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
- Colorless , odorless and tasteless gas .
- It is lighter than air , Because air contains oxygen gas ( 32 g/mol ) which is heavier than nitrogen gas ( 28 g/mol ) .
- It is sparingly soluble in water [ 23 ml ( N2 )/ L ( H2O ) at STP ] .
- It has a neutral effect on litmus paper .
- Its density is ( 1.25 g/L at STP ) .
- Its boiling point is ( −159.79° C ) , it can be liquified at this temperature at normal atmospheric pressure .
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
N2 (g) + O2 (g) → 2NO (g) nitric oxide
Then , 2NO (g) + O2 (g) → 2NO2 (g) nitric dioxide
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
- Colorless gas with a characteristics pungent smell .
- It does not burn readily or sustain combustion , where the glowing splint is extinguished when approached to it .
- 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 .
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 .
- Rushing out the red solution from the lower flask to the upper flask in a form of fountain .
- Changing the color of the red solution once it is rushed out in the upper flask into blue color .
- Rushing out the solution of the lower flask in a form of fountain is an indication that ammonia is highly soluble in water .
- 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 .
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
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 .