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My AQA Chemistry A Level > 2.4 - Transition Metals > Flashcards

2.4 - Transition Metals Flashcards

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1
Q

What is the definition of a transition metal?

A

Metal that can form one or more stable ions with a partially filled d sub-level

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2
Q

What are the two elements that are not transition metals in period 4 d block?

A

Scandium and Zinc

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3
Q

Name the similar physical properties of transition metals.

A

High density
High melting and boiling points
Similar ionic radii

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4
Q

What are the similar chemical properties of transition metals?

A

Can form complex ions.
Form coloured ions.
Good catalysts.
Can exist in variable oxidation states.

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5
Q

Name the vanadium ions, colours, and oxidation states.

A

V^2+ Violet
V^3+ Green
VO^2+ Blue (+4)
VO2^+ Yellow (+5)

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6
Q

Name the chromium ions

A

Cr^3+ Violet (surrounded by water)/Green
Cr2O7^2- Orange (+6)

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7
Q

Name the manganese ions

A

Mn^2+ pale pink
MnO4^- purple (+7)

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8
Q

Name the iron ions

A

Fe^2+ pale green
Fe^3+ purple (surrounded by water)/yellow

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9
Q

Name the cobalt ion.

A

Co^2+ pink

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10
Q

Name the nickel ion

A

Ni^2+ Green

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11
Q

Name the copper ion

A

Cu^2+ blue

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12
Q

Why do transition metals have variable oxidation states?

A

Energy levels of the 4s and 3d sub-levels are very close, so electrons can be gained or lost using similar amounts of energy.

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13
Q

What is a complex?

A

A central metal atom or ion surrounded by co-ordinately bonded ligands

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14
Q

What is a co-ordinate bond?

A

A covalent bond where a pair of electrons are donated from the same atom.

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15
Q

What is a ligand?

A

Species that donates a pair of electrons to a central transition metal ion to form a co-ordinate bond.

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16
Q

What is co-ordination number?

A

Number of co-ordinate bonds with the central metal ion.

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17
Q

Which species can bond with a central metal ion to from 6 co-ordinate bonds? Why?

A

H2O and NH3. They’re small.
They form octahedral shapes (90°). Remember top and bottom arrows normal. Near the top is dashed, near bottom is bold.

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18
Q

What shape(s) is formed from 4 Co-ordinate bonds?

A

Tetrahedral (109.5°). Cl^- atoms are big so only 4 can fit.
Can also form square planar (90°)
E.g Cisplatin which is NH3 on the tops and Cl on the bottoms, paired with a pt centre.

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19
Q

What do silver complexes usually form?

A

Linear shape with 2 Co-ordinate bonds (180°).
E.g [Ag(NH3)2]^+
Tollens’ reagent

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20
Q

What must a ligand have? What are the different types of ligands?

A

Lone pairs. Monodentate can form 1 Co-ordinate bond. 2 is bidentate.
E.g ethane-1,2-diamine and ethanedioate C2O4^2
More is multidentate. EDTA^4- can form 6 Co-ordinate bonds.

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21
Q

What are the properties and structure of haemoglobin?

A

It is a protein in blood that helps transport oxygen around the body. Haemoglobin contains Fe^2+ ions which are hexa-coordinated - six lone pairs are donated to them.
Four of the co-ordinate bonds come from a single multidentate ligand with four nitrogen atoms, which is haem.
The other two Co-ordinate bonds come from a protein called globin, and either an oxygen or a water molecule.
ALWAYS draw lone pairs

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22
Q

Describe how haemoglobin works in the body.

A

In the lungs where O2 concentration is high, an oxygen molecule substitutes the water ligand and bonds co-ordinarily to the Fe^2+ ion to form oxyhemoglobin. Then the oxygen molecule is exchanged for a water molecule and the haemoglobin returns to the lungs.

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23
Q

How does carbon monoxide poisoning occur.

A

Haemoglobin swaps its water ligand for a carbon monoxide ligand, forming carboxyhaemoglobin. CO is a strong ligand and doesn’t readily exchange with oxygen or water ligands, meaning the haemoglobin can’t transport oxygen anymore.

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24
Q

How can complex ions show optical isomerism?

A

Octahedral complexes with 3 bindentate ligands. These ions can exist in two forms that are non-super imposable mirror images.

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25
Q

Where does cis-trans isomerism form?

A

In octahedral and square planar complexes. It is a type of E-Z isomerism. Octahedral complexes with four monodentate ligands and two monodentate ligands of another one can show this. E.g if Cl is on top and bottom it is trans, but if they’re next to each other they’re cis.
Square planar complex ions show this too.

26
Q

How are coloured ions formed?

A

When ligands bond to the ions, some of the orbitals gain energy. This splits the 3d orbitals into two different energy levels. Electrons tend to occupy the lower orbitals. To jump to higher orbitals they need energy equal to change in E, which they get from visible light.

Change in E = hv = hc/lambda
H is plancks constant
C is the speed of light m/s
Lambda is wavelength of light m
V is frequency Hz

27
Q

What affects delta E?

A

Central metal ion and it’s oxidation state, ligands, and Co-ordination number.

28
Q

How does the coloured compound form?

A

When visible light hits the transition metal, some frequencies are absorbed, and others are transmitted or reflected. Electrons become excited. The frequencies absorbed depend on delta E. the larger the energy gap, the higher the frequency of light that is absorbed. The transmitted and reflected frequencies combine to make the complement of the colour of the absorbed frequencies - this is the colour you see.
A colourless/white compound forms when there are no 3d electrons or the 3d sub-level is full.

29
Q

Describe how spectroscopy can be used to find concentrations of transition metal ions.

A

It can determine this by measuring how much light it absorbs. White light is shone through a filter, which is chosen to only let through the colour of light that is absorbed by the sample. The light passes through the sample to a colorimeter, which calculates how much light was absorbed by the sample. More concentrated = higher absorbance.
Produce calibration curve by measuring the absorbance of known concentrations of solutions and plotting the results in a graph.

30
Q

Describe how different ligands form different strength bonds.

A

Ligand substitution reactions can be easily reversed, unless the new complex ion is much more stable than the old one. Multidentate ligands form more stable complexes than monodentate ligands, due to the chelate effect. This is because the number of particles in solution increases, causing a larger entropy. Reactions that result in an increase in entropy and more likely to occur.

31
Q

Show the equations for the reduction of Vanadium ions.

A

Switching between oxidation states is redox. Vanadium ions can be reduced by adding them to zinc in an acidic solution.

2VO2^+ + Zn + 4H^+ -> 2VO^2+ + Zn^2+ + 2H2O

2VO^2+ + Zn + 4H^+ -> 2V^3+ + Zn^2+ + 2H2O

2V^3+ + Zn -> 2V^2+ + Zn^2+

32
Q

What do acidic solutions do to redox potentials?

A

Make them larger (more easily reduced)

33
Q

Give the equation for tollens reagent with an aldehyde.

A

RCHO + 2[Ag(NH3)2]^+ + 3OH^- -> RCOO^- + 2Ag + 4NH3 + 2H2O

34
Q

What are the two transition metal titration redox equations you NEED to memorise?

A

MnO4^- + 8H^+ + 5Fe^2+ -> Mn^2+ + 5Fe^3+ + 4H2O

2MnO4^- + 16H^+ + 5C2O4^2- -> 2Mn^2+ + 8H2O + 10CO2

35
Q

What will the colour change be in a titration?

A

Whatever the coloured ion in the burette is.

36
Q

Why are transition metals good catalysts?

A

They change oxidation states easily.
Positive ions attract negative ions in catalysed process.

37
Q

Give the contact process equations.

A

V2O5 + SO2 -> V2O4 + SO3
V2O4 + 1/2O2 -> V2O5

38
Q

What are heterogeneous catalysts? Give 2 examples.

A

It is in a different phase (physical state) to the reactants. E.g Haber Process gases are passed over a solid iron catalyst. The reaction happens on the surface of the heterogeneous catalyst where the active sites are. Reaction takes place and products desorb/leave the surface.Support mediums are often used to make the area of a catalyst as large as possible, minimising the cost of the reaction.
Contact process is heterogenous.
Haber process is heterogeneous.
N2 + 3H2 -> 2NH3
Fe

39
Q

How can impurities affect heterogeneous catalysts?

A

Heterogeneous catalysts often work by adsorbing reactants onto active sites located on their surface. Impurities in the reaction mixture may also bind to the catalyst’s surface and block reactants from being adsorbed - catalytic poisoning. Catalyst poisoning reduces the surface area. Catalyst poisoning increases the cost of a chemical process because less product can be made in a certain time, or with a certain amount of energy.
E.g sulfur poisons the iron catalyst in the haber process. The hydrogen is produced from methane, which is obtained from natural gas containing impurities such as sulfur compounds. Any sulfur that is not removed is adsorbed onto the iron, forming iron sulfide. The active sites are blocked.

40
Q

What are homogeneous catalysts?

A

They are in the same phase (physical state) of the reactants. It is usually an aqueous catalyst for a reaction between two aqueous solution.
They work by combining with the reactants to form an intermediate species with then reacts to form the products and re-form the catalyst. There are two humps in the enthalpy profile. The activation energy needed to form the intermediates is lower than that needed to make the products directly from the reactants.

41
Q

Give the equations for the reaction of iodide ions with peroxodisulfate. Why is the reaction slow?

A

The reaction is slow because both ions are negatively charged and repel each other. Therefore activation energy is high.
Overall:
S2O8^2- + 2I^- -> I2 + 2SO4^2-

S2O8^2- + 2Fe^2+ -> 2Fe^3+ + 2SO4^2-
2Fe^3+ + 2I^- -> I2 + 2Fe^2+

Fe^2+ is homogenous

42
Q

What is autocatalysis?

A

Another example of a homogenous catalyst is Mn^2+ in the reaction between C2O4^2- and MnO4^-.
It’s an autocatalysis because Mn^2+ is a product and acts as a catalyst. Therefore when the amount of product increases as the reaction progresses, the reaction speeds up.

43
Q

Give equations for manganese with Ethanedioate.

A

2MnO4^- + 16H^+ + 5C2O4^2- -> 2Mn^2+ + 8H2O + 10CO2

MnO4^- + 4Mn^2+ + 8H^+ -> 5Mn^3+ + 4H2O
2Mn^3+ + C2O4^2- -> 2Mn^2+ + 2CO2

44
Q

Describe and explain the hydrolysis reaction with 2+ and 3+

A

Cu(H2O)6^2+ + H2O <=> [Cu(OH)(H2O)5]^+ + H3O^+

3+ ions do the same thing as on top, but they become 2+

They become insoluble, uncharged precipitates.

45
Q

Why are 3+ metal-aqua ions more acidic than 2+?

A

Metal 3+ ions have a higher charger density, making it more polarising than the 2+ ions, and weakening the OH bond. Therefore it’s more likely that a H^+ ion is released.

46
Q

Describe the equations when hydrolysing metal-aqua ions to form precipitates.

A

You have the normal equilibrium. Then you add OH^- ions which removed H3O^+ ions and shift the equilibrium to the right. This makes a new equilibrium with a new OH group on the metal-aqua ion. For every OH group added, take one off the charge until there is no charge. This leaves an insoluble uncharged metal hydroxide.

47
Q

How do metal hydroxides act?

A

These metal hydroxide precipitates will dissolve in acid, act as bases and accept H^+ ions. This reverses the hydrolysis reactions. Some are amphoteric, such as aluminium hydroxide.

48
Q

Show the equations for Al being amphoteric

A

Al(OH)3(H2O)3 + 3H3O^+ -> Al(H2O)6^3+ + 3H2O

Al(OH)3(H2O)3 + OH^- -> Al(OH)4^- + 3H2O

49
Q

Show the equilibrium when ammonia dissolves in water

A

NH3 + H2O <=> NH4^+ OH^-

50
Q

Describe the reaction between a copper complex with 2 OHs and 4H2Os and ammonia

A

copper complex + 4NH3 <=> [Cu(NH3)4(H2O)2]^2+ + 2OH^- + 2H2O

51
Q

What happens when 2+ and 3+ ions react with sodium carbonate

A

[M(H2O)6]^2+ + CO3^2- <=> MCO3 + 6H2O

With 3+:
CO3^2- + 2H3O^+ <=> CO2 + 3H2O
Metal 3+ ions are stronger acids so there is a higher concentration of H3O^+ ions in solution. Therefore carbonate ions react with H3O^+ and act like the OH^- did, removing them. So M(OH)3(H2O)3 forms.

52
Q

What happens to the metal-aqua ions in a reaction with sodium hydroxide?

A

Copper(II), Iron(II), Iron(III) and aluminium(III) will all form precipitates. Copper is a blue precipitate. Fe^2+ is a green precipitate. Al is a white precipitate. Fe^3+ is a brown precipitate (originally a yellow solution). Their charges match the OH groups that they gain. Only aluminium hydroxide precipitate will dissolve in excess sodium hydroxide (because it’s amphoteric) to form a colourless solution [Al(OH)4]^-

53
Q

What happens to metal-aqua ions in reactions with ammonia?

A

All 4 will form precipitates, same colours as OH. But copper hydroxide will dissolve in excess ammonia (because of a ligand exchange reaction) to form a deep blue solution [Cu(NH3)4(H2O)2]^2+

54
Q

What happens to metal-aqua ions with sodium carbonate?

A

All four metal-aqua ions form precipitates. CuCO3 is green-blue precipitate and FeCO3 is green precipitate. Al^3+ and Fe^3+ form bubbles as CO2 is formed (same formulas and colours as when OH was added).

55
Q

Why would Fe^2+ ions be kept away from air?

A

They would oxidise to form Fe^3+ ions.

56
Q

Give an ionic equation for [Fe(H2O)6]^3+ with Na2CO3

A

2[Fe(H2O)6]^3+ + 3CO3^2- -> 2Fe(OH)3(H2O)3 + 3H2O + 3CO2

57
Q

What is the electron configuration for V^3+?

A

1s2 2s2 2p6 3s2 3p6 3d2

58
Q

Write the equation for the reaction of [Fe(H2O)6]^2+ with Cl2

A

2[Fe(H2O)6]^2+ + Cl2 -> 2[Fe(H2O)6]^3+ + 2Cl^-

59
Q

2NaCl + H2SO4 -> Na2SO4 + 2HCl
What is the role of the acid here?
2NaBr + 2H2SO4 -> SO2 + Na2SO4 + Br2 + 2H2O
What is the role of the acid here?

A

Proton donor

Oxidising agent

60
Q

State the meaning of the term heterogeneous catalyst.

A

Different phase to reactants, speeds up reaction by providing an alternate pathway with a lower activation energy, and is not used up.

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