Module 5- Ligand Substitution

Question 1

What colour is aqueous copper ions??

Answer 1

Pale blue

Question 2

Ligand substitution with ammonia and aqueous copper ions:

Colour and formula of intermediate and final molecule, and equation

Answer 2

Intermediate of Cu(OH)2 is solid blue

Final molecule of [Cu(H2O)2(NH3)4] 2+

Equation
[Cu(H2O)6]2+ + 4NH3 -> [Cu(H2O)2(NH3)4]2+ +4H2O

Question 3

Ligand substitution with aqueous copper ions and chloride ions:
Reaction, intermediate and final molecule colour and formula

Answer 3

Cu(H2O)6 2+ + 4Cl- -> CuCl4 4- + 6H2O

Intermediate is green Colour, which is a mixture of the blue aqueous copper ions and the yellow CuCl4- complex ion
Also this changed the shape from octahedral to quadrilateral

Question 4

What colour is aqueous chromium alum (potassium chromium (III) sulphate) And aqueous potassium sulphate, as well as their respective complex ion formula

Answer 4

Chrome alum = pale purple
[Cr(H2O)6]3+

Chromium (III) sulphate = green
[Cr(H2O)5SO4]2+

Chromium ions are both in oxidation state of 3

Question 5

Ligand substitution with aqueous chromium alum and ammonia

Colours and equations, including intermediate precipitate

Answer 5

Equation=
[Cr(H2O)6]3+ + 6NH3 -> [Cr(NH3)6]3+ + 6H2O

Goes from violet to dark purple
Intermediate precipitate of Cr(OH)3 forms which is a green-grey in colour
Both shapes are octahedral

Question 6

Precipitation reactions: what colour are copper, iron 2+, iron 3+ and manganese ions in aqueous solution

Answer 6

Copper 2+= pale blue
Iron 2+= pale green
Iron 3+ = rust orange/ yellow
Manganese 2+ = pale pink

Question 7

Cu2+ reaction with sodium hydroxide

Answer 7

Blue solution reacts to form dark blue precipitate of Cu(OH)2 that doesn’t dissolve in excess NaOH

Question 8

Fe2+ and sodium hydroxide reaction and observations

Answer 8

Pale green solution reacts to form green precipitate of Fe(OH)2 which is insoluble in excess NaOH, but turns brown at its surface on standing from Being oxidise to fe3+

Question 9

Fe3+ And NaOH reaction and observations

Answer 9

Pale yellow solution reacts to form orange brown rust colour precipitate of Fe(OH)3 that is insoluble in excess NaOH

Question 10

Mn2+ And NaOH reaction and observations

Answer 10

Pale pink solution reacts to form light brown precipitate of Mn(OH)2 which isn’t soluble in excess NaOH
- precipitate darkens on standing in air

Question 11

Cr3+ And NaOH reaction and observation

Answer 11

Violet solution forms grey green precipitate of Cr(OH)3 which does dissolve in excess NaOH to form a green solution of [Cr(H2O)6]3+
THIS IS THE SAME AS LIGAND EXCHANGE