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A-level chemistry unit 5 > unit 5 section 2 transition metals > Flashcards

unit 5 section 2 transition metals Flashcards

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1
Q

what is a transition metal
(1)

A

it is a metal that can form 1 or more stable ions with an incomplete d-subshell.

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2
Q

what two metals in the d block are not transition metals
(2)

A

scandium(sc) & zinc(zn)

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3
Q

what are the electron configurations of copper(Cu) and chromium(Cr)
(2)

A

cu - [Ar] 3d^10 4s^1
Cr - [Ar] 3d^5 4s^1

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4
Q

why are scandium and zinc not transition metals
(1)

A

this is because the stable ions they form do not have incomplete 3d subshells

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5
Q

what are the physical properties of transition metals
(2)

A
  • they all have a high density
  • they all have high melting points and boiling points.
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6
Q

what are the chemical properties of transition metals
(4)

A
  • they form complex ions
  • they form coloured ions
  • they are good catalysts
  • they can exist in variable oxidation states
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7
Q

what is the colour of the vanadium ions
(4)

A

VO2^+ yellow +5
VO^2+ brown +4
V3+ green +3
V2+ violet +2

you better get vanadium

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8
Q

what is the coloured ion of cobalt
(1)

A

pink

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9
Q

what is the coloured ion of nickel
(1)

A

green

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10
Q

what are the coloured ions of titanium
(2)

A

Ti2+ violet
Ti3+ purple

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11
Q

what are the coloured ions of Manganese
(3)

A

Mn2+ very pale pink/colourless
MnO4^2- green
MnO4^- purple

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12
Q

what are the coloured ions of Chromium
(2)

A

Cr3+ green
Cr2O7^2- orange

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13
Q

what is a complex ion
(1)

A

it is a metal ion with ligands co-ordinately(dative) bonded to it

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14
Q

what is a ligand
(1)

A

it is an atom, molecule or ion that can donate a pair of electrons to a central metal ion

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15
Q

what does monodentate mean
(1)

A

it is a ligand that can only form one co-ordinate bond

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16
Q

what does multidentate mean
(1)

A

it is ligands that can form more than one co-ordinate bond.

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17
Q

what does bidentate mean
(1)

A

it is ligands that can form 2 co-ordinate bonds

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18
Q

what is the equation used to find the oxidation state of the metal ion.
(1)

A

oxidation state of metal = total charge of complex - sum of charges of ligands

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19
Q

what is the co-ordination number
(1)

A

it is the number of co-ordinate bonds that are bonded to the central metal ion

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20
Q

what determines the shape of a complex
(1)

A

it is dictated by the co-ordination number

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21
Q

how many water and ammonia molecules can form co-ordinates bonds to a central metal ion and what is the shape of the complex
(2)

A

6
- octahedral

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22
Q

how many chlorine atoms can form a co-ordinate bond to a central metal ion and what is the shape of the complex
(2)

A

4
tetrahedral

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23
Q

what shape does the complex Cisplatin form
(1)

A

square planar

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24
Q

what are the two types of isomers that occur in complexes

A

cis-trans isomers and optical isomer

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25
Q

what is an optical isomer

A

same molecular formula but a different orientation of bonds in space

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26
Q

what are optical isomers also known as

A

enantiomers

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27
Q

explain cis and trans

A

cis - the ligands are located on the same side next to each other
trans - when the ligands are located in the opposite direction

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28
Q

give a medical use of cisplatin

A

cisplatin can be used to treat some types of cancer such as lung and bladder cancer, this is because cisplatin stops the cancer cells from reproducing

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29
Q

why does the 3d orbital in transition metals split

A

this is because when ligands bond to ions, some orbitals are given more energy than others.

30
Q

how can electrons in the lower orbital(ground state) jump to a higher orbital(exited state) in the 3d subshell

A

they can move to a higher orbital by having the ΔE required which can be obtain through the absorption of light

31
Q

what is the equation for ΔE (energy absorbed)

A

ΔE= hv = hc / λ
ΔE- energy absorbed
h- planks constant (6.63x10^-34)
v- frequency of light (Hz)
c-speed of light (3.00x10^8)
λ- wavelength (M)

32
Q

what affects the size of ΔE ( the amount of energy required for electrons in a lower orbital to jump to a higher orbital)

A
  • central metal ion and its oxidation state
  • ligands
  • co-ordination number
33
Q

explain why complexes formed from transition metals are coloured

A

this is because when visible light hits the transition metal ion, some frequencies are absorbed as some electrons jump from ground state(lower orbital) to an excited state(higher orbital). the frequencies absorbed depends on the size of the energy gap( ΔE ). the rest of the frequencies are reflected/transmitted and combine to make a complementary colour that is visible to us.

34
Q

why do some compounds appear white or colourless

A

this is because they either have no 3d electrons or the 3d subshell is full. this means that no electrons can jump to a higher orbital, meaning that no frequencies of light is absorbed meaning that all the light is reflected which gives it the white or colourless colour.

35
Q

how does spectroscopy work

A

a white light is shone through a filter, which is chosen to only let the colour of light through that is absorbed by the sample. the light then presses throught the sample to a calorimeter, which shows how much light was absorbed by the sample. the more concentrated a coloured solution is, the more light it will absorb.

36
Q

how do you make a calibration graph

A

you plot the absorbance of light by the concentration. you then connect the points by a line and you can use this to work out the unknown concentration or absorbance.

37
Q

what is ligand substitution

A

it is when one ligand is swapped out for another ligand. ( always causes a colour change )

38
Q

what happens when a substitution reaction occurs with a different size ligand

A

the co-ordination number changes and the shape of the molecule changes.

39
Q

what is a partial substitution of ligands

A

this is when only some of the ligands are replaced

40
Q

how does carbon monoxide poisoning occur

A

this happens when CO is inhaled , the CO is substituted for the water ligands forming carboxyhaemoglobin. the CO forms strong bonds with the Fe2+ which doesn’t readily exchange with oxygen or water, this means that the haemoglobin cannot transport blood around the body. this starves the organs of oxygen which can cause death if it goes untreated.

41
Q

how does the stability of the complex affect the reversibility of the reaction

A

ligand substitution reactions are easily reversed unless a more stable ion is formed. if the new complex forms stronger bonds to the central metal ion then it becomes less easy to reverse the reaction.

42
Q

what type of ligands forms the strongest complex ion

A

multidente ligands then bidente ligands

43
Q

what happens to the entropy when a monodente ligand is substituted with a bidente or multidente ligand

A

the entropy increases because the number of particles increases, which means there is a greater entropy. this means that the reaction is more likely to occur. this is known as the chelate effect.

44
Q

what is redox potential

A

it is a measure of how easily an ion or an atom is reduced to a lower oxidation state. more positive - less stable - more likely to be reduced.

  • this is the same as the electrode potential
45
Q

what are the conditions for a standard electrode potential

A

the concentration of the reactant has to be 1 dm^3 and the standard potential is done against an hydrogen cell

46
Q

what effect does ligands have on the redox potential

A
  • Standard electrodes are measured in aqueous solutions, meaning that any ion will be surrounded by water ligands.
  • different ligands affect the redox potential in different ways depending on how well they bind to the metal ion in a particular oxidation state.
47
Q

how does PH affect redox potential

A
  • the PH of a solution affects the size of the redox potential.
  • redox potential is more positive in an acidic solution as they are easily reduced whereas in an alkali solution, the redox potential is more negative.
48
Q

how do you carry out a transition metal titration

A
  • measure out the quantity of reducing agent with a pipette and put into a conical flask
  • use measuring cylinder to add 20cm^3 of sulfuric acid, this is in excess so that there is plenty H+ so that the oxidation agent can be reduced.
  • add the oxidising agent to the reducing agent using a burette while swirling as you go
  • stop adding the oxidising agent when the mixture in the flask becomes tainted with the colour of the oxidising agent
  • then do accurate titrations until you get two or more concordant results.
49
Q

how do you balance half equations ( Dr Bulmers method )

A

BOHE
Balance the ions
Oxygen - balance the oxygen with water
Hydrogen - balance with H+
Electrons - balance by adding electrons to balance the charge on both sides

50
Q

what is a catalyst

A

it is a substance that speeds up the rate of reaction by providing and alternative pathway with a lower activation energy and does not get used up.

51
Q

why are transition metals good catalysts

A

they are good catalysts as they have variable oxidation states. they can easily transfer electrons to speed up a reaction

52
Q

what is the contact process

A

it is an industrial method that is used to make sulfuric acid

53
Q

what is the overall reaction of the contact process and what is the catalyst for the reaction

A

SO2(g) + 1/2O2(g) = SO3(g)
the catalyst is vanadium oxide
V2O5

54
Q

what are the two steps in which vanadium catalyses the contact process ( SO2 + 1/2O2)

A

V2O5 + SO2 = V2O4 + SO3

V2O4 + 1/2O2 = V2O5

55
Q

what is a heterogeneous catalyst

A

it is a catalyst that is in a different phase than the reactants. ( e.g different physical state )

56
Q

what are the two examples of heterogeneous catalysts you need to know

A

Haber process and the contact process

57
Q

what is a support medium

A

it is something that increases the surface area of a catalyst

58
Q

what is catalyst poisoning
(4)

A

this is when impurities in the mixutre bind with the catalyst and block other reactants from being absorbed
- this slows down the reaction
- may have to be replaced/regenerated
- less product is produced

59
Q

how does a heterogeneous catalyst work

A
  • one reactant settles on the surface of the catalyst and then another one approaches the catalyst ( this is absorption )
  • the electrons of the reactants are rearranged ( this is the reaction )
  • the product is then released from the surface ( this is the desorption )
60
Q

what is a autocatalysing catalyst

A

it is when the catalyst is also the product

61
Q

what is a homogeneous catalyst

A

it is a catalyst that is in the same phase as the reactants

62
Q

how does a homogeneous catalyst work

A

the reactants combine with the catalyst to form an intermediate species that then reacts to form the products and reforms the catalyst.

63
Q

write the overall reaction between S2O8^2- and I^- in the presence of the catalyst Fe2+. and also give the two steps in which Fe2+ catalyses the reaction

A

overall equation
S2O8^2-(aq) + 2I^-(aq) = I2(aq) + 2SO4^2-( aq)

two steps
S2O8^2-(aq) + 2Fe^2+(aq) = 2Fe^3+(aq) + 2SO4^2-(aq)

2Fe^3+(aq) + 2I^-(aq) = I2(aq) + 2Fe^2+(aq)

64
Q

write the overall reaction between MnO4^- and C2O4^2-in the presence of the catalyst Mn^2+. and also give the two steps in which Fe2+ catalyses the reaction

A

overall equation
2MnO4^-(aq) + 16H^+(aq) +5C2O4^2-(aq) = 2Mn^2+(aq) + 8H2O(L) + 10CO2(g)

two steps
4Mn^2+(aq) + MnO4^-(aq) + 8H^+(aq) = 5Mn^3+(aq) + 4H2O(L)

2Mn^3+(aq) + C2O4^2-(aq) = 2Mn^2+(aq) + 2CO2(g)

65
Q

what is the hydration of metals

A

it is when when water molecules forms coordinate bonds with the metal ion when it is dissolved in water

66
Q

what happens in a reaction when a metal aqua 2+ ion and water

A

the metal aqua 2+ ion release H+ ions, so an acidic solution is formed. they only slightly dissociate meaning that the solution is only weakly acidic

67
Q

why is a metal 3+ ion more acidic than a 2+

A

this is because the metal 3+ ion has a big charge meaning it has a high charge density than the metal 2+ ion. this means the metal 3+ ion is more polarising than the metal 2+ ion, this means that they attract the electrons from the oxygen of the coordinated water molecules more strongly. this weakens the O-H bond meaning the hydrogen ions are more likely to be lost. this makes the metal 3+ ion more acidic as more hydrogen is released

68
Q

what does amphoteric mean

A

they can act as both acids and bases

69
Q

what happens when you add OH- ions to a solution of metal aqua 3+ ions
(1)

A

it forms a insoluble precipitate of metal hydroxides.

70
Q

why does an insoluble precipitate form when you react excess OH- ions with a metal aqua 3+ or 2+ ion

A

this is because when the metal aqua ion is in water it forms and equilibrium that produces H3O+ ions and when OH- ions are added the H3O+ ions are removed which causes the equilibrium to shift to counteract that change. this forms another equilibrium as in the previous equilibrium reaction the metal aqua ion had been oxidised, now the oxidised metal aqua ion then reacts with the water forming an equilibrium reaction which produces H3O+ ions again and the excess OH- ions remove it again causing the process to occur again until an insoluble precipitate is formed.

71
Q

how can ammonia(NH3) be in a hydrolysis of a metal aqua ion
(1)

A

this is because when ammonia dissolves in water it can accept a proton from water forming NH4+ & OH- ligands.

72
Q

explain hydrolysis of metal aqua ions using Na2CO3

A
  • Na2CO3 can react with 2+ metal aqua ions to form an insoluble precipitate, this is because the CO3 displaces the water.
    -when Na2CO3 reacts with 3+ metal aqua ions they form hydroxides precipitates. this is because the CO3 reacts with the H3O+ , removing them and producing bubbles of CO2

A-level chemistry unit 5 (3 decks)

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