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a level chemistry aqa > Transition metals > Flashcards

Transition metals Flashcards

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1
Q

What are transition metals?

A

one that forms at least one stable ion with a PARTIAlLLY filled d-shell of electrons.

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2
Q

What are the characteristics of transition metal?

A
  • variable oxidation states
  • formation of coloured ions
  • catalytic activity
  • complex formation
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3
Q

Why isn’t zinc a transition metal?

A

because it’s ion zn^2+ has a full d sub shell not partially filled

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4
Q

What does a “complex” mean?

A

a central metal atom or ion surrounded by ligands linked by coordinate bonds

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5
Q

What is a ligand

A

a molecule or ion that forms a coordinate bond with a transition metal by donating a pair of electrons.

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6
Q

What is the coordination number?

A

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

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7
Q

What is the chelate effect?

A

Bidentate and multidentate ligands replace monodentate ligands from complexes. The complexes formed from multidentate ligands are more stable due to an increase in particles resulting in greater entropy

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8
Q

What are chelates?

A

complexions with polydentate ligands

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9
Q

What are examples of bidentate ligands (draw the structure)

A
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10
Q

What is an example of a multidentate? (draw the structure)

A
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11
Q

What does cis and trans mean?

A
  • When two groups are on the same side, they are cis.
  • When two groups are on opposite sides, they are trans.
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12
Q

When does E/Z isomerism occur in a complex?

A

This can occur in octahedral and square planar that have monodentate ligands

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13
Q

When does optical isomerism occur in a complex?

A

when octahedral complexes have three bidentate ligands

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14
Q

When can ligand substitution reactions be reversed?

A

when the new complex ion is less than or equally stable as the original one

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15
Q

What is haem and what is globin? Describe the structure of haemoglobin.

A

Haem is an iron(II) complex that is hexa-coordinated

Four of the co-ordinate bonds come from four nitrogen atoms from the same molecule co-ordinate around Fe2+ to form a circle. This part of the molecule is called haem.

The other two co-ordinate bonds come from a protein called globin, and either an oxygen or a water molecule - so the complex can transport oxygen to where it’s needed, and then swap it for a water molecule

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16
Q

How does the structure of haemoglobin help transport oxygen around the body?

A
  • In the lungs, where the oxygen concentration is high, an oxygen molecule substitutes the water ligand and bonds co-ordinately to the Fe (ll) ion to form oxyhaemoglobin, which is carried around the body in the blood.
  • When the oxyhemoglobin gets to a place where oxygen is needed, the oxygen molecule is exchanged for a water molecule. The haemoglobin then returns to the lungs and the whole process starts again.
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17
Q

How does carbon monoxide prevent oxygen being transported around the body?

A
  • The haemoglobin swaps its water ligand for a carbon monoxide ligand, forming carboxyhaemoglobin.
  • Carbon monoxide is a strong ligand and doesn’t readily exchange with oxygen or water ligands, meaning the haemoglobin can’t transport oxygen any more.
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18
Q

What are the two different types of catalyst?

A

Heterogenous = catalysts which are in a different phase from the reactants

Homogenous = same phase as reactants

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19
Q

Why are transition metals good catalysts?

A

Catalysts work by changing oxidation states and transition metals can change oxidation states very easily.

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20
Q

How do catalysts work?

A

They provide an alternative route with a lower activation energy - this causes MANY more particles to have E>Ea, so a larger proportion of collision are successful

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21
Q

What is the difference between absorption and adsorption?

A
  • Adsorption iswhere the reactant molecule sticks to the surface of the catalysts
  • Absorption where the molecule is taken up.
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22
Q

What are examples of heterogeneous catalysts?

A
  • V2O5 in the Contact process.
  • Fe in the Haber process.
  • Platinum/rhodium/platinum in the catalytic convertor
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23
Q

What are examples of homogeneous catalysts?

A
  • Aluminium chloride in acylation
  • Cl radicals in the destruction of the ozone layer
  • Fe (3+) in the oxidation of iodide ions by peroxidisulphate (VI) ions
  • The autocatalysis by manganese (II) ions of the oxidation of ethanedioate ions by manganate (VII) ions
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24
Q

How do heterogeneous catalysts work?

A
  • adsorption
  • reaction
  • desorption
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25
Q

What does adsorption do?

A
  • holds the reactant particles on the surface of the catalyst so there is an increase in the collision frequency between the particles
  • weaken bonds = reduces activation energy as it will be easier to break reactant bonds
  • break up the reactant into more reactive particles = reduces activation energy
  • ## hold a reactant in a specific orientation = increases chance of successful collision
26
Q

What catalyst is used in the contact process? What type of catalyst is this an example of? Write the equation

A

Vanadium (V) is used to make sulfuric acid

example of heterogenous catalyst

27
Q

What is the overall equation for the Haber process?

A
28
Q

What is the overall equation for the contact process?

A
29
Q

How do you make heterozygous catalysts more efficient?

A

Since their activity takes place on the surface you can:

  • increase their surface area - the larger the surface area, the better the efficiency.
  • Spread the catalyst onto an inert support medium, or even impregnate it into one. This increases the surface-to-mass ratio so that a little goes a long way.
30
Q

How do heterogenous catalysts become poisoned? What is this process called?

A
  1. Heterogeneous catalysts often work by adsorbing reactants onto active sites located on their surfaces.
  2. ## Impurities in the reaction mixture may also bind to the catalyst’s surface and block reactants from being adsorbed. This process is called catalyst poisoning.
31
Q

How do homozygous catalysts work?

A

Homogeneous catalysts forms intermediate species by reactants combining with the catalyst which reacts form products. The catalyst is reformed again

32
Q

Why is the oxidation of iodine ion by peroxidisulphate ions slow? What is the equation for this reaction?

A

slow because both the ions reacting are negatively charged so the ions will repel each other and the activation energy will be very high

33
Q

What catalyst is used in the oxidation of iodine ion by peroxidisulphate ions. Write the equations

A

iron (II) ions. Can also be catalysted by iron (III), the second equation would happen first.

34
Q

What does an autocatalysis reaction mean?

A

where one of the products acts as a catalyst

35
Q

What is the overall equation for the oxidation of ethanedioate by manganate (VII) ions?

A
36
Q

Give the two equations that show Mn²⁺ is a catalyst for the oxidation of ethanedioate.

A
37
Q

Why are transition metal compounds coloured?

A
  • They have part-filled d-orbitals, hence electrons can move from one d-orbital to another.
  • In an isolated transition metal atom, all the d-orbitals are of exactly the same energy, but in a compound, the presence of other atoms nearby makes the d-orbitals have slightly different energies. This includes when ligands are introduced and join to metal ions.
  • In compounds, the 3d energy level is split into two different energy levels
  • When electrons move from one d-orbital to another of a higher energy level (excited state), they often absorb energy in the visible light region of the spectrum equal to the difference in energy between levels.
  • The rest of the frequencies are transmitted or reflected. These are combined to make the colour that you see
38
Q

Why are non-transition metal compounds not coloured?

A

Because there are either no 3d electrons or the 3d orbital is full, so no electrons will jump, so no energy will absorb, hence the substance will look white

39
Q

How can the energy absorbed when electrons jump up from the ground state to an excited state be calculated?

A
40
Q

What determines the amount of energy needed to make electrons jump and why?

A
  • central metal ion
  • oxidation state
  • coordination number
  • ligands (therefore the shape of the complex ion)

This is because they effect the size of the energy gap

41
Q

How can spectroscopy be used to find concentrations of transition metal ions?

A
  • it measures how much light is absorbed with the aid of a calibration curve:
    1. White light is shone through a filter, which is chosen to only let through the colour of light that is absorbed by the sample.
    2. The light passes through the sample to a colorimeter, which calculates how much light was absorbed by the sample.
    3. The more concentrated a coloured solution is, the more light it will absorb. So you can use this measurement to work out the concentration of a solution of transition metal ions.
42
Q

How do you work out the oxidation state of a complex ion

A

oxidation state of metal ion - oxidation state of ligands

43
Q

What are the common oxidation state of vanadium and what colours do they form? What is the maximum number of electrons vanadium can lose?

A

5

44
Q

Write an equation for the reduction of vanadate ions to vanadium (II) using zinc and an acidic solution

A
45
Q

What are the common oxidation state of chromium and what colours do they form? What is the maximum number of electrons chromium can lose?

A

6

46
Q

What are the common oxidation state of manganese and what colours do they form? What is the maximum number of electrons manganese can lose?

A

7

47
Q

What does the redox potential tell us about an ion?

A

The higher the value:

  • the less stable the ion is
  • the easier the ion can be produced
48
Q

Redox potential will not always be the same as its standard electrode. What are the two factors in the environment which could change the value of a redox potential?

A
  • Ligands - Standard electrode potentials are always measured in aqueous solutions. The metal ion is surrounded by water molecules.
    However, ligands other than water can form stronger bonds to the Metal ions with particular oxidation states. This means the redox potential can be higher or lower than the standard value.
  • PH: the more acidic the solution the larger the the electrode potential which means the metal ions could be reduced more easily
49
Q

How is Tollen’s reagent made?

A

by reacting enough aqueous ammonia to aqueous silver nitrate

50
Q

Draw the complex ion in Tollen’s reagent and explain how this complex ion allows us to identify aldehydes

A
  • this is linear
  • Aldehydes reduce the [Ag (NH3)]+ to Ag (metallic silver), while ketones do not
51
Q

What is the overall reaction for Tollen’s reagent and an aldehyde?

A
52
Q

What is the purpose of redox titrations?

A

to work out the concentration of a reducing or oxidising agent

53
Q

Why is dilute acid added to the redox titrations?

A

to ensure we have sufficient H+ ions to allow the reduction process to occur

54
Q

In general, how do you carry out a practical to determine the concentration of a metal aqua ion in a solution of unknown concentrations ?

A
  • Add an appropriate (or a given correct) ligand to intensify colour (1) e.g. thiocyanate (CNS) or bipyridyl
  • Make up SOME solutions of known concentration
  • Measure absorption or transmission
  • Plot graph of results or calibration curve
  • Measure absorption of unknown and compare
55
Q

How do heterogeneous catalysts work?

A
  1. Reactants form bonds with atoms at active sites on the surface of the catalyst (adsorbed onto the surface)
  2. As a result bonds in the reactants are weakened and break
  3. New bonds form between the reactants held close together on catalyst surface.
  4. This in turn weakens bonds between product and catalyst and product leaves (desorbs).
56
Q

Why isn’t scandium a transition metal?

A

because its ion S3+ has an empty d subshell not partially filled

57
Q

What are the conditions need for a ligand substation reaction with chloride ions and a metal complex?

A

The addition of a high concentration of chloride ions ( from conc HC or saturated NaCl)

58
Q

Why is it important in calorimetry for the containers used in each sample to have the same dimensions?

A

absorption depends on the distance travelled through the solution

59
Q

Why is a coloured filter used in colourimetry?

A

to select the colour that is most strongly absorbed by the sample

60
Q

Suggest why a colourimetric method might be chosen in preference to titration.

A
  • quicker to analyse extracted samples than by titration
  • uses smaller volumes of solution

a level chemistry aqa (30 decks)

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