A Level Chemistry Ocr > Module 5 Chapter 2 > Flashcards

Module 5 Chapter 2 Flashcards

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1
Q

What the transition elements

A

D-block elements that are found between groups 2 and 13

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2
Q

What is a feature of the order in which the sub shells are filled by a d-block element

A

When forming an atom d-block elements fill the 4s sub-shell before the 3d sub-shell

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3
Q

What is a feature of the order in which the sub shells are emptied by a d-block element in ion formation

A

In ion formation loses 4s electrons before 3d electrons

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4
Q

What is an exception to this trend in how subshells are filled

A

For chromium and copper a 4S2 electron is promoted to half full or fully fill the 3D sub-shells respectively

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5
Q

What is the electron configuration of chromium and copper

A

Chromium - [Ar] 3S2 3P6 4S1 3D5
Copper - [Ar] 3S2 3P6 4S1 3D10

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6
Q

Why do chromium and copper atoms fill the subshells in this way

A

Although promoting a 4s electron raises the sub-shells energy level this is negated by creating a more energetically stable half/fully filled 3d sub-shell

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7
Q

What happens when transition metals form positively charged ions

A

They lose their 4s electrons before losing any of the 3d electrons

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8
Q

What is the definition of a transition metals

A

An element that forms an ion with a partially filled d subshell

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9
Q

What elements are transition elements but don’t fit the definition of a transition metals

A

Scandium and zinc as scandium only forms a +3 ion and zinc only forms a +2 ion, with a full 3D subshell in zinc and an empty 3D subshell in scandium

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10
Q

What are the properties of transition metals that are the same as other metals

A

High melting points and boiling points
Shiny
Conduct electricity and heat

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11
Q

What are properties that are unique to transition metals

A

Variable oxidation states
Coloured compounds
Elements and compounds can act as catalysts

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12
Q

What is a feature of how the number of oxidation states in a transition metal varies across a period

A

The number of oxidation states increases across the transition elements until manganese then it will decrease

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13
Q

What is a feature of all transition elements

A

They form compounds with an oxidation number of +2

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14
Q

When are these transition metal compounds coloured

A

When they are dissolved in water = coloured solution

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15
Q

What is colour linked to

A

The partially filled d-orbitals and can vary with oxidation states

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16
Q

What are some examples of transition metals catalyst

A

Haber process - iron catalyst (fertiliser production as makes ammonia)

Contact process - vanadium (v) oxide (sulphuric acid, fetilisers)

Hydrogenation of vegetable fats - nickel catalyst

Decomposition of hydrogen peroxide - manganese (IV) oxide catalyst

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17
Q

When do complex ions form

A

When a metal ion is centrally bonded to one or more molecules or negative ions known as ligands

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18
Q

What do ligands do

A

They donate a pair of electrons to form a dative bond (or coordinate bond) with the central metal ion

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19
Q

What is the coordinate number

A

The number of dative bonds made

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20
Q

What are the two types of ligands

A

Monodentate

Bidentate

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21
Q

What are monodentate ligands and examples

A

Ligands that donate 1 pair of electrons to the central metal ion

Examples: water, ammonia, chloride, cyanide, hydroxide

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22
Q

What are bidentate ligands and examples

A

Donate 2 pairs of electrons to central metal ion

Examples: diaminoethane, oxalate

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23
Q

What is the shape of complex ions with 6 coordinate numbers

A

They have an octahedral shape with a bond angle of 90*

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24
Q

What is the shape of 4 coordinate complex ions

A

Tetrahedral - 109.5* around the central ion
Square planar - bond angle of 90*

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25
What are examples of square planar complex ions
Platinum complexes (platin) Palladium and gold complexes too
26
Why do palladium, gold and platinum have a square planar shape
As the transition metals with 8d electrons in their highest energy d-subshell
27
What are hexaaqua complexes
Complexes with 6 water molecules
28
What does the colour of a complex ions depend on
It relies on the central metal atom, its oxidation state and the ligands bonded
29
What determines the colour of a transition metals form positively of a particular oxidation state
What colours are not absorbed and instead reflected determines the colour of the complex ion
30
What is a Ligand substitution reaction
It occurs when a ligand in a complex ion is replaced with another ligand
31
What are the 3 ligand substitution reactions that we need to know
[Cu(H2O)6]2+ with NH3 [Cu(H2O)6]2+ with CL- [Cr(H2O)6]2+ with NH3
32
what occurs in the reaction with Cu2+ and ammonia
Copper sulphate solutions forms a pale-blue octahedral complex ion [Cu(H2O)6]2+ With the addition of ammonia, 4 water ligands are substituted for 4 ammonia ligands in 2 steps
33
What are the two steps for the substitution of water with ammonia
1. Precipitation of the pale blue precipitate Cu(OH)2 2. Precipitate dissolves in excess ammonia to form a dark blue solution of [Cu(NH3)4(H2O)2]2+
34
What is the overall equation from the substitution of ammonia into the complex copper ion
[Cu(H2O)6]2+ + 4NH3 —> [Cu(NH3)4(H2O)2]2+ + 4H2O
35
What is the colour change for the hydrated copper ions reacting with ammonia
Pale Blue —> dark blue
36
What is the reaction with copper sulphate complex ions with chloride
With the addition of chloride ions all the water ligands are substituted for 4 chloride ligands The yellow tetrahedral [CuCl4]2- complex ions forms
37
What is the colour of the intermediate solution
Green when there are equal amounts of each complex ions
38
Why are only 4 chlorides substituted
As the chlorides are larger than H2O so can fit around the Cu2+
39
What is the overall equation
[Cu(H2O)6]2+ + 4Cl- <-> [CuCl4]2- + 6H2O
40
What are the different colours of chromium (III) potassium sulphate and chromium (III) sulphate in water
Chromium (III) potassium sulphate (KCr(SO4)2*12H2O dissolves in water to give the pale purple complex ion When chromium (III) sulphate is dissolved in water and a green solution is formed [Cr(H2O)5SO4]+ is the complex ions
41
What is the oxidation state of chromium in both of the complex ions
3+
42
What happens when the water ligands are substituted with ammonia ligands
A grey-green precipitate of Cr(OH)3 forms Excess ammonia dissolves the precipitate to form the dark purple complex ion [Cr(NH3)6]3+
43
What is the overall equation for the reaction of the complex chromium ions with water
[Cr(H2O)6]3+ + 6NH3 —> [Cr(NH3)6]3+ + 6H2O
44
What does haemoglobin consists of
4 portion chains that are held together by weak intermolecular forces. Each chain contains a haem group with a central Fe2+ ion that can bind to oxygen
45
What ioes the iron form in haemoglobin
It has 4 dative bonds with nitrogen atoms in the Haem group, a fifth to a nitrogen on the protein and a sixth with a water molecule
46
What occurs int he presence of oxygen to haemoglobin
In the prescence of oxygen (high conc) the loosely held water molecule is substituted forming oxyhemoglobin —> as there are 4 O2 molecules are bound
47
How are the oxygen molecules removed from oxyhemoglobin
They can be carried by oxyhaemoglobin which can be removed again at cells by substituting the water back. Red blood cells can carry O2 there and CO2 back
48
What is the equation of haemoglobin binding to oxygen
Haemoglobin + oxygen <-> oxyhaemoglobin
49
What can carbon monoxide do to haemoglobin
They can substitute the water molecule and bind to Fe2+ in haemoglobin to form carboxyhaemoglobin Haemoglobin + CO —> carboxyhaemoglobin
50
What is a feature of the CO once bound to the Fe2+
It binds to the Fe2+ much stronger than that of O2 and so can’t be removed Small concentrations of CO can therefore dramatically effect blood O2 levels
51
What can CO binding to haemoglobin do
It can therefore dramatically effect blood O2 levels This can lead to death —> the only fix is the oversaturation of pure O2
52
How can each of these precipitate tests be done experimentally (1)
Add 20cm3 of copper sulphate solution to a test tube then add ammonia dropwise (pale blue —> dark blue)
53
How can each of these precipitate tests be done experimentally (2)
Add 2cm3 of copper sulphate solution to a second test tube, then add conc HCL dropwise. when complete slowly add water back into the test tube (pale blue —> yellow —> green)
54
How can each of these precipitate tests be done experimentally (3)
Add 2cm3 of chromium (II) potassium sulphate solution to a third test tube then add ammonia dropwise (pale purple —> grey-green —> purple)
55
What is the colour of Cu2+ in solution, with NaOH, its solubility with excess NaOH, with NH3 and with excess NH3
Blue, Blue precipitate, insoluble, Blue ppt, soluble (dark blue solutioN0
56
What is the colour of Fe2+ in solution, with NaOH, its solubility with excess NaOH, with NH3 and with excess NH3
Pale green, green ppt, insoluble, green ppt, insoluble
57
What is the colour of Fe3+ in solution, with NaOH, its solubility with excess NaOH, with NH3 and with excess NH3
Pale yellow, orange-brown ppt, insoluble, orange brown ppt, insoluble
58
What is the colour of Mn2+ in solution, with NaOH, its solubility with excess NaOH, with NH3 and with excess NH3
Pale pink, light-brown ppt, insoluble, light brown ppt, insoluble
59
What is the colour of Cr3+ in solution, with NaOH, its solubility with excess NaOH, with NH3 and with excess NH3
violet, grey green, soluble (dark-green), grey-green, soluble (purple)
60
What occurs in the reaction between iron (II) ions and MnO4- ions
The Fe2+ is oxidised to Fe3+ MnO4-2 is reduced to Mn2+
61
What is the change in colour in the reaction between iron (II) ions and MnO4- ions
The solution containing MnO4- ions is purple and decolorised by Fe2+ ions to form a colourless solution containing Mn2+ ions
62
What is the colour change when Fe3+ reacts with iodide ions
The orange-brown Fe3+ ions are reduced to pale green Fe2+ions this colour change however is obscured by the oxidation of iodide to form iodine which is brown
63
What is the equation with the colour changes of Fe3+ reacting with iodide ions
2Fe3+ (aq) + 2I- (aq) —> 2Fe2+ + I2 Orange-brown - Fe3+ Pale green - Fe2+ Brown - I2
64
What do is the colourless of dichromate ions and chromium Cr3+ ions
Cr2O7 2- orange colour and Cr3+ ions have a green colour
65
What occurs in the reaction between acidified Cr2O72- and zinc
The acidified Cr2O72- ions are reduced to Cr3+ ions by the addition of zinc
66
What is the equation of the reaction between acidified Cr2O7 2- and zinc
Cr2O7 2- + 14H+ + 3Zn —> 2Cr3+ + 7H2O + 3Zn 2+
67
What happens when an excess of zinc is added and the reaction
The chromium (III) ions are reduced to chromium (II) ions which is a pale blue colour Zn (s) + 2Cr3+ (aq) —> Zn 2+ (aq) + 2Cr2+ (aq) Cr3+ - green Cr2+ - pale blue colour
68
What is a feature of hydrogen peroxide
It is a powerful oxidising agent
69
What is the reaction between H2O2 and Cr3+ ions and what is the colour change
3H2O2 + 2Cr3+ + COOH- —> 2CrO4 2- + 8H2O Cr3+ - green CrO4 2- - vibrant yellow
70
What happens when aqueous copper (II) ions react with iodide ions
I- is oxidised to form brown I2 Cu2+ is reduced to form Cu+ The Cu+ forms a white precipitate of copper (I) iodine
71
What is the equation of copper reacting with iodine
2Cu2+ + 4I- —> 2CuI (s) + I2 (s) Cu2+ - pale blue CuI - white precipitate I2 - brown
72
What happens when solid Cu2O reacts with dilute H2SO4
It forms a brown precipitate of copper is formed together with a blow solution of copper (II) sulphate
73
What is the overall reaction of Cu2O + H2SO4
Cu2O + H2SO4 —> Cu + CuSO4 + H2O
74
What can the reaction between sodium hydroxide and metals be used to do
they can be used to identify transition metal ions in an unknown solution
75
What is the test for ammonium ions
Add concentrated NaOH and as ammonia and as ammonia is produced it will turn damp red litmus paper blue
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