Ammonia 3c5861

Ammonia Occurrence : Free ammonia occurs due to bacterial decomposition of urea present in the animal wastes. Hence urinals smells of ammonia. General methods of preparation : (i) From ammonium salts : Ammonium salts + alkali → salt + ammonia + water 2NH4Cl + Ca(OH)2 → CaCl2 + 2H2O + 2NH3 Ammonium nitrate salt is not used because ammonium nitrate decomposes explosively forming nitrous oxide and water (ii) From metallic nitrides : Nitrides of metals like Mg , Ca and Al produces metallic hydroxides and ammonia on being treated with warm water. Mg3N2 + 6H2O → 3Mg(OH)2 + NH3 ↑ 2AlN + 6H2O → 2Al(OH)2 + NH3 ↑ The above two methods can be used for the laboratory preparation of ammonia. Note : (i) More amount of Ca(OH)2 is used to counteract loss of NH4Cl due to sublimation (ii) Slaked lime is used instead of NaOH or KOH because it is not deliquescent Drying of gas : The gas is dried by ing it through the layers of quicklime ( CaO ). Conventional drying agents like conc. H2SO4 , phosphorus pentoxide and anhydrous calcium chloride cannot be used since ammonia reacts with the compounds to produce salts . Collection of gas : Ammonia gas is collected by downward displacement of air . Reasons behind the method of collection : (i) Ammonia is lighter than air (ii) Ammonia is highly soluble in water Preparation of aqueous solution of ammonia : Aqueous solution of ammonia is prepared by dissolving ammonia gas in water using funnel arrangement The funnel arrangement is used to prevent back suction of water. Saturated solution of ammonia in water is called liquor ammonia fortis. Industrial manufacture of ammonia : The process is called Haber’s process. (i) Reactants : N2 and H2 in the ratio 1 : 3 N2 + H2 (ii) Reaction : N2 + 3H2 ⇔ 2NH3 (iii) Catalyst : Finely divided iron or a Compresso mixture of Fe2O3 , K2O and Al2O3 r (iv) Promoter : Molybdenum (v) Temperature : 450oC - 500oC Catalyst Chamber (vi) Pressure : 200 atm - 900 atm

Unreacted gases

Condensor Ammonia gas is recovered from the unreacted mixture by liquefaction to liquid ammonia . Physical Properties : (i) Colourless gas with pungent odour (ii) Lighter than air (iii) Can be easily liquefied by applying pressure of 8 – 10 atm. (iv) Highly soluble in water :1 vol of water dissolves 750 vols of ammonia High solubility of ammonia in water can be demonstrated by fountain experiment Observation : Blue fountain is obtained using red litmus solution . Chemical Properties : (i) Reaction with oxygen : Ammonia burns in oxygen with a greenish yellow flame to produce nitrogen and water. 4NH3 + 3O2 → 6H2O + N2

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(ii)

(iii)

(iv)

(v)

(vi)

(vii)

In presence of platinum as catalyst , ammonia gets oxidized to nitric oxide which further gets oxidized to nitrogen dioxide. Observation : Reddish brown vapours are evolved. 4NH3 + 5O2 → 4NO + 6H2O 2NO + O2 → 2NO2 The catalytic oxidation of ammonia is used in Ostwald process for industrial manufacture of nitric acid. Reaction with water : Reacts with water to form ammonium hydroxide also called liquor ammonia . NH3 + H2O → NH4OH NH4OH solution undergoes partial dissociation to yield NH4+ and OH- ions. Hence the solution is slightly alkaline. Action on indicators : (a) Litmus : Turns moist red litmus paper blue . (b) Phenolphthalein : Colourless to pink (c) Methyl orange : Orange to yellow Action with acids : NH3 + HCl → NH4Cl NH3 + H2SO4 → (NH4)2SO4 Reducing nature : Ammonia reduces oxides of lower metals to respective metals . 3CuO + 2NH3 → 3Cu + N2 + 3H2O ( Black ) ( Pink ) 3PbO + 2NH3 → 3Pb + N2 + 3H2O ( Yellow ) ( Greyish white ) Action of aqueous ammonia on metal salts : Aqueous ammonia precipitates metallic hydroxides when reacted with aqueous solution of metal salts . FeSO4 + 2NH4OH → Fe(OH)2 + (NH4)2SO4 Dirty green ppt FeCl3 + 3NH4OH → Fe(OH)3 + 3NH4Cl Reddish brown ppt Reaction with chlorine : Ammonia reacts with chlorine to produce N2 ( neutral gas ) and hydrogen chloride . 2NH3 + 3Cl2 → 6HCl + N2 With excess ammonia : 8NH3 + 3Cl2 → 6NH4Cl + N2 With excess chlorine : NH3 + 3Cl2 → NCl3 + 3HCl

Tests for ammonia : (i) Ammonia turns moist red litmus paper blue. (ii) Produces dense white fumes with a rod dipped in HCl (iii) Turns Nessler’s reagent ( K2HgI4) brown. Uses of ammonia : (i) Used as a refrigerant due to high volatility and high latent heat of vapourisation. (ii) Used to remove grease stains. (iii) Used in the manufacture of fertilizers.

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REVIEW THE CHAPTER YOURSELF 1. (i)

Laboratory preparation of ammonia : Ammonia is prepared by heating ammonium salt with an ___________. The ammonium salt commonly used is _________ and the other reactant is __________ . Slaked lime is used since it is easily ____________ and __________ ( cheap / expensive ) Reaction : NH4Cl + ____________ → ___________ + H2O + ___________.

(ii)

Drying of ammonia : Ammonia is dried by ing it through _________ ( CaO / conc . H2SO4 ). _________ is used as a drying agent since it is a __________ ( acidic / basic ) oxide and does not react with basic ammonia gas .

(iii)

Method of collection: Dry NH3 gas is collected by _________ ( upward/downward ) displacement of air , since it is _________ (lighter/heavier) than air.

2.

Preparation of ammonia from metallic nitrides : Metallic nitrides are obtained by the reaction of burning metal with nitrogen gas. Mg + N2 → __________ ; Al + N2 → __________ . Equation : Mg3N2 + H2O → __________ + NH3 AlN + H2O → ___________ + NH3

3.

Manufacture of ammonia : ( Haber’s process ) Reactants : N2 and H2 in the ratio _________ Catalyst : ______ ( Fe / Pt / Pd ) Promoter : _____________ Temperature : _________ Pressure : __________ atm

4.

Demonstration of solubility of NH3 in water : Dry round bottom flask is filled with __________. The trough is filled with _________ ( blue / red ) litmus solution . Water is squeezed into the flask through a dropper . Ammonia dissolves in water due to its _________ ( high / low ) solubility that creates a _________ ( complete/partial ) vacuum in the flask. The ________ ( blue / red ) litmus solution is pushed in the flask to equalize the pressure . The litmus solution comes out of the tube in the form of _________ ( blue / red ) fountain.

5. (i)

Properties of ammonia gas : Combustion : Ammonia burns in an atmosphere of O2 with a ___________ flame to form ___________ and water. Reaction : NH3 + O2 → _________ + H2O. Catalytic oxidation of ammonia : NH3 reacts with O2 in presence of ____________ catalyst to produce ___________ vapours (colour ) of ___________. Reaction : NH3 + O2  P →t __________ + __________. This reaction is used for the manufacture of ____________ and the process is called the ____________ . Reaction of NH3 : NH3 + HCl → ___________. NH3 + H2SO4 → ___________. NH3 + HNO3 → ___________. Reducing action of NH3 : CuO + NH3 → ________ + N2 + ________. PbO + NH3 → ________ + N2 + ________ Action with chlorine : NH3 + Cl2 → _________ + ____________ NH3 + Cl2 → _________ + ____________ ( ammonia is in excess ) NH3 + Cl2 → _________ + ____________ ( chlorine is in excess ) Reaction of aqueous ammonia with metal salts : FeSO4 + NH4OH → _________ + __________ . FeCl3 + NH4OH → _________ + __________ . Pb(NO3)2 + NH4OH → _________ + __________ . CuSO4 + NH4OH → _________ + __________ .

(ii)

(iii)

(iv)

(v)

(vi)

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Cu(OH)2 + (NH4)2SO4 → _________ + ___________ + H2O The process is used to identify __________ ( metallic / non-metallic ) radicals from the salts. PRACTICE QUESTIONS ( MODULE 1)

1. (i) (ii) (iii) (iv) (v)

Name the following : A metallic nitride of a trivalent metal which reacts with warm water to give ammonia. A drying agent which forms an addition compound with ammonia The catalyst other than iron which may be used in Haber’s process. An amphoteric oxide which cannot be reduced by ammonia. The neutral gas obtained when excess ammonia reacts with chlorine .

2.

How is ammonia prepared in laboratory from : (i) aluminium nitride (ii) ammonium chloride

3.

Give reasons why : (i) Ammonia is not collected over water (ii) Ammonia is dried over quicklime (iii) Ammonia is not collected by downward displacement of water

4.

Give a chemical test to identify ammonia gas .

5.

Following question relate to the large scale preparation of ammonia : (i) Name the process used . (ii) Name the reactants used (iii) In what ratio are the reactants taken ? (iv) Why should the reactants be pure ? (v) Write the balanced equation (vi) What is the pressure applied ? (vii) Name the catalyst and the promoter used . (viii) Give two methods used to recover ammonia from the gaseous mixture obtained.

6.

Write your observations only : (i) A glass rod dipped in HCl acid is brought near ammonia gas. (ii) A glass jar filled ammonia is inverted in a trough filled with water (iii) A moist red litmus paper is brought in the jar of ammonia (iv) Ammonia is burnt in a current of oxygen.

7.

Write the equation for the formation of ammonia by the action of water on magnesium nitride. (i ) How is ammonia collected ? (ii) Why is ammonia not collected over water ?

[2003]

8.

Name a gas whose solution is alkaline , state one important use of quicklime .

[1989]

9.

State the products of the following reaction when a well ground mixture of ammonium chloride and slaked lime was heated . [1989]

10.

State what will you observe when ammonium hydroxide is reacted with copper sulphate solution .

11.

Write balanced equations for the following reactions : (i) Preparation of ammonia from ammonium chloride and calcium hydroxide. (ii) Reaction of ammonia with hydrogen chloride. (iii) Oxidation of ammonia with copper(II)oxide.

12. 13.

The first step in the manufacture of nitric acid is catalytic oxidation of ammonia . What is the name of the catalyst ? [2002] Name the ions formed when ammonia dissolves in water .

14.

Of the two gases ammonia and hydrogen chloride , which is more dense ? Name the method of collection of gas .

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PRACTICE QUESTIONS ( MODULE 2 ) 1.

Give a chemical test to identify : (i) ammonia gas

2.

Give balanced equation for the following : (i) Excess of ammonia reacts with chlorine (ii) Ammonium sulphate is heated with sodium hydroxide solution .

3.

Give one experiment to show that ammonia is a good reducing agent .

4.

Ammonia is used as a refrigerant in ice plants . Why ?

5.

Name four important fertilizers obtained from ammonia .

6.

State two advantages of using the funnel arrangement while preparing aqueous ammonia .

7.

List the properties of ammonia that makes it : (i) a good refrigerant (ii) a cleansing agent

8.

What are the necessary conditions for getting the maximum yield of ammonia .

9.

Ammonia is highly soluble in water yet its aqueous solution can not be prepared by ing it directly into distilled water. Explain . Also describe the method used to dissolve it in water.

10.

How soluble is ammonia soluble in water ?

11.

(ii) ammonium hydroxide solution (iii) ammonium salt

E Alkaline gas C

Nitric oxide D

Ammonium salt A

O2 Nitrogen

Nitrogen dioxide

G Colourless and coloured gas (i) (ii)

Calcium nitrate

F Nitric acid

Name the ammonium salt A and alkaline gas C How is C converted to nitric oxide.

12.

Give reason why ammonium nitrate is not used in the laboratory preparation of ammonia.

13.

Give balanced equation for the conversion of ammonia into nitrogen using an amphoteric oxide.

14.

State two physical properties of ammonia which are involved in separating ammonia from unreacted gases in the manufacture of ammonia.

15.

Give balanced equation for the following conversions A , B and C. Ammonia  A → Ammonium hydroxide B→ Ammonium sulphate ↓ Iron(III)hydroxide

Authored by Partha Protim Sen : Tring :: 9670075025

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