Metalaqua Ion Colours + Reactions

Question 1

Cu2+ solution - colour

Answer 1

🔵 Blue - [Cu(H2O)6] 2+ 🔵

Question 2

Fe2+ solution - colour

Answer 2

🟢Green 🟢

[Fe(H2O)6 ]2+

Question 3

Fe3+ solution colour

Answer 3

🟡Yellow 🟡

[Fe(H2O)6 ]3+

Question 4

Cr3+ solution colour (chromium)

Answer 4

🟪Violet 🟪

[Cr(H2O)6 ]3+

(But often appears green due to impurities in the solution )

Question 5

Co 2+ solution colour (cobalt )

Answer 5

🌸Pink 🌸

[Co(H2O)6 ] 2+

Question 6

Addition of NH3 or NaOH to Metal-Aqua ion solution - reaction type

(NOT EXCESS)

Answer 6

• acid base reaction
• :NH3 or :OH- acts as a base, and accepts a proton from one of the water ligands ( technically acting as a nucleophile)

Question 7

Addition of NaOH / NH3 to a copper solution : colour change

Answer 7

blue precipitate forms from blue solution

🔵Cu(H2O)4(OH)2🔵 (s)

Question 8

Addition of NaOH / NH3 to Fe2+ solution : colour change

Answer 8

-green precipitate forms ( which is oxidised upon exposure to air turning brown)

Fe(H2O)4(OH)2 (s)

Question 9

Addition of NaOH or NH3 to an Fe3+ solution

Answer 9

-brown precipitate forms from yellow solution

Fe(H2O)3(OH)3

Question 10

Addition of NaOH or NH3 to Cr3+ solution : colour change

Answer 10

• green precipitate forms (from violet solution)

Cr(H2O)3(OH)3 (s)

Question 11

Addition of NaOH or NH3 to Co2+ solution : colour change

Answer 11

• blue precipitate forms (from pink solution)

Cr(H2O)4(OH)2 (s)

Question 12

Only transition metal solution to react with excess NaOH? - and reaction type

Answer 12

• Cr3+ solution
• As the Cr(OH)3(H2O)3 chromium hydroxide is amphoteric
• acid base

Question 13

Addition of excess NaOH to Cr3+ solution : observation

Answer 13

• green precipitate redissolves to give green solution

[Cr(OH)6 ] 3- (aq)

Formed by further acid base reaction

Question 14

Addition of excess NH3 to metal aqua ions solutions - which ones react and what is the reaction type

Answer 14

• Cu2+ , Cr3+ , Co2+
  -Ligand substitution reaction

Question 15

Addition of excess NH3 to Cu2+ solution

Answer 15

-DARK blue solution forms after blue precipitate redissolves

[Cu(NH3)4(H2O)2 ]2+

(2 Water ligands and 2 OH ligands replaced)

Question 16

Addition of excess NH3 to Cr3+ solution

Answer 16

Purple solution forms (after green precipitate redissolves)

[ Cr(NH3)6 ]3+

(Given [Cr(H2O)6]3+ is violet it makes sense for [Cr(NH3)6]3+ to be a similar colour)

Question 17

Addition of excess NH3 to Co2+ solution

Answer 17

Yellow solution forms (after blue precipitate dissolves)

[Co(NH3)6 ]2+

Question 18

Addition of chloride ions to a Cu2+ solution

Answer 18

-Solution turns yellow
-complex change shape (ligand substitution with significantly larger ligands) than H2O

[CuCl4]2-

Question 19

Addition of chloride ions to Co2+ solution

Answer 19

• solution turns blue (from pink)
  -cobalt tetrachloride
  [CoCl4]2-

Question 20

Give the equation of the chromate- dichromate equilibrium and state the colour change

Answer 20

2 (CrO4)2- + 2H+ —> (Cr2O7)2- + H2O

(CrO4)2- is yellow - chromate (IV)

(Cr2O7)2- is orange - dichromate (VI)

Question 21

Colour of V2+

Answer 21

Violet

Question 22

Colour of V3+

Answer 22

Green

Question 23

Colour of VO 2+ - where oxidation state or vanadium is +4

Answer 23

Blue

Question 24

Colour of VO2 + , where the oxidation sate of vanadium is +5

Answer 24

Yellow

Question 25

Why does substituting monodentate with bi- or multi-dentate ligands increase entropy?

Answer 25

-chelate effect
-A solution with more particles in it is created when you replace the mono-dentate ligands, leading to an increase in entropy e.g

[Cr(H2O)6]3+ + EDTA4- —> [Cr(EDTA]- + 6H2O

Question 26

Colour of MnO4- (where oxidation state of manganese is +7)

Answer 26

Dark purple

Question 27

Colour of Mn2+

Answer 27

-pale pink (appears colourless when there’s a low concentration of Mn2+)

Question 28

When KMnO4 (potassium permanganate) is used as a reducing agent, what is manganese in MnO4- reduced to?

Answer 28

-Mn2+

Question 29

Give the ionic equation for the reduction of MnO4- to Mn2+

Answer 29

MnO4- + 8H+ + 5e- —-> Mn2+ + 4H2O

Question 30

Give the ionic equation for the reduction of Cr2O72- to Cr3+

Answer 30

Cr2O7 2- +14H+ + 6e- —-> 2Cr3+ + 7H2O

Question 31

What type of isomerism is exhibited in octahedral complexes ?

Answer 31

-When there’s 6 individual ligands there can be cos/trans isomerism

-If you have a multidentate (EDTA4- ) or bidentate (ethylenediamine or ethanedioate) you can can optical isomerism

Question 32

Describe the cistrans isomerism seen in square planar and octahedral complexes

Answer 32

• When the two groups are next to each other (cisters) you have the cis isomer

-when the two groups are opposite each other(transverse to one another) you have the trans isomer