Transition metals pt 2

Question 1

What causes colour changes in transition metals?

Answer 1

oxidation state
coordination number
ligand

Question 2

Why do colour changes occur in translation metals

Answer 2

electron promotion

due to the partially filled d sub levels

electrons sitting in this sub level can shift up and down between the un occupied orbitals

Question 3

Outline electron promotion

Answer 3

• d orbitals split energy levels
• d electrons are promoted to higher energy d orbitals by absorbing energy in the form of light
• the colour transmitted is the light not absorbed

Question 4

What is an energy gap?

Answer 4

d orbitals are at specific energy values therefore the gap between them has a specific energy gap value ΔE

an electron must be given at least the ΔE value to be promoted from the ground state to the excited state

Question 5

How are electrons in a transition metal promoted

Answer 5

The TM must absorb a specific frequency of light

Question 6

What are the 2 equations for ΔE

Answer 6

ΔE = hv

ΔE = hc/λ

Question 7

What is ‘v’ and its units

Answer 7

the frequency of the wave of light absorbed

s-1

Question 8

What is ‘c’ and its units

Answer 8

the speed of light

3.00 x 10-8 ms-1

Question 9

What is λ and its units

Answer 9

wavelength of light

m

Question 9

What are the units for ΔE

Answer 9

Joules

Question 10

How do you change wavelength from nanometres (nm) to meters (m)

Answer 10

times by 10^-9

Question 11

Why are aqueous cobalt ions always pink

Answer 11

d orbitals split in energy levels

d electrons ate promoted to higher energy d orbitals by absorbing energy in the form of light

pink light is not absorbed it is transmitted and observed

Question 12

why do complexes of magnesium aluminium and zinc all per colourless in solution?

Answer 12

They don’t have partially filled d sub levels

Question 13

What changes colour

Answer 13

Changing colour arise due to the size of ΔE between the d orbital’s changing

If ΔE changes different frequencies of light will be absorbed and different frequencies of light will be transmitted (then observed) through the sample

Question 14

What can cause a change to ΔE thus change the colour of the complex

Answer 14

• Ligands bonded to the TM on
• Coordinate number
• Oxidation state

Question 15

What is a colorimeter for

Answer 15

used to measure the absorbance of light in the visible and uv region

• contains a coloured filter. The colour of the filter is chosen to allow wavelengths of light that would be most strongly absorbed by the coloured solution

Question 16

What is the relationship with light absorbed and the complex ion

Answer 16

The amount of light absorbed is proportional to the concentration of the complex ion

Question 17

How could the colour of a complex be intensified?

Answer 17

Add a suitable ligand to intensify the colour

Question 18

how can you determine the concentration of a transition metal ion?

Answer 18

• add an appropriate ligand to intensify the colour
• set the colorimeter wavelength to λmax
• make a series of standard solutions of known concentrations of the metal ion
• Measure the absorbance of the standard solutions
• Plot a graph of absorbance v. concentration (calibration graph)
• Measured the absorbance of the unknown solution and determine its concentration from the calibration graph

Question 19

what is a catalyst?

Answer 19

A substance that increases the rate of reaction but isn’t used up

Question 20

How do catalysts work?

Answer 20

Provide an alternative route with a lower activation energy

Question 21

How does a catalyst affect a reaction at equilibrium?

Answer 21

catalyst has no effect on the position of equilibrium as it increases the rate of the reaction forwards AND backwards equally

It only decreases the time taken to reach equilibrium

Question 22

What are the properties of a catalytic converter

Answer 22

Platinum Pallidium or Rhodium are sprayed over a ceramic honeycomb structure to limit costs and maximise surface area

Question 23

What is a heterogeneous catalyst?

Answer 23

catalyst which are in a different state to the react

The catalyst is usually a solid and the reaction takes place on the surface

Question 24

What are examples of heterogeneous catalytic processes?

Answer 24

Hebrew process – industrial production of ammonia Contact process – for making sulphuric acid (most common) do you think about the day that we sat down smoking? I don’t drinking hazel the other way is it the other way? Catalytic converter

Question 25

how do heterogeneous catalysts work?

Answer 25

1. reactants are adsorbed onto active site on the catalyst surface. 2. reaction occurs with a low activation energy as bonds of weed or new buns are made between reactants held close together. 3. The products are desorbed (the surface).

Question 26

how can adsorption resort in an increased reaction?

Answer 26

- Adsorption onto the surface **concentrates the reactants** so increase in the likelihood of collision - May **weaken some of the bonds** in a molecule making a reaction easier - **Positions the molecule** in a favourable orientation for reaction

Question 27

what happens if adsorption is too strong?

Answer 27

not many molecules will be adsorbed so the catalyst will have very little effect

Question 28

what happens if adsorption is too weak?

Answer 28

Molecules won’t be able to move around in the active sites so will be less likely to meet another reactant therefore be less likely to react

Question 29

what is adsorption?

Answer 29

going **onto** something

Question 30

how can you maximise the efficiency of a surface catalyst?

Answer 30

- Maximising surface area has important cost savings - Surface area is maximised by using a thin coating of the catalyst on a **support medium**

Question 31

What is the equation for the Haber process?

Answer 31

N2 + 3H2 ⇌ 2NH3 Fe is a catalyst

Question 32

what is the overall equation for the contact process?

Answer 32

SO2 + 1/2O2 > SO3 Catalyst - Vanadium(V) oxide / V2O5

Question 33

what is the equation of the first step of the contact process?

Answer 33

V2O5(g) + SO2(s) > SO3(g) + V2O4(s)

Question 34

What is the second step of the contact process?

Answer 34

regeneration of catalysts V2O4 + 1/2O2 > V2O5

Question 35

How does catalyst poisoning occur?

Answer 35

**other substances adsorb strongly** onto the surface blocking the active sites - **Lowers the efficiency of the catalyst/makes it ineffective** depending on the extent of the poisoning - poisons are very **difficult to remove** and the catalyst is **ruined** which can be costly

Question 36

How does lead poisoning occur

Answer 36

The radium and platinum catalysts are poisoned by lead from leaded petrol this is very expensive to replace

Question 37

how does sulphur poisoning occur?

Answer 37

In the Haber process the hydrogen is obtained from natural gas which is contaminated by sulphur if not removed this will poison the Fe catalyst Sulphur is added to natural gas to give it an older so leaks can be smelt

Question 38

What is a homogeneous catalyst?

Answer 38

catalyst which are in the same state as the reactants Most reactions involving a homogeneous catalyst take place in solution. The alternative reaction pathway involves formation of an intermediate – with a different oxidation state

Question 39

Why can transition metals act as a catalyst?

Answer 39

Because of the variable oxidation states

Question 40

outline the equation for the reaction between iodide ions and Persulfate ions

Answer 40

(homogeneous catalytic process) S2O8 ^2-(aq) + 2I-(aq) > 2SO4 ^2-(aq) + I2(aq)

Question 41

What is an example of a homogeneous catalytic process?

Answer 41

reaction between iodide ions and persulphate ions has a **high activation energy** as both reactants are **negative so they repel**

Question 42

why will the reaction with iodide ions and persulfate ions be faster with Fe2+ ions

Answer 42

Opposite charges on the ions attract and the activation energy is lowered

Question 43

Why does the reaction between iodide ions and persulfate ions have a high activation energy

Answer 43

both reactants are negatively charged so will repel

Question 44

In a reaction with iodide ions and persulfate ions what is the reducing agent

Answer 44

I-

Question 45

In a reaction with iodide ions and persulfate ions what is the oxidation agent

Answer 45

S2O8^2-

Question 46

What is the first step of the equation with iodide ions and persulfaste ions with Fe as a catalyst

Answer 46

S2O8^2- +2Fe^2+ > 2SO4^2- +2Fe^3+

Question 47

What is the second step of the equation with iodide ions and persulfaste ions with Fe as a catalyst

Answer 47

2Fe^3+ + 2I- > 2Fe^2+ + I2

Question 48

What is the overall equation between ethane dioate ions and magnate (VII) ions with Mn2+

Answer 48

2MnO4- + 5CrO4^2- +16H+ > 2Mn^2+ + 10CO2 + 8H2O

Question 49

Why is the reaction between ethane dioate ions and Maganate (VII) ions very slow without a catalyst

Answer 49

Both reactants are negative and repel eachother

Question 50

Why can Mn2+ act as a catalyst

Answer 50

it has variable oxidation states - Mn2+ and Mn3+

Question 51

How does Mn2+ work as a catalyst

Answer 51

its a product of the reaction - the initial reaction is slow until Mn2+ is formed then its sped up

Question 52

What does a normal concentration/time graph look like

Answer 52

a curve (downwards) - reaction starts quickly and the conc of reactants is high - reaction then slows down snd eventually stops as reactants are used up

Question 53

What does an auto catalyst

Answer 53

occurs when one of the products from a reaction is a catalyst of the reaction - the reaction starts out slowly and as the concentration of the catalyst product increases the rate also increases

Question 54

What does an auto-catalysed concentration graph look like

Answer 54

a slope (s shape) - reaction starts slowly then rate increases as the catalyst is produced - then it slows down and stops