AMMONIA

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

H2 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 NH3.

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 NH3 is 17.

IMPORTANT CONCEPTS

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.

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.

1.1

Cooling Fractional

Compression Distillation

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.

AIR LIQUID AIR

OXYGEN

(b.p.: 1830 C)

ARGON

(b.p.: 1860 C)

NITROGEN

(b.p.: 1960 C)

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)

1.2

Moist Blue Litmus Paper

Cotton Wool

Moist Blue Litmus Paper

Solid ammonium chloride

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 Cotton wool soaked

in concentrated in concentrated

Ammonia Solution White fumes of ammonium chloride Hydrochloric Acid

Diffusion of Gases

Red litmus paper charges colour

first before blue litmus paper.

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) Laboratory preparation

(ii) Industrial preparation

B. Properties of Ammonia

C. Test and uses of Ammonia

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

1.3

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.

YEILD OF AMMONIA (%)

70

60

50

40

30

20

10

0

50 100 150 200 250 300 350 400

PRESSURE (atm)

3500C

4000C

4000C

5000C

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 4500C. It would produce even more ammonia

but the reaction would be very slow.

e) An optimum condition 250 atm and 4500C. 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.

N2 + H2

Unreacted N2 and H2 are Pumped back

into the Converter for further reaction

NITROGEN

( 1 VOLUME )

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 .

COMPRESSOR

Mixture of gases is

compressed to 200 - 300

atm and heated to 4500C .

HYDROGEN

( 3 VOLUME )

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

4500 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.

TEST YOURSELF:

Explain the displacement of ammonia from its salts

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.

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 Calcium Oxide To

And Calcium Hydroxide 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

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 =rM

Mass =

�.�

��.� = 0.075 mol

COMMON ERROR

ACTUAL FACT

When a mixture of ammonia chloride and calcium hydroxide is heated, ammonium hydroxide is produced .

Ammonium chloride + calcium hydroxide

Ammonium hydroxide + calcium chloride

When a mixture of ammonium chloride and calcium hydroxide is heated, ammonia is produced .

Ammonium chloride + calcium hydroxide

Ammonia + calcium chloride + water

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/ dm3 NaOH required.

Number of moles = Concentration ( mol/dm3 ) X Volume ( dm3 )

0.075 = 2.0 X V

V = �.���

�.� = 0.0375 dm3

Volume of NaOH(aq) required = 37.5 cm3

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.

NH4+ + OH- NH3 (g) + H2O

Ammonium salt alkali ammonia The ammonium salt and the alkali most often used are ammonium chloride and calcium hydroxide (slaked lime), used in higher ratio

2NH4Cl + Ca(OH)2 CaCl2 + 2H2O + 2NH3 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 NH3 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. 2NH3 + H2SO4 (NH4)2SO4 (conc.) ammonium sulphate 6NH3 + P2O5 + 3H2O 2(NH4)3 PO4 Ammonium phosphate 8NH3 + CaCl2 CaCl2 . 8NH3

(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 NH3 = 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 20oC and 1 atmospheric pressure).

8. Give the preparation of NH3 from metal nitrides ? Ans. Metal nitrides undergo hydrolysis and are decomposed by water to give NH3 gas. Metal nitride + Water Metal hydroxide + Ammonia Mg3N2 + 6H2O 3Mg(OH)2 + 2NH3 (g) Magnesium nitride Ammonia Ca3N2 + 6H2O 3Ca (OH)2 +2NH3 (g) Calcium (warm) Ammonia Nitride AIN + 3H2O Al (OH)3 + NH3

Formation of metal nitrides: Burning metal + nitrogen metal nitrides

3Mg + N2 Mg3N2 3Ca + N2 Ca3N2

2Al + N2 2AIN

9. Give the chemical equation for the preparation of NH3 (g) from ammonium sulphate.

Ans. (NH4)2SO4 + Ca(OH)2 CaSO4 + 2H2O + 2NH3 (g)

10. How is ammonia manufactured by Haber’s process ?

450-5000c Ans. N2 + 3H2 2NH3 + 22,400 cal (1 vol) (3 vols) 200 atm, Fe/ Mo (2 vols) Conditions:

i. Temperature – 450-5000C (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 450oC to

500oC? 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 450oC – 500oC is kept.

12. Why should the catalyst be free from impurities? Ans. Impurities like CO, Co2 and H2S 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 NH3 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 NH3 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 NH3 gas is demonstrated by the fountain experiment.

i) An inverted flask containing dry NH3 gas is arranged as shown in the diagram.

ii) When the dropper containing water is squeezed, the water enters the

flask and since NH3 gas is highly soluble in water, it dissolves creating a partial vaccum in the flask.

iii) 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 NH3(g) in O2.

Ans. Ammonia burns in oxygen in the absence of catalyst with a greenish flame forming nitrogen. 4NH3 + 3O2 2N2 + 6h2O Ammonia on catalytic oxidation (Pt/8000C) gives nitric oxide which undergoes further oxidation to give reddish brown vapour of NO2

4NH3 + 5O2

Pt 4NO + 6H2O

800℃ colorless

[2NO + O2 2NO2]

Reddish brown

17. Why an aqueous solution of ammonia is basic in nature? Ans. The aqueous solution of ammonia (NH4OH) acts as a weak base, since it undergoes partial dissociation in aqueous solution to give hydroxyl ions ( OH-) in low concentration NH3 + H2O NH4OH Liquor ammonia NH4OH 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 (NH4OH) acts as a weak base, since it undergoes partial dissociation in aqueous solution to give hydroxyl ions (OH-) in low concentration. NH3 + H2O NH4OH

Liquor ammonia

19. Give balanced equation to show the formation of ammonium salts? Ans. Ammonia in aq. Soln. (NH4OH) neutralizes acids forming respective ammonium salts. NH3 + H+ NH+

4 Weak base proton ammonium ion Preparation of ammonium salts:

i. NH3 + HCl NH4Cl (ammonium chloride)

ii. NH3 + HNO3 NH4NO3

(ammonium nitrate)

iii. 2NH3 + H2SO4 (NH4)2 SO4 (ammonium sulphate)

Neutralization reaction: NH4OH + HCl NH4Cl + H2O NH4OH + HNO3 NH4NO3 + H2O 2NH4OH + H2SO4 (NH4)2SO4 + 2H2O

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 NH3gas.

Ans. NH4OH reacts with soluble salts of metals in their solution state to give insoluble precipitate of respective metallic hydroxide. FeSO4 + 2NH4OH (NH4)2SO4 + Fe(OH)2

Dirty green ferrous hydroxide (insoluble in excess of NH4OH)

FeCl3 + 3NH4OH 3NH4Cl + Fe(OH)3 Reddish brown ferric hydroxide (insoluble in excess of NH4OH) Pb(NO3)2 + 2NH4OH 2NH4NO3 + Pb(OH)2 Lead hydroxide chalky white (insoluble in excess of NH4OH) Zn(NO3)2 + 2NH4OH 2NH4NO3 + Zn(OH)2 White gelatinous Zinc hydroxide (soluble in excess of NH4OH) CuSO4 + 2NH4OH (NH4)2SO4 + Cu(OH)2

Pale blue Copper hydroxide (soluble in excess of NH4OH) Cu(OH)2 + (NH4)2SO4 + 2 NH4OH [Cu(NH3)4] SO4+4H2O Tetrammine copper (II) sulphate (deep blue or inky blue solution)

21. Give reaction to show ammonia as a reducing agent. Ans. 2NH3 + 3CuO 3Cu + 3H2O + N2 (g) Copper (II) oxide Reduced (basic oxide) product 2NH3 +3PbO 3Pb + 3H2O + N2 (g) Lead (II) oxide Reduced product (amphoteric oxide) 8NH3 + 3Cl2 6NH4Cl + N2 (g) Excess dense white fumes NH3 + 3Cl2 3HCl + NCl3 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.

NH3

NH3 – 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. 2NH4Cl + Ca(OH)2 CaCl2 + 2H2O + 2NH3 (g) Ammonium Calcium calcium water ammonia

chloride hydroxide chloride

2. Convert ammonium sulphate to ammonia using alkali. Give equation only.

Ans. (NH4)2SO4 + Ca(OH)2 CaSO4 + 2H2O + NH3 (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 + N2 Mg3N2

Magnesium nitrogen magnesium nitride Mg3N2 + 6H2O 3Mg(OH)2 + 2NH3 (g) Magnesium water magnesium Ammonia Nitride (warm) hydroxide ii) 3Ca + N2 Ca3N2 Calcium Nitrogen Calcium nitride Ca3N2 + 6H2O 3Ca(OH)2 + 2NH3(g) Calcium warm Calcium Ammonia Nitride water hydroxide

iii) 2Al + N2 2AlN Aluminium Nitrogen Aluminium nitride AlN + 3H2O Al(OH)3 + NH3(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 NH3) 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 NH3 is used as a cleansing agent ?

Ans. Liquor NH3 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. NH4OH NH4

+ + OH- Weak (ions) Electrolyte 12. What is the action of NH3 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 NH3 gas is excess is mixed with chlorine. Ans. Dense white fumes of ammonium chloride are seen.

vii) When NH3 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 (NH4)2SO4 + 2NaOH Na2SO4 + 2H2O + 2NH3

(NH4)2SO4 + Ca(OH)2 CaSO4 + 2H2O + 2NH3 NH4Cl + NaOH NaCl + H2O + NH3

2NH4Cl + Ca(OH)2 CaCl2 + 2H2O + 2NH3

b. Reactions of Ammonia with drying agents: 2NH3 + H2SO4 (NH4)2SO4 (conc.) 6NH3 + P2O5 + 3H2O 2(NH4)3PO4 8NH3 + CaCl2 CaCl2. 8NH3 Fused

c. Laboratory preparation:

From metal nitrides Mg3N2 + 6H2O 3Mg(OH)2 + 2NH3 Warm Ca2N2 + 6H2O 3Ca(OH)2 + 2NH3

Warm AlN + 3H2O Al(OH)3 + NH3

d. Manufacture of Ammonia:

Haber’s process N2 + 3H2 2NH3 + 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 4NH3 + 3O2 2N2 + 6H2O

4NH3 + 5O2 Pt

500 ℃ 4NO + 6H2O

ii) Basic nature of ammonia: NH3 + HCl NH4Cl NH3 + HNO3 NH4NO3

2NH3 + H2SO4 (NH4)2SO4 NH4OH + HCl NH4Cl + H2O 2NH4OH + H2SO4 (NH4)2SO4 + 2H2O

NH4OH + HNO3 NH4NO3 + H2O

iii) Ammonia with metallic salt solution : FeSO4 + 2NH4OH (NH4)2SO4 + Fe(OH)2 FeCl3 + 3NH4OH 3NH4Cl + Fe(OH)3

Pb(NO3)2 + 2NH4OH 2NH4NO3 + Pb(OH)2

f. Ammonia gas as a reducing agent 2NH3 + 3CuO 3Cu + 3H2O + N2 2NH3 + 3PbO 3Pb + 3H2O + N2 2NH3 + 3Cl2 5HCl + N2 NH3 + HCl NH4Cl 8NH3 (excesss) + 3Cl2 6NH4Cl + N2 NH3 + 3Cl2 3HCl + NCl3 Excess

Name the following:

i) The Process by which Ammonia is manufactured. Ans. Haber’s process.

ii) Drying agent for ammonia gas. Ans. Quicklime.

iii) Metal nitride which on hydrolysis gives ammonia gas. \ Ans. Magnesium nitride (Mg3N2), Calcium nitride (Ca3N2), Aluminum nitride (AlN).

iv) Catalyst used in Haber’s process. Ans. 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 (NH4Cl) and sodium nitrite( NaNO2)

vii) Two gases which gives dense white fumes with ammonia. Ans. Chlorine (Cl2) and hydrogen chloride (HCl)(g).

viii) The solution which turns brown when it comes in contact with ammonia.

Ans. Nessler’s reagent.

ix) Experiment which demonstrate the extreme solubility of ammoinia. Ans. 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) Aqueous solution of ammonia gas in water. Ans. Liquid ammonia

xiii) Ammonia gas liquefied at low temperature. Ans. Liquid ammonia.

xiv) An amphoteric oxide reduced by NH3 (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) Ammonia reduces chlorine to hydrogen chloride. (nitrogen chloride / hydrogen chloride / ammonium chloride).

iii) The gas most difficult to liquiefy is hydrogen. (nitrogen / hydrogen / ammonia)

iv) The salt solution which does not give an insoluble precipitate on addition of ammonium hydroxide in small amount is NaNO3.

( Mg(NO3)2 / NaNO3 / Cu(NO3)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) NCl3 NH3 NH 4Cl

D C

N2 NH3 NH 4OH

F E

Mg3N2 NH3 N2

Ans.:

A : 8NH� + 3Cl� 6NH�Cl + N�

excess or

NH� + HCl NH�Cl

B : NH� + 3Cl� NCl� + 3HCl

excess

C : NH� + H�O NH�OH

D : 4NH� + 3O� △→ 2N� + 6H�O

450-5000c E : N2 + 3H2 2NH3 + ∆ (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)�

↓ ECuO

Ans.:

A : NH� + HCl NH�Cl

B : NH�Cl + NaOH NaCl + H�O + NH�

C : NH� + H�O NH�OH

D : CuSO� + 2NH�OH Cu(OH)� ↓ + (NH�)�SO�

E : Cu(OH)� ∆→ CuO + H�O

(i) NH� A

NO B

NO� C

HNO�

↓ DCu(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

H2 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 NH3.

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 NH3 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