Nitrogen and sulfur

Question 1

Why does nitrogen lack reactivity

Answer 1

1) Strong triple covalent bond
2) N2 is non-polar

Question 2

Strong triple covalent bond

Answer 2

• the electron configuration of a nitrogen atom is 1s2 2s2 2p3
• to achieve a full outer shell of electrons, it needs to gain 3 electrons, therefore it forms a triple covalent bond between 2 nitrogen atoms in which they share 3 electrons
• the triple bond has a high enthalpy energy and so it is difficult to break it, therefore nitrogen (only during a thunderstorm) and oxygen gas will not react with each other

Question 3

N2 is non-polar

Answer 3

• electrons are being shared equally between the nitrogen atoms
• due to the lack of polarity, nitrogen gas is not attracted to or likely to react with other molecules

Question 4

The basicity of ammonia, using the Bronsted-Lowry theory

Answer 4

• can act as a Bronsted-Lowry base by accepting a proton (H+) using the lone pair of electrons on the nitrogen atom to form an ammonium ion

NH3 (aq) + H+ (aq) = NH4+ (aq)
NH3 (aq) + H2O (I) = NH4+ (aq) + OH- (aq)
reversible reaction

Question 5

NH3 (aq) + H2O (I) = NH4+ (aq) + OH- (aq)
reversible reaction

Answer 5

*water is amphoteric
- since the position of equilibrium lies well to the left, the ammonia solution is only weakly alkaline
- there is a higher concentration of ammonia molecules than hydroxide ions in the solution
- ammonia is therefore a weak base

Question 6

Structure of ammonium ion and its formation by an acid-base reaction

Answer 6

NH3 (aq) + H2O (I) reversilbe NH4+ (aq) + OH- (aq)
- the nitrogen in ammonia is covalently bonded to 3 hydrogen atoms and has 1 lone pair of electrons, causing the ammonia molecule to have a pyramidal shape
- the nitrogen in ammonia uses its lone pair to form a dative covalent bond with a proton to form the ammonium ion
- the ammonium ion has a tetrahedral shape in which all bonds have the same length

Question 7

The displacement of ammonia from ammonium salts by an acid-base reaction

Answer 7

2NH4CI (s) + Ca(OH)2 (s) = CaCI2 (s) + 2H2O (l) + 2NH3 (g)
*NH4+ acts as an acid
*OH- acts as a base

Question 8

What does the displacement of ammonia from ammonium salts by an acid-base reaction test for

Answer 8

• used to test if an unknown solution contains ammonium ions
• if the unknown solution does contain ammonium ions, it will react with calcium hydroxide to form ammonia gas (this will turn litmus paper blue)
• calcium hydroxide is used as a drying agent to dry the ammonia to remove the steam (water)
• reaction is heated

Question 9

Natural occurrences of oxides of nitrogen

Answer 9

• due to nitrogen’s lack of reactivity it will only react with oxygen under extreme conditions (such as lighting) to form gaseous nitrogen oxides
• in the case of lightning it can trigger the formation of nitrogen(II) and nitrogen (IV) oxides (NO and NO2)

N2 (g) + O2 (g) = 2NO (g)
N2 (g) + 2O2 (g) = 2NO2 (g)

Question 10

Man-made occurrences of oxides of nitrogen

Answer 10

• in the engine of a car, a mixture of air and fuel are compressed and ignited by a spark - air consists of 78% nitrogen and 21% oxygen
• under high temperature and pressure inside the engine, the nitrogen can react with the oxygen to form nitrogen oxides
• the nitrogen oxides are released into the atmosphere through the cars exhaust fumes

Question 11

Catalytic removal of nitrogen oxide

Answer 11

• car exhaust systems are fitted with catalytic converters to reduce the pollutants from motor vehicles
• the nitrogen oxides are reduced on the surface of the hot catalyst (example platinum) to form unreactive nitrogen gas, which is released from the vehicles exhaust pipe into the atmosphere

Question 12

Reduction of nitrogen oxide to nitrogen gas by a catalyst

Answer 12

2CO (g) + 2NO (g) = 2CO2 (g) + N2 (g)

Question 13

Primary pollutant

Answer 13

pollutants given off directly into the air from the source of pollution

Question 14

Secondary pollutant

Answer 14

pollutants not given off directly into the air from human activity

Question 15

Nitrogen oxides (NO, NO2)

Answer 15

• primary
• lightening, car exhausts and power plants

Question 16

Volatile organic compounds (VOCs)

Answer 16

• primary
• unburnt hydrocarbons from fuel and their oxidised products in exhaust fumes

Question 17

PAN

Answer 17

• secondary
• photochemical reaction between nitrogen oxides and VOCs from car exhausts
• sun provides energy required for the reaction between nitrogen and VOCs to take place
• PAN is a harmful pollutant found in photochemical smog and affects lungs, eyes and plant-life

Question 18

Role of NO and NO2 in the formation of acid rain both directly and in their catalytic role in the oxidation

Answer 18

Lightening triggers the formation of nitrogen oxides
- N2 (g) + O2 (g) = 2NO (g)

Gets further oxidised
- 2NO (g) + O2 (g) = 2NO2 (g)

NO2 gets further oxidised to nitric acid when dissolved in water
- 4NO2 (g) + 2H2O + O2 (g) = 4HNO3

*clouds rise and droplets get larger
*droplets with HNO3 which are heavy enough will fall as acid rain

Question 19

Nitrogen oxide as a catalyst

Answer 19

• acid rain also contains sulfuric acid (H2SO4)
• Sulfur(IV) oxide (SO2) is another pollutant found in the atmosphere
• when SO2 is oxidised it forms SO3 which reacts with rainwater to form dilute sulfuric acid

Question 20

The formation of dilute sulfuric acid is catalysed by the nitrogen oxides

Answer 20

NO2 (g) + SO2 (g) = SO3 (g) + NO (g)
SO3 (g) + H2O (l) = H2SO4 (aq)