5. AMMONIA - TopperLearning

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5. AMMONIA

THE WARM COILY FRIDGE SPEAKS-

Molecular Formula: 3NH

Relative molecular mass: 17

1. Occurence

Free state: Ammonia is present in small amounts in air and in traces, in natural water.

Combined state: In nature, ammonia occurs in combined form in many compounds such as ammonium chloride (Hindi : Nausadar), ammonium sulphate, etc.

5.2 Ammonia

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PLANCESS CONCEPTS

Ammonia and ammonium compounds are miscible with water, but does not burn readily.

In the storage tank, NH3 is a pressurized liquid. When applied directly to the soil, it immediately becomes a vapor. Ammonia is always placed at least 10 to 20 centimeters below the soil surface to prevent its loss as a vapor back to the atmosphere.

Shivam Agarwal

AIR 3, NSO

PLANCESS CONCEPTS

Uday Kiran G

KVPY Fellow

Forms of ammonia

Ammonia is used commonly in the following forms:

(i) Gaseous ammonia -dry ammonia gas

(ii) Liquid ammonia:-A high pressure is applied on dry ammonia to give liquid ammonia.

Figure 5.1: Decomposition of urea

5.3 Foundation for Chemistry

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(iii) Liquor ammonia fortis A saturated solution of ammonia in water, also called as 880 ammonia. It has a relative density of 0.880. It is stored in tightly stoppered bottles in a cold place.

(iv) Laboratory bench reagent : Dilute solution of liquor ammonia is used as a laboratory reagent.

Illustration 1: Ammonium compounds do not occur as minerals. Explain

Sol: (a) Ammonium compounds are highly soluble in water, hence do not occur in minerals.

2. Preparation of Ammonia Gas

2.1 General Methods of Preparation

Ammonia gas can be prepared by warming an ammonium salt with caustic alkali, such as slaked lime or caustic soda or caustic potash.

2.2 Laboratory Preparation

(1) From ammonium chloride

Reactants: Ammonium chloride (NH4Cl) and calcium hydroxide [Ca(OH)2] in the ratio of 2 : 3 by weight.

Reaction: 4 2 2 2 32NH Cl Ca(OH) CaCl 2H O 2NH→

Procedure: Reactants are �nely grinded and taken in a round-bottom �ask �tted in a slanting position, mouth downwards as shown in Fig. On heating the mixture, ammonia gas is evolved.

Figure 5.2: Experimental set up for preparation of ammonia from ammonium chloride (NH4Cl) and calcium hydroxide

5.4 Ammonia

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Precautions: �e �ask is tilted in such a way that the water formed in the reaction does not trickle back into the heated �ask and thus break it.

Drying of ammonia gas: In order to get dry ammonia, the gas is passed through a drying tower containing lumps of quicklime (CaO).

2.2.1 Unsuitability of Other Drying Agents

�e usual drying agents such as conc. Sulphuric acid, phosphorous pentoxide and anhydrous calcium chloride are not used, as ammonia is basic and it reacts with them.

3 2 4 4 2 42NH H SO (NH ) SO→

→3 2 5 2 4 3 4Ammonium phosphate

6NH P O 3H O 2(NH ) PO

2 3 2 3(addition compound)

CaCl 4NH CaCl .4NH→

2.2.2 Collection

Ammonia gas is collected in inverted gas jars by the downward displacement of air because it is

(i) lighter than air (V.D. of NH3- 8.5; that of air- 14.4),

(ii) highly soluble in water and therefore, it cannot be collected over water.

PLANCESS CONCEPTS

1. �e reactants NH4Cl and Ca(OH)2 are taken in the ratio of 2 : 3 by weight, higher ratio by weight of the alkali may counteract the loss by sublimation of NH4Cl.

2. Calcium hydroxide is used, as it is cheap and not deliquescent like other alkalis.

3. �ough all ammonium salts, on heating with alkalis give NH3, yet NH4NO3 is not used as it is explosive in nature and it decomposes forming nitrous oxide and water vapour.

Neeraj Toshniwal

Gold Medalist, INChO

(2) From metal nitrides

Ammonia can also be obtained by the action of warm water on nitrides of metals like magnesium or Aluminium. �is method is quiet expensive.


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Reaction: 3 2 2 2 3Mg N 6H O 3Mg(OH) 2NH→ or

2 3 3AlN 3H O Al(OH) NH→

Procedure:

1. Magnesium nitride or Aluminium nitride is kept in a round bottom �ask �tted with a thistle funnel and a delivery tube. Warm water is added very slowly.

2. Ammonia gas escapes through the delivery tube and magnesium hydroxide or aluminium hydroxide formed remains in the �ask.

3. �e ammonia gas formed is collected by holding the jar with its mouth downwards over the delivery tube.

4. �e gas can be dried by passing it through quicklime packed in a drying tower.

3. Preparation of Aqueous Ammonia

An aqueous solution of ammonia is obtained by dissolving ammonia in water. �e rate of dissolution of ammonia in water is very high, therefore, back suction of water is possible. To avoid this, a funnel is attached to the outer end of the delivery tube with rubber tubing (the process is similar to the method used to change HCl gas into hydrochloric acid).

�e funnel provides a larger surface area for dissolution of ammonia in water and prevents back suction of water into the hot �ask.

Procedure: Water is taken in a container and only a small portion of the mouth of the funnel is dipped in water.

As ammonia dissolves in water at a higher rate than its production in the �ask, the pressure in the funnel above water level decreases for a moment, and water rushes into the funnel. As a result, the rim of the funnel loses its contact with water. Since, ammonia produced pushes the water down, the funnel comes in contact with water again. In this way, ammonia dissolves in water without back suction of water.

4. Manufacture of Ammonia (Haber Process)

Reactants: Nitrogen and hydrogen in the ratio of 1: 3 by volume.

Sources of reactants:

Nitrogen gas is obtained by fractional distillation of liquid air.

Hydrogen gas is obtained from water gas (Bosch process) or from natural gas.

Reaction: N2 + 3H2

2NH3 + heat.

�e reaction is reversible, exothermic and proceeds with a decrease in volume.

5.6 Ammonia

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Figure 5.3 Manufacture of ammonia by haber process

Favourable conditions :

Temperature: Optimum temperature is 450-500 °C.

Pressure: Above 200 atm.

Catalyst: Finely divided iron.

Promoter: Traces of molybdenum or Al2O3.

Rate of conversion: 8% to 12% of the reacting gases get converted to ammonia.

Recovery of ammonia: Ammonia is separated from the unreacted nitrogen and hydrogen by:-

1. Liquefaction, as ammonia compared to N2 and H2 is easily lique�able.

2. Absorbing in water, because NH3 is highly soluble in water, while N2 and H2 are very slightly soluble.

Process:

1. Nitrogen and hydrogen is dried, puri�ed and then mixed in the ratio of 1:3 respectively, at a relatively high pressure. �is mixture is passed in an electrically heated catalytic chamber containing �nely divided iron with aluminium oxide or a little amount of molybdenum at a temperature of 500°C. Mixture of ammonia formed along with residual nitrogen and hydrogen exchange their heat with the incoming unreacted nitrogen and hydrogen mixture.

2. �e hot mixture of the outgoing gases contains nearly 10% ammonia. �e mixture is passed through the cooling pipes (condenser).

3. Ammonia lique�es �rst, whereas nitrogen and hydrogen do not liquefy easily.

4. �e unchanged nitrogen and hydrogen are recirculated through the plant to get more ammonia.


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Note:

(i) �e reaction is exothermic, hence low temperature will favour the synthesis. However, at low temperature, the reaction proceeds slowly. In practice, the optimum temperature has been found to be in the range of 450°C to 500°C.

(ii) Four volumes of reactants produce two volumes of product, hence high pressure favours the formation of ammonia. �e optimum pressure is found to be 200 to 900 atm. Practically, a pressure of about 250 atm. is used.

(iii) Catalyst and promoter: �e speed of the reaction can be improved by using a catalyst, which is �nely divided iron, obtained by the reduction of iron oxide. A promoter molybdenum or Al2O3 is used to increase the e�ciency of the catalyst.

(iv) Since the reaction is exothermic, the heat evolved further maintains the temperature. External heating is, therefore, not required after the reactants are initially heated.

PLANCESS CONCEPTS

�e puri�cation of nitrogen and hydrogen is necessary as impurities like carbon dioxide, carbon monoxide and traces of sulphur compounds (H2S) poisons the catalyst. �e removal of these catalytic poisons from nitrogen and hydrogen is very essential.

Vaibhav Gupta

AIR 2, NSO

Flow chart of Haber Process

Figure 5.4: Haber’s process

5.8 Ammonia

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5. Physical Properties of Ammonia

1. Colour: Colourless.

2. Odour: Strong, pungent choking smell.

3. Taste: Slightly bitter (alkaline) taste.

4. Physiological action: Non-poisonous. If inhaled, a�ects the respiratory system and brings tears to eyes. It is a powerful heart stimulant and may cause death when inhaled in large quantities.

5. Density: Vapour density = 8.5 [Lighter than air]

6. Nature: Alkaline nature

7. Liquefaction : Easily lique�ed at 10°C by compressing it at 6 atm. pressure.

8. Boiling point : Liquid ammonia boils at - 33.5°C.

9. Freezing point : Solid NH3 melts at - 77.7°C.

10. Solubility: Highly soluble in water, 1 vol. of water dissolves about 702 vols. of ammonia at 20°C and 1 atm. pressure.

PLANCESS CONCEPTS

Is ammonia a liquid or a gas?

Ammonia quickly turns to a gas when exposed to air. But ammonia is easily and inde�nitely stored as a liquid at about 150 psi, a very low pressure which doesn’t require special high pressure tanks like hydrogen.

Vijay Senapathi

KVPY Fellow

Fountain Experiment

To demonstrate the high solubility of ammonia gas in water.

Apparatus:

1. A round bottom �ask �lled with ammonia gas.

2. Mouth of the �ask is �tted with a rubber stopper with two holes, one for jet tube and the other for a dropper containing water.

3. A trough containing red litmus solution.

4. A retort stand is used to �x the round bottom �ask in an inverted position.


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Figure 5.5: Experimental setup for fountain experiment

Procedure:

1. �e dropper containing water is squeezed.

2. As few drops of water enter the �ask, ammonia gas present in the �ask gets dissolved in water, due to its high solubility. �is creates a partial vacuum in the �ask.

3. Since, outside pressure is higher, the red litmus solution rushes up through the jet tube and emerges as a blue fountain. [Ammonia gas being basic, changes red litmus solution blue.]

PLANCESS CONCEPTS

A bottle of liquor ammonia should be opened very carefully, only after cooling it in ice or cold water. �ere is high pressure inside the bottle and on cooling, the pressure drops. �is prevents sudden �ushing out of the gas.

Krishan Mittal

KVPY Fellow

Illustration 2: Is ammonia more dense or less dense than air? What property of ammonia is demonstrated by the Fountain Experiment? Write the correctly balanced equation for the reaction between ammonia and sulphuric acid?

Sol: Ammonia gas is less denser than air. In fountain experiment, two properties of Ammonia are illustrated. It is very soluble in water. It is an alkaline gas. If some drops of phenolphthalein Sol: were previously added to the water, it would turn pink on entering the �ask.

3 2 4 4 2 4(Conc.)

2NH H SO [NH ] SO→

5.10 Ammonia

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6. Chemical Properties of Ammonia

6.1 Thermal Dissociation

Ammonia gas dissociates into nitrogen and hydrogen at a high temperature or by electric sparks.

3 2 22NH N 3H

6.2 Basic Properties

Dry ammonia is a covalent molecule. So, it is neutral even in lique�ed form. Its aqueous solution is a weak base, the basicity is due to a lone pair of electrons on its nitrogen atom.

An aqueous solution of ammonia [NH4OH] is a weak base. It dissociates partially to give hydroxyl ions.

�e alkaline behaviour is due to the hydroxyl ions [OH‒]

3 2 4NH H O NH OH

; 4 4NH OH NH OH

Action on indicators

Table 5.1: Ammonia’s action an indicator

Indicator Change in colour

Original To

Moist litmus Red Blue

Methyl orange Orange Yellow

Phenolphthalein Colourless Pink

Illustration 3: Conc. 2 4H SO is a good drying agent, yet it is not used to dry 3NH . Why?

Sol: Conc. 2 4H SO is not used to dry 3NH as ammonia being basic reacts with conc. 2 4H SO

3 2 4 4 2 4Ammonium sulphate

2NH H SO [NH ] SO→


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PLANCESS CONCEPTS

A close-up view of two pieces of magnesium oxide, obtained by burning magnesium metal in air.

�e reaction gives mostly MgO, but some Mg3N2 also forms by reaction with nitrogen in the air. When a drop of water containing phenolphthalein indicator was added to the magnesium oxide at the top, the Mg3N2 in it reacted with the water to give insoluble Mg(OH)2 and NH3. Being a weak base, the NH3 caused the phenolphthalein to turn pink.

Rohit Kumar

NSEC 2011 Quali�ed

6.3 Reaction with Acids

Ammonia being a weak base accepts protons [hydrogen ions] to form ammonium ions. It reacts with acids to form ammonium salts.

Table 5.2: Reaction of gasses ammonia with di�erent acids

Ammonia gas Acid Ammonia salt

NH3 (gas) + HCl (gas) → NH4Cl (solid) (Ammonium chloride)

NH3 (gas) +HNO3 →

NH4NO3 (Ammonium nitrate)

2NH3 (gas) + H2SO4 → (NH4)2SO4 (Ammonium sulphate)

Illustration 4: Ammonium nitrate is not used in the preparation of ammonia.

Sol: 4 3NH NO (Ammonium nitrate) is not used in preparation of ammonia as it is explosive in nature and it decomposes forming nitrous oxide and water vapour.

Ammonium chloride is a good example, where two colourless gases react to form a white solid directly.

Note: Ammonium nitrate and ammonium chloride both show thermal dissociation reaction.

4 3NH Cl NH HCl

; 4 3 2 2NH NO N O 2H O

�e same salts, which are produced by the action of ammonia on acids, are produced if ammonia is �rst dissolved in water to form ammonium hydroxide.

NH3 + H2O → NH4OH

5.12 Ammonia

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Table 5.3: Reaction of ammonium hydroxide with di�erent acids

Ammonia [aq.] + Acid → Ammonium salt + water

4NH OH HCl → 4NH Cl 2H O

4NH OH3HNO → 4 3NH NO 2H O

4NH OH2 4H SO → 4 2 4(NH ) SO 22H O

PLANCESS CONCEPTS

How does ammonia act when it enters inside the body?

When ammonia enters the body as a result of breathing, swallowing or skin contact, it reacts with water to produce ammonium hydroxide. �is chemical is very corrosive and damages cells in the body on contact.

Chen Reddy Sandeep Reddy

KVPY Fellow

6.4. Reaction with Soluble Metal Salts

Ammonium hydroxide reacts with soluble salts of metals to give insoluble precipitates of their respective metallic hydroxides, (except sodium and potassium).

�is behaviour is similar to NaOH solution and KOH solution.

�e precipitates formed by di�erent metallic hydroxides di�er in colour and solubility. Hence, ammonium hydroxide is used in qualitative analysis for identifying cations.

Table 5.4: Reaction of ammonium hydroxide with metal salt

Metallic salt solution

Ammonium hydroxide

Ammonium salt

Metallic hydroxide [ppt]

Colour of precipitate

Solubility in excess of NH4OH

4FeSO42NH OH → 4 2 4(NH ) SO 2Fe(OH) Dirty green Insoluble

3FeCl43NH OH → 43NH Cl 3Fe(OH) Reddish

brownInsoluble


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Metallic salt solution

Ammonium hydroxide

Ammonium salt

Metallic hydroxide [ppt]

Colour of precipitate

Solubility in excess of NH4OH

3 2Pb(NO )42NH OH → 4 32NH NO 2Pb(OH) White Insoluble

3 2Zn(NO )42NH OH → 4 32NH NO 2Zn(OH) White

gelatinousSoluble

4CuSO42NH OH → 4 2 4(NH ) SO

2Cu(OH) Pale blue Soluble

�e pale blue precipitate of copper hydroxide dissolves in excess of ammonium hydroxide forming tetraamine copper [II] sulphate, an azure blue (deep blue) soluble complex salt.

Cu(OH)2 + (NH4)2SO4 + 2NH4OH → [Cu(NH3)4]SO4 + 4H2O

Illustration 5: State what is observed when:-

Excess of ammonia is passed through an aqueous solution of lead nitrate.

Sol: Chalky white precipitate of lead hydroxide is obtained

6.5. Reaction with Oxygen

Ammonia is not a supporter of combustion. It extinguishes a burning splint and does not burn in air. It burns in oxygen with yellowish green �ame.

Experiment: Burning of ammonia in oxygen

Figur 5.6: Burning of ammonia gas

Reaction: 4NH3 + 3O2 → 2N2 + 6H2O

Procedure: A wide glass tube is �tted with a cork carrying two tubes, one of which reaches just near the

5.14 Ammonia

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top and the other remains lower. Ammonia is passed through the longer tube, and oxygen through the shorter tube and a lighted match is applied.

Observation: Ammonia burns with a yellowish green �ame and produces water vapour and nitrogen. It shows that ammonia contains nitrogen and hydrogen.

�e reaction is irreversible and strongly exothermic.

PLANCESS CONCEPTS

Mixture of ammonia and oxygen is explosive and therefore dangerous.

T P Varun

KVPY Fellow

Catalytic oxidation of ammonia

In the presence of platinum at 800°C, ammonia reacts with oxygen to give nitric oxide and water vapour

Procedure: Pass dry ammonia gas and oxygen gas through inlets over heated platinum placed in the combustion tube, which in the heated state emits a reddish glow.

Reaction: Pt.800 C3 2 24NH 5O 6H O 4NO Heat→

2 22NO O 2NO→

Observations:

(i) Reddish brown vapours of nitrogen dioxide [NO2] are seen in the �ask due to the oxidation of nitric oxide [NO].

2 22NO O 2NO→

Figure 5.7: Catalytic oxidation of ammonia

(ii) �e platinum [catalyst] continues to glow even after the heating is discontinued since the catalytic oxidation of ammonia is an exothermic reaction.


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6.6 Reaction with Carbon Dioxide

Ammonia reacts with carbon dioxide at 150°C and 150 atm. pressure to give urea which is a valuable nitrogenous fertiliser.

150 C3 2 2 2 2150 atm

urea2NH CO NH CONH H O→

6.7 Ammonia as a Reducing Agent

(i) Reduction of chlorine to hydrogen chloride

When chlorine reacts with ammonia, it is reduced to HCl, which further combines with excess of ammonia and forms NH4Cl.

(a) When ammonia is in excess,

3 2 2

3 4

3 2 2 4excess

2NH Cl 3N 6HCl

6NH 6HCl 6NH Cl

8NH 3Cl N 6NH Cl

→

→

→

Observation: �e yellowish-green colour of chlorine disappears and white fumes of ammonium chloride are formed.

(b) When chlorine is in excess, then the products are hydrogen chloride and yellow coloured highly explosive liquid, nitrogen trichloride

3 2 3NH 3Cl 3HCl NCl→

�ese reactions show that:

(a) Chlorine has a great a�nity for hydrogen.

(b) Ammonia is a reducing agent.

(ii) Reduction of metallic oxides

Ammonia reduces heated metallic oxides to give metals, water vapour and nitrogen.

Procedure: Pass ammonia gas over heated copper oxide in a hard glass tube.

Reaction: 3 2 2reddish gasbrown solid

2NH 3CuO 3Cu 3H O N→

Observation: �e black copper oxide is reduced to reddish brown copper.

Similarly, Ammonia reduces heated yellow lead monoxide to greyish metallic lead.

3 2 2(yellow) (greyish)3PbO 2NH 3Pb 3H O N→

5.16 Ammonia

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Collection of gas: Nitrogen is collected over water in a gas jar.

�e water formed is collected in the U-tube and is tested with anhydrous copper sulphate which turns blue.

Figure 5.8: Reduction of metal oxide by ammonia

Note: �is reaction proves that ammonia is made up of nitrogen and hydrogen and is, therefore, a nitrogen hydride.

Illustration 6: �e following reactions are carried out:

A. Nitrogen + metal → compound X

B: X + water → ammonia + another compound

One metal that can be used for reaction A is magnesium.

(a) Write the formula of the compound X formed.

(b) Write the correctly balanced equation for reaction B where X is the compound formed.

(c) What property of ammonia is demonstrated by reaction C?

Sol: Magnesium metal is heated and N2 gas is passed over it, Magnesium nitride is formed.

2 3 2(Pale yellow residue)Magnesium nitride

A : 3Mg N Mg N→

(a) Formula of compound X is 3 2Mg N

(b) B: X + water → Ammonia + Another compound

3 2 2 32Mg N 6H O 3Mg OH 2NH g→

(c)

3 2 2

C : Ammonia Metal oxide Metal Water Nitrogen

2NH 3MgO 3Mg 3H O N

→

→

�is reaction shows that ammonia is a strong reducing agent and reduces less active metal oxide to its respective metal.


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PLANCESS CONCEPTS

Collecting a gas over water: As the gas bubbles through the water, water vapor goes into the gas, so the total pressure inside the bottle includes the partial pressure of the water vapor at the temperature of the water.

Vijay Senapathi

KVPY Fellow

7. Tests for Ammonia Gas and Ammonium Ion

All ammonium salts generally produce ammonia gas when alkali like sodium hydroxide is added to them.

Ammonia gas can easily be recognised by the following characteristics:

(1) It has a sharp characteristic odour.

(2) It turns moist red litmus blue, moist turmeric paper brown and phenolphthalein solution pink.

(3) It gives dense white fumes with conc. hydrochloric acid.

3 4NH HCl NH Cl→ (dense white fumes)

(4) It �rst forms a blue precipitate with copper sulphate solution and then dissolves it to form a deep blue coloured solution on addition of excess of ammonia solution.

(5) Ammonium salt gives brown colour or precipitates with Nessler’s solution, K2HgI4 (a slightly alkaline solution of potassium mercuric iodide made by adding KOH).

Illustration 7: A gas ‘P’ gives dense white fumes with chlorine. Its aqueous solution gives a blue colour with copper (II) hydroxide. (a) Name the gas P. (b) Give its formula. (c) Give three uses of P.

Sol: (i) Name of gas P is Ammonia.

(ii) NH3

(iii) Uses

(a) It is used in ice factories

(b) In the manufacture of nitric acid by Ostwald’s Process.

(c) In the manufacture of nylon and rayon.

Illustration 8: A gas ‘A’ reacts with another gas ‘B’ in the presence of a catalyst to give a colourless gas ‘C’. �e gas ‘C’ when comes in contact with air produces a brown gas, ‘D’. �e solution of ‘A’ in water turns red litmus blue. Explain the observations.

5.18 Ammonia

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Sol: �e gas ‘A’ is Ammonia (NH3)

Gas ‘B’ __________ Oxygen (O2)

Catalyst → Pt

Colourless gas ‘C’ obtained → NO (Nitric oxide)

Colourless gas

With air NO forms → NO2 [Brown gas]-gas ‘D’

Pt.800 C

3 2 2

2 2Brown gas

4NH 5O 4NO 6H O

2NO O 2NO

→

→

Solution of NH3 in water, NH4OH turns Red litmus Blue

3 2 4NH H O NH OH→

8. Uses of Ammonia

1. Liquid ammonia is used as a refrigerant in ice plants. Liquid ammonia takes a lot of energy to vaporize (5700 calories per mole at —33 °C). �is heat is taken from the surrounding bodies which are consequently cooled down.

Anhydrous ammonia is a clear, colourless liquid under pressure. It evaporates rapidly and produce cooling e�ect. �is makes ammonia a good refrigerant.

�e main refrigerants used are freon ,chloro�uoro carbon (CFC) which deplete ozone layer and also contribute to global warming. �us, these refrigerants are harmful to life. �e chloro�uoro carbons are decomposed by the ultraviolet rays to highly reactive chlorine which is produced in the atomic form.

Ultraviolet2 2 2

(free radical)CF Cl (g) CF Cl(g) Cl(g)→

�e free radical [Cl] reacts with ozone and chlorine monoxide is formed.

3 2Cl(g) O (g) ClO(g) O (g)→

�is causes depletion of ozone. Chlorine monoxide further reacts with atomic oxygen and produces more free chlorine radicals.

2ClO(g) O(g) Cl(g) O (g)→

Again this free radical [Cl] destroys ozone and the process continues thereby giving rise to ozone depletion.


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PLANCESS CONCEPTS

Ozone layer acts as a blanket in the atmosphere above 16 km height from the earth’s surface. It absorbs the harmful ultraviolet rays coming from the Sun and thus protects life on earth.

Anand K

AIR 1, NSO 2011

Advantages of Ammonia as a refrigerant

(i) Ammonia is environmentally compatible. It does not deplete ozone layer and does not contribute to global warming.

(ii) It has superior thermodynamic qualities. As a result, ammonia refrigeration systems use less electricity.

(iii) Ammonia has a recognizable odour and so leaks are not likely to escape.

Answer to the Warm Coily Fridge Speaks-

Refrigeration and Air Conditioning

�e fact that the evaporation of a liquid is endothermic and the condensation of a gas is exothermic, forms the basis for the operation of refrigerators and air condition-temperature-ammonia or a halogenated hydrocarbon to pump heat from one place to another.

In a refrigerator, a compressor squeezes the gas into a small volume, which causes the pressure to increase. At the same time, the work done compressing the gas becomes stored as heat, the gas becomes warm. �e warm gas is then circulated through cooling coils that are usually located on the back of the refrigerator. (Did you ever notice that these coils are warm?) When the gas cools under pressure, it lique�es when its temperature drops below a certain value called the gas’s critical temperature.

Condensation of the gas is exothermic and releases the substance’s heat of vaporization, which is also given o� to the surroundings. After being cooled, the pressurized liquid moves back into the refrigerator where it passes through a nozzle into a region of low pressure. At this low pressure, the liquid evaporates, and heat equal to the heat of vaporization is absorbed, which causes the inside of the refrigerator to cool. �en the gas is sucked back into the compressor, and the cycle is repeated.

�rough condensation and evaporation, the compressor uses the gas as the �uid in a heat pump, that absorbs heat from inside the refrigerator and dumps it outside. An air conditioner works in essentially the same way, except that a room becomes the equivalent of the inside of a refrigerator, and the heat pump dumps the heat into the air outside.

5.20 Ammonia

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8.1 Disadvantages of Ammonia

1. It is not compatible with copper, so it cannot be used in any system with copper pipes. Ammonia is poisonous in high concentration although it is easily detectable due to its peculiar smell and also being lighter than air goes up in the atmosphere not a�ecting the life too much on earth.

2. Aqueous NH3 emulsi�es or dissolves fats, grease, etc. So it is used:

(i) To remove grease and perspiration stains from clothes,

(ii) For cleaning tiles, windows, etc.

3. Ammonia solution is used as an important laboratory reagent in qualitative analysis as it gives characteristic coloured metallic hydroxide precipitates.

4. Ammonia is used in the manufacture of:

(a) Nitrogenous fertilisers like ammonium sulphate, diammonium hydrogen phosphate, ammonium nitrate and urea.

(b) Explosives like ammonium nitrate. Ammonium nitrate decomposes explosively leaving no residue behind

4 3 2 2NH NO N O(g) 2H O(vap.)→

(c) Other ammonium salts such as ammonium carbonate (used as smelling salt for reviving a fainted person), ammonium chloride - used in dry cells and in the preparation of nitrogen gas.

→2 4 4 2Sodium nitrite

NaNO (aq) NH Cl(aq) NaCl(aq) NH NO (aq)

4 2 2 2Ammonium nitriteNH NO (aq) N (g) 2H O(g)→

(d) Nylon rayon, sodium cyanamide, plastics, dyes, organic chemicals, explosives and wood pulp.

(e) Sodium carbonate by Solvay process:-�is process involves the interaction of ammonia, carbon dioxide, and sodium chloride in water solution resulting in the precipitation of sodium hydrogen carbonate.

3 2 2 3 4NaCl NH CO H O NaHCO NH Cl→

�e sodium hydrogen carbonate is separated and ignited to obtain sodium carbonate.

3 2 3 2 22NaHCO Na CO H O CO→

(f ) Nitric acid by the Ostwald process.


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Illustration 9: Ammonium solution gives a blue precipitate when it combines with a solution of copper salt. �e blue precipitate further dissolves in excess of ammonia solution to give azure blue solution. Explain with equation.

Sol: 4 4 4 42 2(Pale Blue ppt.)

CuSO 2NH OH NH SO Cu OH→

�e pale blue ppt. of copper hydrogen dissolves in excess of Ammonium hydroxide forming an AZURE BLUE (deep blue) soluble complex salt. [Tetra amine copper II] Sulphate

3 4 24Cu NH SO 4H O is formed.

4 4 4 3 4 22 2 4[Amm.Hydroxide[Pale blue [Tetra amine copper II sulphate]in excess]ppt .] (Deep blue colouration)or Azure blue Sol

Cu OH NH SO 2NH OH Cu NH SO 4H O→

9 Manufacture of Nitric Acid

A German chemist Ostwald, in 1914, developed Ostwald process.

�e process is explained in three steps :

Step I : Catalytic oxidation of ammonia

A mixture of dry air (free from carbon dioxide and dust particles) and dry ammonia in the ratio of 10 : 1 by volume, is �rst compressed and then passed into the catalytic chamber containing platinum gauze as catalyst at about 800°C (Fig.).

�is results in the oxidation of ammonia into nitrogen monoxide (Nitric oxide).

Figure 5.9: Manufacture of nitric acid by ostwald process

5.22 Ammonia

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Pt3 2 2800 C

4NH 5O 4NO 6H O Heat→

�e reaction is exothermic and the heat evolved maintains the temperature of the catalytic chamber.

�e hot gases are then passed through a heat exchanger, where they are mixed with air and passed into another cooling chamber called oxidising chamber.

Step II : Oxidation of nitric oxide in oxidation chamber

In this chamber, nitric oxide combines with oxygen to form nitrogen dioxide at about 50°C.50 C

2 22NO(g) O (g) 2NO (g)→

Step III : Absorption of nitrogen dioxide in water

�e nitrogen dioxide together with the remaining air (sometimes more air is added at this stage) is passed through the absorption tower (a steel tower �lled with quartz stone packed in layers), from the top of which warm water trickles.

�e nitrogen dioxide and oxygen present in the air react with water to form nitric acid.

2 2 2 34NO (g) 2H O(l) O 4HNO (aq)→

�e nitric acid obtained at the bottom of the tower is concentrated above 50%.

�e above acid on further distillation gives 68% nitric acid. �is acid is concentrated nitric acid which is used in laboratories.

Concentration of nitric acid

Nitric acid up to 98% (fuming nitric acid) is obtained by distilling 68% HNO3 over conc. sulphuric acid.

Pure 100% nitric acid is obtained by strongly cooling the 98% acid, when colourless crystals of pure nitric acid get separated at - 42°C.

PLANCESS CONCEPTS

Nitric acid cannot be concentrated beyond 68% by the distillation of a dilute solution of HNO3.

Nitric acids forms a constant boiling mixture with water containing 68% acid. �e mixture boils constantly at the constant boiling point without any change in composition. At this temperature, the gas and the water vapour escape together. Hence the composition of solution remains unchanged. �at is why nitric acid cannot be concentrated beyond 68% by the distillation of dilute solution of HNO3.

Makarand Manda

KVPY Fellow


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Note: In the manufacture of nitric acid,

(i) Higher ratio of air is used because oxygen is only 1/5th in air and it is required in all the three chambers.

(ii) Quartz is acid resistant and when packed in layers it helps in dissolving nitrogen dioxide uniformly in water.

Illustration 10: Name: (a) one salt of ammonia in each case which is used in: (i) dry cell (ii) explosives (iii) medicine (b) a metallic chloride soluble in ammonium hydroxide. (c) an amphoteric oxide reduced by the basic gas. (d) a white salt produced by an acid gas and a basic gas.

Sol:

(a) (i) In dry cell-Ammonium Chloride

(ii) Explosive-Ammonium Nitrate

(iii) Medicine-Ammonium Carbonate

As smelling salt (for receiving a faint person)

(b) FeCl3 (Ferric chloride)

(c) Amphoteric oxide is PbO (lead monoxide)

(d) White salt is NH4Cl -Ammonium Chloride.

PLANCESS CONCEPTS

Shivam Agarwal

AIR 3, NSO

Figure 5.10: Acid rain

5.24 Ammonia

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Flowchart 5.1: Manufacture of HNO3


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SUMMARY

• Dry ammonia is a covalent molecule, so it is nuclear even in lique�ed form.

• An Aqueous solution of ammonia [ 4NH OH] is a weak base and dissociates partially to give [OH ]ions.�e basicity of this solution is due to lone pair of electrons on its nitrogen atom.

3 2 4NH H O NH OH

and 4 4NH OH NH OH

• �ermal dissociation of 3NH produced 2N and 2H

3 2 22NH N 3H

• Ammonia reacts with acids to form Ammonium salts 4 4 4 4 3NH Cl,NH SO ,NH NO . i.e.

3 3 4 3NH HNO NH NO→

• 4[NH OH] Ammonium hydroxide reacts with soluble salts of metals to give insoluble precipitates of their respective metallic hydroxides [except Na and K].

• Ammonia is a reducing agent and has great a�nity for hydrogen. It reduces metal oxide (CuO).

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SOLVED EXAMPLES

Example 1. Ammonia can be obtained adding water to: [select the correct word]

(a) Ammonium chloride (b) Ammonium nitrate

(c) Magnesium nitride (d) Magnesium nitrate

Sol: (c) Magnesium nitride.

Example 2. Name: An alkaline gas ‘A’ which gives dense white fumes with hydrogen chloride.

Sol: Ammonia gas.

Example3. Write the equation for the following reaction: Aluminium nitride and water.

Sol: AlN + 3H2O → Al(OH)3 + NH3 [g]

Example 4. Copy and complete the following table relating to an important industrial process. Output refers to the product of the process not the intermediate steps.

Name of process Haber Process

Inputs Hydrogen +

Catalyst

Equation for catalyze reaction

Outputs

Sol:

Name of process Haber process

Inputs Hydrogen +Nitrogen

Catalyst Finely divided Fe

Equation for catalyzed reaction2 2N 3H

32NH

Outputs NH3

Example 5. i. Write an equation for solutions of ammonium chloride and sodium hydroxide are heated.

ii. Ammonium salts decompose on heating. What other property do ammonium salts have in common?


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iii. Choose the correct word from the bracket and write a balanced equation for the same: Heating ammonium chloride with sodium hydroxide produces ______ [ammonia / nitrogen].

iv. Name [formula is not acceptable] the gas produced on warming ammonium sulphate with sodium hydroxide solution.

v. Write the equation for the preparation of NH3 from ammonium chloride and calcium hydroxide.

vi. Write the equation for the reaction when a mixture of ammonium chloride and slaked lime is heated.

vii. From the list of substances given – Ammonium sulphate, Lead carbonate, Chlorine, Copper nitrate, Ferrous sulphate – State : A compound which on heating with sodium hydroxide produces a gas which forms dense white fumes with hydrogen chloride.

Sol:

i. NH4Cl + NaOH → NaCl + H2O + NH3.

ii. (a) Ammonium salts liberate ammonia on treatment with alkalis.

(b) All ammonium salts are soluble in water.

iii. Ammonia.

4 2 3NH Cl NaOH NaCl H O NH→

iv. Ammonia

v. 2NH4Cl + Ca(OH)2 → CaCl2 + 2H2O + 2NH3

vi. 2NH4Cl + Ca(OH)2 → CaCl2 + 2H2O + 2NH3

vii. Ammonium sulphate.

Example 6.

(i) How is ammonia collected? Why is ammonia not collected over water?

(ii) Which compound is normally used as a drying agent for ammonia?

(iii) Name a substance used for drying ammonia.

Sol:

(i) (a) Ammonia gas is lighter than air and hence collected by the downward displacement of air.

[V.D. of NH3 = 8.5, V.D. of air = 14.4]

(b) Ammonia is not collected over water since it is highly soluble in water.

[1 vol. of water dissolves about 702 vol. at 20 ºC and 1 atmos. pressure].

(ii) Quicklime [CaO]. (iii) Quicklime [CaO].

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Example 7.

(i) �e following reactions are carried out:

A : Nitrogen + Metal → Compound X.

B : X + Water → Ammonia + Another compound.

C : Ammonia + Metal oxide → Metal + Water + N2.

(1) One metal that can be used for reaction A is magnesium.

(a) Write the formula of the compound X formed.

(b) Write the correctly balanced equation for reaction B where X is the compound formed.

(c) What property of ammonia is demonstrated by reaction C.

(ii) Write the equation for the formation of ammonia by the action of water on magnesium nitride.

(iii) Write the equation for the reaction of Aluminium nitride and water.

Sol:

(i) (a) Magnesium nitride. [Mg3N2]

(b) Mg3N2 + 6H2O → 3Mg(OH)2 + 2NH3 ↑.

(c) Reducing property.

(ii) Mg3N2 + 6H3O → 3Mg(OH)2 + 2NH3 ↑.

(iii) AlN + 3H2O → Al(OH)3 + NH3 ↑.

Example 8.

i. What is the purpose of Haber’s Process?

ii. Name the gaseous inputs of the Haber’s process and state the ratio by volume in which the gases are mixed.

iii. What is done to increase the rate of the reaction in the Haber’s process.

iv. Give two di�erent ways by which the product can be separated from the reactant.

v. Write the equation for the reaction in the Haber’s Process that forms ammonia.

vi. State the purpose of liquefying the ammonia produced in the process.

vii. With reference to Haber’s Process for the preparation of ammonia, write the equation and the conditions required.

Sol:

i. Manufacture of Ammonia.

ii. Nitrogen [N2] and Hydrogen [H2] in the ratio 1:3 by volume.


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iii. Temperature is kept low and pressure high.

iv. (a) Liquefaction – Ammonia is easily lique�ed and hence separated from nitrogen and hydrogen.

(b) Dissolving in water – Ammonia is highly soluble in water and hence separated from nitrogen and hydrogen.

v. N2 + 3H2 → 2NH3 + ∆.

vi. Ammonia is easily lique�ed while nitrogen and hydrogen are not easily separated. Hence ammonia is separated from nitrogen and hydrogen.

vii. N2 + 3H2 → 2 NH3 + ∆.

Ratio of nitrogen and hydrogen is taken as 1:3. Temperature is kept at 450-500ºC and pressure at 200 to 900 atmos. Catalyst iron with promoter molybdenum is used.

Example 9.

(i) How soluble is ammonia in water?

(ii) Give two reasons to show that the solution of ammonia in water contains hydroxide ions.

(iii) Is ammonia more dense or less dense than air?

Sol:

(i) Ammonia is highly soluble in water. 1 vol. of water dissolves 702 vol. of ammonia at 20 ºC and 1 atm. pressure.

(ii) (a) Ammonia turns red litmus solution blue.

(b) Ammonia reacts with acids to form salt and water.

(iii) Ammonia is less dense than air. [V.D. of ammonia = 8.5 while V.D. of air = 14.4].

Example 10.

(i) Write equation for the following:

(a) Burning of ammonia in oxygen

(b) Catalytic oxidation of ammonia.

What do you observe in (a)?

Name the catalyst used in (b).

In the reaction referred to in (b), the catalyst glows red hot. Why? What is the name of the industrial process which starts with the reaction referred to in (b).

(ii) From the gases – ammonia, hydrogen chloride, hydrogen sulphide, Sulphur dioxide – Select the following:

(a) When this gas is bubbled through copper sulphate solution, a deep blue coloured solution is formed.

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(b) �is gas burns in oxygen with a green �ame.

Sol:

(i) (a) Pt3 2 2 24NH 3O 2N 6H O. →

(b) 800 C3 2 24NH 5O 4NO 6H O .→

Observation – Dry ammonia does not burn when passed through ignited tube. When ammonia is passed through ignited tube with a passage of oxygen, ammonia burns with a greenish yellow �ame forming nitrogen and water.

Catalyst – Catalyst used is Platinum. �e catalyst glows since the catalytic oxidation of ammonia is an exothermic reaction.

�e industrial process is known as ‘Ostwald’s Process’ for the manufacture of Nitric Acid.

(ii) (a) When ammonia gas is passed through Copper sulphate solution, pale blue precipitate of copper hydroxide is formed. On passage of excess ammonia, the pale blue precipitate turns into deep blue coloured solution due to formation of tetra amine copper(II) sulphate.

CuSO4 + 2NH4OH → (NH4)2SO4 + Cu(OH)2 ↓

Cu(OH)2 + (NH4)2SO4 + 2NH4OH → [Cu(NH3)4]SO4 + 4H2O.

(b) Ammonia.

Example 11.

i. Name a simple method you would employ to prepare ammonium salts in your laboratory.

ii. What property of ammonia is demonstrated by the Fountain Experiment? Write the balanced equation for the reaction between ammonia and sulphuric acid.

iii. Choose the correct word from the brackets for each sentence and write a balanced equation for the same.

(a) Ammonium chloride is a soluble salt prepared by _________ (precipitation, neutralization).

(b) When ammonium chloride is heated, it undergoes thermal _________ (decomposition / dissociation).

iv. Name a gas whose solution in water is alkaline.

v. Name the ion other than ammonium ion formed when ammonia dissolves in water.

vi. Select the correct compound from the list given – Ammonia, Copper oxide, Copper sulphate, Hydrogen chloride, Hydrogen sulphide, Lead bromide – which matches the description given below:


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Although this compound is not a metal hydroxide, its aqueous solution is alkaline in nature.

Sol:

i. Neutralization : - Ammonia in the gaseous form or in aqueous solution [NH4OH] neutralizes acids forming the respective ammonium salts.

ii. Fountain Experiment demonstrate the high solubility of ammonia gas in water.

2NH3 + H2SO4 → (NH4)2SO4.

iii. (a) Neutralization.

NH4OH + HCl → NH4Cl + H2O

(b) Dissociation.

iv. Ammonia.

v. Hydroxyl ion [OH– ]

vi. Ammonia.

Example 12.

(i) How would you distinguish between Zn2+ ans Pb2+ using ammonium hydroxide solution.

(ii) State what is observed when excess of ammonia is passed through an aq. solution of lead nitrate.

Sol:

(i) Zn2+ with NH4OH gives white precipitate of zinc hydroxide which dissolves in excess of NH4OH,

ZnCl2 + 2NH4OH → Zn(OH)2 ↓ + 2NH4Cl

Zn(OH)2+ 2NH4OH + 2NH4Cl → Zn(NH3)4Cl4 + 4H2O

Aqueous solution of lead salt do not show any change on treatment with NH4OH.

(ii) When ammonia is passed through an aq. solution of lead nitrate, chalky white precipitate of lead hydroxide is formed which is insoluble in excess of ammonia.

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

Example 13.

(i) What are the products formed when ammonia is oxidized with copper oxide?

(ii) From the following gases – ammonia, chlorine, hydrogen chloride, Sulphur dioxide, select the gas that matches the description given below:

(a) �e gas [B] turns moist red litmus paper blue. What is the name of gas [B]?

5.32 Ammonia

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(b) Write the equation for the reaction that takes place when gas [B] is passed over heated CuO.

(iii) Write an equation for the reaction of chlorine with excess of ammonia.

(iv) Write a balanced chemical equation to illustrate the reducing nature of ammonia.

Sol:

(i) Nitrogen, Copper and water.

2NH3 + 3CuO → 3Cu + 3H2O + N2.

(ii) (a) Ammonia.

(b) 3CuO [heated] + 2NH3 → 3Cu + N2 + 3H2O

(iii) 8NH3 [excess] + 3Cl2 → 6NH4Cl + N2

(iv) 3CuO + 2NH3 → 3Cu + N2 + 3H2O

Example 14.

(i) What do you observe when ammonia gas is bubbled through red litmus solution?

(ii) State what you observe when a piece of moist red litmus paper is placed in a gas jar of ammonia.

Sol:

(i) �e red litmus solution becomes blue.

(ii) �e red litmus paper turns blue.

Example 15.

(i) Write an equation for solutions of ammonium chloride and sodium hydroxide are heated.

(ii) Ammonium salts decompose on heating. What other property do ammonium salts have in common?

(iii) Choose the correct word from the bracket and write a balanced equation for the same : Heating ammonium chloride with sodium hydroxide produces [ammonia / nitrogen].

(iv) Name [formula is not acceptable] the gas produced on warming ammonium sulphate with sodium hydroxide solution.

(v) Write the equation for the preparation of NH3 from ammonium chloride and calcium hydroxide.

(vi) Write the equation for the reaction when a mixture of ammonium chloride and slaked lime is heated.

(vii) From the list of substances given – Ammonium sulphate, Lead carbonate, Chlorine, Copper nitrate, Ferrous sulphate – State : A compound which on heating with sodium hydroxide produces a gas which forms dense white fumes with hydrogen chloride.


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Sol:

(i) NH4Cl + NaOH → NaCl + H2O + NH3.

(ii) (a) Ammonium salts liberate ammonia on treatment with alkalis.

(b) All ammonium salts are soluble in water.

(iii) Ammonia.

NH4Cl + NaOH → NaCl + H2O + NH3

(iv) Ammonia.

5.34 Ammonia

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EXERCISE 1 – For School Examinations

Long Answer Questions

Directions: Give answer in four to �ve sentences.Q.1. State type of bonding is present in ammonia with the help of a diagram?

Q.2 Name di�erent forms of ammonia.

Q.3. What is the formula of liquid ammonia? Account for the basic nature of these compounds.

Q.4. Ammonia gas can be prepared by warming an ammonium salt with caustic alkali. Give two equations.

Q.5. (a) Write balanced chemical equations for the lab preparation of ammonia.

(b) How is ammonia dried and collected in the laboratory?

(c) Ammonia cannot be collected over water. Give reason.

Q.6. Ammonium salt decompose on heating. What other property do ammonium salts have in common?

Q.7. State what you observe when a piece of moist red litmus paper is placed in a gas jar of ammonia.

Q.8. A gas ‘P’ gives dense white fumes with chlorine. Its aqueous solution gives a blue colour with copper (II) hydroxide. (a) Name the gas ‘P’. (b) Give its formula. (c) Give three uses of P.

Q.9. How do you prove that NH3 contains nitrogen and hydrogen?

Q.10. What do you observe when ammonium hydroxide is added to the aqueous solution of?

(a) FeSO4 (b) Iron (III) Chloride

(c) Lead Nitrate (d) Zinc Nitrate

(e) ZnSO4 (f ) CuSO4

Q.11. Give the balanced equation for the following conversation.

(a) Ammonia to nitrogen using an acidic acid.

(b) Ammonia to brown gas.

(c) Ammonia to nitrogen trichloride.

(d) Ammonia solution to an amphoteric hydroxide.

(e) A nitride of a trivalent metal to ammonia.

(f ) Lead oxide to lead.


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Q.12. Choose the correct word or phrase from the brackets to complete the following sentences and write balanced equations for the same.

(a) Ammonium chloride is a soluble salt prepared by [Precipitation/ neutralization]

(b) When ammonium chloride is heated, it undergoes [thermal decomposition/dissociation]

(c) Heating ammonium chloride with sodium hydroxide produces [ammonia, nitrogen].

Q.13. What is the alternative of chloro�uro carbon?

Q.14. State the advantages of using ammonia as refrigerant?

Q.15. Name a compound prepared by ammonia and is used as

(a) Explosive (b) Fertilizer

(c) Medicine (d) Laboratory reagent

Q.16. Write the equation for the action heat on

(a) Ammonium chloride (b) Ammonium nitrate

Q.17. (a) Write the equation for the formation of ammonia by the action of water or magnesium nitride.

(b) How is ammonia collected?

(c) Why is ammonia not collected over water?

(d) Which compound is normally used as a drying agent for ammonia?

Q.18. (a) Which feature of ammonia molecule leads to the formation of the ammonium ion when ammonia dissolves in water?

(b) Name the other ion formed when ammonia dissolves in water.

(c) Give one test that can be used to detect the presence of the ion produced in (b).

Q.19. Write the equations for the following reactions which results in the formation of ammonia.

(a) A mixture of ammonium chloride and slaked lime is heated.

(b) Aluminium nitride and water.

Q.20. Give one example of a reaction between the ammonia and hydrogen chloride which produces a solid compound.

Q.21. Write balanced equation for a reaction in which ammonia is oxidized by

(a) a metal oxide; (b) a gas which is not oxygen.

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Q.22. Write the equation for the following reactions:

Aluminium nitride and water

Q.23. Choose correct from the following:

Ammonia can be obtained by adding water to:

(a) Ammonium chloride (b) Ammonium nitrile

(c) Magnesium nitride (d) Magnesium nitrate


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EXERCISE 2 – For Competitive Examinations

Long Answer Questions

Directions: Give answer in four to �ve sentences.Q.1. Name a drying agent for ammonia. Why are other drying agents like H2SO4, P2O5, and CaCl2

are not used?

Q.2. Ammonia is manufactured by Haber process

(a) Under what conditions do the reactants combine to form ammonia? Give a balanced equation for the reaction.

(b) In what ratio by volume, are the above gases used?

(c) State one possible source of each reactant used in Haber process.

(d) State whether the formation of ammonia prompted by the use of high pressure or low pressure?

(e) Mention two possible ways by which ammonia produced is removed from unchanged gases.

(f ) What is function of (i) �nely divided iron, (ii) molybdenum in the above process ?

Q.3. Explain with a diagram the preparation of aqueous ammonia.

Q.4. Draw a labelled diagram and give balanced equation for the lab preparation of ammonia. Also state physical properties of ammonia.

Q.5. Give reason for the following.

(a) Liquid ammonia is used as a refrigerant in ice plants.

(b) Aqueous solution of ammonia is used for removing grease stains from woolen clothes.

(c) Aqueous solution of ammonia gives a pungent smell.

(d) Aqueous solution of ammonia conducts electricity.

Q.6. Copy and complete the following equations.

(a) 2AlN H O → (b) 32NH 3PbO →

(c) 3 2NH 3Cl → (d) 3 2NH CO →

Q.7. Why ammonium hydroxide is used in qualitative analysis. Give two equations to justify your answer.

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Q.8. Give a chemical test to distinguish between the following:

(a) Ammonium chloride and sodium chloride.

(b) Ferric salt and ferrous salt.

(c) Sodium sulphate and ammonium sulphate.

Q.9. (a) Explain catalytic oxidation of ammonia.

(b) Give two reactions to show reducing property of ammonia.

Q.10. When ammonium hydroxide is added to solution B, a pale blue precipitate is formed. �is pale blue precipitate dissolves in excess of ammonium hydroxide giving an inky blue solution. What is the cation [positive ion] present in solution B?

What is the probable colour of solution B.

Q.11. When an ammonium salt is warmed with sodium hydroxide solution, ammonia gas is evolved. State three ways in which you could identify this gas.

Q.12. Complete the following equations. What property of ammonia is illustrated by the reaction in (b).

3 2 2(a) Mg N 6H O → 3(b) 2NH 3CuO →

3 2(c) 8NH 3Cl → 3 2(d) 4NH 5O →

What important process starts with the reaction in (d) above? Name the catalyst used.

Q.13. Which common refrigerant is used? How does it deplete ozone layer?

Q.14. Ammonia is good refrigerant but it shows some disadvantages when used as refrigerant. State its disadvantages.

Q.15. Ammonia is used in the Ostwald process.

(a) Give the source of reactants used in this process.

(b) Name the catalyst used in the process.

(c) Name the oxidizing agent used in the process.

(d) What is the ratio of ammonia and air taken in this process?

(e) Why is quartz used in this process?

Q.16. (a) Write the equation for the reaction in Haber process that forms ammonia.

(b) State the purpose of liquefying the ammonia produced in the process.

(c) Predict the group of an element X if its atomic number is 16.

(d) State one reason why tap water is not used to prepare a solution of silver nitrate in the laboratory.


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SOLUTIONS

EXERCISE 1 – For School Examinations

Sol:1. Bonding present in Ammonia is Covalent Bonding.

..H N H

|H

Sol:2. Forms of Ammonia:

(i) Gaseous ammonia (ii) Liquid ammonia

(iii) Liquor ammonia fortis

(iv) Laboratory bench reagent.

Sol:3. Formula of liquid Ammonia is NH3. Liquid Ammonia is lique�ed ammonia BASIC NATURE. It dissolves in to water to give ammonium Hydroxide which ionizes to give hydroxyl ions.

(aq)3 2 4NH H O NH OH→

4 4NH OH NH (aq) OH (aq)

�erefore it turns red litmus blue, turmeric paper Brown and PHENOLPHTHALEIN Solution Pink.

Sol:4. Two equations to prepare Ammonia:

(i) 4 2 4[NH ] SO 2NaOH → 2 4 3 2Na SO 2NH 2H O

(ii) 4 2 4 2 4 3 2[NH ] SO 2KOH K SO 2NH 2H O→

Sol:5. (a) 4 2 2 2 3NH Cl Ca(OH) CaCl 2H O 2NH→

(b) Ammonia gas is dried by passing through quick lime (CaO).

(c) Ammonia cannot be collected over water because it is higly soluble in water.

Sol:6. Reducing property

Sol:7. A piece of moist red litmus paper turns blue in a jar of ammonia.

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Sol:8. (i) Name of gas P is ammonia

(ii) NH3

(iii) Uses

(a) It is used in ice factories.

(b) In the manufacture of nitric acid by Ostwald’s process.

(c) In the manufacture of nylon and rayon.

Sol:9. When electric spark is passed through NH3 gas, it dissociates into nitrogen and Hydrogen.

3 2 22NH N 3H .

�is proves that Ammonia gas contains nitrogen and hydrogen.

Sol:10. (a) Action with FeSO4

4 4 4 2 4 2(Dirty green ppt)

FeSO 2NH OH [NH ] SO Fe(OH)→

Insoluble in excess of NH4OH

(b) Action with FeCl3

3 4 4 3(Reddish brown ppt)

FeCl 3NH OH 3(NH )Cl Fe(OH)→


(c) Action with lead nitrate

3 2 4 4 3 2(White ppt)

Pb[NO ] 2NH OH 2NH NO Pb[OH]→


(d) Action with zinc nitrate

3 2 4 4 3 2(Whitegalatinous)

Zn[NO ] 2NH OH 2NH NO Zn(OH)→

Soluble in excess of NH4OH

(e) Action with ZnSO4

4 4 4 2 4 2(galatin whiteppt. soluble)

ZnSO 2NH OH [NH ] SO Zn(OH)→

(f ) Action with CuSO4

4 4 4 2 4 2(Pale blue ppt .)

CuSO 2NH OH [NH ] SO Cu(OH)→

Soluble in excess of NH4OH


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Sol:11. 3 2 2 4(a) 8NH 3Cl N 6NH Cl→

Pt. 900 C3 2 2(b) 4NH 5O 4NO 6H O→

2 2brown gas

2NO O 2NO→

3 2 3(c) NH 3Cl NCl 3HCl→

4 4 4 2 4 2(d) ZnSO 2NH OH [NH ] SO Zn(OH)→

2 3 3[Aluminium [Aluminiumnitride] Hydroxide]

(e) AlN 3H O Al(OH) NH (g)→

3 2 2(f) 3PbO 2NH 3Pb 3H O N (g)→

Sol:12.

(a) Neutralisation

4 4 2NH OH HCl NH Cl H O→

(b) �ermal Decomposition

4 3NH Cl NH HCl→

(c) Ammonia (NH3)

4 2 3NH Cl NaOH NaCl H O NH→

Sol:13. Anhydrous ammonia is alternative of chloro�uro carbon.

Sol:14. Advantages of using ammonia as refrigerant are

(i) It does not deplete on ozone layer and does not contribute to global warming.

(ii) Saves electricity.

(iii) Helps in recognising leaks.

Sol:15. (a) Ammonium Nitrate (NH4NO3) is used as explosive.

(b) Ammonium sulphate (NH4)2SO4 is used as fertilizer.

(c) Ammonium Carbonate is used in medicine for receiving a faint person.

(d) Ammonium Hydroxide as laboratory reagent.

Nitric acid [HNO3] is a laboratory reagent.

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Sol:16. (a) 4 3NH Cl NH HCl

[�ermal dissociation]

(b) 4 3 2 2NH NO 2H O N O

[�ermal decomposition]

Sol:17.

(a) 3 2 2 3 2Mg N 6H O 2NH 3Mg(OH)→

(b) By the upward displacement of air.

(c) Because it is soluble in water.

(d) Quick lime.

Sol:18. (a) It is the basic nature of ammonia molecule.

(b) Hydroxyl ion ( 3 2 4NH H O NH OH→ ).

(c) �e red litmus paper turns blue in the solution.

Sol:19.

4 2Ammonium chloride Slaked lime

(a) 2NH Cl(s) Ca(OH) → 2 2 3Ammonia

CaCl (s) 2H O(l) 2NH

2 3 3Aluminium nitride Ammonia

(b) AlN(s) 3H O(l) Al(OH) (s) 2NH (g)→

Sol:20. 3 4Ammonium Chloride

(b) NH HCl NH Cl(s)→

Sol:21. 3 2 2(a) 3CuO 2NH 3Cu N 3H O→

3 2 2 4(b) 8NH 3Cl N 6NH Cl→

Or 3 2 22NH 3Cl N 6HCl→

Sol:22. 2 3 3Aluminium nitride Aluminium hydroxide Ammonia

AlN 3H O Al(OH) NH→

Sol:23. (c) Magnesium Nitride


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EXERCISE 2 – For Competitive Examinations

Sol:1. Drying agent is Quick lime [CaO]. Drying agents like H2SO4, P2O5 and CaCl2 are not used as ammonia being basic react with them.

(i) Conc. H2SO4 reacts with ammonia forming ammonium sulphate.

3 2 4 4 2 42NH H SO [NH ] SO→

(ii) 3 2 5 2 4 3[Ammoniummetaphosphate]

2NH P O H O 2NH PO→

(iii) Anhydrous calcium chloride reacts with ammonia to form solid complex compound

2 3 2 3[a complex compound]

CaCl 4NH CaCl .4NH→

Sol:2. (a) Conditions for reactants to combine:

Temperature – Optimum temperature is 450 - 500 C

Pressure – Above 200 atm.

Catalyst – Finely divided Iron.

Promoter – Traces of molybdenum or Al2O3.

Reaction - 2 2 3N 3H 2NH heat

(b) Nitrogen and Hydrogen in ratio 1 : 3 by volume is used.

(c) Nitrogen gas is obtained by fractional distillation of liquid air.

Hydrogen gas is obtained from water gas (Bosch process) or from natural gas.(Fe Mo) at 450 C to 500 C

2 2 (200 900 atms)

3

(d) N 3H

2NH 22400 cals

High pressure favours the forward reaction i.e. formation of ammonia.

(e) Two possible ways by which NH3 produced is removed from unreacted N2 and H2 by:

(i) Liquefaction: NH3 is easily lique�able.

(ii) Absorbing in water : As ammonia is highly soluble in water.

(f ) (i) Finely divided iron increases the rate of reaction.

(ii) Molybdenum acts catalyst to �nely divided iron.

Sol:3. Preparation of Aqueous Ammonia: An aqueous solution of ammonia is prepared by dissolving ammonia in water. �e rate of dissolution of ammonia in water is very high, therefore, back suction of water is possible. To avoid this, a funnel is attached to the outer end of the delivery

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tube with rubber tubing.

Procedure: Water is taken in a container and only a small portion of the mouth of the funnel is dipped in the water.

As ammonia dissolves in water at a higher rate than its production in the �ask, the pressure in the funnel above water level decreases for a moment, and water rushes into the funnel. As a result, the rim of funnel loses its contact with water. Since, ammonia produced pushes the water down, the funnel comes in contact with water again. In this way, ammonia dissolves in water without back solution of water.

Sol:4. (a) Physical properties of Ammonia:

(i) It is colourless.

(ii) Odour: Strong, pungent choking smell.

(iii) Taste: Slightly alkaline (bitter) taste.

(iv) Non-poisonous

(v) B.P. – 33.5 C.

(vi) Alkaline nature.

(vii) Freezing point: Solid NH3 melts at – 77.7 C

(viii) Highly soluble in water.

1 vol. of water dissolves about 702 vols. Of ammonia at 20 C and 1 atm. pressure.

(ix) Density: V.D. = 8.5 lighter than air.

(x) Liquefaction: Lique�es at 10 C by compressing it at 6 atm. pressure.

Reaction:

4 2 2 2 32NH Cl Ca(OH) CaCl 2H 2NH→


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Sol:5. (a) Liquid Ammonia is used as a REFRIGERANT in ICE PLANTS because its heat of vaporisation is very high [5700 calories per gram molecule]. �is heat is taken from the surrounding bodies which are consequently cooled down.

(b) Aqueous solution of Ammonia is a good EMULSIFIER i.e., it dissolves in FATS or GREASE. �us it is used for removing grease stains from woolen clothes.

(c) Aqueous solution of Ammonia gives a pungent smell, because Ammonium Hydroxide when exposed to air gives Ammonia gas due to which it gives pungent smell.

(d) Aqueous solution of Ammonia [Ammonium Hydroxide] conducts electricity due to the presence of ions 4[NH and OH ] in it.

3 2 4NH H O NH OH→ 4NH OH

Sol:6. (a) 2 3 3AlN H O Al(OH) NH→

(b) 3 2 22NH 3PbO 3Pb 3H O N→

(c) (i) When ammonia is in excess

3 2 2

3 4

3 2 2 4

2NH 3Cl N 6HCl

6NH 6HCl 6NH Cl

8NH 3Cl N 6NH Cl

→

→

→

(ii) When chlorine is in excess,

3 2 3NH 3Cl 3HCl NCl→

(d) 3 2 2 2 22NH CO NH CONH H O→

(i) Equation (c) illustrates that ammonia it is strong reducing agent.

(ii) Urea fertiliser is prepared.

Sol:7. When correct amount of ammonium hydroxide is added drop wise to solutions of the metallic salts, ppts. (coloured generally) are formed. �ey help us to identify their metal ions.

4 4 4 2 4 2(green) (dirty green)

FeSO 2NH OH [NH ] SO Fe(OH)→

Shows the presence of [ 2Fe ion.]

3 4 4 3(Brown) (Reddish Brown)FeCl 3NH OH 3NH Cl Fe[OH]→

Shows the presence of [ 3Fe ion.]

5.46 Ammonia

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Sol:8. (a) heat4 3NH Cl NH HCl

4NH Cl on strong heating, sublimes to form dense white fumes which condense to white powdery mass on cooler parts of tube whereas no white fumes on heating NaCl.

(b) When Ammonium Hydroxide is added drop wise to solution to be tested.

Ferrous salt: gives dirty green ppt.

Ferric salt: gives Reddish brown ppt of their hydroxides.

(c) 4 2 4(NH ) SO on warming with NaOH solution gives NH3 gas. Sodium sulphate does not liberate NH3 gas.

Sol:9. Ammonia gas is neither combustible nor supporter of combustion. However, ammonia can be catalytically oxidized as below:

(a) Catalyst oxidation of ammonia:

(i) Experiment: Pass the electric current through platinum �lament such that it starts glowing with reddish glow. Pass a mixture of ammonia and oxygen gas in the ratio of 2 : 1 by volume.

Observation: Reddish brown fumes are seen in the �ask. �ese vapours are formed due to further oxidation of nitric oxide gas.

Pt 900 C3 2 24NH 5O 4NO 6H O→

2 22NO O 2NO→

(ii) Experiment. Stop the passage of electric current but continue passing the mixture of ammonia and oxygen.

Observation. (i) �e platinum �lament continues glowing.

(ii) Reddish brown fumes of nitrogen dioxide are formed.

Conclusion: (i) �e reaction between ammonia and oxygen is exothermic.

(ii) Platinum acts as catalyst.

(b) (1) 3 2 23CuO 2NH 3Cu 3H O N (g)→

(2) 3 2 23PbO 2NH 3Pb 3H O N (g)→

Sol:10. 4 4 4 4 2(Pale Blue ppt)

CuSO 2NH OH NH SO Cu[OH]→

�e cation [positive ion] in soluble B is Cu++

�e probable colour of solution B is blue.


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�e pale blue ppt. of copper hydroxide dissolves in excess of Ammonium hydroxide forming an Azure blue (deep blue) soluble complex salt. [Tetra amine copper II] sulphate 3 4 4[Cu(NH ) ]SOis formed.

2 4 2 4 4[Pale blue ppt] [Amm. hydroxide in excess]Cu[OH] (NH ) SO 2NH OH → 3 4 4 2

[Tetra amine copper II sulphate](Deep blue colouration) or Azure blue solution

[Cu(NH ) ]SO 4H O

Sol:11. Tests for Ammonia gas:

(1) It has sharp characteristic odour.

(2) It gives dense white fumes with conc. HCl.

(3) It turns phenolphthalein solution PINK.

Sol:12. 3 2 2 2 3(a) Mg N 6H O 3Mg[OH] 2NH→

3 2 2[Black solid] [Brown solid][reducing agent](b) 2NH 3CuO 3Cu 3H O N→

3 2 2 4Excess

(c) 8NH 3Cl N 6NH Cl→

Pt 800 C3 2 2 [21.5 Kcal]

(d) 4NH 5O 6H O 4NO Heat→

Sol:13. �e common refrigerant used is Freon chloro�urocarbon (CFC). �ese are decomposed by the U.V. rays producing free radical (Cl) which react with ozone to form chlorine monoxide ClO reacts with atomic oxygen and produces more chlorine free radicals, which further destroys ozone and causes ozone depletion.

ultraviolet2 2 2

Free radical(i) CF Cl (g) CF Cl(g) Cl(g)→

3 2ozone

(ii) Cl(g) O (g) ClO(g) O (g)→

3 2(iii) ClO(g) O (g) Cl(g) O (g)→

Sol:14. Disadvantages of using Ammonia.

(i) It is poisonous in high concentration. �ough it is lighter than air and dilutes easily and it can be detected easily by its strong smell.

(ii) It is not compatible with copper, so it cannot be used in copper pipes.

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Sol:15. (a) Source of ammonia gas is Ammonia from Haber’s process.

(b) Catalyst used is platinum gauze (Pt).

(c) Oxidising agent is oxygen.

(d) Ratio of ammonia and air taken in this process is 1 : 10.

(e) Quartz is acid proof and when packed in layers it helps in dissolving nitrogen dioxide (NO2) uniformly in water.

Sol:16. (a) 2 2 3N 3H 2NH

(b) To favour or increase the forward reaction or to separate ammonia gas.

(c) Group 6A or Group number 16.

(d) It contains chloride ions so white precipitate of silver chloride is formed.

5. AMMONIA - TopperLearning

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