P block - 15 and 16

Question 1

Which are the metals, non-metals and metalloids of group 15

Answer 1

Non-metals - Nitrogen, Phosphorous
Metalloids - Arsenic and Antimony
Metals - Bismuth and Moscovium

Question 2

How is nitrogen found in the atmosphere

Answer 2

NaNO3 - Chile saltpetre
KNO3- Indian saltpetre
Proteins in plants and animals

Question 3

Where are arsenic, antimony and bismuth found

Answer 3

sulphide minerals

Question 4

Comment of the atomic and ionic radii of group 15

Answer 4

Increase down the group

Considerable increase from N to P due to presence of completely filled f and d block

Question 5

Comment on the melting point of group 15

Answer 5

Increase upto Arsenic and then decrease

Question 6

What are the anomalous properties of Nitrogen

Answer 6

forms pπ - pπ bonds with itself
Forms triple bond
High bond enthalpy
Catenation tendancy is weaker

Question 7

What is the trend of stability of hydrides of group 15

Answer 7

decreases from NH3 to BiH3

Question 8

What is the trend of reducing character of hydrides

Answer 8

Increases from NH3 to BiH3

Question 9

Why does NH3 have higher boiling and melting point than PH3

Answer 9

H bonding in solid and liquid phase

Question 10

What is trend of basicity in hydrides

Answer 10

NH3>PH3>AsH3>SbH3>BiH3

Question 11

What type of oxides does group 15 form. Which is more acidic

Answer 11

E2O3 and E2O5. The oxide in higher oxidation state is more acidic. Acidic char decreases down the group.

Question 12

Comment on covalency of halides of group 15

Answer 12

EX5 is more covalent than EX3. +5 has more polarising power. Covalency decreases down the group

Question 13

How to prepare N2

Answer 13

1. liquefaction and fractional distillation of air. Liquid N2 distils out first.
2. 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
3. Very pure nitrogen obtained by thermal decomposition of sodium or barium azide

Question 14

What is Habers process

Answer 14

N2 + 3H2 at 773K = 2NH3

Question 15

How to form nitric oxide

Answer 15

N2 + O2 at around 2000K

Question 16

How to prepare ammonia

Answer 16

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)

Question 17

What are the optimum conditions for prep of ammonia

Answer 17

high pressure (200atm) and temperature around 700K. Use of catalysts such as iron oxide with small amounts of K2O and Al2O3

Question 18

What is the structure of ammonia molecule

Answer 18

Trigonal pyramidal. 3bp and 1 lp

Question 19

How to prepare Nitric acid

Answer 19

1. Heating KNO3 or NaNO3 and conc H2so4
2. 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

Question 20

What is structure of HNO3

Answer 20

planar molecule

Question 21

How does zinc react with HN3

Answer 21

dilute HNO3 to give Zn(NO3)2 + N2O

Conc HNO3 to give Zn(NO3)2 + NO2

Question 22

What is brown ring test

Answer 22

Fe2+ reduces nitrates to nitic oxide which reacts with Fe2+ to give a brown coloured complex

Question 23

What is group 16 also called

Answer 23

Chalcogens

Question 24

What is the trend of electron gain enthalpy of group 16

Answer 24

OSe>Te>Po . Because of compact nature of oxygen

Question 25

Why is there a large difference in melting and boiling points of S and O

Answer 25

Atomicity. O exists as O2 and S exists as S8

Question 26

What is the trend of thermal stability

Answer 26

decreases from H2O to H2Po

Question 27

What is the trend of reducing property of hydrides and oxides

Answer 27

hydrides increase from H2S to H2Te | oxides reducing property decreases from SO2 to TeO2

Question 28

What is the structure of hexaflourides

Answer 28

octahedral

Question 29

What is structure of tetraflourides

Answer 29

bipyramidal structure with see-saw geometry

Question 30

How to prepare dioxygen

Answer 30

1. By heating oxygen containing salts 2. By thermal decomposition of oxides of metals low in the electrochemical series 3. H2O2 readily decomposes into water and O2 by catalysts such as finely divided metals and MnO2 4. From air by fractional distillation

Question 31

Name some neutral oxides

Answer 31

CO, NO, N2O

Question 32

How to prepare ozone

Answer 32

slow dry stream of oxygen passed through silent electrical discharge

Question 33

What are colours of ozone

Answer 33

pale blue gas, dark blue liquid, violet black- solid

Question 34

What is a quantitative method for determining O3

Answer 34

ozone + excess KI soln buffered with borate buffer - iodine is liberated which can be titrated against standard solution of sodium thiosulphate

Question 35

How to form rhombic sulphur crystals

Answer 35

evaporating solution of roll sulphur in CS2

Question 36

How to prepare monoclinic sulphur

Answer 36

by melting rhombic sulphur

Question 37

What happens to monoclinic sulphur at 369 K

Answer 37

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

Question 38

How is SO2 prepared

Answer 38

sulphur burnt in air/O2 treating sulphite with dil sulphuric acid roasting on sulphide ores

Question 39

How is sulphuric acid manufactured

Answer 39

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

Question 40

How is sulphuric acid manufactured

Answer 40

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

Question 41

What are the properties of sulphuric acid

Answer 41

``` Strong dehydrating agent moderately strong oxidising agent low volatility strong affinity for water strong acidic character ```