Transition Metals

Question 1

define transition metals

Answer 1

a d-block element which has at least one stable ion with an incomplete d- subshell

Question 2

why are Scandium and Zinc not transition metals?

Answer 2

Sc3+ have no electrons in the 3d subshell

Zn2+ have a full 3D subshell

Question 3

why are transition metal ions coloured?

Answer 3

• colours arise from d- electrons absorbing energy from visible light at particular wavelengths
• the d-electrons are promoted from the lower energy level to the higher energy level
• the wavelengths of light not absorbed by the solution are transmitted through it and absorbed by the human eye
• the solution has a colour corresponding to these transmitted wavelengths

Question 4

where does the colour of a transition metals result from?

Answer 4

• most TM are coloured
• colours result from movement of electrons from partially filled d-orbitals
• if a compound has no electrons in the d orbital, it appears colourless

Question 5

why are 4s electrons lost before 3d?

Answer 5

4s subshell is higher in energy

-

Question 6

what is the relationship between oxidation state and oxidising power? + eg

Answer 6

-higher oxidation state= readily accept electrons (be reduced) = makes them powerful oxidising agents

E.g.
Mn7+ in potassium permanganate (VII) and Cr6+ in potassium dichromate (VII) (K2Cr2O7)

Question 7

what is a disproportionation reaction?

Answer 7

one where a species is both oxidised and reduced in the same reaction

Question 8

whats a catalyst?

Answer 8

speeds up reaction by providing an alternative reaction route and is not used up or chemically changes in the process

Question 9

why are TMs able to act as catalysts?

Answer 9

because of their variable oxidation states

E.g. Fe is the catalyst used in the Haber Process

Question 10

advantages + disadvantages of catalysts?

Answer 10

+
used in industry to speed to reactions pr to make them more energy- efficient
-
they can be toxic or damaging to the environment so when no longer needed, they must be disposed of carefully

Question 11

define complex

Answer 11

a central metal atom or ion surrounded by ligands

Question 12

define ligand

Answer 12

a molecule or ion that forms a co-ordinate bond with a transition metal by donating a lone pair of electrons

Question 13

define coordinate number

Answer 13

the number of co-ordinate bonds to the central metal atom or ion

Question 14

define monodentate ligand + give 3 common ones

Answer 14

a molecule or ion that can donate just one lone pair of electrons forming 1 co-ordinate bond

water :OH2 neutral charge
ammonia :NH3 neutral charge
chloride :Cl- charge = -1

Question 15

define multidentate + give common ones

Answer 15

a molecule or ion that can donate multiple lone pairs o electrons from different atoms within the ligand, forming multiple coordinate bonds

ethane-1,2-diamine NH2Ch2CH2NH2 is a bidentate ligand 2lp often referred to as ‘en’

ethanedioate C2O42- is bidentate, 2lp

DTA is hexadentate, its present as EDTA 4- in complexes and has 6lp. Its a chelating agent + used in detergents, food and medicine

Question 16

although Zn and Cu are next to each other in the periodic table why is copper (II) sulfate solution blue whilst zinc (II) sulfate solution colourless?

Answer 16

this is because Cu2+ has a partially filled d- subshell whereas Sn2+ doesn’t

Question 17

what is the equation for calculating the difference in energy (energy gap)?

Answer 17

ΔE = hv = hc/λ
ΔE= difference in energy (J)
h= Planck's constant (6.63 *10^-34 Js)
v= frequency of light absorbed (s-1 or Hz) 
c= speed of light in vacuum (3.00 * 10^8 ms-1)
λ= wavelength of light absorbed (m)

Question 18

what are some factors effecting the magnitude of ΔE and therefore the colour of the complex?

Answer 18

• the ligand
• oxidation state
• co-ordination number

Question 19

how do you find the conc of transition metals in solution?

Answer 19

simple colorimetry
1- the absorbance of solutions of known concentrations is measured using the colorimeter

2-a calibration curve (absorbance vs conc graph) is produced

3-the absorbance of the solution of unknown conc is measured, and the calibration curve is used to find its conc

Question 20

what is the chelate effect?

Answer 20

its an entropically driven process where multidentate ligands replace monodentate ligands in complexes (EDTA replacing H2O)

-its always more favourable for a TM ion to exchange monodentate ligands for those which can form more co-ordinate bonds

Question 21

what needs to happen for a reaction to be thermodynamically feasible? how

Answer 21

the Gibbs free energy chnage must be negative and for it to be negative, there needs to a large increase in entropy for example making 7 molecules from 2

Question 22

what does ΔG (Gibbs free energy) depend on?

Answer 22

enthalpy change, entropy change and temp of the reaction

Question 23

whats the equations for ΔG (Gibbs free energy)?

Answer 23

ΔG = ΔH - TΔS 
ΔG = Gibbs free energy (Jmol-1)
ΔH = enthalpy change (Jmol-1)
T = temperature (K)
ΔS = entropy change (J K-1 mol-1)

Question 24

colours + electron config of Fe (II) and Fe (III)?

Answer 24

green = Fe(II)
1s2,2s2,2p6,3s2,3p6,4s2,3d6
pale brown = pale brown
1s2,2s2,2p6,3s2,4s2,3d5

Question 25

what are the 2 types of stereoisomers in TM?

Answer 25

cis-trans isomers (E/Z)
optical isomers (non superimposable images

Question 26

define ligand substitution reactions

Answer 26

when a ligand in a complex is replaced by a different ligand that forms stronger co-ordinate bonds

Question 27

why does the ligand substitution of H2O for NH3 occur? is there a chnage in coordination number?

Answer 27

no chnage in coordination number as the ligands are similar in size.
the exchange occurs because NH3 is a better ligand and forms stronger co-ordinate bonds than H2O

Question 28

whats the colour of Aqueous copper (II) solution? what happens when you add small amounts of ammonia and also excess amounts of ammonia? Does the coordination number change?

Answer 28

-contains pale blue [Cu(H2O)6]2+ complex
-adding small amounts o ammonia, the ammonia acts as base, accepts protons form the H2O forming blue copper hydroxide precipitate
[Cu(H2O)6]2+ (aq) + 2NH3 (aq) → [Cu(OH)2(H2O)4] (s) + 2NH4+ (aq)
-adding excess ammonia, the precipitate dissovolves and the ammonia replaces the OH- and 2 of the H2O in a ligand sub reaction forming deep blue solution
[Cu(OH)2(H2O)4] (s) + 4NH3 (aq) ⇌ [Cu(NH3)4(H2O)2]2+ (aq) + 2H2O (l) + 2OH– (aq)

overall reaction as equilibrium = [Cu(H2O)6]2+ (aq) + 4NH3 (aq) ⇌ [Cu(NH3)4(H2O)2]2+ (aq) + 4H2O (l)

-coordination number= 6 and doesn’t change. This ligand sub is said to be incomplete as only four of the original 6 ligands are replaced

Question 29

whats the colour of aqueous cobalt (II) + what happens when you add excess ammonia + does the coordination number change?

Answer 29

-[Co(H2O)6]2+ = pink complex
-excess ammonia replaces the H2O ligands forming straw coloured solution
[Co(H2O)6]2+ (aq) + 6NH3 (aq) ⇌ [Co(NH3)6]2+ (aq) + 6H2O (l)
co-ordination number= 6 and doesn’t change. this ligand sub is said to be complete as all of the original 6 ligands are replaced

Question 30

what happens when aqeuous copper (II) mix with HCl?

Answer 30

sub of H2O with Cl- ligand
-Cl- ligand is bigger so co-ordination number decreases from 6 to 4
colour change from pale blue to green to yellow solution the green is from the mixing of yellow and blue
[Cu(H2O)6]2+ (aq) + 4Cl– (aq) ⇌ [Cu(Cl)4]2– (aq) + 6H2O (l)

Question 31

what happens aqeuous copper mixes with HCl?

Answer 31

from pink to blue solution

[Co(H2O)6]2+ (aq) + 4Cl– (aq) ⇌ [CoCl4]2– (aq) + 6H2O (l)

Question 32

what happens when aqueous iron (III) ions mix with HCl?

Answer 32

colour chnage from purple to yellow solution

[Fe(H2O)6]3+ (aq) + 4Cl– (aq) ⇌ [FeCl4]– (aq) + 6H2O (l)

Question 33

how is tollens reagent formed? [Ag(NH3)2]+

and how does it work?

Answer 33

reacting ammonia solution with silver nitrate solution
-used to distinguish between aldehydes and ketones

Tollens oxidises aldehydes to carboxylic acids, reducing Ag+ to Ag forming a silver mirror inside of tube but not ketones

Question 34

define heterogenous catalyst

Answer 34

a catalyst is in a different phase to the reactants.

the reaction occurs at active sites on the surface of the catalyst

Question 35

how do heterogenous catalysts work?

Answer 35

1- adsorption -1+ reactants become attached to the surface of the catalyst

2- reaction-the weakening of bonds from adsorption cause the activation energy of the reaction to decrease so the reaction can occur

3-desorption- the product detaches from the catalyst

Question 36

how do we minimise the cost of heterogenous compounds especially as they’re difficult to replace and you need to replace after impurities?

Answer 36

spread into a support medium and maximise SA

Question 37

explain the Haber process

Answer 37

• used in industry to produce ammonia
• increases rate and makes it feasible at lower temps
• become contaminated with S + are replaced

Question 38

explain the Contact process

Answer 38

-reactants at high temp + pressure so are in gas phase. The V2O5 catalyst is in the solid phase.

1-adsorption- SO2 absorbs onto V2O5
V2O5 (s) + SO2 (g) –> V2O4 (s) +SO3 (g)
2- V2O4 reacts with oxygen to regenerate the catalyst
V2O4 (s) + 1/2O2(g) –> V2O5 (s)
reabsorption: SO3 reabsorbs and diffuses away

Question 39

define homogenous catalyst

Answer 39

a catalyst in the same phase as the reactants. the catalysts are always gaseous or in aqeuous solution and form an intermediate species during the reaction