AC20: Transition Metals

Question 1

Define a transition metal

Answer 1

Transition metals are d-block elements that can form at least one stable ion with a partially complete d-subshell

Question 2

What two d-block elements are not Transition metals

Answer 2

Scandium and Zinc

Question 3

Why is Scandium not a transition metal

Answer 3

can only form Sc 3+ ion which has an empty d-subshell

Question 4

Why is Zinc not a transition metal

Answer 4

can only form Zn 2+ ion which has a fully filled d-subshell

Question 5

What colour are scandium and zinc compound and how is this significant

Answer 5

they are white, compared with other d-block compounds that are often coloured

Question 6

What are the 2 transition metal atoms that do not follow the electron configuration for all other transition metal atoms and how can you remember them

Answer 6

Chromium (Cr) and copper (Cu)
Crafty and Cunning

Question 7

How does Chromium not follow the rules for electron configuration of T.M. atoms

Answer 7

chromium - 4s1 3d5
it has a half-filled 3d-subshell rather than a full 4s subshell as this is more stable than 4s2 3d4

Question 8

How does Copper not follow the rules for electron configuration of T.M. atoms

Answer 8

copper - 4s1 3d10
it has a fully-filled 3d-subshell rather than a full 4s subshell as hit is more stable than 4s2 3d9

Question 9

What is different in the electron configuration of T.M. ions compared to other ions

Answer 9

remove electrons from 4s subshell before 3d subshell

Question 10

State the properties of all metals

Answer 10

shiny when freshly cut
relatively high densities
high melting/boiling points - due to giant metallic lattice structure
good conductors of heat and electricity - due to mobile electrons

Question 11

State 3 properties that only transition metals have (that other metals may not)

Answer 11

1- can form coloured compounds
2- some T.M.s and T.M. compounds can act as catalysts
3- ability to form variable oxidation states

Question 12

Explain how T.M.s can form coloured compounds and give an example with Fe

Answer 12

Due to partially filled d-subshells, these can be different for a particular T.M. depending on its O.N.
e.g. Fe 2+ (aqueous) = pale green
Fe 3+ (aqueous) = yellow

Question 13

Explain how some T.M.s and T.M. compounds can act as catalysts and give an example with nickel/platinum acting as a catalyst in the hydrogenation of alkenes

Answer 13

Variable O.N.s allow T.M.s to act as catalysts as they can : -donate/accept electrons to/from reactants
-allow reactants to adsorb to its surface and weaken the reactants’ bonds in the process
e.g. alkaline adsorption between nickel and C=C pi-electron which weakens the pi-bond
H2 adsorbs to nickel and weakens bond

Question 14

List all the variable oxidation states for T.M.s

Answer 14

Sc, +3
Ti, +2, +3,+4
V, +2,+3,+4,+5
Cr, +2,+3,+4,+5,+6
Mn, +2,+3,+4,+5,+6,+7
Fe, +2,+3,+4,+5,+6
Co, +2,+3,+4,+5
Ni, +2,+3,+4
Cu, +1,+2,+3
Zn, +2

Question 15

How can oxidation numbers of >+3 in transition metals exist and give an example for Mn, and for Cr

Answer 15

cannot exist in monatomic ions but can exist in polyatomic ions where the metal is bonded to oxygen
e.g. MnO4 -, Cr2O7 2-

Question 16

Explain what a complex ion is

Answer 16

A complex ion consists of a central metal ion datively bonded to a number of ligands, which donate electron pairs to form dative covalent (coordinate) bond(s)

Question 17

Explain what a ligand is

Answer 17

A ligand is a species with at least one lone pair of electrons that donates to a central metal ion, forming coordinate bond(s)

Question 18

What property of transition metal ions allow them to form coordinate bonds with ligands

Answer 18

high charge density and therefore strong electrostatic attraction

Question 19

How do you work out the coordination number of a complex ion

Answer 19

number of coordinate bonds = coordination number

Question 20

What are the bond angles in an octahedral complex ion

Answer 20

90 and 180

Question 21

What is a monodentate/unidentate ligand and give an example

Answer 21

a ligand that can form only ONE coordinate bond with 1 electron pair to a central metal ion
e.g. H2O, Cl-, NH3

Question 22

What are bidentate ligands and give the 2 common examples for OCR

Answer 22

ligands that can form 2 coordinate bonds with 2 electron pairs to a central metal ion.
e.g. 1,2-diaminoethane (“en”)
ethandioate ion

Question 23

What are multidentate ligands and give an example found in our bodies

Answer 23

ligands that can form more than 2 coordinate bonds with more than 2 electron pairs to a central metal ion
e.g. haemoglobin - tetradentate (4)

Question 24

When does ligand substitution occur

Answer 24

1- a ligand capable of forming stronger coordinate bonds is added
2- a high concentration of a ligand is added to displace another, since ligand substitution is a reversible process, it will follow Le Châtelier’s principle

Question 25

Give the equation for the reaction between aqueous copper (2) and concentrated HCl, giving the colours for each reaction stage

Answer 25

[Cu(H2O)₆]²⁺(aq) + 4Cl⁻ (aq) <-> [CuCl₄]²⁻ (aq) + 6H₂O (l) where [Cu(H2O)₆]²⁺(aq) is blue [CuCl₄]²⁻ (aq) is yellow and at equilibrium is green

Question 26

Give the equation for the reaction between aqueous copper (2) and excess aqueous ammonia, giving the colours for each reaction stage

Answer 26

[Cu(H2O)₆]²⁺(aq) + 4NH₃(aq) <-> [Cu(H2O)₂(NH₃)₄]²⁺ (aq) + 4H₂O (l) where [Cu(H2O)₆]²⁺(aq) is blue [Cu(H2O)₂(NH₃)₄]²⁺ (aq) is deep blue

Question 27

Give the equation for the reaction between aqueous chromium (3) and excess aqueous ammonia, giving the colours for each reaction stage

Answer 27

[Cr(H2O)₆]³⁺(aq) + 6NH₃(aq) <-> [Cr(NH₃)₆]³⁺ (aq) + 6H₂O (l) where [Cr(H2O)₆]³⁺(aq) is violet [Cr(NH₃)₆]³⁺ (aq) is purple

Question 28

what property of CO makes CO so dangerous to humans and what are you given if you have CO poisoning

Answer 28

The binding affinity of CO is around 200x greater than O2 and so CO can reduce the ability of Hb to bind with O2 significantly. Patients with CO poisoning are given high [O2] to breathe to shift the equilibrium and dispalce CO via ligand substitution

Question 29

What are the 2 types of stereoisomerism that complex ions carry out

Answer 29

1- cis-trans 2- optical

Question 30

What shapes of complex ions does cis-trans isomerism only occur in

Answer 30

octahedral and square planar complex ions, not in tetrahedral

Question 31

What is the key difference in function of cis-platin and trans-platin

Answer 31

cis-platin is a cancer treatment which binds to DNA to prevent cel division trans-platin does not prevent cell division

Question 32

In octahedral complex ions, what is the difference in bond angles for cis and trans isomers, use [Co(Cl)₂(NH₃)₄]⁺ as an example

Answer 32

in cis-isomer of [Co(Cl)₂(NH₃)₄]⁺, Cl- ligands are at 90º apart in trans isomer of [Co(Cl)₂(NH₃)₄]⁺, Cl- ligands are at 180º apart

Question 33

In octahedral complex ions, what is the difference in bond angles for cis and trans isomers, use [Cr(Cl)₃(NH₃)₃]⁰ as an example

Answer 33

in cis-isomer of [Cr(Cl)₃(NH₃)₃]⁰, Cl- ligands are all at 90º apart in trans isomer of [Cr(Cl)₃(NH₃)₃]⁰, at least one pair of Cl- are at 180º apart

Question 34

What shapes of complex ions does optical isomerism only occur in

Answer 34

octahedral complex ions with 2 or more bidentate ligands

Question 35

What is the colour of Cu²⁺(aq) ( or [Cu(H2O)₆]²⁺(aq) )

Answer 35

blue

Question 36

What is the colour of Fe²⁺(aq) ( or [Fe(H2O)₆]²⁺(aq) )

Answer 36

pale green

Question 37

What is the colour of Fe³⁺(aq) ( or [Fe(H2O)₆]³⁺(aq) )

Answer 37

pale yellow

Question 38

What is the colour of Cr³⁺(aq) ( or [Cr(H2O)₆]³⁺(aq) ), and what colour is it often due to the presence of common anions

Answer 38

violet or often green

Question 39

What is the colour of Mn²⁺(aq) ( or [Mn(H2O)₆]²⁺(aq) )

Answer 39

pale pink

Question 40

What are the 2 types of precipitation reactions that occur with T.M. hexaaqua ions, what charges of T.M. hexaaqua ions do they only occur with, and what is formed

Answer 40

with NaOH (aq) and NH3(aq) only with T.M. hexaaqua ions of 2+ or 3+ charges forms insoluble metal hydroxides

Question 41

What is the colour of Cu(OH)₂ (s)

Answer 41

blue ppt

Question 42

What is the colour of Fe(OH)₂ (s)

Answer 42

green ppt

Question 43

What is the colour of Fe(OH)₃ (s)

Answer 43

orange/brown ppt

Question 44

What is the colour of Cr(OH)₃ (s)

Answer 44

grey-green ppt

Question 45

What is the colour of Mn(OH)₂ (s)

Answer 45

light brown ppt

Question 46

What happens when excess OH-(aq) is added to T.M. hydroxide ppts

Answer 46

Cr(OH)₃ (s) redissolves to form Cr(OH)₃ (aq) which is a dark green solution Mn(OH)₂ (s), Fe(OH)₃ (s), Fe(OH)₂ (s), Cu(OH)₂ (s) are insoluble in excess OH- (aq)

Question 47

What are the 2 stages of hexaaqua ions reacting with aqueous ammonia

Answer 47

1- ammonia in water reacts to form OH- ions NH3 + H2O <-> NH4+ + OH- The hydroxide ions react with hexaaqua T.M. ions to form T.M. hydroxide ppts 2- in excess ammonia, only Cu(OH)₂ (s) and Cr(OH)₃ (s) redissolve

Question 48

What are the two hexaaqua transition metal ions that redissolve in excess ammonia and how do you remember them

Answer 48

only Cu(OH)₂ (s) and Cr(OH)₃ (s) Cunning and Crafty

Question 49

What is the colour of [Cu(H2O)₂(NH₃)₄]²⁺ (aq)

Answer 49

[Cu(H2O)₂(NH₃)₄]²⁺ (aq) is deep blue solution

Question 50

What is the colour of [Cr(NH₃)₆]³⁺ (aq)

Answer 50

[Cr(NH₃)₆]³⁺ (aq) is purple solution

Question 51

What is the colour of the solution formed when Fe²⁺ is oxidised to Fe³⁺ by MnO4-

Answer 51

very pale pink/solution

Question 52

What is the colour of the solution formed when Fe³⁺ is reduced to Fe²⁺ by I-

Answer 52

(pale green + brown) dirty green

Question 53

What is the colour of the solution formed when Cr2O7 2- is reduced to Cr³⁺ by Zn(s)

Answer 53

green (due to presence of other anions, colour is green not violet)

Question 54

What is the colour of CuI (s)

Answer 54

white solid

Question 55

What is the colour of Cu₂O (s)

Answer 55

red solid

Question 56

What is a coordinate bond

Answer 56

a covalent bond where both electrons in the shared pair come from the same atom

Question 57

Explain why carbon monoxide is highly toxic

Answer 57

CO can replace O2 as a ligand. CO forms a stronger coordinate bond than O2 and so will bind preferentially, so the Hb loses its ability to transport O2

Question 58

What is the shape of platinum complexes

Answer 58

square planar

Question 59

Explain the term 'coordination number'

Answer 59

number of coordinate bonds formed by the ligands to the metal ion in a complex