Chapter 24 - Transition Elements

Question 1

D-block elements with different electron config.

Answer 1

• chromium - 1s2 2s2 2p6 3s2 3p6 3d10 4s1
• copper - 1s2 2s2 2p6 3s2 3p6 3d10 4s1

Question 2

elements that are not transition metals in d-block

Answer 2

Sc³⁺ - has config. 1s2 2s2 2p6 3s2 3p6
Zn²⁺ - has config. 1s2 2s2 2p6 3s2 3p6 3d10

Question 3

colour of titanium ions

Answer 3

2+ - colourless
3+ - purple
4+ - colourless
5+ - colourless

Question 4

colour of vanadium ions

Answer 4

2+ - purple
3+ - green
4+ - blue
5+ - yellow

Question 5

colour of chromium ions

Answer 5

2+ - blue
3+ - violet – green with sulfate
4+ - colourless
5+ - colourless
6+ - orange

Question 6

colour of manganese ions

Answer 6

2+ - pale pink
3+ - colourless
4+ - brown
5+ - colourless
6+ - green
7+ - purple

Question 7

Colour of iron ions

Answer 7

2+ - pale green
3+ - pale yellow
4+ - colourless
5+ - colourless
6+ - colourless

Question 8

colour of nickel ions

Answer 8

2+ - green
3+ - colourless
4+ - colourless

Question 8

colour of cobalt ions

Answer 8

2+ - pink
3+ - green
4+ - colourless
5+ - colourless

Question 9

colour of copper ions

Answer 9

1+ - colourless
2+ - blue
3+ - colourless

Question 10

what is a complex ion

Answer 10

has central metal ion with one or more molecules/charged ions (ligands) bound to it by dative covalent bonds

Question 11

what is a ligand

Answer 11

a molecule/ion that donates a pair of electrons to a central metal atom by dative bonding - requires lone pair

Question 12

what is a coordination number

Answer 12

number of coordinate/dative covalent bonds to central metal atomm

Question 13

shapes of complex ions

Answer 13

• tetrahedral - 4 bonds
• square planar - usually with 8d electrons (platinum) - 4 bonds
• octahedral - 6 bonds

Question 14

monodentate ligand

Answer 14

a ligand that donates 1 pair of electrons

Question 15

bidentate ligands

Answer 15

a ligand that donates 2 pairs of electrons

Question 16

which compounds show cis/trans isomerism

Answer 16

• square planar (2 grps)
• octahedral ( 4 of 1 ligand and 2 of another)

Question 17

which compounds show optical isomerism

Answer 17

• octahedral with 2 bidentate and 2 monodentate ligands
  (only cis isomer)
• octahedral with 3 bidentate ligands

Question 18

dropwise adding NaOH/NH₃ to Cu²⁺

Answer 18

blue precipitate - Cu(OH)₂

Question 19

excess NH₃ with Cu²⁺

Answer 19

Dissolves to form dark blue solution [Cu(NH₃)₄(H₂O)₂]²⁺

Question 20

excess NaOH with with Cu²⁺

Answer 20

insoluble

Question 21

[Cu(H₂O)₆]²⁺ with Cl^-

Answer 21

• octahedral blue to tetrahedral yellow
• chloride ligands are bigger

Question 22

dropwise adding NaOH/NH₃ to Fe²⁺

Answer 22

• green precipitate - Fe(OH)₂
• turns orange - brown on standing Fe(OH)₃

Question 23

excess NH₃ to Fe²⁺

Answer 23

insoluble - stays same

Question 24

excess NaOH to Fe²⁺

Answer 24

insoluble

Question 25

dropwise adding NaOH/NH₃ to Fe³⁺

Answer 25

orange-brown precipitate

Question 26

excess NH₃ to Fe³⁺

Answer 26

insoluble

Question 27

excess NaOH to Fe³⁺

Answer 27

insoluble

Question 28

dropwise adding NaOH/NH₃ to Mn²⁺

Answer 28

light brown precipitate - darkens in air
Mn(OH)₂

Question 29

excess NH₃ to Mn²⁺

Answer 29

insoluble

Question 30

excess NaOH to Mn²⁺

Answer 30

insoluble

Question 31

dropwise adding NaOH/NH₃ to Cr³⁺

Answer 31

grey green precipitate forms
Cr(OH)₃

Question 32

excess NH₃ to Cr³⁺

Answer 32

dissolves to form purple solution
[Cr(NH₃)₆]³⁺

Question 33

excess NaOH to Cr³⁺

Answer 33

dissolves to form dark green solution
[Cr(OH)₆]^3-

Question 34

why does Cr³⁺ appear green sometimes

Answer 34

e.g. alcohols
due to sulfate group - acidified potassium dichromate
[Cr(H₂O)₅SO₄]⁺

Question 35

haemoglobin

Answer 35

• Fe²⁺ ion in centre - bonds to multidentate ligand and oxygen
• throughout blood stream undergoes substitution with oxygen
• CO forms stronger bonds

Question 36

Oxidation of Iron

Answer 36

Fe²⁺ to Fe³⁺
by reducing MnO₄^- to Mn²⁺
- goes purple to colourless

Question 37

reduction of iron

Answer 37

• reacts with iodide ions
• Fe³⁺ to Fe²⁺
• iodide to iodine
• orange brown to pale green but can’t see due to brown colour of iodine

Question 38

Oxidation of Cr³⁺ to CrO₄^2-

Answer 38

• use hot alkaline hydrogen peroxide
• check eq.

Question 39

reduction of Cr₂O₇^2- to Cr³⁺

Answer 39

• react with zinc, changes from orange to green
• with excess zinc can go from Cr³⁺ (green) to Cr²⁺ (pale blue)

Question 40

reduction of Cu²⁺ to Cu⁺

Answer 40

• reacts with iodide ions which are oxidised to iodine
• goes from Cu²⁺ - pale blue to Cu⁺ - white precipitate
• brown iodine also forms

Question 41

disproportionation of Cu⁺

Answer 41

• copper (I) oxide reacts with hot dilute sulfuric acid to form a brown precipitate of copper
• also forms blue solution of copper (II) sulfate