2O)2]2+ + 2H2O + 2OH-
blue precipitate → deep blue solution
ligand exchange: four NH3 molecules replace two H2O molecules and two OH- ions

Question 9

the equation, colour change and type of reaction for the reaction between copper(II) sulfate and concentrated hydrochloric acid is:

Answer 9

[Cu(H2O)6]2+ +4Cl- ⇌ [CuCl4]2- + 6H2O
when the acid is added slowly and continuously, the colour change is :
pale blue → green → yellow
green is the mixture of the two complex ions due to equilibrium
ligand exchange and change in coordination number: all six H2O ligands have been substituted by four Cl- ion. the coordination number has changed from 6 to 4, but note that there is no change in Fe2+’s oxidation number, though the overall charge on the ion has changed.