The most famous elements in 5A group ( Nitrogen properties , Preparation & compounds )

Nitrogen is considered as the most famous element in 5A group , Nitrogen gas is collected during its preparation by downward displacement of water , because nitrogen gas is lighter than the water and sparingly soluble in it and nitrogen is collected over mercury surface to get dried .

Preparation of nitrogen gas in the lab

From the atmospheric air : Nitrogen can be prepared from the atmosphere air , by removing of carbon dioxide , water vapour , oxygen gas , The atmospheric air is passed through sodium hydroxide solution , To remove carbon dioxide gas .

2NaOH ( aq )  + CO2 ( g ) H2O ( l ) + Na2CO3 ( aq )         sodium carbonate

Then it is passed through conc. sulphuric acid , To absorb water vapor , Finally it is passed over red hot copper turnings , To remove oxygen gas , Nitrogen is collected over mercury surface to get dried .

2Cu ( s ) + O2 ( g )  2CuO ( s )     copper oxide                 

From the chemical compounds : By dropping sodium nitrate solution slowly on ammonium chloride solution with heating , Nitrogen gas is collected during its preparation by downward displacement of water , because nitrogen gas is lighter than water and sparingly soluble in it .

NaNO2 ( aq ) + NH4Cl ( aq ) NaCl ( aq ) + 2H2O ( l ) + N2 ( g )

The properties of nitrogen

Physical properties
  1. Colorless , odorless and tasteless gas .
  2. It is lighter than air , Because air contains oxygen gas ( 32 g/mol ) which is heavier than nitrogen gas ( 28 g/mol ) .
  3. It is sparingly soluble in water [ 23 ml ( N2 )/ L ( H2O ) at STP ] .
  4. It has a neutral effect on litmus paper .
  5. Its density is ( 1.25 g/L at STP ) .
  6. Its boiling point is ( −159.79° C ) , it can be liquified at this temperature at normal atmospheric pressure .
Chemical properties

The reactions of nitrogen gas with the other elements occur in the presence of an electric spark ( 550° C ) or an electric arc ( 3000° C ) or by strong heating , Because of the difficulty of breaking the triple bond between the two nitrogen atoms in one molecule of it .

The reaction of nitrogen with the other elements

The reaction of nitrogen with Hydrogen ( H2) : In the presence of an electric spark ( 550° C ) , ammonia gas ( NH3 ) is formed .

N2 ( g ) + 3H2 ( g ) 2NH3 ( g )  ammonia

The reaction of nitrogen with oxygen : In the presence of an electric arc ( 3000° C ) , nitric oxide ( NO ) gas is formed which is instantly changing into ( oxidized ) nitrogen dioxide ( NO2 )

N2 (g) + O2 (g) 2NO (g)     nitric oxide

Then ,    2NO (g) + O2 (g) 2NO2 (g)      nitric dioxide

The reaction of nitrogen with metals : At high temperature , nitrogen reacts with metals like magnesium giving the metal nitride which easily decomposes in water and ammonia gas evolves .

3Mg ( s ) + N2 ( g ) Mg3N2 ( s )     magnesium nitride

Mg3N2 ( s ) + 6H2O ( l ) 3Mg( OH)2 ( aq ) + 2NH3 ( g )  ↑

The reaction of nitrogen with calcium carbide ( CaC2 ) : In the presence of the electric arc ( 3000° C ) , calcium cyanamide ( CaCN2 ) is formed which is used as a fertilizer .

CaC2 ( s ) + N2 ( g ) CaCN2 ( s ) + C ( s )  

Calcium cyanamide is used as a fertilizer , Because it reacts with water and produces ammonia gas in the agricultural soil , when the land is being irrigated .

CaCN2 ( s ) + 3H2O ( l )  CaCO3 ( s ) + 2NH3 ( g )  ↑  ammonia

The most famous nitrogenous compounds

The most famous nitrogenous compounds are Ammonia gas NH3 , Nitric acid HNO3 .

Ammonia gas NH3

Preparation of ammonia in the lab

Put in the flask a mixture of ammonium chloride NH4Cl and calcium hydroxide ( slaked lime ) Ca ( OH )2 , Put a drying agent ( quicklime CaO ) in the U-shaped tube , Heat the contents of the flask , then collect the ammonia gas by downward displacement of air .

 2 NH4Cl ( s ) + Ca( OH )2 ( s )CaCl2 ( s ) +2H2O ( v ) + 2NH3 ( g )  ↑ 

Ammonia gas is collected by downward displacement of air , Because it is lighter than air , Conc. sulphuric acid is not used in drying ammonia gas when it is prepared in the lab , Because it reacts with ammonia gas , producing ammonium sulphate .

Preparation of ammonia gas in industry ( Haber-Bosch’s method ) 

The scientists Haber-Bosch had reached a method to prepare ammonia gas in industry from nitrogen and hydrogen , in the presence of a catalyst ( iron , molybdenum ) , under 200 atmospheric pressure and 500° C .

N2 ( g ) + 3H2 ( g ) 2NH3 ( g )  

The properties of ammonia gas
  1. Colorless gas with a characteristics pungent smell .
  2. It does not burn readily or sustain combustion , where the glowing splint is extinguished when approached to it .
  3. It is highly soluble in water forming an alkaline solution ( ammonium hydroxide ) , it turns to blue color by adding a few drops of litmus solution to it , as shown in the following fountain experiment .
Fountain experiment
Fountain experiment of ammonia

Fountain experiment of ammonia

The lower flask is filled with an acidified aqueous solution added to it a few drops of litmus solution , So , the color of the solution becomes red , The upper flask is filled with ammonia gas , Blow a stream of air to the lower flask .

Observation :

  1. Rushing out the red solution from the lower flask to the upper flask in a form of fountain .
  2. Changing the color of the red solution once it is rushed out in the upper flask into blue color .

Conclusion :

  1. Rushing out the solution of the lower flask in a form of fountain is an indication that ammonia is highly soluble in water .
  2. Changing the color of the red solution into blue is an indication for the formation of a solution which has an alkaline effect on litmus solution ( ammonium hydroxide ) .

 NH3 ( g ) + H2O ( l )NH4OH ( aq )     ammonium hydroxide

Ammonia gas is considered as a base anhydride , Because it reacts with water forming ammonium hydroxide ( weak base ) .

Detection of ammonia gas

Ammonia gas forms dense white fumes of ammonium chloride ( solid substances that sublimates ) , when subjected to a glass rod wetted with conc. hydrochloric acid , Sublimation is the change of the matter from a solid state to a gaseous state directly without changing into liquid state .

NH3 ( g ) + HCl ( g ) NH4Cl ( s )     ammonium chloride 

The role of ammonium in the manufacture of fertilizers 

Nitrogen is present in soil in the form of inorganic & organic substances , it is considered one of the main sources of nutrition in plant , Because it is an essential element to form protein , However , the amount of nitrogen in the soil decreases by time , so , the soil should be enriched by nitrogen either by adding Synthetic nitrogenous fertilizers or natural fertilizers ( manure ) .

Although nitrogen forms about 4/5 of the air volume , plant can not use it by a direct way in its gaseous form , Accordingly , it must to provide the soil by nitrogen in the form of ammonium salts or urea which dissolve in the irrigation water , where they absorbed by the plant roots , Ammonia is considered the essential starting material for manufacturing most of nitrogenous fertilizers & nitrogenous phosphorus fertilizers .

Nitrogenous fertilizers

The inorganic nitrogenous fertilizers ( ammonium salts ) are synthesized by a neutralization reaction between ammonia and the suitable acid .

Some of the important inorganic nitrogenous fertilizers :

Ammonium nitrate fertilizers : preparing method by reacting ammonia with nitric acid .

NH3 ( g ) + HNO3 ( l ) NH4NO3 ( aq )     ammonium nitrate

Properties : It has a high nitrogen content ( 35 % ) , It is highly soluble in water , Using an excess amount of it , causes an acidic effect on the soil .

Ammonium sulphate fertilizers : preparing method by reacting ammonia with sulphuric acid .

2NH3 ( g ) + H2SO4 ( aq ) → ( NH4)2SO4 ( aq )     ammonium sulphate

Properties : The continuous use of it , causes an increase in the acidity of the soil , thus it is important to neutralize the soil by basic substances .

The slaked lime is added to the soil which is provides with ammonium sulphate fertilizers , To neutralize the soil , as ammonium sulphate acts to increase the soil acidity .

Nitrogenous phosphorus fertilizers :

They are prepared by reacting ammonia with phosphoric acid .

3NH3 ( g ) + H3PO4 ( aq ) ( NH4)3PO4 ( aq )     ammonium phosphate

Nitrogenous phosphorus fertilizers ( Ammonium phosphate ) is an important fertilizer because it provides the soil with two essential elements which are nitrogen and phosphorus .

Notes of some common fertilizers

Urea fertilizer : It has high nitrogen content ( 46% ) , It is the most suitable fertilizer for hot areas , Because the high temperature increases its dissociation to ammonia and carbon dioxide .

Anhydrous liquified ammonia fertilizer ( future fertilizer ) : It has the highest nitrogen content overall fertilizers ( 82 % ) , it is supplied to the soil in a depth nearly 12 cm .

Nitric acid properties , Passivity phenomenon & Economic importance of the 5A group elements

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