3.3 Chemistry Of The P-block Flashcards
What is an amphoteric substance
A substance that can react with both acids and bases
Reaction of Al3+ (aq) with
• NaOH dropwise
• NaOH in excess
• immediate white precipitate
Al3+(aq) + 3OH-(aq) –> Al(OH)3(s)
• the precipitate dissolves and forma a colourless solution of aluminate
Al(OH)3(s) + OH-(aq) –> [Al(OH)4]-(aq)
Reaction of Al(OH)3 with acid
Al(OH)3(s) + 3H+(aq) –> Al3+(aq) + 3H2O(l)
Reaction of Pb2+ (aq) with
• NaOH dropwise
• NaOH in excess
• white precipitate
Pb2+(aq) + 2OH-(aq) –> Pb(OH)2(s)
• ppt redissolves into a colourless solution of plumbage
Pb(OH)2(s) + 2OH-(aq) –> [Pb(OH)4]2-(aq)
Reaction of PbO with acid
PbO + 2H+ –> Pb2+ + H2O
What is an inert pair
A ns2 pair of electrons not involved in bonding
What is the pattern in the inert pair effect
Increasing reluctance as you move down the group of the s2 pair of electrons in the bonding level to become involved in bonding
Explain the trend in the inert pair effect down group 3,4,5
There is an increasing stability of inter pair cations and the d and f-orbitals don’t effectively shield the inert pair so they becomes strongly attracted to the nucleus
Trend in stability of lower oxidation state down a group
Increases down the group
What is octet expansion
The ability of elements to use available d-orbitals so there are more than 8 electrons in the outer shell
Which groups can show octet expansion
Some elements in group 5,6,7
Examples of octet expansion
PCl5 and PCl3
Which elements are exceptions to the octet rule and can form electron deficient molecules and give examples
Al and B
BF3 and AlCl3
What can electron deficient molecules do
Readily accept electron pairs from donors to form a co-ordinate bond
What forms Al2Cl6
2 monomers of AlCl3
What kind of molecule is Al2Cl6
Dimer
What is a dimer
A species created when 2 of the same molecules join together
How does Al2Cl6 form
Co-ordinate bonds form between a Cl of one monomer and the Al of another
What is a donor-acceptor compound
When a lone pair is donated by one compound and accepted by another, forming a co-ordinate bond
Example of a donor-acceptor compound and why can it be classified as so
NH3.BF3
The BF3 accepts a lone pair from nitrogen in ammonia
General similarities between boron nitride and carbon
• they’re isoelectronic as both have a total of 12 electrons on 2 atoms
• almost the same atomic radii
• similar relationship in their electronegatives
• BN can exist in forms similar to that of the allotropes of C
What i hexagonal boron nitride
Layers of hexagons formed by covalent bonds
Differences between h-BN and graphite
• atoms in adjacent laters in h-BN are in register whilst in graphite they’re out of register
• the pi electrons are more localised in h-BN as each N has a lone pair of electrons and so it can act as an electrical insulator whilst they’re relatively evenly delocalised in graphite so it acts as an electrical conductor
• h-BN has electronegativity difference between the B and N so has polar bonds, carbon does not
Similarities between h-BN and graphite
• soft - both have weak forces between layers so they can slide over eachother
• both can be used as lubricant
What is cubic boron nitride
Tetrahedral arrangement of boron atoms around nitrogen and nice versa
Differences befween c-BN and diamond
• c-BN is better for grinding materials
• diamond is harder
• c-BN is more stable as there is an electronegativity difference
• diamond can react with transition metals such as iron
• above 800 degrees celsius diamond can react with air to form carbon dioxide
Similarities between c-BN and diamond
• same structures
• both are hard, strong, have high melting points, heat conductors and chemically unreactive
Uses of hexagonal boron nitride
• semi-conductors in electronics
• ceramics
• microwave windows
• catalyst carrier in fuel cells and batteries
• wrap around carbon nanotubes to act as an insulating later around the conducting C-nanotube in order to keep the current within the nanotube
Uses of cubic boron nitride
• wear-resistant coating for toolbits
• support for catalysts
What is the maximum oxidation state of group 4
+4
How does the inert pair effect effect the oxidation states of group 4
Down the group the lower elements have an oxidation state of +2
Discuss the oxidising states of the oxides of carbon
• the C in CO2 has an oxidation state of +4 and this is more stable than the C in CO which has an oxidation state of +2
• this means the CO will act as a reducing agent as it tries to reach the +4 oxidation state
• C is easily oxidised from +2 to +4
Uses of oxides of Carbon
CO is used in the extraction of metal from their oxides
Eg
Fe2O3(s) + 3CO(g) –> 2Fe(s) + 3CO2(g)
Discuss the oxidation states of the oxides of lead
• Pb in PbO has an oxidation state of +2 which is more stable than the Pb in PbO2 which has an oxidation state of +4
• PbO2 will act as an oxidising agent to reach the +2 oxidation state
• Pb is easily reduced from +4 to +2
Example of reaction of PbO2 being reduced to reach the +3 oxidation state
PbO2(s) + 4HCl(conc) –> PbCl2(s) + Cl2(s) + 2H2O(l)
Nature of carbon dioxide
Colourless gas
Simple molecular
Linear
Nature of lead(II) oxide
• yellow/orange solid
• ionic bonding with some covalent character
Physical properties of carbon dioxide
• sublimes to dry ice
• oudourless
• is a good fire extinguisher as it is heavier than air
Physical properties of lead(II) oxide
• high boiling point
• high melting point
Acid-base properties of carbon dioxide
• acidic oxide
• dissolves in water to form carbonic acid
• reacts with alkalise to form carbonate salts
Reaction of carbon dioxide and water
CO2(g) + H2O(l) –> H+(aq) + HCO3-(aq)
Reaction of carbon dioxide and sodium hydroxide
2NaOH(aq) + CO2(g) –> Na2CO3(aq) + H2O(l)
Acid-base properties of lead(II) oxide
• amphoteric oxide
• forms colourless solutions
Lead(II) oxide with nitric acid
PbO + 2HNO3 –> Pb(NO3)2+ + H2O
Lead(II) oxide with sodium hydroxide
PbO + 2NaOH –> Na2[Pb(OH)4]
Bonding in CCl4
Covalent
Bonding in SiCl4
Covalent
Bonding in PbCl2
Ionic
Structure of CCl4
Tetrahedral
Structure of SiCl4
Tetrahedral
Structure of PbCl2
Giant ionic lattice
Reaction of water with CCl4
• doesn’t dissolve
• forms 2 immiscible layers
• there are no available d-orbitals in the C valence shell so it cannot expand its octet to form a co-ordinate bond with the lone pair on the water molecule
Reaction of water with SiCl4 including equations
• SiCl4 hydrolyses violently
• Si has available 3d-orbitals which he water can form co-ordinate bonds with
Steamy fumes of HCl are seen
White precipitate of SiO2 is seen
SiCl4 + 2H2O –> SiO2 + 4HCl
Reaction of water with PbCl2
• no reaction
PbCl2 only reacts with hot water
Observation and precipitate seen when Pb2+ (aq) reacts with aqueous NaOH
Dropwise - white precipitate of Pb(OH)2
Excess - ppt redissolves to form a colourless solution of [Pb(OH)4]
Observation and precipitate seen when Pb2+ (aq) reacts with aqueous Cl-
White precipitate of PbCl2
Observation and precipitate seen when Pb2+ (aq) reacts with aqueous I-
Canary/bright yellow precipitate of PbI2
Equation for the reaction between chlorine and cold aqueous NaOH and what kind of reaction is it
Cl2(g) + 2NaOH(aq) –> NaCl(aq) + NaOCl(aq) + H2O(l)
Disproportionation reaction
Equation for the reaction between chlorine and warm aqueous NaOH and what kind of reaction is it
3Cl2(g) + 6NaOH(aq) –> 5NaCl(aq) + NaClO3(aq) + 3H2O(l)
Disproportionation reaction
What kind of agents are chlorine and chlorate (I) iond and why
Oxidising agents
Both are more stable as Cl-
Equation for reduction of Cl2
Cl2 + 2e- –> 2Cl-
Equation for reduction of chlorate (I) ions
ClO- + 2H+ + 2e- –> Cl- + H2O
How is chlorine used as disinfectant and why can this happen
• used to disinfect water supplies
• kills bacteria as it oxidises many essential biological molecules in the bacteria including the DNA which can then no longer control the cell so the bacterium dies
How is sodium chlorate (I) used as disinfectant and bleach
Disinfectant as it kills the bacteria as it oxidises many essential biological molecules including the DNA which can no longer control the cells so the bacterium dies
Bleach as it can oxidise dyes to form colourless compounds
Trend in oxidising power of halogens
Decreases down the group
How can you use electrode potentials to figure out the oxidising power of halogens
A big positive electrode potentials means a system is more likely to gain electrons and thus more likely to be reduced and so a positive electrode potential signifies a stronger oxidising agent
As chlorine has the most positive electrode potential it is the stronger oxidising agent
Reaction of NaCl with conc H2SO4
With observations and explanation
NaCl + H2SO4 –> NaHSO4 + HCl
Steamy fumes of HCl gas is produced
No further reaction as the HCl cannot be oxidised by the H2SO4
Reaction of NaBr with conc H2SO4
With observations and explanation
NaBr + H2SO4 –> NaHSO4 + HBr
• steamy fumes of HBr gas
Then
HBr is oxidised to Br2 by the H2SO4 and orange fumes can be seen
This is because the Br- is a strong enough reducing agent to reduce sulfur from +6 to +4
Reaction of NaI with conc H2SO4
With observations and explanation
NaI + H2SO4 –> NaHSO4 + HI
• steamy fumes of HI gas
Then
HI is oxidised to I2 by H2SO4 and a black solid/purple fumes are seen
The I- can reduce sulfur from +6 (NaHSO4) to +4 (SO2) to 0 (S, a yellow solid) to -2 (H2S(g), a smell of rotten eggs)
