P block - 15 and 16 Flashcards
Which are the metals, non-metals and metalloids of group 15
Non-metals - Nitrogen, Phosphorous
Metalloids - Arsenic and Antimony
Metals - Bismuth and Moscovium
How is nitrogen found in the atmosphere
NaNO3 - Chile saltpetre
KNO3- Indian saltpetre
Proteins in plants and animals
Where are arsenic, antimony and bismuth found
sulphide minerals
Comment of the atomic and ionic radii of group 15
Increase down the group
Considerable increase from N to P due to presence of completely filled f and d block
Comment on the melting point of group 15
Increase upto Arsenic and then decrease
What are the anomalous properties of Nitrogen
forms pπ - pπ bonds with itself
Forms triple bond
High bond enthalpy
Catenation tendancy is weaker
What is the trend of stability of hydrides of group 15
decreases from NH3 to BiH3
What is the trend of reducing character of hydrides
Increases from NH3 to BiH3
Why does NH3 have higher boiling and melting point than PH3
H bonding in solid and liquid phase
What is trend of basicity in hydrides
NH3>PH3>AsH3>SbH3>BiH3
What type of oxides does group 15 form. Which is more acidic
E2O3 and E2O5. The oxide in higher oxidation state is more acidic. Acidic char decreases down the group.
Comment on covalency of halides of group 15
EX5 is more covalent than EX3. +5 has more polarising power. Covalency decreases down the group
How to prepare N2
- liquefaction and fractional distillation of air. Liquid N2 distils out first.
- In lab, NH4Cl + NaNO2. Small amounts of NO and HNO3 are formed which can be removed by passing gas through sulphuric acid containing potassium dichromate
- Very pure nitrogen obtained by thermal decomposition of sodium or barium azide
What is Habers process
N2 + 3H2 at 773K = 2NH3
How to form nitric oxide
N2 + O2 at around 2000K
How to prepare ammonia
In nature - decay of nitrogenous organic matter like urea
From ammonium salts which decompose on treatment with caustic soda or calcium hydroxide
On large scale by Haber’s process (N2 + H2)
What are the optimum conditions for prep of ammonia
high pressure (200atm) and temperature around 700K. Use of catalysts such as iron oxide with small amounts of K2O and Al2O3
What is the structure of ammonia molecule
Trigonal pyramidal. 3bp and 1 lp
How to prepare Nitric acid
- Heating KNO3 or NaNO3 and conc H2so4
- Ostwald’s process - catalytic oxidation of NH3 by atmospheric oxidation. No is formed which comines with oxygen to give NO2. NO2 dissolves in water to give HNO3
What is structure of HNO3
planar molecule
How does zinc react with HN3
dilute HNO3 to give Zn(NO3)2 + N2O
Conc HNO3 to give Zn(NO3)2 + NO2
What is brown ring test
Fe2+ reduces nitrates to nitic oxide which reacts with Fe2+ to give a brown coloured complex
What is group 16 also called
Chalcogens
What is the trend of electron gain enthalpy of group 16
OSe>Te>Po . Because of compact nature of oxygen
Why is there a large difference in melting and boiling points of S and O
Atomicity. O exists as O2 and S exists as S8
What is the trend of thermal stability
decreases from H2O to H2Po
What is the trend of reducing property of hydrides and oxides
hydrides increase from H2S to H2Te
oxides reducing property decreases from SO2 to TeO2
What is the structure of hexaflourides
octahedral
What is structure of tetraflourides
bipyramidal structure with see-saw geometry
How to prepare dioxygen
- By heating oxygen containing salts
- By thermal decomposition of oxides of metals low in the electrochemical series
- H2O2 readily decomposes into water and O2 by catalysts such as finely divided metals and MnO2
- From air by fractional distillation
Name some neutral oxides
CO, NO, N2O
How to prepare ozone
slow dry stream of oxygen passed through silent electrical discharge
What are colours of ozone
pale blue gas, dark blue liquid, violet black- solid
What is a quantitative method for determining O3
ozone + excess KI soln buffered with borate buffer - iodine is liberated which can be titrated against standard solution of sodium thiosulphate
How to form rhombic sulphur crystals
evaporating solution of roll sulphur in CS2
How to prepare monoclinic sulphur
by melting rhombic sulphur
What happens to monoclinic sulphur at 369 K
for beta - above it is stable and below it becomes alpha
for alpha below it is stable and above it becomes beta
at 369 both are stable
How is SO2 prepared
sulphur burnt in air/O2
treating sulphite with dil sulphuric acid
roasting on sulphide ores
How is sulphuric acid manufactured
Contact process:
1. burning of sulphur/ sulphide ored in air to generate SO2
2. conversion of So2 to So3 by reaction with oxygen in presence of catalyst (V2O5)
Absorption of SO3 in H@SO$ to give oleum
low temp high pressure
dilution of oleum with water gives H2SO4
96-98% pure
How is sulphuric acid manufactured
Contact process:
1. burning of sulphur/ sulphide ore in air to generate SO2
2. conversion of So2 to So3 by reaction with oxygen in presence of catalyst (V2O5)
Absorption of SO3 in H@SO$ to give oleum
low temp high pressure
dilution of oleum with water gives H2SO4
96-98% pure
What are the properties of sulphuric acid
Strong dehydrating agent moderately strong oxidising agent low volatility strong affinity for water strong acidic character
