P-block Flashcards
What electrons do Pb ions in their most stable state use?
Only p2 electrons
What is the inert pair effect?
Where does it occur?
The increased tendency for the s2 pair not to be used in the bonding on decent of the group.
In groups 3,4&5 the lower valencies (+2) become more stable as the group is descended.
What is the max covalency of period 2 and why?
Max covalency is 4 as they can only bond using s and p orbitals (s1 p3)
They have no d available
How does phosphorous bond in PCl5
It can promote a 3s electron to a 3d orbital, allowing 5 electrons to be available for bonding
What happens when NaOH(aq) is added to Al3+ (aq)
White ppt of Al(OH)3(H2O)3 is formed
OH- ions remove protons from complex to turn the H2Os to OH-s
What is formed when both Al and Al2O3 is added to NaOH?
Na(Al(OH)4) is formed With H2(g) for Al and H2O for Al2O3
What does Al(aq) do when it acts amphotercially?
Liberates H2(g)
What happens when excess NaOH(aq) is added to Al(OH)3(H2O)3
White ppt redissolves and Al(OH)4 -
With which element does a similar thing occur when Al(aq) is added to NaOH? And with which element does this trend not occur?
Pb2+
Mg
When PbO is added to HCl two things can happen- explain
If warm (above 20°) forms PbCl2(aq) If cool (below 20°) forms PbCl4(aq)
Why does AlCl3 tend to bond with group 5 elements?
It is electron deficient so forms coordinate bonds as G5 element donates lone pair to form a stable octet
What is an ionic liquid? Give 2 uses an 2 properties
An organic salt with mpt below 100° so are liquid over a wide temp range
Can replace volatile organic compounds as solvents and catalysts (eg polymerisation of alkenes)
Why are ionic liquids useful?
-Allows reactions to be performed under mild conditions
(Reduced energy costs, won’t thermally decompose reactants)
-immiscible in organic products so can be separated easily
-non volatile
Boron nitride exists in two forms and is-
Isoelectronic with carbon
Hexagonal and cubic forms
Compare Boron nitride and graphite
Both- Layers of hexagonal rings with weak bonds between the layers 3 bonds with one unbonded p-orbital Can be used as a lubricant Can form nanotubes BN- No delocalised electron (empty unbonded p-orbital) between layers Insulator and inert Used as reaction vessel
Compare boron nitride and diamond
Both- cubic structures with 4 covalent bonds from each atom Really hard High thermal conductivity Wear resistant
Why is CO a reducing agent and give an example
Readily loses electrons to return to +4 oxidation state
Can be used to extract metals from their ores
Fe2O3 +3CO -> 3CO2 + 2Fe
Give an example of why Pb4+ is interesting (with eqn)
Strong oxidising agent
PbO2+ 4HCl -> PbCl2 + Cl2 +2H2O
What happens when CO2 reacts with water?
Acidic solutions formed in equilibrium
HCO3- +H+ (CO3)2- + 2H+
What is formed when CO2 reacts with NaOH?
Na2CO3 and water are formed if alkali is in excess
Forms NaHCO3 is CO2 is in excess
What makes limewater milky?
CaCO3(s)
Why can’t you isolate Ca(HCO3)2
It will decompose to form CaCO3, CO2 and water
What happens if excess CO2 is added to lime water?
Form colourless solution of Ca(HCO3)2 ions
What two forms does lead(11)oxide exist as?
Yellow form and red form
What lead compounds are insol and sol in water?
PbSO4 insol
PbCl2 sp sol
Pb(NO3)2 sol
What happens when PbO is heated in NaOH?
Pb(OH)4 2- is formed as a colourless solution
What chloride reacts with water vigorously? Why?
SiCl4
Due to Si being able to accept oxygen’s lone pair in its d orbital
CCl4 does what with water?
Doesn’t react, forms an immiscible layer- no access to d orbitals
What do you observe when SiCl4 comes into contact with water?
Reacts vigorously forming fumes of HCl and SiO2(s)
What does PbCl2 do with HCl?
Dissolves in conc HCl to form PbCl4 2-
When lead(2)nitrate reacts with NaOH what happens? What happens with excess NaOH?
White ppt of Pb(OH)2 formed
Redissolves in a colourless solution of Pb(OH)4 2- (aq)
What happens when Cl- ions are added to Pb(NO3)2?
Forms white ppt of PbCl2 that is sol in hot, sparingly sol in cold and soluble in HCl
Lead(2) nitrate and I-?
Bright yellow ppt of PbI2 formed (but sol in hot)
What is Iodine at STP? And when heated?
And with starch?
Grey black solid
Purple fumes
Blue black
Oxidising power trend in G(7)?
Decreases down group
Displacement reactions show this as -1 ox state of Cl- is more stable than -1 ox state of Br- and I-
Chlorine reacts with NaOH in two different ways- explain and give eqns
Cold NaOH(aq) -> NaCl + NaClO + H2O (disproportionation) Warm conc NaOH-> NaCl + NaClO3 + H2O
Chlorine reacts with water-
Cl2 + H2O-> ClO- + Cl- + 2H+
The ClO- is a powerful disinfectant (bleach) (water supplies) (inexpensive)
ClO3 - is used as?
Effective weed killer
Powerful oxidising agent
Explosive with organic materials :o
What happens when conc sulphuric acid is added to NaCl?
Steamy fumes of HCl + NaHSO4
What happens when conc sulphuric acid is added to NaBr?
Steamy fumes of HBr which acts as a reducing agent -> Br2 (red brown fumes) SO2 (choking gas) and steam
What happens when conc sulphuric acid is added to NaI?
Steamy fumes of HI which is the strongest reducing agent-> I2 (purple fumes) H2S (rotten egg smell) steam and S (yellow solid)
2 uses of F?
CFCs as aerosol propellant
PTFE as non stick frying pans
4 uses of Cl?
ClO- sterilises drinking water
ClO3 - weed killer
PVC guttering
DDT pesticides
2 uses of Br?
Silver bromide in photography
Dyes and medicines
2 uses of I?
KI kept near nuclear plants to reduce conc of radioactive I in body
Antiseptic (I2 in ethanol)
