transition elements

Question 1

What is a transition element?

Answer 1

A d-block element with at least one ion with an incomplete d-orbital. Eg, Cu has [Ar] 3d104s1 where Cu2+ has [Ar] 3d94s0.

Question 2

Which transition metals have anomalous e- structures and why

Answer 2

Copper ([Ar] 3d104s1) and chromium ([Ar] 3d54s1).
Having half-built/full-built 3d subshells is lower in energy than a full-built 4s subshell.

Question 3

Why aren’t zinc and scandium transition elements

Answer 3

Zinc can only form 2+ ion which has a complete d-subshell. ○ Zn has [Ar] 3d104s2 whereas Zn2+ has [Ar] 3d104s0.
Scandium can only form 3+ ions which has an empty d- subshell.
○ Sc has [Ar] 3d14s2 whereas Sc3+ has [Ar] 3d04s0.

Question 4

What are the characteristics of all transition elements?

Answer 4

Formation of coloured ions. Variable oxidation state.
Eg, Fe (II) and Fe (III) since their 4s and 3d energy levels are so close, they can easily lose another e-.
● Catalytic activity.
● Complex ion formation in solution.

Question 5

Why do transition elements make good catalysts?

Answer 5

They can change oxidation states by gaining/losing e-’s ⇒ can transfer e-’s to speed up reactions.

Question 6

How are (aq) complex ions written

Answer 6

● When they contain ligands that aren’t water or hydroxide ions, you need to include all water ligands.
● Eg, [Cu(NH3)4(H2O)2]2+ cannot be rewritten whereas [Cu(OH)2(H2O)4]2+ can be written as Cu(OH)2.

Question 7

What is a complex ion?

Answer 7

A central metal ion surrounded by ligands.

Question 8

What is a ligand?

Answer 8

An atom, ion, or molecule that can forms a coordinate bond to a central metal ion.

Question 9

What is coordination number

Answer 9

The number of coordinate bonds formed to a central metal ions.

Question 10

What is a monodentate ligand?

Answer 10

● Ligands that form 1 dative/coordinate bond. ● Examples include: H2O, NH3 and Cl-

Question 11

What is a bidentate ligand?

Answer 11

● Ligands that form 2 dative/coordinate bonds.
● Examples include: C2O42- (ethanedioate), ethene-1,2-diamine
/ en.

Question 12

What is a multidentate ligand? (with an example)

Answer 12

● Ligands that form several coordinate bonds.
● Examples include: EDTA4- (forming 6 coordinate bonds).

Question 13

What complex ions show cis- trans isomerism?

Answer 13

Square planar and octahedral complex ions with at least two pairs of different ligands

Question 14

Why is cisplatin used as an anticancer drug? What are its drawbacks?

Answer 14

● Prevents replication of of cancer cells by binding to the DNA. ● Can prevent replication of healthy cells (∴ suppresses immune
system).

Question 15

Describe the reaction of copper (II) with hydroxide which colours

Answer 15

● [Cu(H2O)6]2+ (aq) + 2HO- (aq) → [Cu(H2O)4(OH)2] (s) + 2H2O (l) ○ The complex loses its 2+ charge since HO- has joined
to it.
○ Goes from pale blue to blue ppt (since no charge)

Question 16

Describe the reaction of copper (II) with ammonia and excess ammonia (with colours)

Answer 16

● [Cu(H2O)6]2+ (aq) + 2NH3 (aq) → [Cu(H2O)4(OH)2] (s) + 2NH4+ (aq)
○ The ammonia acts as a base accepting a H+.
○ Goes from pale blue to blue ppt.
● In excess NH3, [Cu(H2O)2(NH3)4]2+ (aq) is formed which is dark
blue.

Question 17

Which ligands are similar in size and which are different?
What does this mean?

Answer 17

The ligands H2O, NH3 and CN- are SIMILAR in size so coordinate number doesn’t change under substitution.
The ligands H2O and Cl- are DIFFERENT (Cl- is larger) in size so coordination number and shape changes under substitution.

Question 18

Describe how copper (II) react with chlorine ions (with colours

Answer 18

[Cu(H2O)6]2+ (aq) + 4Cl- (aq) ⇌ [CuCl4]2- (aq) + 6H2O (l) ○ Goes from blue to yellow.
○ Reversible reaction so greenish colour

Question 19

Describe how iron (II) react with hydroxide ions and ammonia (with colours)

Answer 19

[Fe(H2O)6]2+ (aq) + 2HO- (aq) → [Fe(OH)2(H2O)4] (s) + 2H2O (l) [Fe(H2O)6]2+ (aq) + 2NH3 (aq) → [Fe(OH)2(H2O)4] (s) + 2NH4+ (aq)
From pale green solution to green ppt.

Question 20

Describe how iron (III) react with hydroxide ions and ammonia (with colours)

Answer 20

[Fe(H2O)6]3+ (aq) + 3HO- (aq) → [Fe(OH)3(H2O)3] (s) + 3H2O (l) [Fe(H2O)6]3+ (aq) + 3NH3 (aq) → [Fe(OH)3(H2O)3] (s) + 3NH4+ (aq)
From pale yellow solution to orange brown ppt.

Question 21

Describe how manganese (II) react with hydroxide ions and ammonia (with colours)

Answer 21

[Mn(H2O)6]2+ (aq) + 2HO- (aq) → [Mn(OH)2(H2O)4] (s) + 2H2O (l) [Mn(H2O)6]2+ (aq) + 2NH3 (aq) → [Mn(OH)2(H2O)4] (s) + 2NH4+ (aq)
● From pale pink solution to pink ppt.

Question 22

Describe how chromium (III) reacts with hydroxide ions and excess hydroxide ions with colours

Answer 22

WITHOUT EXCESS:
● [Cr(H2O)6]3+ (aq) + 3HO- (aq) → [Cr(OH)3(H2O)3] (s) + 3H2O (l)
● From violet solution to grey-green ppt.
WITH EXCESS:
● [Cr(H2O)6]3+ (aq) + 6HO- (aq) → [Cr(OH)6]3- (aq) + 6H2O (l)
● From violet solution to dark green solution.

Question 23

What is ‘haem?’

Answer 23

An Fe (II) complex with a multidentate ligand.

Question 24

What does haemoglobin do and how

Answer 24

Enables O2 to be transported in the blood as O2 bonds to the Fe2+ ions in haemoglobin (and is released when required).

Question 25

How does CO affect haemoglobin?

Answer 25

It forms a coordinate bond with haemoglobin stronger than O2 (more stable) preventing O2 from attaching.

Question 26

Describe how iron (II) is oxidised (with colours)

Answer 26

● Fe2+ → Fe3+ using acidified manganate (VII) which is H+/MnO4- .
● The reaction goes from purple (MnO4-) to colourless (Mn2+). ● Yet, Fe2+ (aq) is green and Fe3+ (aq) is brown.
Oxygen in the air can bring this change also.
The equation below is not required according to the specification, relevant information will be provided to work it out.

● Overall Equation:
○ MnO4- (aq)+ 8H+ (aq) + 5Fe2+ (aq) → Mn2+ (aq) + 4H2O
(l) + 5Fe3+ (aq) ● Formed From:
○ MnO4- (aq) + 8H+ (aq) + 5e- → Mn2+ (aq) + 4H2O (l)
○ Fe2+ → Fe3+ + e-
Oxygen in the air can bring this change also.

Question 27

Describe how iron (III) is reduced (with colours)

Answer 27

● Fe3+ (aq) is brown and Fe2+ (aq) is green.
The equation below is not required according to the specification, relevant information will be provided to work it out.
● Fe3+ → Fe2+ using I- (from KI)
● Equation: 2Fe3+ (aq) + 2I- (aq) → I2 (aq) + 2Fe2+ (aq)

Question 28

Describe how Cr3+ is oxidised to Cr2O72- (with colours

Answer 28

Step One:
● Cr3+ in [Cr(OH)6]3- is oxidised to CrO42- by warming with H2O2 in alkaline conditions.
● This goes from dark green to yellow.
Step Two:
● Add dilute sulfuric acid to the chromate (VI) solution to produce dichromate (VI) Cr2O72-.
● This goes from yellow to orange.
The equation below is not required according to the specification, relevant information will be provided to work it out.
● Step 1 full equation:
○ 3H2O2 + 2Cr(OH)63- → 2HO- + 2CrO42- + 8H2O
● Step 1 half equations:
○ H2O2 + 2e- → 2HO-
○ 2Cr(OH)63- + 4HO- → 2CrO42- + 8H2O + 6e-. ● Step 2 full equation:
○ 2CrO42- + 2H+ → Cr2O72- + H2O

Question 29

Describe how Cr2O72- is reduced to Cr3+ (with colours)

Answer 29

● Cr2O72- is reduced to Cr3+ by acidified zinc. ● This goes from orange to green.

The equation below is not required according to the specification, relevant information will be provided to work it out.
● Full equation:
○ Cr2O72- + 14H+ + 3Zn → 2Cr3+ + 7H2O + 3Zn2+
● Half equations:
○ Zn → Zn2+ + 2e-
○ Cr2O72- + 14H+ + 6e- → 2Cr3+ + 7H2O

Question 30

Describe how Cu2+ is reduced to Cu+ (with colours)

Answer 30

● Cu2+ is reduced to copper (I) iodide by iodide ions, I-. ● From pale blue to off-white ppt.
The equation below is not required according to the specification, relevant information will be provided to work it out.
● Full equation:
○ 2Cu2+ (aq) + 4I- (aq) → 2CuI (s) + I2 (aq)

Question 31

Describe the disproportionation of Cu+ (equation and why it happens

Answer 31

2Cu+ (aq) → Cu (aq) + Cu2+ (aq)
This spontaneous disproportion happens since Cu+ is unstable