CL 24- transition metals

Question 1

electron configuration of Cr

Answer 1

1s² 2s² 2p⁶ 3s² 3p⁶ 4s¹ 3d⁵

Question 2

electron configuration of Cu

Answer 2

1s² 2s² 2p⁶ 3s² 3p⁶ 4s¹ 3d¹⁰

Question 3

transition metal

definition

Answer 3

• a d-block element that has an ion with an incomplete d-sub-shell

Question 4

colours of Cu²⁺ and Mn²⁺

Answer 4

blue and pale pink

Question 5

two examples of transition-metal elements that form compounds with more than one oxidation state

Answer 5

• Fe²⁺ / Fe³⁺
• Mn²⁺ / MnO₄⁻
• Cu²⁺ / Cu⁺

Question 6

ligand

definition

Answer 6

• a species that can donate one or more lone pairs to form dative covalent bonds to a central metal ion forming a complex ion

Question 7

monodentate ligand examples

Answer 7

• only form one dative covalent bond
• H₂O
• NH₃
• OH⁻
• Cl⁻

Question 8

bidentate ligand examples

Answer 8

• forms two dative covalent bonds
• ethane-1,2-diamine

Question 9

complex ion

definition

Answer 9

• a central transition metal bonded to one or more electron donating species (ligands) by dative covalent bonds, from the ligand to the metal

Question 10

coordination number

definition

Answer 10

• the no. of dative covalent bonds between the ligands and the central metal ion

Question 11

octahedral complex ion

reasoning for shape, example of complex ion

Answer 11

• element connected to central metal ion in period 2, so there is room for 6 dative covalent bonds
• e.g. H₂O, NH₃
• [Cr (H₂O) ₆] ³⁺

Question 12

tetrahedral complex ion

reasoning for shape, example of complex ion

Answer 12

• element connected to central metal ion in period 3, larger donor atoms so there is only room for 4 dative covalent bonds
• Cl
• [Cu (Cl) ₄] ²⁻

Question 13

square planar complex ion

reasoning for shape, example of complex ion

Answer 13

• an exception to the rule, only with Pt and Ni
• 4 ligands attached
• [Pt (Cl) ₂ (NH₃)₂ ]

Question 14

linear complex ions

Answer 14

• only Ag with 2 donor atoms

Question 15

cis-trans isomerism (only) in complex ions

when does it occur

Answer 15

• in an octahedral complex, monodentate ligands - 4 of one, and 2 another
• square planar complex, monodentate ligands- 2 of each

Question 16

optical isomerism (only) in complex ions

Answer 16

• octahedral complex
• 3 bidentate ligands

Question 17

optical and cis-trans isomerism in complex ions

Answer 17

• octahedral complex
• 2 bidentate ligands and 2 monodentate ligands
• 3 different isomers- trans isomer doesn’t have optical isomerism

Question 18

cis-platin

idk if you need to know this

Answer 18

• [Pt (Cl)₂ (NH₃) ₂ ]
• attacks tumours, and in many cases it works to shrink the tumour, but it has many unpleasant side effects and can lead to kidney damage

Question 19

ligand substitution reactions for adding NH₃ to Cu²⁺ (in water)

first precipitation reaction, then ligand substitution with excess NH₃

Answer 19

• [Cu (H₂O)₆ ] ₍ₐ₎+ 2NH₃ ₍ₐ₎ –> [Cu (OH)₂ (H₂O)₄ ] ₍ₛ₎ +2NH₄⁺₍ₐ₎
• pale blue solution to pale blue precipitate (initially)
• [Cu (H₂O)₆ ] ₍ₐ₎ + 4NH₃ ₍ₐ₎ –> [Cu (NH₃)₄ (H₂O)₂ ] ²⁺₍ₐ₎ + 4H₂O₍ₗ₎
• pale blue solution to dark blue solution

Question 20

ligand substitution reactions for adding HCl to Cu²⁺ (in water)

Answer 20

• [Cu (H₂O)₆ ] + 4Cl⁻ –> [CuCl₄]²⁻ + 6H₂O
• pale blue solution to yellow solution

Question 21

ligand substitution reactions for adding with NH₃ with Cr³⁺

first precipitation reaction, then ligand substitution with excess NH₃

Answer 21

• [Cr (H₂O)₆ ] ³⁺ + 3NH₃ –> [Cr (H₂O)₃ (OH)₃ ] + 3NH₄⁺
• violet solution to grey precipitate
• [Cr (H₂O)₆ ] ³⁺ + 6NH₃ –> [Cr (NH₃) ₆ ] ³⁺ + 6H₂O
• violet solution to purple solution

Question 22

importance of iron in haemoglobin

Answer 22

• Fe has 4 dative bonds with N atoms on haem, and 1 dative bond to the protein globin
• this leaves 1 space for carrying O₂ or CO
• O₂ reversibly binds to the Fe ion; however if O₂ levels are low, water is susbtituted instead
• if CO is present, this will bind over to O₂ as it binds more strongly than oxygen, and binds irreversibly
• if conc of carboxyhaemoglobin becomes too high, O₂ transport is prevented, leading to death

Question 23

precipitation reaction with NaOH/NH₃
Cu²⁺

Answer 23

• Cu²⁺ + 2OH⁻ –> Cu (OH)₂
• blue solution to blue precipitate
• Cu also reacts with excess NH₃ (ligand substitution reaction)

Question 24

precipitation reaction with NaOH/NH₃
Fe²⁺

Answer 24

• Fe²⁺ + 2OH⁻ –> Fe (OH) ₂
• pale green solution to green precipitate

Question 25

precipitation reaction with NaOH/NH₃ Fe³⁺

Answer 25

* Fe³⁺ + 3OH⁻ --> Fe (OH)₃ * yellow solution to orange precipitate

Question 26

precipitation reaction with NaOH/NH₃ Mn²⁺

Answer 26

* Mn²⁺ + 2OH⁻ --> Mn (OH) ₂ * pale pink solution to pale brown solution

Question 27

precipitation reaction with NaOH/NH₃ Cr³⁺

Answer 27

* Cr³⁺ + 3OH⁻ --> Cr (OH)₃ * violet solution to grey precipitate * Cr reacts with excess NH₃ in a ligan substitution reaction

Question 28

oxidation of Fe²⁺/Fe³⁺ and reduction of MnO₄⁻/Mn²⁺ form overall equation and state colour changes

Answer 28

* 5Fe²⁺ + MnO₄⁻ + 8H⁺ --> Mn²⁺ + 5Fe³⁺ + 4H₂O * purple solution to colourless solution (Mn)

Question 29

oxidation of I⁻/I₂ and reduction of Fe³⁺/Fe²⁺ form overall equation and state colour changes

Answer 29

* 2Fe³⁺ + 2I⁻ --> 2Fe²⁺ + I₂ * orange solution to pale green solution (Fe) and I₂ is brown

Question 30

oxidation of Cr³⁺/CrO₄²⁻ and reduction of H₂O₂/OH⁻ form overall equation under alkaline conditions

Answer 30

* 3H₂O₂ + 2Cr³⁺ + 10OH⁻ --> 2CrO₄²⁻ + 8H₂O

Question 31

oxidation of Zn/Zn²⁺ and reduction of Cr₂O₇²⁻/Cr³⁺ form overall equation and state colour changes explain what happens when excess Zn added

Answer 31

* 3Zn + Cr₂O₇²⁻ + 14H⁺ --> 3Zn²⁺ + 2Cr³⁺ + 7H₂O * orange solution to green solution (Cr) * when excess Zn is added, Cr³⁺ ions are reduced further to Cr²⁺ Zn + 2Cr³⁺ --> Zn²⁺ + 2Cr²⁺ green solution to blue solution (Cr)

Question 32

write an equation for the reaction of Cu²⁺ with I⁻ state colour changes associated with this reaction

Answer 32

* 2Cu²⁺ + 4I⁻ --> 2CuI + I₂ * pale blue solution to white precipitate (Cu) and I₂ is brown