Complex ions and their Colours

Question 1

What is at the centre of a comlex ion?

Answer 1

A transition metal ion.

Question 2

What is the definition of a complex ion?

Answer 2

A central transition metal ion surrounded by ligands

Question 3

What is a ligand?

Answer 3

A molecule or ion which donates a pair of electrons to the central metal ion to form a coordinate bond

Question 4

What is a coordinate bond?

Answer 4

A shared pair of electrons between 2 atoms where both electrons come from the same atom.

Question 5

What is coordination number?

Answer 5

The total number of bonds formed between the ligand and the central metal ion

Question 6

Give an example of 3 monodentate ions?

Answer 6

H20, NH3, Cl-

Question 7

Give an example of two bidentate loigands.

Answer 7

Ethanedioate, C2O4-
The lone bonds are made via the single bonded oxygen’s lone pairs

Ethane-1,2-diamine (ethylenediamine/en)
The Nh2 groups lone pairs make the bonds

Question 8

Give an example of a multidentate ligand.

Answer 8

EDTA, EDTA4-
It can form 6 coordinate bonds

Ethane-1,2-diamine
It can form 6 coordinate bonds (6 NH2)

Question 9

What is the shape and bond angle of a complex ion with 6 ligands?

Answer 9

Octahedral, 90 degrees

Question 10

What ic cisplatin?

Answer 10

Pt(NH3)2Cl2

Question 11

What is the shape and bond angle of cis platin?

Answer 11

Square planar, bond angle 90 degrees

Question 12

What type of isomerism do complex ions show?

Answer 12

Cis-trans and optical isomerism

Question 13

How do you identify cis and trans isomers of complex ions?

Answer 13

Cis - like ligands are 90 degrees apart
Trans - like ligands are 180 degrees apart

Question 14

What is an optical isomer?

Answer 14

Isomers that are non superimposable images of eachother

Question 15

What are the 3 ways complex ions can show optical isomerism?

Answer 15

3 bidentate ligands
2 bidentate ligands and 2 monodentate ligands in cis orientation
1 hexadentate ligand, [Cu(EDTA)]2+

Question 16

What is the use of cisplatin in medicine?

Answer 16

Used as an anti cancer drug. Binds to DNA in cancer cells, preventing cell division. So, the cell dies
It has unwanted side effects (hair loss as it targets quick replicating cells like hair follicles) so trials continue with other platinum based drugs

Question 17

What is Cu2+ (aq) as a complex ion and its colour?

Answer 17

[Cu(H2O)6]2+ is a blue solution

Question 18

What is Copper (II) hydroxide as a complex ion and its colour?

Answer 18

Cu(OH)2 = [Cu(OH)2(H2O)4] IS A BLUE PRECIPITATE

Question 19

What formula, state and colour is the copper (II) ion in with 4 ammonia and 2 water ligands?

Answer 19

[Cu(NH3)4(H2O)2]2+ is a deep blue solution

Question 20

What state, colour is [CuCl4]2-?

Answer 20

Yellow solution

Question 21

When reacting Copper (II) with HCL why does it look green?

Answer 21

The reaction between the aqueous copper 2 ions [Cu(H2O)6] ions and the chlorine ions is reversible so both blue and yellow species are present

Question 22

What is the clour of aqueous Fe2+

Answer 22

Pale green. [Fe(H20)6]2+

Question 23

What is the colour, state and complex ion of iron II hydroxide, Fe(OH)2?

Answer 23

[Fe(OH)2(H2O)4], Green precipiate

Question 24

Why does Fe II hydroxide precipitate start to turn brown?

Answer 24

The Fe 2+ ions are being oxidised to Fe 3+ ions, forming iron III hydroxide

Question 25

What is the equation, state and colour of Fe3+ (aq)?

Answer 25

Yellow solution. [Fe(H2O)6]3+

Question 26

What state, oxidation number and formula is iron 111 hydroxide, Fe(OH)3?

Answer 26

[Fe(OH)3(H2O)3] orange-brown precipitate

Question 27

What state, oxidation number and formula is Mn2+ (aq)

Answer 27

Very pale pink
[Mn(H2O)6]2+

Question 28

What state, oxidation number and formula is manganese 2 hydroxide, Mn(OH)2?

Answer 28

[Mn(OH)2(H2O)4]
Pale brown precipitate. Darkens in air

Question 29

What state, oxidation number and formula is aqueous Chromium III, Cr3+?

Answer 29

[Cr(H2O)6]3+
Pale purple. Heat to green. Can appear green in solution due to impurities

Question 30

What state, oxidation number and formula is Chromium 3 hydroxide

Answer 30

Cr(OH)3
[Cr(OH)3(H2O)]
Dark green precipitate

Question 31

What happens when you add excess OH-, Chromium 3 hydroxide?

Answer 31

[Cr(OH)6]3-
Dark green precipitate dissolves to dark green solution

Question 32

What state, oxidation number and formula is chromium 3 with 6 ammonia ligands?

Answer 32

[Cr(NH3)6]3+ purple solution

Question 33

WHt colour is CoCl42-?

Answer 33

From CoCl2.6H2O (s) plus water and excess HCl = BLUE SOLUTION

Question 34

What colour is CrO42-?

Answer 34

Yellow. From addition of Cr3+ with hot alkaline H202