5.3.1 Transition elements

Question 1

Definition of a transition element?

Answer 1

A d-block element that forms at least one ion with a partially filled d-subshell.

Question 2

Properties of a transition element. (7)

Answer 2

Contains metallic bonding: high melting and boiling points.

Hard

Shiny

High density

Forms coloured compounds

Has different oxidation stages when in a compound.

Their elements and compounds can act as catalysts.

Question 3

Why is scandium not a transition element?

Answer 3

Sc only forms one ion: Sc3+

This ion has no electrons in the d- subshell.

Question 4

Why is Zinc not a transition element?

Answer 4

Only forms one ion: Zn2+

Since the 4S sub-shell empties before the 3d sub-shell, the 3d sub-shell is filled.

Fully filled d-sub shell, therefore cannot be a transition element.

Question 5

What is the electronic configuration of Chromium and why is it like this?

Answer 5

[Ar] 4s^1 3d^5

The 3d sub-shell prefers having a half occupied/ fully occupied sub- shell due to spin pair repulsion/ stability.

Question 6

What is the electronic configuration of Copper and why is it like this?

Answer 6

[Ar] 4s^1 3d^10

The 3d sub-shell prefers having a fully occupied sub- shell due to stability so an electron is removed from the 4s sub-shell.

Question 7

What is a complex ion?

Answer 7

Central metal ion surrounded by ligands.

Question 8

What is a ligand?

Answer 8

Molecule/ ion that donates a pair of electrons to metal ion to form a dative covalent bond/ co-ordinate bond.

Question 9

What are the coloured compounds of Fe2+ and Fe3+

Answer 9

Fe2+: pale green

Fe3+: yellow

Question 10

What are the coloured compounds of Cr3+ and Cr6+

Answer 10

Cr3+: green

Cr6+: yellow/ orange

Question 11

Give four examples of how transition metals act as heterogeneous catalysts.

Answer 11

Haber process: Solid iron catalyst used

Contact process, SO2 + O2: Solid V2O2 used

Hydrogenation: solid Nickel catalyst used.

Decomposition of hydrogen peroxide: Manganese (IV) oxide solid is used (MnO2)

Question 12

Give an example of how a transition metal acts as a homogeneous catalyst.

Answer 12

Reaction between iodide ions and peroxodisulfate ions:

Fe3+ (aq) catalyst used.

Question 13

What is a monodentate ligand?

Answer 13

A ligand that donates ONE pair of electrons to a central metal ion.

Question 14

What is the shape of a complex ion with a co-ordinate number of six?

Answer 14

Octahedral: 90 degree bond angle.

Question 15

Shape of a complex ion with co-ordinate number:
2
4
5

Answer 15

2: linear- 180 degrees
4: tetrahedral (109.5 degree)/ square-planar- 90 degrees
5: trigonal bipyramidal- 90 and 120 degrees

Question 16

What type of isomerism can occur in complex ions?

Answer 16

Stereoisomerism:

Optical
Cis-Trans

Question 17

Cis-Trans isomerism in complex ions.

Answer 17

Can occur in complex ions with:

4/6 co-ordinate bonds that are monodentate, with 2 different monodentate

6 co-ordinate bonds with monodentate and/or bidentate ligands

Cis- Same ligands are adjacent (90 degrees)
Trans- Same ligands are opposite (180 degree)

Question 18

Optical isomerism in complex ions.

Answer 18

Occurs in complex ions with:

6 co-ordinate bonds that contains two or more bidentate ligands.

Trans isomers are not optical isomers as they form symmetrical molecules.

Question 19

How can you differentiate between two complex ion, optical isomers?

Answer 19

Pass the molecules through plane polarised light.

Each isomer will rotate the light in a different direction.

Question 20

Describe Platin and how it is used in medicine.

Answer 20

Platin: Pt(NH3)Cl2

Cis-Platin is used in chemotherapy to shrink and stop cancerous growth.

Cis-Platin attaches to DNA and prevents DNA replication which prevents cell division.
This leads to cell mechanism uniting apoptosis.

However: negative side effects include kidney damage

Question 21

Describe how haemoglobin uses a complex ion?

Answer 21

Contains haem group:
Fe2+ and porphyrin ring with 4 nitrogens

This forms an octahedral structure with two bonds free.

One bond can attach to a polypeptide in a protein.

Another bond can attach to a molecule of oxygen.

Carbon monoxide can displace oxygen as it form a strong bond with Fe2+

Question 22

Describe the reaction between Copper (II) and OH-

Answer 22

Precipitation reaction:

Copper solution is original light blue

A light blue Copper Hydroxide precipitate forms. This is not soluble in excess OH-

This ppt is soluble in excess ammonia to form a deep blue solution: Cu(NH3)4 (H2O)2

Question 23

Colour of Cu2+ solution

Answer 23

Light blue

Question 24

Colour of Cu(OH)2 precipitate

Answer 24

Light blue

Question 25

Colour of Cu(NH3)4(H2O)2

Answer 25

Deep blue

Question 26

Describe the reaction of Mn2+ with hydroxide ions

Answer 26

Mn2+ is originally a pale pink solution It forms a light brown precipitate: Mn(OH)2 Pale pink---> light brown Precipitate is not soluble in excess OH-

Question 27

Describe the reaction between Fe2+ and hydroxide ions

Answer 27

Fe2+ is originally a green solution It forms a green precipitate: Fe(OH)2 Green ----> green ppt Precipitate is not soluble in excess OH- Precipitate can be oxidised to an orange brown ppt---> Fe(OH)3

Question 28

Reaction between Fe3+ and hydroxide ions

Answer 28

Fe3+ is originally a yellow solution An orange/ brown precipitate forms Yellow ---> orange/brown The precipitate is not soluble in excess OH-

Question 29

Reaction between Cr3+ and hydroxide ions

Answer 29

Cr3+ is originally a violet solution It forms a grey-green ppt: Cr(OH)3 It is soluble in excess NH3: forms purple solution Also soluble in excess OH-: forms dark green solution

Question 30

Describe the qualitative analysis when oxidising Fe2+

Answer 30

Fe2+ is reacted with MnO4-, an oxidising agent. MnO4- is added in a burette and is initially purple. A colour change from colourless to light pink the the conical flask confirms the end point.

Question 31

Describe the qualitative analysis when reducing Fe3+

Answer 31

Iodide ions are used as a reducing agent. Fe3+ is originally orange/brown. The solution turns brown as Iodide ions are oxidised to Iodine. Fe3+ is reduced to Fe2+ (which is pale green).

Question 32

Describe the qualitative analysis when reducing Cr2O7 2-

Answer 32

Zinc is used as a reducing agent, with HCl or H2SO4. Dichromate is originally orange but then is reduced to a green colour- Cr3+ This is further reduced to Cr2+ which forms a pale blue solution. This only occurs when there is an excess of zinc.

Question 33

Describe the qualitative analysis when oxidising Cr3+

Answer 33

Cr3+ is reacted with hot, alkaline Hydrogen peroxide. Cr3+ is oxidised with hydroxide ions and H2O2. This shows a colour change from green to orange (CrO4 2-).

Question 34

Describe the qualitative analysis when reducing Cu2+.

Answer 34

Cu2+ reacts with excess iodide ions. Iodide ions are oxidised to iodine, which forms a brown solution. Cu2+ is originally pale blue but a white precipitate forms when CuI(s) is formed.