MODULE 5: Transition Elements

Question 1

What are the unique features of the transition metals?

Answer 1

They act as catalysts, they have variable oxidation states, they form colourful compounds

Question 2

What is the definition of a transition metal?

Answer 2

An element with one or more stable ions that have an incomplete d-orbital

Question 3

What happens in the formation of ions in the transition metals?

Answer 3

The 4s orbital is depleted first as it is a higher energy level

Question 4

What is the pattern of oxidation states in transition metals?

Answer 4

Increases across group up to manganese, then decreases.

Question 5

For iron and chromium, what does the colour of their compound depend on?

Answer 5

Oxidation state

Question 6

Give some examples of transition metals acting as heterogenous catalysts

Answer 6

Harber process (iron) and contact process (vanadium oxide (V))

Question 7

What is a complex ion?

Answer 7

When a central metal ion is coordinately bonded to one or more ligand

Question 8

What is a ligand?

Answer 8

A ligand is a compound with one or more active lone pairs that can form a coordinate bond

Question 9

What is a coordination number?

Answer 9

The number of coordinate bonds a complex ion has

Question 10

What are multidentate ligands?

Answer 10

A ligand with more than one active lone pair that can form 2 or more coordinate bonds.

Question 11

What is the shape of a complex ion with 6 coordinate bonds?

Answer 11

Octahedral

Question 12

What is the shape of a complex ion with 4 coordinate bonds?

Answer 12

Tetrahedral or square planar

Question 13

What is the difference between tetrahedral and square planar structures?

Answer 13

Tetrahedral have a bond angle of 109.5, whereas square planar structures have bond angles of 90 (therefore are flat)

Question 14

What complex ions are square planar?

Answer 14

Transition metals with 8 electrons in the highest energy d-sub-shell (gold, palladium and platinum)

Question 15

What forms of isomerism occur in complex ions?

Answer 15

Cis-trans and optical

Question 16

What is cis-trans isomerism in complex ions?

Answer 16

Cis = 90 degrees between ligands
Trans = 180 degrees between ligands

Question 17

What is optical isomerism in complex ions?

Answer 17

With multidentate ligands, when both molecules are cis but are non-superimposable over each other- they are mirror images of each other.

Question 18

What is ligand substitution?

Answer 18

When one ligand in a complex ion is replaced with another one

Question 19

What is the colour change when hexaaquacopper II ([Cu (OH2)6] (2+) is reacted with ammonia?

Answer 19

Pale blue solution to dark blue solution with a precipitate intermediate
[Cu(H2O)6]2+ + 4NH3 –> [Cu(NH3)4(H2O)2]2+ + 4H2O

Question 20

What is the colour change when hexaaquacopper II ([Cu (OH2)6] (2+) is reacted with chloride ions?

Answer 20

Pale blue to yellow solution with a green solution intermediate (change in shape to tetrahedral)
[Cu(H2O)6]2+ + 4Cl- –> [CuCl4]2- + 6H2O

Question 21

What is the colour change when hexaaquachromium III ([Cr (OH2)6] (3+) is reacted with ammonia?

Answer 21

Violet solution, grey-green precipitate intermediate, dissolves in excess to form purple solution
[Cr(H2O)6]3+ + 6NH3 –> [Cr(NH3)6]3+ + 6H2O

Question 22

What is the solution to precipitate colour change of Cu2+ with sodium hydroxide?

Answer 22

Blue solution to blue precipitate

Question 23

What is the solution to precipitate colour change of Fe2+ with sodium hydroxide?

Answer 23

Pale green solution to green precipitate

oxidises to Fe3+ when stood in air, so colour change to brown

Question 24

What is the solution to precipitate colour change of Fe3+ with sodium hydroxide?

Answer 24

Pale yellow solution to orange-brown precipitate

Question 25

What is the solution to precipitate colour change of Mn2+ with sodium hydroxide?

Answer 25

Pale pink solution to light brown precipitate (darkens in air)

Question 26

What is the solution to precipitate colour change of Cr3+ with sodium hydroxide?

Answer 26

Violet solution to grey-green precipitate (soluble in excess to form dark green solution)

Question 27

What is the colour of the precipitate that forms when Cr3+ reacts with ammonia?

Answer 27

Green precipitate that dissolves in excess to form a purple solution

Question 28

How do Fe2+, Fe3+ and Mn2+ react with ammonia?

Answer 28

Same as sodium hydroxide, but do not dissolve in excess.