Complexes/trans Metals

Question 1

Colour of Fe2+(aq)

Answer 1

Pale green solution

Question 2

Colour of Cu2+(aq)

Answer 2

Pale blue solution

Question 3

Colour of Fe3+(aq)

Answer 3

Yellow solution

Question 4

Colour of Mn2+(aq)

Answer 4

Pale pink solution

Often appears colourless due to low concentration

Question 5

Colour of Cr3+(aq)

Answer 5

Pale purple solution

Question 6

Adding NaOH dropwise to aqueous metal complex ions what is observed

Answer 6

A precipitate is formed as OH- ions de-protonate the metal complex and make it neutral.

Question 7

Excess NaOH is added to different solutions of aqueous metal ions, which metal will form a precipitate that redissolves.

Answer 7

Chromium (Cr3+)

will form a charged complex with 6 OH- ligands.

Question 8

Dropwise ammonia is added to a solution of aqueous metal ions, what is observed

Answer 8

Precipitates are formed,

colour depends on which metal ion

Question 9

Excess ammonia is added to different solutions of aqueous metal ions, which metals will form a precipitate that redissolves

Answer 9

Cu2+ and Cr3+ will redissolve into solution

Chromium substitutes 6 ammonia ligands

Copper substitutes 4 ammonia ligands

Question 10

Colour change when HCl(aq) is added to aqueous copper2+ ions

Answer 10

Pale blue solution -> yellow solution

Question 11

Colour change when DROPWISE NaOH or NH3 is added to Fe3+(aq)

Answer 11

Yellow solution -> brown PPT

Question 12

Colour change when DROPWISE NaOH or NH3 is added to Mn2+(aq)

Answer 12

Pale pink solution -> brown PPT

Question 13

Colour change when excess NH3 or NaOH is added to Cr3+(aq)

Answer 13

Excess NH3 causes pale purple solution -> (deeper) purple solution

Excess NaOH causes
Pale purple solution -> green solution

Question 14

Reagent and observation to reduce Fe3+

Answer 14

Potassium iodide (I-)
Yellow solution -> brown solution

Question 15

Reagent and observation to oxidise Fe2+

Answer 15

Acidified Manganate (MnO4-/H+)
Purple solution -> colourless solution

Question 16

Reagent and observation to oxidise Cr3+

Answer 16

Alkali Hydrogen peroxide (H2O2/OH-)
Green solution -> yellow solution

Forms chromate

Question 17

Reagent and observation to reduce Cr6+ (dichromate)

Answer 17

Acidified zinc
Orange solution ->pale purple solution

Question 18

How to switch between dichromate and chromate

Answer 18

Acid- to favour dichromate

Alkali to favour chromate

Question 19

Colour of Mn2+ precipitate when dropwise NaOH or NH3 is added

Answer 19

Brown

Question 20

Colour of Fe2+ precipitate when dropwise NaOH or NH3 is added

Answer 20

Green ppt

Question 21

Reagent and observation to reduce copper2+

Answer 21

Potassium iodide (I-) produces a white precipitate

Question 22

Describe how haemoglobin works

Answer 22

A central Fe2+ ion has 4 coordinate bonds Haem and one bond to a protein globin. The remaining bond is filled by an O2 ligand which is weak and can be substituted by CO2 or H2O

Question 23

Describe the use of cis platin complex

Answer 23

Cis platin [Pt(NH3)2Cl2] is used to treat cancer, both Cl atoms can bond to DNA and stop cell growth as they are on the same side.