Module 5: Section 3

Question 1

Give the definition of a transition element.

Answer 1

A transition element is a d-block element that can form at least one stable ion with an incomplete d sub-shell.

Question 2

When transition elements form positive ions, which electrons are removed first?

Answer 2

The s electrons are removed first, then the d electrons.

Question 3

Why aren’t scandium and zinc transition elements?

Answer 3

Scandium and zinc cant’t form stable ions with incomplete d sub-shells.

Question 4

Why do transition elements and their compounds make good catalysts?

Answer 4

They can change oxidation states by gaining or losing electrons within their d orbitals. They can transfer electrons to speed up reactions.

Question 5

In aqueous solutions, what form do transition elements take?

Answer 5

[M(H2O)6] ^n+

Question 6

Give the equation for the reaction of Cu(II) in aqueous solution, with OH- and also with NH3.
Give the colour change.

Answer 6

[Cu(H2O)6]^2+ + 2OH- —> [Cu(OH)2(H2O)4] + 2H2O
[Cu(H2O)6]^2+ 2NH3 —> [Cu(OH)2(H2O)4] + 2NH4+
Excess NH3 = [Cu(OH)2(H2O)4] —> [Cu(NH3)4(H2O)2]

Goes from a pale blue solution to a dark blue ppt.

Question 7

Give the equation for the reaction of Iron (II) in aqueous solution, with OH- and also with NH3.
Give the colour change.

Answer 7

[Fe(H2O)6]^2+ + 2OH- —> [Fe(H2O)4(OH)2] + 2H2O
[Fe(H2O)6]^2+ + 2NH3 —> [Fe(OH)2(H2O)4] + 2NH4+

Goes from a pale green solution to a dark green ppt.

Question 8

Give the equation for the reaction of Iron (III) in aqueous solution, with OH- and also with NH3.
Give the colour change.

Answer 8

[Fe(H2O)6]^3+ + 3OH- —> [Fe(H2O)3(OH)3] + 3H2O
[Fe(H2O)6]^3+ + 3NH3 —> [Fe(OH)3(H2O)3] + 3NH4+

Goes from yellow solution to a orange ppt.

Question 9

Give the equation for the reaction of Manganese (II) in aqueous solution, with OH- and also with NH3.
Give the colour change.

Answer 9

[Mg(H2O)6]^2+ + 2OH- —> [Mg(OH)2(H2O)4] + 2H2O
[Mg(H2O)6]^2+ + 2NH3 —> [Mg(OH)2(H2O)4] + 2NH4+

Goes from a plae pink solution to a pink ppt.

Question 10

Give the equation for the reaction of Chromium (III) in aqueous solution, with OH- and also with NH3.
Give the colour change.

Answer 10

[Cr(H2O)6]^3+ + 3OH- —> [Cr(H2O)3(OH)3] + 3H2O
[Cr(H2O)6]^3+ + 3NH3 —> [Cr(H2O)3(OH)3] + 3NH4+

Goes from a green solution to a grey-green ppt.

Excess NaOH: [Cr(H2O)3(OH)3] –> Cr(OH)6 ^3-
Dark green in colour
Excess NH3: [Cr(H2O)3(OH)3] —> [Cr(NH3)6] ^3+
Purple colour

Question 11

What is a complex ion?

Answer 11

A complex ion is a metal ion surrounded by coordinately bonded ligands.

Question 12

What is a coordinate bond?

Answer 12

Covalent bond in which both electrons in the shared pair come from the same atom. (dative covalent bond)

Question 13

What is a ligand?

Answer 13

A ligand is an atom, ion or molecule that donates a pair of electrons to a central metal atom or ion.

Question 14

What is the coordinate number?

Answer 14

The number of coordinate bonds that are formed with the central metal atom/ion.

Question 15

What shape occurs with 6 coordinate bonds?

Answer 15

Octahedral shape.

Question 16

What shape occurs with 4 coordinate bonds?

Answer 16

Tetrahedral shape OR square planar shape.

Question 17

Why must ligands have at least one lone pair of electrons?

Answer 17

It must have a lone pair of electrons, to form a coordinate bond with.

Question 18

What is a ligand with one lone pair available for bonding called?

Answer 18

Monodentate.

Question 19

What is a ligand with two lone pairs available for bonding called?

Answer 19

Bidentate.

Question 20

What is a ligand that forms 2 or more coordinate bonds called?

Answer 20

Multidentate

Question 21

What type of isomerism can complex ions show and why?

Answer 21

Optical isomerism. It happens when an ion can exist in 2 non-superimposable mirror images.
Happens in the octahedral complexes when 3 bidentate ligands are attached to the central ion.

Question 22

Describe the structure of cis-platin.

How is cis-platin used to treat cancer?

Answer 22

Cis-platin is a complex of platinum (II) with 2 chloride ions and 2 ammonia molecules in a square planar shape.
The 2 chloride ligands are very easy to displace. So it loses them and bonds to 2 nitorgen atoms on the DNA molecule inside the cancerous cell instead. This block on its DNA prevents the cancerous cell from reproducign by division.

Question 23

Describe the structure of haemoglobin.

Answer 23

Haemoglobin contains Fe2+ ions with 6 coordinate bonds.
4 of the lone pairs come from nitrogen atoms called ‘haem’.
The fifth lone pair comes from a nitrogen atom on a protein (globin)
The last position holds either a water ligand or a oxygen ligand. They get substituted around the body.

Question 24

How does carboxyhaemoglobin form?

Why is this bad?

Answer 24

Carbon monoxide is inhaled and the haemoglobin swaps its water ligand for a carbon monoxide ligand, forming carboxyhaemoglobin.
Carbon monoxide has a strong ligand and doesn’t readily exchange with water or oxygen ligands, meaning the haemoglobin can’t transport oxygen anymore. Can lead to oxygen deprivation and death.