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Chemistry A level > Developing Metals > Flashcards

Developing Metals Flashcards

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1
Q

Where is the D-block on the periodic table?

A

It is the 10 wide section between the s-block and the p-block

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2
Q

How different are the elements in the D-block?

A

They are all very similar

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3
Q

What is the electronic configuration of D-block elements?

A

The D-block elements have a partially filled 3D shell and the 4S shell has already been filled. The outermost shell is the 4S shell.
As you move across the block each element has one more proton in the nucleus

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4
Q

What is the electronic configuration trend of each row?

A

As you move across, another electron is added to the 3D orbitals (one in each of the 5 orbitals) until 2 electrons occupy each orbital. Chromium and copper break the rule?

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5
Q

How do chromium differ? why?

A

Chromium should have 4 electrons in its 3D shell but instead it has 5 because one has been taken out of its 4S shell.
Its configuration is [Ar] 3d5 4s1
Because this configuration has a lower energy

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6
Q

How does copper differ? why?

A

Copper should have 9 electrons in its 3D shell instead it has 10 and the 4S shell has one (one has been taken out).
Its configuration is [Ar] 3d10 4s1
This configuration has a lower energy because electrons have been pushed to a lower orbital

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7
Q

Talk about the why two electrons in an orbital has more energy?

A

It has more energy because the charges of the electrons repel so two in an orbital has more repulsion so more energy is needed to put them there

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8
Q

How do transition metals lose electrons?

A

They lose electrons first from the 4S orbital then the 3D orbital.

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9
Q

What is the definition for a transition metal?

A

It is a metal with one or more stable ions with a partially filled d-orbital

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10
Q

What two metals are not considered transition metals?

A

Zinc and Scandium

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11
Q

Why is zinc not a transition metal?

A

It only forms a stable Zn2+ ion which has a full d-orbital. This makes it not a transition metal.

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12
Q

Why is scandium not a transition metal/

A

It only forms Sc3+ which has an empty d-orbital so therefore it is not a transition metal

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13
Q

What are the most stable arrangement of electrons for transition metals? what does this mean?

A

Having 5 or 10 electrons in the d shell. This means that a lot of the ions of transition metals have this electronic configuration

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14
Q

How is iron content analysed using redox reactions with MnO4-?

A

Iron(II) can be oxidised to iron (III) by potassium manganate(VII). If potassium manganate of a known concentration is titrated with an iron solution, the amount of iron can be calculated.
It is a redox reaction because the iron loses electrons and the manganate gains them

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15
Q

How is iron content analysed using redox reactions with Acidified potassium dichromate?

A

Acidified potassium dichromate can be titrated the same way as the potassium manganate and this can then be used to work out the iron content.

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16
Q

Define the function of a catalyst

A

They offer an alternative reaction pathway with a lower activation enthalpy than that of an uncatlysed reaction

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17
Q

What makes a transition metal a good catalyst? (2)

A

The availability of the 3d shell and the 4s electrons.

The ability to change oxidation state.

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18
Q

How do transition metals catalyse a reaction (heterogeneous)?

A

3d and 4s electrons of atoms on the metals surface forms weak bonds with the reactants (chemisorption). Once as the reaction has occurred then the bonds break to release the products.

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19
Q

What is the bonding of reactants to the surface of a transition metal catalyst called?

A

Chemisorption

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20
Q

How can a transition metal form a homogeneous catalyst?

A

When it is aquius in solution.

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21
Q

How do transition metals catalyse a reaction (homogeneous)?

A

They form an intermediate compound with one or more of the reactants which then later break down releasing the catalyst in its original form

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22
Q

Are transition metals good catalysts for redox reactions?

A

Yes

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23
Q

Are transition metals coloured?

A

Yes, most of them are

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24
Q

What is the colour of Fe2+?

A

Green

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25
Q

What is the colour of Fe3+ ?

A

Orance/Brown

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26
Q

What is the colour of Cu2+?

A

Blue

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27
Q

How does a substance apear coloured?

A

By absorbing some wavlengths of light in the VISIBLE spectrum.
The light that isnt absorbed is reflected and this produces the colour seen.
The absense of the absorbed colour makes it apear coloured.

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28
Q

What is an absorbtion spectrum (with regards to a coloured compound)?

A

It is a graph of wavelength (xaxis) against absorbance (yaxis). It shows the wavelengths of light that are absorbed.

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29
Q

What does the absorbtion spectrum depend on?

A

The number of electrons in the d subshell and the difference in the energy levels.

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30
Q

What is a ligand?

A

It is a molecule with lone pairs of elecrons that attatches itself to a transition metal ion.
The ligand donates its electrons (datively or by forming a cooridnate bond) and surrounds it.

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31
Q

What are some typical ligands? What can a ligand be?

A

Typical ligands are H20 and NH3 but thet can also be anything like a Cl- I on or CN- or OH-

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32
Q

What are the different types of ligands? What do each of them say about the bonding?

A

Monodentate (The ligand forms 1 bond)
Bidentate (The ligand forms 2 bonds)
Polydentate (the ligand forms more than 2 bonds.

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33
Q

What is EDTA?

A

It is a special type of ligand that can form 6 bonds with a single transition metal ion. It is a hexadentate.

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34
Q

How do ligands affect the orbitals of atoms?

A

Orbitals close to the ligands push the orbitals to a slightly higher energy level than those further away. As a result the D-subshell electrons split into two groups each with a different energy level (one of 2 orbitals and the other 3 orbitals).

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35
Q

How does the Dshell splitting pattern affect the colour of light that is absorbed?

A

Photons of visible light are able to excite electrons so that they move between the split D-shell orbitals. This allows visible light to be absorbed by the transition metal ligand complex and this gives aqueous transition metals colour.

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36
Q

What determines the movement of electrons between energy levels in an atom?

A

The energy of the photon and the difference between the energy of each of the energy levels.

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37
Q

Why specifically do transition metals become coloured?

A

Because the difference between the energy levels is such that it absorbs light in the visible spectrum and therefore apears coloured

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38
Q

How can the same element be coloured differently?

A

If the element has a different oxidation state. If it is surrounded by ligands.

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39
Q

What does the colour of a transition metal depend on?

A

The number of d-electrons present in the transition metal ion. The number and arrangement of ligands around the ion and the subsequent splitting pattern. The nature of the ligands.

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40
Q

Some ligands have a more…

A

… Powerful effect on the splitting patter of the d-shell

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41
Q

Which has a greater effect on the splitting pattern: water or ammonia?

A

Ammonia

42
Q

What is colorimetry?

A

This is the use of the colour (shade) of the solution to determine the concentration.

43
Q

Describe the process of colorimetry

A

White light is shone through a (specific) coloured filter and into a solution that is being tested. The amount of light passes through the solution is then beasured and this is used to calculate the amount of light of the specific colour that is being absorbed.

44
Q

What is the equation for absorbance in colorimetry?

A 
A = kc. 
A = absorbance 
k =  constant for the type of solution
c = the concentration
45
Q

What does A=kc say about the conentration of a solution and absorbance?

A

The absorbance of a solution is directly praportional to the concentration of the solution

46
Q

What is a redox reaction?

A

This is a reaction that involves the movement of electrons

47
Q

How can a redox reaction be turned into a cell?

A

Each half reaction can be isolated in its own half cell. One half cell produces electrons the other accepts electrons. They are then connected with wires to allow electrons to flow between the two reactions.

48
Q

What type of a reaction can the following reaction be classified as? : Zn + CuSO4 ==> ZnSO4 + Cu

A

It is a redox reaction

It is also a displacement reaction

49
Q

What is the SO4- in the reaction: Zn + CuSO4 ==> ZnSO4 + Cu ?

A

It is a spectator ion

50
Q

What happens in the reaction: Zn + CuSO4 ==> ZnSO4 + Cu ?

A

The zinc ions transfer electrons to the copper ions. The half reactions are:
Zn ==> Zn2+ + 2e-
Cu2+ + 2e- ==> Cu

51
Q

Which is the oxidising or reducing agent in the reaction: Zn + CuSO4 ==> ZnSO4 + Cu
Why?

A

Zinc is the reducing agent. It looses electrons.

Copper(2+) is the oxidising agent. It gains electrons.

52
Q

Can the reaction: Zn + CuSO4 ==> ZnSO4 + Cu run in reverse?

A

No, this is not energetically possible

53
Q

What determines the directions that a redox reaction (like Zn + CuSO4 ==> ZnSO4 + Cu ) occurs?

A

What each of the half equations is reacting with

54
Q

How are two half reactions combined?

A

The electrons need to be balanced and the charge on either side needs to be the same. Then the reactions can be combined.

55
Q

How does two combined half cells to form a cell become useful?

A

The moving electrons can be used to do work

56
Q

What is the unit of:

a) charge
b) current

how do they relate?

A

a) coulombs
b) amperes

1 amp is once coulomb passing a point per second

57
Q

What is potential difference?

A

This is the joules per coulomb of charge passing a point

58
Q

What is used to measure potential difference?

A

A high resistance voltmeter

59
Q

What does a half cell look like?

A

There is a liquid solution filled with aqueous ions and then there is a solid electrode mate either of a metal, carbon or platinum. If necessary a gas may be pumped into the solution.

60
Q

How are two half cells connected?

A

There is a salt bridge connecting the two solutions together and then the electrodes are connected by a wire.

61
Q

What is Ecell?

A

This is the potential difference between two connected half cells.

62
Q

How is Ecell calculated?

A

It is the difference between the half-cell electrode potentials.

63
Q

How can the electrode potential for a specific reaction be calculated?

A

By connecting it up to a hydrogen half cell which has an electrode potential of 0 so the potential difference measured is the half-cell electrode potential.

64
Q

What are the conditions used to work out the standard electrode potential?

A

1 moldm^-3 concentration of solution
Any gas is pumped in at 10^5 Pa of pressure (1 atm)
The reaction is run at atmospheric pressure.
298*K temperature.

65
Q

What is the definition of a standard electrode potential for a half cell?

A

This is the potential difference between the half-cell and a standard hydrogen half cell.

66
Q

What is the symbol for the standard electrode potential of a half cell?

A

Eø

67
Q

How can the direction of the half cell determined from the Eø value?

A

Whether the value is negative or positive

68
Q

What does it mean if the Eø value is positive?

A

It is likely to accept electrons

69
Q

What does it mean if the Eø value is negative?

A

It is likely to give out electrons

70
Q

How is the direction of a cells reaction determined?

A

The most negative reaction runs in reverse, therefore the other reaction (most positive) runs to the right. The full cell equation is then determined from that.

71
Q

How are half cell equations written?

A

With the ion on the left hand side with the added electron and the elemental atom on the right hand side.
E.g. Cl2 + 2e- ==> 2Cl-

72
Q

What is an electrode potential chart?

A

It is a chart showing the half-cell Eø value for half cell reactions. The most NEGATIVE value is on the top with 0v in the middle and then the most positive value on the bottom.

73
Q

What can electrode potentials be used for?

A

They can be used to determine the feasability of a reaction between two different half cell reactions.

74
Q

How is it possible for a reaction to be feasable but not be useful for generating electricity?

A

It may be feasable but the rate of the reaction is low so it therefore only produces a low current and isnt useful.

75
Q

What can be said if the reaction has a slow rate but is feasable?

A

It means that the reaction has a high activation enthalpy

76
Q

How could you increase the rate of a reaction?

A

By including a catalyst

77
Q

How can you make an unfeasable reaction feasable?

A

By changing the reaction conditions so that it can now happen

78
Q

What conditions can be changed to make a reaction feasable?

A

Temperature
Pressure
pH value.

79
Q

What type of process is rusting?

A

It is an electrochemical process

Redox

80
Q

What are the two half equations for rusting?

A

Fe2+(aq) + 2e- <=> Fe(s)

0.5O2(g) + H2O + 2e- <=> 2OH-(aq)

81
Q

What i the process for the production of rust with a water droplet on the surface of iron?

A
  1. The iron becomes Fe(2+) and produces two electrons at the centre of the water droplet on the surface of the iron where dissolved oxygen is low.
  2. These electrons flow through the iron metal and react with higher concentrations of dissolved oxygen at the edges of the water droplet to produce 2OH-
  3. These OH- ions then react with the Fe(2+) to produce Fe(OH)2
  4. This Fe(OH)2 then reacts with oxygen again to form Fe2O3•xH20
82
Q

Where is corrosion the greatest?

A

At the centre of the droplet of water on the surface of the paint because the oxygen concentration is low.
Pits are formed where iron has dissolved away.

83
Q

Why is zinc a good sacrificial metal?

A

It is good because it has a much more negative electrode potential. This causes the iron reaction to proceed to the right preventing Fe(2+) from forming.

84
Q

Why is chromium a good at protecting metal?

A

It forms a Chromium(III) oxide layer which protects it

85
Q

What is the simplest way to protect against rusting? give examples.

A

It is to provide a barrier between the metal and the atmosphere.
Examples:
Oil, Paint, plastic

86
Q

What is the process of coating a metal with zinc?

A

Galvanising

87
Q

How does galvanising work? when will it stop working?

A

It works by coating the metal in zinc which then produces a protective zinc oxide layer.
It will stop working when the zinc layer is damaged and scratched

88
Q

What happens after a galvanised metal is damaged? what is this called?

A

It is still protected because the zinc corrodes in preference to the metal
The zinc is now a sacrificial metal

89
Q

What is another method to protect iron form rusting that does not require added material?

A

Impressed current (applied EMF)

90
Q

What is impressed current? how does it work?

A

It is applying a EMF to the metal and causing it to become a cathode. It works because the oxidation of the metal occurs at an anode site where electrons are taken from the iron. If it is made into a cathode site it moves the position of equilibrium for the half reaction equation.

91
Q

Electrically how is an EMF applied?

A

The negative end of a battery of DC supply is attached to the metal

92
Q

Where is impressed current most commonly applied?

A

To underground pipelines, where lots of oxygen is present

93
Q

What is a complex?

A

It consists of a central metal atom / ion surrounded by a number of negatively charged ions or neutral molecules with lone pairs of electrons. These surrounding molecules are called ligands

94
Q

What is a complex with an overall charge called?

A

A complex ion

95
Q

What is the charge of each atom in [NiCl4]2- ?

A

Cl is always 1-
Ni + 4(1-) = 2-
Ni is 2+

96
Q

What can be said about the charges of a complex ion?

A

It is delocalised over the whole structure

97
Q

What is a common way that a ligand bonds with an metal?

A

Electron pairs are often shared with a central atom. This is a form of dative bonding (also called coordinate boning)

98
Q

What is the number of bonds from ligands called?

A

the coordination number

99
Q

What are 4 common types of shapes of complexes and how many coordinate bonds do they have?

A

Octahedral = 6 bonds
Tetrahedral = 4 bonds
Square planar = 4 bonds
Linear = 2 bonds

100
Q

How can the ligand for a dissolved molecule change?

A

They can be displaced

101
Q

What is the equation where chlorine displaces water as the ligand for Copper(II)?

A

[Cu(H2O)6]2+ + 4Cl- ==> [CuCl4]2- + 6H2O

102
Q

Why does ligand substitution occur?

A

Because the new complex is more stable than the previouse one

Chemistry A level (13 decks)

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