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CH5 > P-block Chemistry > Flashcards

P-block Chemistry Flashcards

1
Q

Describe briefly the amphoteric behaviour of aluminium

Lead will react in the same way

A

Add aqueous sodium hydroxide to a solution of aluminium ions
Al3+ + 3OH- –> Al(OH)3 which is a white ppt
Add excess sodium hydroxide and the white ppt dissolves
Al(OH)3 + OH- –> [Al(OH)4]-

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2
Q

Explain the inert pair effect

A

The outermost ns2 pair of electrons have the tendency to become inert during bonding. This allows the stability of lower oxidation states to increase going down groups

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3
Q

What is the octet expansion, and what does it allow?

A

The octet expansion is only present in element from period 3 down. It is where they promote one of their ns2 bonding electrons to the d sub-shell in order to create more bonds. This is why phosphorus can form PCl3 and PCl5

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4
Q

Define electron deficient

A

A species with fewer than eight electrons in its outer shell

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5
Q

What is a co-ordinate bond?

A

A bond where the shared pair of electrons both come from the same atom

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6
Q

What is a lone pair?

A

A pair of electrons in the outer shell which are not involved in bonding

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7
Q

What is Al2Cl6?

A

This is a dimes formed by the joining of two AlCl3 molecules. Aluminium is no longer electron deficient in the dimer because a chlorine molecule from one monomer, which contains a lone pair, forms a co-ordinate bond with the aluminium on the other providing it with a full outer shell of electrons

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8
Q

How is AlCl4- formed? Describe two reactions where it is used

A

AlCl3 can form a co-ordinate bond with a chloride ion which will remove its electron deficiency.
The alumina the ion is used as a halogen carrier in the chlorination of benzene, and as a catalyst in the polymerisation of alkenes.

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9
Q

What are donor-acceptor compounds?

A

Molecules which are electron deficient, like BF3 and AlCl3, will try to react with species which have lone pairs to get rid of the electron deficiency. The compound formed as a result is called a donor-acceptor compounds.

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10
Q

What is meant by isoelectric?

A

Boron nitride and carbon are classed as isoelectric because they have the same number of electrons in their outer shells

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11
Q

Describe and explain the structure of hexagonal boron nitride by comparison with graphite

A

Both have hexagonal layers formed by covalent bonds
Both exhibit lubricating properties; weak forces between layers allow them to slide over each other
Graphite conducts electricity; fourth valence electron on each carbon is delocalised and able to carry charge
BN can’t conduct electricity; each N has a lone pair which remain localised, so electrons can’t move and can’t conduct
Similarities between BN and graphite are due to them being isoelectric

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12
Q

Describe the structure of cubic boron nitride, two properties and two uses

A

Structure : Cubic BN has a similar structure to diamond with a tetrahedral arrangement
Properties : High melting temp, one of the hardest materials, excellent heat conductor, chemically unreactive
Uses : mounting high power electronic components, wear-resistant coatings, supports for catalysts

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13
Q

Describe one use of boron nitride nanotubes

A

Hexagonal boron nitride can be used to wrap around carbon nanotubes in order insulate them and maintain the current

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14
Q

Define amphoteric

A

A substance which can react with both acids and bases

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15
Q

Describe the trend in oxidation states in group 4

A

Typically the elements have an oxidation state of +4, but the inert pair becomes more significant down the group, so the lower elements have a +2 oxidation state as well. Tin and lead both show +2 and +4 oxidation states, for lead, the +2 oxidation state is the most stable

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16
Q

Give an example of the +2 oxidation state in carbon and describe a use of this

A

The only common example is CO, which will act as a reducing agent as it is trying to reach the stable +4 oxidation state in CO2

17
Q

The +4 oxidation state is more stable than +2 in tin, give a specific use of this

A

Tin (II) compounds can act as reducing agents, for example, in the reduction of nitrobenzene

18
Q

Lead (IV) compound are able to act as oxidising agents. Explain

A

Lead is the only group 4 element where the +2 oxidation state is more stable. As they go from the +4 to the +2 oxidation state they are themselves reduced and thus act as oxidising agents

19
Q

What type of structure does PbO adopt?

A

Giant ionic structure due to ionic bonding

20
Q

Describe the reaction of CCl4 with water

A

No reaction with water, it forms a separate colourless liquid layer. CCl4 cannot bond with water due to lack of d-orbitals on the carbon for bonding to initiate reaction

21
Q

Describe the reaction of SiCl4 with water

A

The two liquids react very quickly according to the equation;
SiCl4(l) + 2H2O(l) –> SiO2(s) + HCl(g)
SiO2 ~ white solid
HCl ~ steamy fumes
The d-orbitals in the outer shell of silicon allow a lone pair from oxygen to bond and initiate a reaction

22
Q

Describe the reaction of PbCl2 with water

A

No reaction with water as ionic chlorides are in soluble in water
PbCl2 will remain as a white solid

23
Q 
Aqueous lead (II) ions with aqueous chloride ions
(Equation and observation)
A

Pb2+ + 2Cl- –> PbCl2

Forms a white precipitate

24
Q

Aqueous lead ions with aqueous iodide ions

Equation and observation

A 
Pb2+ + 2I- --> PbI2
Yellow precipitate (only other metal than silver to form a yellow ppt with iodide ions)
25
Q

Carbon dioxide is an acidic oxide, give an equation to show this

A

2NaOH(aq) + CO2(g) –> Na2CO3(aq) + H2O(l)

26
Q

Lead oxide is amphoteric so it reacts with acids and bases to form colourless solutions, give two equations which show this

A

With acid : PbO(s) + 2HNO3(aq) –> Pb(NO3)2(aq) + H2O(l)

With base : PbO(s) + 2NaOH(aq) + H2O(l) –> Na2Pb(OH)4

27
Q

Which of chlorine, bromine and iodine are the most oxidising? Explain how this links to displacement reactions

A

Chlorine is the most oxidising because it has the highest E°, followed by bromine and then iodine.
In a displacement reaction, the most reactive halogen displace the least reactive, in terms of redox, the stronger oxidising agent (e.g. Chlorine) will oxidise a weaker one from its ions to its element (e.g. Bromide to bromine)

28
Q

What is a disproportionation reaction?

A

A reaction where atoms of the same element become oxidised and reduced to form two different products

29
Q

Equation for the reaction of chlorine with dilute sodium hydroxide in COLD conditions, what is this reaction called?

A

Cl2 + 2NaOH –> NaCl + NaOCl + H2O

Disproportionation reaction

30
Q

Equation for the reaction of chlorine with dilute sodium hydroxide in WARM conditions, what is this reaction called?

A

Cl2 + 6NaOH –> 5NaCl + NaClO3 + 3H2O

Disproportionation reaction

31
Q

Do halogens or halides act as oxidising agents?

A

Halogens act as oxidising agents while halides act as reducing agents

32
Q

Explain the reaction of sodium chloride with concentrated sulphuric acid
(Equations and observations)

A

NaCl + H2SO4 –> NaHSO4 + HCl
~ steamy fumes of HCl gas
This is the only reaction that occurs with NaCl because it has a higher E° value and is therefore harder to oxidise

33
Q

Explain the reaction of sodium bromide with concentrated sulphuric acid
(Equations and observations)

A

NaBr + H2SO4 –> NaHSO4 + HBr
~ steamy fumes of HBr gas
The HBr is then oxidised by H2SO4 to form
~ Br2 as orange fumes
While the bromide reduces the sulphur in NaHSO4 to
~ SO2 as a colourless gas
Bromide is a strong enough reducing agent to reduce sulphur from +6 to +4

34
Q

Explain the reaction of sodium iodide with concentrated sulphuric acid
(Equations and observations)

A

NaI + H2SO4 –> NaHSO4 + HI
~ steamy fumes of HI gas
HI can be oxidised by sulphuric acid to form
~ I2 as a black solid or purple fumes
While the iodide reduces the sulphur in NaHSO4 to
~ SO2 as a colourless gas (+4)
~ S as a yellow solid (0)
~ H2S gas which smells of rotten eggs (-2)
Iodide is a much stronger reducing agent because it has a lower E° and therefore reduces sulphur from +6 to -2

35
Q

4 uses of halogen containing compounds

A
  1. Chlorine in the disinfection of water supplies
  2. Sodium chlorate (I) as bleach
  3. Sodium chlorate (V) as a weed killer
  4. Polytetrafluoroethene (PTFE) as a non-stick layer on frying pans
  5. Polychloroethene (PVC) as a waterproof coating
  6. TCP as an antiseptic
  7. Iodine as an antiseptic
  8. Silver bromide in photographic film

CH5 (4 decks)

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