Topic 15 - Transition Metals

Question 1

What is a transition metal?

Answer 1

An element that forms one or more stable ions with incompletely filled d orbitals

Question 2

What is a ligand?

Answer 2

A species that uses a lone pair of electrons to form a dative covalent bond with a metal ion

Question 3

Why do transition metals have variable oxidation states?

Answer 3

Because they have a large number of unpaired electrons in their d orbitals allowing them to bond to many other molecules in different ways

Question 4

Why do transition metals form coloured compounds?

Answer 4

Because the d orbitals occupy different energy levels, different transition metal species absorb different wavelengths of energy to excite electrons on lower energy levels to a higher one.

Question 5

Why do some transition metals not form coloured compounds?

Answer 5

Because they have either no electrons in, or a full d sub shell, and therefore no room for electrons to be excited

Question 6

What is a coordination number?

Answer 6

The coordination number is the number of dative bonds in a complex

Question 7

What is a monodentate ligand?

Answer 7

A monodentate ligand forms only one dative bond to the central ion of a complex

Question 8

Give an example of a square planar complex ion

Answer 8

Cisplatin Cl2Pt(NH3)2

Question 9

Why is cis-platin used as a cancer treatment, but not trans-platin?

Answer 9

Because while cis-platin prevents the DNA in cancer cells from dividing, preventing mitosis, trans-platin has a different structure, and so is less effective and more toxic.

Question 10

What is the colour of V5+ (VO2^+)?

Answer 10

Yellow

Question 11

What is the colour of V4+ (VO^2+)?

Answer 11

Blue

Question 12

What is the colour of V3+?

Answer 12

Green

Question 13

What is the colour of V2+?

Answer 13

Purple

Question 14

How can the dichromate ion be reduced to Cr2+?

Answer 14

In acidic conditions:
Cr2O7 2- +14H+ + 3Zn –> 2Cr3+ + 7H2O + 3Zn2+
2Cr3+ + Zn –> 2Cr2+ + Zn2+

Question 15

How can the dichromate ion be converted into chromate ions?

Answer 15

Cr2O72−+ H2O ⇌ 2CrO42−+ 2H+

Question 16

How can chromium(III) ions be oxidised to chromate ions?

Answer 16

2Cr(OH)3 + 3H2O2 +4OH- –> 2CrO4 2- + 8H2O

Question 17

Describe the reactions that would occur when [Fe(H2O)6]2+ reacts with NaOH, and NaOH in excess

Answer 17

The initial reaction would, from the green solution, form a green precipitate of [Fe(H2O)4(OH)2], that would darken to brown on standing as it oxidises to [Fe(H2O)3(OH)3]. The excess would cause no further reaction.

Question 18

Describe the reactions that would occur when [Fe(H2O)6]2+ reacts with NH3, and NH3 in excess

Answer 18

The initial reaction would form a green precipitate from the green solution of [Fe(H2O)4(OH)2] and ammonium ions. The precipitate would darken to brown as it oxidises to [Fe(H2O)3(OH)3]. The excess would cause no further reaction.

Question 19

Describe the appearance of aqueous Fe3+ ions

Answer 19

[Fe(H2O)6]3+ appears pale violet in solution, but can appear orange due to hydrolysis to [Fe(H2O)5(OH)]2+

Question 20

Describe the reactions that would occur when [Fe(H2O)6]3+ reacts with NaOH, and NaOH in excess

Answer 20

The initial reaction would, from the violet or orange solution, form a brown precipitate of [Fe(H2O)3(OH)3], The excess would cause no further reaction.

Question 21

Describe the reactions that would occur when [Fe(H2O)6]3+ reacts with NH3, and NH3 in excess

Answer 21

The initial reaction would, from the violet or orange solution, form a brown precipitate of [Fe(H2O)3(OH)3] and ammonium ions, The excess would cause no further reaction.

Question 22

Describe the reactions that would occur when [Cu(H2O)6]2+ reacts with NaOH, and NaOH in excess

Answer 22

The initial reaction would, from the blue solution, form a blue precipitate of [Cu(H2O)4(OH)2]. The excess would cause no further reaction.

Question 23

Describe the reactions that would occur when [Cu(H2O)6]2+ reacts with NH3 and NH3 in excess

Answer 23

The initial reaction would, from the blue solution, form a blue precipitate of [Cu(H2O)4(OH)2]. The excess would cause a reaction producing a deep blue solution of [Cu(H2O)2(NH3)4]2+.

Question 24

Define amphoteric behaviour

Answer 24

The ability of a species to react with both acids and bases

Question 25

Describe the reactions that would occur when [Co(H2O)6]2+ reacts with NaOH

Answer 25

The reaction would consist of the pink solution forming a blue precipitate of [Co(H2O)4(OH)2]. If left to stand, the colour of the precipitate gradually changes to pink.

Question 26

Describe the reactions that would occur when [Co(H2O)6]2+ reacts with NH3 and NH3 in excess

Answer 26

The initial reaction would consist of the pink solution forming a blue precipitate of [Co(H2O)4(OH)2] with ammonium ions present. When excess is added, the precipitate dissolves into a brown solution of [Co(NH3)6]2+ (+ 4H2O + 2OH-)

Question 27

Describe the reactions that would occur when [Cr(H2O)6]3+ reacts with NaOH

Answer 27

The reaction would consist of a green or violet solution forming a green precipitate of [Cr(H2O)3(OH)3].

Question 28

Describe the reactions that would occur when [Cr(H2O)6]3+ reacts with NH3 and NaOH in excess

Answer 28

The reaction would consist of a green or violet solution forming a green precipitate of [Cr(H2O)3(OH)3] with ammonium ions. When the excess NaOH is added, the precipitate is reduced to form a green solution of [Cr(OH)6]3-

Question 29

Describe the reactions that would occur when [Cr(H2O)6]3+ reacts with NH3 and NH3 in excess

Answer 29

The reaction would consist of a green or violet solution forming a green precipitate of [Cr(H2O)3(OH)3] with ammonium ions. When the excess NH3 is added, the precipitate slowly dissolves to form a violet or purple solution of [Cr(NH3)6]3+ (+ 3H2O + 3OH-)

Question 30

Describe the reactions that would occur when concentrated HCl is added to [Cu(H2O)6]2+

Answer 30

A green solution of [CuCl4]2- would form from the original blue solution

Question 31

Describe the reactions that would occur when concentrated HCl is added to [Co(H2O)6]2+

Answer 31

A blue solution of [CoCl4]2- would form from the original pink solution

Question 32

Describe the appearance of aqueous Co2+ ions

Answer 32

They form a pink solution of [Co(H2O)6]2+

Question 33

Show how Vanadium(V) Oxide is used in the contact process with two equations with reference to oxidation numbers

Answer 33

V2O5 + SO2 –> V2O4 + SO3
+5 —-> +4
V2O4 + 1/2O2 –> V2O5
+4 —-> +5

Question 34

Define adsorption

Answer 34

The process that occurs when reactants form weak bonds with a solid catalyst

Question 35

Define desorption

Answer 35

The process that occurs when products leave the surface of a solid catalyst

Question 36

Describe the process carried out by catalytic converters to reduce carbon and nitrogen monoxide emissions

Answer 36

The NO and CO are adsorped onto the surface of the catalyst, where they react together to form N2 and CO2, which are less harmful to the environment.