24 Transition Elements

Question 1

Why is the 4s sub-shell usually filled before 3d?

Answer 1

It has a lower energy.

Question 2

What is a transition element?

Answer 2

d-block elements that form at least one ion with a partially filled d-orbital.

Question 3

What are the properties of transition metals?

Answer 3

Variable oxidation states.
Formation of coloured compounds.
Can be used as catalyst.

Question 4

Give examples of transition metals that act as catalysts in named reactions.

Answer 4

Haber process - Fe.
Contact process - vanadium (V) pentoxide.
Hydrogenation of fat - Ni.
(and more)

Question 5

What is a complex ion?

Answer 5

Transition metal ion bonded to ligands by coordinate bonds.

Question 6

Monodentate ligand

Answer 6

Can only donate one pair of electrons to a central metal ion.

Question 7

Bidentate ligand

Answer 7

Can donate two lone pairs, forming two coordinate bonds.

Question 8

What is the bond angle around the central metal ion in six-coordinate complexes?

Answer 8

90

Question 9

What is the bond angle around the central metal ion in tetrahedral complexes?

Answer 9

109.5

Question 10

When can a square planar complex be formed?

Answer 10

When the central metal ion has 8 d-electrons in the highest energy d sub-shell.

Question 11

Cis-isomer in a square planar complex

Answer 11

Two identical groups are adjacent (90 degrees).

Question 12

Trans-isomer in square planar complex

Answer 12

Two identical groups are opposite (coordinate bonds are 180 degrees apart).

Question 13

When does optical isomerism occur in octahedral complexes?

Answer 13

Only if complex has two or more bidentate ligands.

Trans-isomers cannot form optical isomers as mirror image is exactly the same.

Question 14

What is cis-platin used for in medicine?

Answer 14

Anti-cancer drug, attacks tumours by binding to DNA and preventing cell division.

Question 15

Ligand substitution

Answer 15

When one ligand in a complex ion is replaced by another ligand.

Question 16

Precipitation reaction

Answer 16

Two aqueous solutions containing ions react together to form an insoluble ionic solid.

Question 17

What are the colours of the precipitates formed when these ions react with NaOH?

Cu 2+
Fe 2+
Fe 3+
Mn 2+
Cr 3+

Answer 17

Cu 2+ = blue  
Fe 2+ = green
Fe 3+ = brown
Mn 2+ = light brown
Cr 3+ = grey green (precipitate soluble in excess Na OH)

Question 18

Oxidation of Fe 2+ to Fe 3+

Answer 18

Acidic conditions, MnO4- ions.

Question 19

Reduction of Fe 3+ to Fe 2+

Answer 19

Iodide ions.

Question 20

Oxidation of Cr 3+ to CrO4 2-

Answer 20

Hot alkaline H2O2.

Question 21

Reduction of Cu 2+ to Cu +

Answer 21

Excess iodide ions.

Question 22

Disproportionation of Cu 2+ ions

Answer 22

Cu2O reacts with hot, dilute sulfuric acid.

Question 23

What is disproportionation?

Answer 23

Same element is both oxidised and reduced.

Question 24

How can the presence of ammonium ions be tested for?

Answer 24

When heated with OH- ions, ammonia is produced, causes damp red indicator to turn blue.

Question 25

How can the presence of transition metal ions be tested for?

Answer 25

Transition metal ions react with aqueous NaOH to produce precipitates of different colours.