AMMONIA IMPORTANT CONCEPTS Ammonia was initially called alkaline air. It occurs combined in the free and in the chemically combined state small quantities of ammonia occurs in atmospheric air and natural water. In the combined state, ammonium salts and ammonium liquor also gives ammonia. Nitrogen required for the manufacture of ammonia is obtained from air and H 2 by electrolysis of aq. Solution of sodium chloride. Nitrogen is a colourless and odourless gas. It is slightly soluble in water. It is lighter than air. Nitrogen is not poisonous but animals die in an atmosphere of nitrogen for want of oxygen. Hydrogen is a colorless, odorless gas. It pops with a lighted splint. Molecular formula of ammonia in NH 3. Atomic number of Nitrogen is 7 electronic configuration is 2,5. Atomic number of hydrogen is 1 electronic configuration is 1. Structural formula of Ammonia Relative molecular mass of NH 3 is 17.
A chemical reaction that can proceed in both the forward and reverse direction is called Reversible Reaction. An industrial process for making ammonia from nitrogen and hydrogen under some conditions is called Haber Process. TEST YOURSELF: Describe the use of (a) nitrogen, from air, and (b) hydrogen, from the cracking of crude oil in the manufacture of ammonia. 1.1 THE USE OF NITROGEN AND HYDROGEN IN THE MANUFACTURE OF AMMONIA 1. The raw materials for the manufacture of ammonia are nitrogen and hydrogen. 2. Nitrogen is obtained by the fractional distillation of liquid air. The fractional distillation of liquid air is shown in the diagram below.
NITROGEN (b.p.: 196 0 C) AIR Cooling Compression LIQUID AIR Fractional Distillation ARGON (b.p.: 186 0 C) OXYGEN (b.p.: 183 0 C) During the fractional distillation of liquid air, nitrogen is distilled over first because it has the lowest boiling point compared to oxygen and argon. 2. Hydrogen is obtained by the cracking of crude oil that is used for the manufacture of ammonia. TEST YOURSELF: Understand that some chemical reactions are reversible.
1.2 REVERSIBLE REACTIONS: 1. Many chemical reaction can be proceed in one direction only. EXAMPLE: Sodium hydroxide reacts with dilute sulfuric acid to form sodium sulfate and water 2NaOH (aq) + H2SO4 (aq) Na2SO4(aq) + 2 H2O (l) The reaction is irreversible. It is not possible to make sodium sulfate react with water to form sodium hydroxide and sulfuric acid. 3. Some reactions are called Reversible reaction because the reaction can proceed in two directions. EXAMPLE When ammonium chloride is heated, it decomposes to form ammonia and Hydrogen chloride. Heat NH4Cl (s) NH3 (g) + HCl(g)
Moist Blue Litmus Paper Cotton Wool Moist Blue Litmus Paper Solid ammonium chloride Red litmus paper charges colour first before blue litmus paper. Heat HEATING AMMONIUM CHLORIDE However, when ammonia gas comes into contact with hydrogen chloride fumes, solid ammonium chloride is formed. NH3(g) + HCl(g) NH4Cl(s) Cotton wool soaked in concentrated Cotton wool soaked in concentrated Ammonia Solution White fumes of ammonium chloride Hydrochloric Acid Diffusion of Gases
FORMATION OF AMMONIUM CHLORIDE The reaction is reversible and is indicated by the sign NH4Cl (aq) NH3(g) + HCl(g) The reaction from left to right is called the Forward Reaction. The reaction from right to left is called the Reverse Reaction or Backward Reaction. Forward Reaction NH4Cl (s) NH3(g) + HCl(g) Reverse Reaction II. POINTS OF CONTENT: A. Preparation of Ammonia (i) (ii) Laboratory preparation Industrial preparation
B. Properties of Ammonia C. Test and uses of Ammonia 1.3 THE MANUFACTURE OF AMMONIA BY THE HABER PROCESS: 1. The Haber Process is the industrial process for making ammonia using nitrogen gas and hydrogen gas. 2. Nitrogen is unreactive. Under normal laboratory conditions, nitrogen does not react with hydrogen. 3. The equation for the Haber Process: Finely divided iron N2 (g) + 3H2 (g) 2NH3 (g) H = - 92 KJ Without Catalyst N2 + 3H2 ( The reaction has high E4 ) With Catalyst 2NH3 PROGRESS OF REACTION
The reaction in which the two elements, nitrogen and hydrogen, combines to from ammonia is a reversible reaction. 4. Effect of temperature, pressure and catalyst on the yield of ammonia a) A high yield of ammonia is obtained by using high pressure and low temperature. b) The graph shows the yield of ammonia at different temperature and pressure. 70 YEILD OF AMMONIA (%) 60 350 0 C 50 400 0 C 40 400 0 C 30 20 500 0 C 10 0 50 100 150 200 250 300 350 400 PRESSURE (atm)
c) Using pressure above 200 atm would produce even more ammonia, but this would be more costly because a stronger structure is needed to achieve the high pressure. d) Using temperatures below 450 0 C. It would produce even more ammonia but the reaction would be very slow. e) An optimum condition 250 atm and 450 0 C. A catalyst is therefore used to speed up the reaction. f) The catalyst is in finely divided form. The bigger the surface area of the catalyst, the faster the speed of reaction.thus, the finely divided iron ensures a faster process. TIPS FOR STUDENTS: Take note that an increase in temperature will increase the speed of reaction. However, for exothermic reactions, an increase in temperature will decrease the yield. For such reactions, a low temperature is used to increase the yield, an a catalysts is used to increase the speed of reactions.
5. The flow diagram for the manufacture of ammonia by the Haber process is shown below. NITROGEN ( 1 VOLUME ) HYDROGEN ( 3 VOLUME ) COMPRESSOR Mixture of gases is compressed to 200-300 atm and heated to 450 0 C. Unreacted N2 and H2 are Pumped back into the Converter for further reaction N2 + H2 CONVERTER The gases are passed over finely divided iron catalyst N2 + 3H2 2NH3 The reaction is exothermic. Only 10-15 % of nitrogen and hydrogen combine to form ammonia. CONDENSER Gases are cooled to form liquid ammonia.
6. Operating conditions in the Haber process are: RAW MATERIALS Nitrogen from fractional distillation of air Hydrogen from cracking petroleum PROPORTION 1 Volume of nitrogen to 3 volumes of hydrogen TEMPERATURE 450 0 C PRESSURE 200-300 atm CATALYST Finely divided iron EXAMPLE: 1.1 At certain conditions of temperature and pressure, 15% of nitrogen and hydrogen react to form ammonia. What is the mass of ammonia produced when 2.80 tonnes of nitrogen react excess hydrogen under this conditions? SOLUTION: STEP 1: Calculate the theoretical yield of ammonia. N2 (g) + 3H2 (g) 2NH3 (g) Mr of Nitrogen ( N2 ) = 2 X 14 = 28 Mr of Ammonia ( NH2 ) = 14 + ( 1 X 3 ) = 17
From the equation, 1 mol (28g) of nitrogen will produce 2 mol ( or 2 x 17g ) of NH3. That is, 28 tonnes of N2 will produce 2 x 17 tonnes of NH3 2.80 tonnes of N2 will produce. X ( 2 X 17 ) = 3.4 tonnes of NH3 Theoretical yield = 3.4 tonnes STEP 2: Calculate the actual yield of ammonia. The reaction is reversible and only 15% of nitrogen reacted. Hence, mass of ammonia produced = 3.4 X = 0.51 tonnes. COMMON ERROR ACTUAL FACT When 1 mol of nitrogen reacts with 3 mol of hydrogen, 2 mol of ammonia are produced. Less than 2 mol of ammonia are produced because this is a reversible reaction. Some nitrogen and hydrogen remain unreacted. TEST YOURSELF: Explain the displacement of ammonia from its salts
LABORATORY PREPARATION OF AMMONIA 1. Whenever an ammonium salt is heated with an alkali, ammonia is displaced from its salt. The ionic equation for the reaction between an ammonium salt and an alkali is: NH4 + (aq) + OH- (aq) NH3(g) + H2O (I) 2. a) In the laboratory, ammonia is made by heating any ammonium salt with an alkali (solid or in aqueous solution). Heat 2NH4Cl (aq) + NaOH (aq) NCl (s) + H2O(l) + NH3(g) Ammonium Sodium Sodium Water Ammonia Chloride Hydroxide Chloride Heat 2NH4Cl (s) + Ca(OH)2 (s) CaCl2 (s) + 2H2O(I) + 2NH3(g) Ammonium Calcium Calcium Water Ammonia Chloride Hydroxide Chloride
Dry Ammonia Cover Heat Ammonium Chloride And Calcium Hydroxide Calcium Oxide To Dry The Ammonia LABORATORY PREPARATION OF AMMONIA b) The ammonia produced is damp because it is mixed with water vapour. Calcium Oxide is used to dry ammonia by the following reaction. CaO(s) + H2O(l) Ca(OH)2(s) Calcium Oxide Water Calcium Hydroxide
COMMON ERROR ACTUAL FACT When a mixture of ammonia chloride and calcium hydroxide is heated, ammonium hydroxide is produced. When a mixture of ammonium chloride and calcium hydroxide is heated, ammonia is produced. Ammonium chloride + calcium hydroxide Ammonium chloride + calcium hydroxide Ammonium hydroxide + calcium chloride Ammonia + calcium chloride + water EXAMPLE:1.2 A mixture of 4.0 g of ammonium chloride and calcium hydroxide is heated. The ammonia produced is passed into aqueous sodium hydroxide of concentration 2.0 mol/dm3. What is the volume of sodium hydroxide solution required to react completely with the ammonia produced? SOLUTION: STEP 1: Calculate the number of moles of NH4 Cl used. Mr of NH4 Cl = 14 + ( 4 X 1 ) + 35.5 = 53.5 Number of moles of NH4 Cl used = Mass. = M. r = 0.075 mol
STEP 2 : Calculate the number of moles of NH3 produced. NH4 + + OH - NH3 + H2O 1 mol NH4 Cl produces 1 mol of NH3 Number of moles of NH3 produced = 0.075 mol STEP 3: Calculate the volume of 2.0 mol/ dm 3 NaOH required. Number of moles = Concentration ( mol/dm 3 ) X Volume ( dm 3 ) 0.075 = 2.0 X V V =.. = 0.0375 dm 3 Volume of NaOH(aq) required = 37.5 cm 3 Preparation of Ammonia (i) Laboratory preparation 1. How is ammonia prepared in the laboratory? Ans. In the laboratory ammonia is prepared by heating an ammonium salt with an alkali. + OH - NH 3 (g) + H 2 O Ammonium salt alkali ammonia NH 4 + The ammonium salt and the alkali most often used are ammonium chloride and calcium hydroxide (slaked lime), used in higher ratio
2NH 4 Cl + Ca(OH) 2 CaCl 2 + 2H 2 O + 2NH 3 Ammonium Calcium hydroxide calcium chloride Ammonia chloride 2. In the preparation of Ammonia gas why solid Ammonium chloride and slaked lime are taken in the ratio 2:3 by weight? Ans. Solid ammonium chloride is a sublimable solid which could be lost during direct heating. The higher ratio of slaked lime may counteract the loss. 3. Why ammonium nitrate is not used in the preparation of Ammonia? Ans. Ammonium nitrate is not used since it is explosive in nature and may itself decompose forming nitrous oxide and water vapour. 4. How is ammonia gas dried? Ans. It is dried using the drying agent, quick lime (CaO), which is basic and does not react with NH 3 which is also basic. 5. Why ammonia gas is not dried by using drying agents like conc. Sulphuric acid calcium chloride and phosphorous pentoxide? Ans. Drying agents like conc. sulphuric acid, calcium chloride and phosphorous pentoxide are not used for drying because all these drying agents react with ammonia. 2NH 3 + H 2 SO 4 (NH 4 ) 2 SO 4 (conc.) ammonium sulphate 6NH 3 + P 2 O 5 + 3H 2 O 2(NH 4 ) 3 PO 4 Ammonium phosphate 8NH 3 + CaCl 2 CaCl 2. 8NH 3 (fused) addition product 6. How is ammonia gas collected? Ans. Ammonia gas is lighter than air and hence collected by the downward displacement of air V.D of air = 14.4, V.D of NH 3 = 8.5
7. Why cannot ammonia gas be collected over water? Ans. It is not collected over water since it is highly solouble in water (1 vol. of water dissolves about 702 vols. At 20 o C and 1 atmospheric pressure). 8. Give the preparation of NH 3 from metal nitrides? Ans. Metal nitrides undergo hydrolysis and are decomposed by water to give NH 3 gas. Metal nitride + Water Metal hydroxide + Ammonia Mg 3 N 2 + 6H 2 O Magnesium nitride Ca 3 N 2 + 6H 2 O Calcium (warm) Nitride 3Mg(OH) 2 + 2NH 3 (g) Ammonia 3Ca (OH) 2 +2NH 3 (g) Ammonia AIN + 3H 2 O Al (OH) 3 + NH 3 Formation of metal nitrides: Burning metal + nitrogen metal nitrides 3Mg + N 2 Mg 3 N 2 3Ca + N 2 Ca 3 N 2 2Al + N 2 2AIN 9. Give the chemical equation for the preparation of NH 3 (g) from ammonium sulphate. Ans. (NH 4 ) 2 SO 4 + Ca(OH) 2 CaSO 4 + 2H 2 O + 2NH 3 (g) 10. How is ammonia manufactured by Haber s process?
450-500 0 c Ans. N 2 + 3H 2 2NH 3 + 22,400 cal (1 vol) (3 vols) 200 atm, Fe/ Mo (2 vols) Conditions: i. Temperature 450-500 0 C (optimum temp.) ii. Pressure 200 900 atm. iii. Catalyst Finely divided iron iv. Promoter Moleybdenum (Mo) The above reaction is reversible, exothermic and proceeds with a decrease in volume. Low temperature and high pressure favours the forward reaction. 11. Why is the reaction temperature in the above process around 450 o C to 500 o C? Ans. According to the Le chatelier s principle, if a reaction is exothermic the forward reaction is favoured by lowering the temperature therefore an optimum temperature of 450 o C 500 o C is kept. 12. Why should the catalyst be free from impurities? Ans. Impurities like CO, Co 2 and H 2 S poison the catalyst and hence the nitrogen hydrogen reactant mixture must be free from them. 13. What are the function of catalyst and promoter? Ans. The catalyst speeds up the reaction but does not increase the yield of ammonia whereas promoter enhances the efficiency of the catalyst. 14. How is ammonia separated from nitrogen and hydrogen? Ans. Mixute of NH 3 along with residual nitrogen and hydrogen under pressure is allowed to expand suddenly through a small nozzle into a region of low pressure. This results in the fall in temperature thereby liquefying easily liquefiable NH 3 gas while nitrogen and Hydrogen are difficult to liquefy. A. Properties of Ammonia 15. Give an experiment to show the high solubility of ammonia gas in water. Ans. The high solubility of NH 3 gas is demonstrated by the fountain experiment.
i) An inverted flask containing dry NH 3 gas is arranged as shown in the diagram. ii) iii) When the dropper containing water is squeezed, the water enters the flask and since NH 3 gas is highly soluble in water, it dissolves creating a partial vaccum in the flask. The outside pressure being higher than the inside pressure it forces the red litmus solution to move upwards through the jet tube emerging out as a blue fountain. 16. Give the equation for the burning of NH 3 (g) in O 2. Ans. Ammonia burns in oxygen in the absence of catalyst with a greenish flame forming nitrogen. 4NH 3 + 3O 2 2N 2 + 6h 2 O Ammonia on catalytic oxidation (Pt/800 0 C) gives nitric oxide which undergoes further oxidation to give reddish brown vapour of NO 2 4NH 3 + 5O 2 Pt 800 4NO + 6H 2 O colorless [2NO + O 2 2NO 2 ] Reddish brown 17. Why an aqueous solution of ammonia is basic in nature? Ans. The aqueous solution of ammonia (NH 4 OH) acts as a weak base, since it undergoes partial dissociation in aqueous solution to give hydroxyl ions ( OH - ) in low concentration NH 3 + H 2 O NH 4 OH Liquor ammonia NH 4 OH NH + 4 + OH - The aq. Solution turns red litmus blue and phenolphthalein soln. pink. 18. What is liquor ammonia?
Ans. An aqueous solution of ammonia (NH 4 OH) acts as a weak base, since it undergoes partial dissociation in aqueous solution to give hydroxyl ions (OH - ) in low concentration. NH 3 + H 2 O NH 4 OH Liquor ammonia 19. Give balanced equation to show the formation of ammonium salts? Ans. Ammonia in aq. Soln. (NH 4 OH) neutralizes acids forming respective ammonium salts. NH 3 + H + NH + 4 Weak base proton ammonium ion Preparation of ammonium salts: i. NH 3 + HCl NH 4 Cl (ammonium chloride) ii. NH 3 + HNO 3 NH 4 NO 3 (ammonium nitrate) iii. 2NH 3 + H 2 SO 4 (NH 4 ) 2 SO 4 (ammonium sulphate) Neutralization reaction: NH 4 OH + HCl NH 4 OH + HNO 3 2NH 4 OH + H 2 SO 4 NH 4 Cl + H 2 O NH 4 NO 3 + H 2 O (NH 4 ) 2 SO 4 + 2H 2 O 20. Aqueous solution of ammonium hydroxide precipitates hydroxide of metals from the solution of their sales. Give the reactions and observation showing the basic nature of NH 3 gas.
Ans. NH 4 OH reacts with soluble salts of metals in their solution state to give insoluble precipitate of respective metallic hydroxide. FeSO 4 + 2NH 4 OH (NH 4 ) 2 SO 4 + Fe(OH) 2 Dirty green ferrous hydroxide (insoluble in excess of NH 4 OH) FeCl 3 + 3NH 4 OH 3NH 4 Cl + Fe(OH) 3 Reddish brown ferric hydroxide (insoluble in excess of NH 4 OH) Pb(NO 3 ) 2 + 2NH 4 OH 2NH 4 NO 3 + Pb(OH) 2 Lead hydroxide chalky white (insoluble in excess of NH 4 OH) Zn(NO 3 ) 2 + 2NH 4 OH 2NH 4 NO 3 + Zn(OH) 2 White gelatinous Zinc hydroxide (soluble in excess of NH 4 OH) CuSO 4 + 2NH 4 OH (NH 4 ) 2 SO 4 + Cu(OH) 2 Pale blue Copper hydroxide (soluble in excess of NH 4 OH) Cu(OH) 2 + (NH 4 ) 2 SO 4 + 2 NH 4 OH [Cu(NH 3 ) 4 ] SO 4 +4H 2 O Tetrammine copper (II) sulphate (deep blue or inky blue solution) 21. Give reaction to show ammonia as a reducing agent. Ans. 2NH 3 + 3CuO 3Cu + 3H 2 O + N 2 (g) Copper (II) oxide Reduced (basic oxide) product 2NH 3 +3PbO Lead (II) oxide (amphoteric oxide) 8NH 3 + 3Cl 2 Excess 3Pb + 3H 2 O + N 2 (g) Reduced product 6NH 4 Cl + N 2 (g) dense white fumes NH 3 + 3Cl 2 3HCl + NCl 3 Excess Nitrogen trichloride
B. Tests and Uses of Ammonia 22. Give some important tests for ammonia gas. Ans. i) It turns moist red litmus blue. ii) A glass rod dipped in conc. HCl acid brought near ammonia gas, dense white fumes of ammonium chloride are formed. iii)ammonia gas passed through Nesseler s reagent gives brown coloured ppt. iv) Ammonia gas passed through copper sulphate soln. gives a pale blue ppt of copper hydroxide, which turns into a deep blue coloured solution due to the formation of soluble complex tetrammine copper (II) sulphate. 23. Give few large scale or industrial uses of ammonia. Ans. i) Manufacture of fertilizers e.g. urea, ammonium sulphate, ammonium nitrate, ammonium phosphate etc. ii) In the manufacture of important ammonium compounds such as: a) Ammonium chloride used in dry cells, medicine and textile industry and cleaning metal surfaces. b) Ammonium carbonate (constituent of smelling slat) helps in reviving a fainted person and is also used in baking and dyeing industry. c) Ammonium sulphate is used in the manufacture of alum. 24. What is liquid ammonia and give its use? Ans. Ammonia gas liquefied at low temperature. It is used as a refrigerant in ice plants. Liquid ammonia on evaporation absorbs heat from the surroundings and hence cools the surroundings.
NH NH 3 3 5.7 k cals Heat of evaporation of ammonia is 5.7 k cals at 33. 25. Give two uses of liquor ammonia. Ans. 1. It is ued as a cleansing agent. It emulsifies or dissolves fats, grease stains from clothes. 2. It is also used for cleaning window panes, porcelain articles etc. SHORT ANSWER TYPE QUESTION 1. Give the work equation with balanced molecular equation for lab preparation of ammonia. Ans. 2NH 4 Cl + Ca(OH) 2 CaCl 2 + 2H 2 O + 2NH 3 (g) Ammonium Calcium calcium water ammonia chloride hydroxide chloride 2. Convert ammonium sulphate to ammonia using alkali. Give equation only. Ans. (NH 4 ) 2 SO 4 + Ca(OH) 2 CaSO 4 + 2H 2 O + NH 3 (G) Ammonium calcium calcium water ammonia Sulphate hydroxide sulphate 3. How will you convert i) Mg ii) Ca iii) Al to ammonia? give equation only. Ans. i) 3Mg + N 2 Mg 3 N 2 Magnesium nitrogen magnesium nitride Mg 3 N 2 + 6H 2 O 3Mg(OH) 2 + 2NH 3 (g) Magnesium water magnesium Ammonia Nitride (warm) hydroxide ii) 3Ca + N 2 Ca 3 N 2 Calcium Nitrogen Calcium nitride Ca 3 N 2 + 6H 2 O 3Ca(OH) 2 + 2NH 3 (g) Calcium warm Calcium Ammonia Nitride water hydroxide
iii) 2Al + N 2 2AlN Aluminium Nitrogen Aluminium nitride AlN + 3H 2 O Al(OH) 3 + NH 3 (g) Aluminium warm Aluminium Ammonia Nitride water hydroxide 4. Why is the reaction temperature in in the Haber s process is kept around 450 to 500? Ans. For the exothermic reaction, Le Chatelier principle s says that the forward reaction is favoured by lowering the temperature. But if the temperature is too low the reaction is slow hence, an optimum temperature of 450 500 is used. 5. Why an optimum pressure of 200 900 atm. is used in the process? Ans. According to Le Chatelier s principle if a reaction proceeds with decrease in volume then the forward reaction is favoured (i.e. higher percentage field of NH 3 ) by increasing the pressure. 6. What are the catalyst and promoter used in the Heber s process? Name them. Ans. Finely divided iron is used as catalyst and Molybdenum is used as promoter. 7. State i) a light neutral gas ii) an acid iii) an explosive iv) a fertilizer obtained from ammonia. Ans. i) Nitrogen gas ii) Nitric acid iii) Ammonium nitrate iv) Ammonium sulphate 8. Name an ammonium salt which is a constituent of smelling salt and give reason for its use. Ans. Ammonium carbonate is a constituent of smelling salt. It dissociate evolving pungent ammonia gas and revives a fainted person.
9. Why liquor NH 3 is used as a cleansing agent? Ans. Liquor NH 3 emulsifies or dissolves fats, grease, etc. hence is used for removing oil or grease stains from clothes. 10. Give 2 household uses of ammonia. Ans. i) For removing grease stains from clothes. ii) For cleaning window panes, tiles, porcelain etc. 11. A solution of ammonia in water conducts electricity. Explain. Ans. Ammonium hydroxide formed is a weak electrolyte and dissociates partially forming ammonium and hydroxyl ions. + NH 4 OH NH 4 + OH - Weak (ions) Electrolyte 12. What is the action of NH 3 solution on methyl orange and phenolphthalein indicators? Ans. Methyl orange changes from orange to yellow. Phenolphthalein changes from colorless to pink. OBSERVATION REACTIONS 26. State the observation for the following. i) Ammonia gas bubbled through red litmus soln. Ans. Red litmus solution turns blue. ii) Ammonia burns in oxygen. Ans. it burns with greenish yellow flame forming nitrogen and water. iii) Ammonia burns in oxygen in the prescence of catalyst Pt. Ans. The colourless nitric oxide undergoes further oxidation, to give reddish brown fumes of nitrogen dioxide. The platinum continues to glow even after the heating is discontinued. iv) Ammonia is passed over heated copper oxide. Ans. Black colored copper oxide changes to pinkiish red metal, a colourless liquid is obtained which turns anhydrous copper sulphate blue.
v) Ammonia is passed over heated Lead (II) oxide. Ans. Buff yellow lead (II) oxide is reduced to grayish metallic lead, a colourless liquid is obtained which turns anhydrous copper sulphate blue. vi) When NH 3 gas is excess is mixed with chlorine. Ans. Dense white fumes of ammonium chloride are seen. vii) When NH 3 gas is passed through neutral litmus solution. Ans. Neutral litmus (purple) turns blue in alkaline solution. SUMMARY OF EQUATIONS: a. Preparation of Ammonia : Laboratory preparation (NH 4 ) 2 SO 4 + 2NaOH Na 2 SO 4 + 2H 2 O + 2NH 3 (NH 4 ) 2 SO 4 + Ca(OH) 2 CaSO 4 + 2H 2 O + 2NH 3 NH 4 Cl + NaOH NaCl + H 2 O + NH 3 2NH 4 Cl + Ca(OH) 2 CaCl 2 + 2H 2 O + 2NH 3 b. Reactions of Ammonia with drying agents: 2NH 3 + H 2 SO 4 (NH 4 ) 2 SO 4 (conc.) 6NH 3 + P 2 O 5 + 3H 2 O 2(NH 4 ) 3 PO 4 8NH 3 + CaCl 2 CaCl 2. 8NH 3 Fused c. Laboratory preparation: From metal nitrides Mg 3 N 2 + 6H 2 O 3Mg(OH) 2 + 2NH 3 Warm Ca 2 N 2 + 6H 2 O 3Ca(OH) 2 + 2NH 3 Warm AlN + 3H 2 O Al(OH) 3 + NH 3
d. Manufacture of Ammonia: Haber s process N 2 + 3H 2 2NH 3 + 22,400cals Conditions : Temperature : low temperature of 450-500 Pressure : High pressure 200-900 atmospheres Catalyst : Finely divided iron (Fe) Promoter : Molybdenum (Mo) e. Chemical properties of ammonia: i) Combustibility 4NH 3 + 3O 2 2N 2 + 6H 2 O Pt 4NH 3 + 5O 2 500 4NO + 6H 2 O ii) Basic nature of ammonia: NH 3 + HCl NH 4 Cl NH 3 + HNO 3 NH 4 NO 3 2NH 3 + H 2 SO 4 (NH 4 ) 2 SO 4 NH 4 OH + HCl NH 4 Cl + H 2 O 2NH 4 OH + H 2 SO 4 (NH 4 ) 2 SO 4 + 2H 2 O NH 4 OH + HNO 3 NH 4 NO 3 + H 2 O iii) Ammonia with metallic salt solution : FeSO 4 + 2NH 4 OH (NH 4 ) 2 SO 4 + Fe(OH) 2 FeCl 3 + 3NH 4 OH 3NH 4 Cl + Fe(OH) 3 Pb(NO 3 ) 2 + 2NH 4 OH 2NH 4 NO 3 + Pb(OH) 2 f. Ammonia gas as a reducing agent 2NH 3 + 3CuO 3Cu + 3H 2 O + N 2 2NH 3 + 3PbO 3Pb + 3H 2 O + N 2 2NH 3 + 3Cl 2 5HCl + N 2 NH 3 + HCl NH 4 Cl 8NH 3 (excesss) + 3Cl 2 6NH 4 Cl + N 2 NH 3 + 3Cl 2 3HCl + NCl 3 Excess
Name the following: i) The Process by which Ammonia is manufactured. Ans. Haber s process. ii) Ans. Drying agent for ammonia gas. Quicklime. iii) Metal nitride which on hydrolysis gives ammonia gas. \ Ans. Magnesium nitride (Mg 3 N 2 ), Calcium nitride (Ca 3 N 2 ), Aluminum nitride (AlN). iv) Ans. Catalyst used in Haber s process. Finely divided iron. v) Two metallic oxides which are reduced by ammonia Ans. Copper oxide (CuO) and lead oxide (PbO). vi) Two solutions which react together to produce nitrogen. Ans. Ammonium chloride (NH 4 Cl) and sodium nitrite( NaNO 2 ) vii) Ans. Two gases which gives dense white fumes with ammonia. Chlorine (Cl 2 ) and hydrogen chloride (HCl)(g). viii) The solution which turns brown when it comes in contact with ammonia. Ans. Nessler s reagent. ix) Ans. Experiment which demonstrate the extreme solubility of ammoinia. Fountain experiment x) A colorless gas which becomes reddish brown when it comes in contact with atmosphere (oxygen). Ans. Nitric oxide (NO). xi) Metal which directly combines with nitrogen on heating.
Ans. Magnesium, calcium, aluminium. xii) Ans. Aqueous solution of ammonia gas in water. Liquid ammonia xiii) Ammonia gas liquefied at low temperature. Ans. Liquid ammonia. xiv) An amphoteric oxide reduced by NH 3 (g) Ans. Lead (II) oxide (PbO). Complete the statement by selecting the correct word from the brackets: i) The alkaline behavior of liquor ammonia is due to the presence of hydroxyl ions. (ammonium ion / hydronium ion / hydroxyl ion) ii) iii) iv) Ammonia reduces chlorine to hydrogen chloride. (nitrogen chloride / hydrogen chloride / ammonium chloride). The gas most difficult to liquiefy is hydrogen. (nitrogen / hydrogen / ammonia) The salt solution which does not give an insoluble precipitate on addition of ammonium hydroxide in small amount is NaNO 3. ( Mg(NO 3 ) 2 / NaNO 3 / Cu(NO 3 ) 2 ) v) When ammonium chloride is heated, it under goes thermal dissociation. (thermal decomposition / thermal dissociation) vi) Heating ammonium chloride with sodium hydroxide produces ammonia. (nitrogen / ammonia) IMPORTANT CONVERSION REACTIONS FOR AMMONIA:
B A (i) NCl 3 NH 3 NH 4 Cl D C N 2 NH 3 NH 4 OH F E Mg 3 N 2 NH 3 N 2 Ans.: A : 8NH + 3Cl 6NH Cl + N excess or NH + HCl B : NH + 3Cl NH Cl NCl + 3HCl excess C : NH + H O NH OH D : 4NH + 3O 2N + 6H O 450-500 0 c E : N 2 + 3H 2 2NH 3 + (1vol) (3vols) 200 atm, Fe/ Mo (2vols) F : 3Mg + N Mg N G : Mg N + 6H O warm 3Mg(OH) + 2NH (ii) NH Cl B A NH C NH OH D Cu(OH) E CuO
Ans.: A : NH + HCl B : NH Cl + NaOH C : NH + H O D : CuSO + 2NH OH NH Cl NaCl + H O + NH NH OH Cu(OH) + (NH ) SO E : Cu(OH) CuO + H O (i) NH A NO B NO C HNO D Cu(NO ) Ans.: A : 4NH + 5O Pt 800 c 4NO + 6H O B : 2NO + O 2NO C : 4NO + 2H O + O 4HNO D : CuO + 2HNO Cu(NO ) + H O dil SUMMARY AND KEY POINTS 1.) Ammonia was initially called alkaline air. It occurs combined in the free and in the chemically combined state small quantities of ammonia occurs in atmospheric air and natural water.
2.) In the combined state, ammonium salts and ammonium liquor also gives ammonia. 3.) Nitrogen required for the manufacture of ammonia is obtained from air and H 2 by electrolysis of aq. Solution of sodium chloride. 4.) Nitrogen is a colourless and odourless gas. It is slightly soluble in water. It is lighter than air. 5.) Nitrogen is not poisonous but animals die in an atmosphere of nitrogen for want of oxygen. 6.) Hydrogen is a colorless, odorless gas. It pops with a lighted splint. 7.) Molecular formula of ammonia in NH 3. 8.) Atomic number of Nitrogen is 7 electronic configuration is 2,5. 9.) Atomic number of hydrogen is 1 electronic configuration is 1. 10.) Structural formula of Ammonia Relative molecular mass of NH 3 is 17. 11.) A chemical reaction that can proceed in both the forward and reverse direction is called Reversible Reaction.
12.) An industrial process for making ammonia from nitrogen and hydrogen under some conditions is called Haber Process. 13.) The raw materials for the manufacture of ammonia are nitrogen and hydrogen. 14.) Nitrogen is obtained by the fractional distillation of liquid air. 15.)During the fractional distillation of liquid air, nitrogen is distilled over first because it has the lowest boiling point compared to oxygen and argon. 16.)Hydrogen is obtained by the cracking of crude oil that is used for the manufacture of ammonia. 17.) The Haber Process is the industrial process for making ammonia using nitrogen gas and hydrogen gas. 18.)Nitrogen is unreactive. Under normal laboratory conditions, nitrogen does not react with hydrogen. Finely divided iron N2 (g) + 3H2 (g) 2NH3 (g) H = - 92 KJ The reaction in which the two elements, nitrogen and hydrogen, combines to from ammonia is a reversible reaction. 19. Whenever an ammonium salt is heated with an alkali, ammonia is displaced from its salt. The ionic equation for the reaction between an ammonium salt and an alkali is: NH4 + (aq) + OH- (aq) NH3(g) + H2O (I)
20.) In the laboratory, ammonia is made by heating any ammonium salt with an alkali (solid or in aqueous solution). Heat 2NH4Cl (aq) + NaOH (aq) NCl (s) + H2O(l) + NH3(g) Ammonium Sodium Sodium Water Ammonia Chloride Hydroxide Chloride KEY POINTS: Take note that an increase in temperature will increase the speed of reaction. However, for exothermic reactions, an increase in temperature will decrease the yield For such reactions, a low temperature is used to increase the yield, an a catalysts is used to increase the speed of reactions. When a mixture of ammonium chloride and calcium hydroxide is heated, ammonia is produced. Ammonium chloride + calcium hydroxide Ammonia + calcium chloride + water