Study of Compounds — Ammonia

(a) State the type of bonding present in ammonia, show by a diagram.

(b) What is the formula of liquid ammonia? Account for the basic nature of this compound.

Answer

(a) Covalent bonding is present in ammonia as shown below —

(b) The formula of liquid ammonia is NH₄OH.

The aqueous solution of ammonia [NH₄OH] is a weak base. It dissociates partially to give hydroxyl ions [OH^1-].

The basic nature of NH₄OH is due to the presence of hydroxyl ions [OH^1-].

NH₃ + H₂O ⟶ NH₄OH

NH₄OH ⇌ NH₄⁺ + OH^-

(a) Write a balanced chemical equation 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.

Answer

(a) 2NH₄Cl + Ca(OH)₂ ⟶ CaCl₂ + 2H₂O + 2NH₃ [g]

(b) In order to get dry ammonia, the gas is passed through a drying tower containing lumps of quicklime [CaO]. Ammonia gas is collected in inverted gas jars by the downward displacement of air.

(c) As ammonia gas is highly soluble in water, therefore, it is not collected over water.

(a) Explain with a diagram the preparation of aqueous ammonia.

(b) Why drying agents such as P₂O₅ and CaCl₂ are not used to dry NH₃ ?

Answer

(a) The diagram below shows the preparation of aqueous ammonia:

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 it's production in the flask, 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 it's 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.

(b) Ammonia being basic in nature reacts chemically with P₂O₅ and CaCl₂

6NH₃ + P₂O₅ + 3H₂O ⟶ 2(NH₄)₃PO₄

4NH₃ + CaCl₂ ⟶ CaCl₂.4NH₃

Hence, P₂O₅ and CaCl₂ are not used to dry NH₃

A substance 'A' was heated with slaked lime and a gas 'B' with a pungent smell was obtained. Name the substances A and B and give a balanced equation.

Answer

Substance A is Ammonium chloride (NH₄Cl) and gas B is Ammonia

2NH₄Cl + Ca(OH)₂ ⟶ CaCl₂ + 2H₂O + 2NH₃ [g]

Ammonia is manufactured by Haber's 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 is promoted 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 the function of

    (i) finely divided iron,

    (ii) molybdenum

in the above process?

(g) What is the percentage formation of ammonia?

(h) How can this percentage formation be increased?

Answer

(a) Nitrogen reacts with hydrogen under specific conditions liberating ammonia

N₂ + 3H₂ ⇌ 2NH₃ + Δ

Conditions :

Temperature : 450-500°C [Optimum temperature]

Pressure : 200 to 900 atmospheres [Optimum pressure]

Catalyst : Finely divided iron [Fe]

Promotor : Molybdenum [Mo]

[Catalyst - iron [III] oxide [Fe₂O₃] may also be used containing promoters about 1% K₂O and 3% Al₂O₃]

(b) According to the above equation, nitrogen and hydrogen combines in 1:3 ratio by volume.

(c) Nitrogen is obtained by fractional distillation of liquid air. Hydrogen is obtained from the water gas (Bosch process) or from natural gas.

(d) The formation of ammonia is promoted by the use of high pressure as it favours the forward direction.

(e) Two possible ways by which ammonia produced is removed from unchanged gases are:

1. By Liquefaction — ammonia is liquefied easily as compared to nitrogen and hydrogen.
2. By Absorbing in water — because ammonia is highly soluble in water, as hydrogen and nitrogen are very slightly soluble.

(f) Function of finely divided iron and molybdenum are:

1. Finely divided iron increases the rate of reaction.
2. Molybdenum acts as a promoter to increase the efficiency of the catalyst.

(g) 15%

(h) The unchanged nitrogen and hydrogen are recirculated through the plant to get more ammonia, by this way we can achieve 98% of ammonia.

Give reason —

Ammonium compounds does not occur in minerals.

Answer

Due to the high solubility of Ammonium compounds in water it does not occur in minerals.

Give reason —

Ammonium nitrate is not used in the preparation of ammonia.

Answer

As ammonium nitrate is explosive in nature and may itself decompose forming nitrous oxide and water vapour, hence it is not used in the preparation of ammonia.

NH₄NO₃ $\xrightarrow{\Delta}$ N₂O + 2H₂O

Give reason —

Conc. H₂SO₄ is a good drying agent, yet it is not used to dry NH₃.

Answer

As sulphuric acid reacts chemically with ammonia to form ammonium sulphate hence, it is not used as a drying agent for drying ammonia.

2NH₃ + H₂SO₄ ⟶ (NH₄)₂SO₄

Give reason —

In the lab. preparation of ammonia

1. calcium hydroxide is used in excess.
2. Flask is fitted in slanting position.

Answer

1. In the lab preparation of ammonia, ammonium chloride is used. Ammonium chloride is sublime, during the reaction, the heat will cause ammonium chloride to vapourise. To prevent this, calcium hydroxide is used in excess. It absorbs excess heat and prevents the loss of ammonium chloride as vapours.
2. The flask is fitted in slanting position so that the water formed in the reaction does not trickle back into the heated flask and thus break it.

State the following conditions required in the Haber's process-

(a) Temperature

(b) Pressure

(c) Catalyst

Answer

Conditions :

(a) Temperature : 450-500°C [Optimum temperature]

(b) Pressure : 200 to 900 atmospheres [Optimum pressure]

(c) Catalyst : Finely divided iron [Fe]

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].

Answer

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

NH₃ (gas) + HCl (gas) ⟶ NH₄Cl (solid)

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

NH₄Cl ⇌ NH₃ + HCl

(c) Heating ammonium chloride with sodium hydroxide produces ammonia.

NH₄Cl + NaOH ⟶ NaCl+ H₂O + NH₃

An element has 2 electrons in it's N shell. It reacts with a non-metal of atomic number 7. The compound formed reacts with warm water and produces a basic gas. Identify the elements and write the balanced chemical reactions.

Answer

An element has 2 electrons in it's N shell, hence, it has

1. 2 (electrons in K shell) +
2. 8 (electrons in L shell) +
3. 8 (electrons in M shell) +
4. 2 (electrons in N shell) = 20 electrons total i.e. Calcium

Non metal (atomic number 7) is Nitrogen

Calcium and Nitrogen react to form calcium nitride.

3Ca + N₂ ⟶ Ca₃N₂

Ca₃N₂ reacts with water to give calcium hydroxide and ammonia.

Ca₃N₂ + 6H₂O ⟶ 3Ca(OH)₂ + 2NH₃ [g]

The following reactions are carried out

A: Nitrogen + metal ⟶ compound X.

B: X + water ⟶ ammonia + another compound.

C: Ammonia + metal oxide ⟶ metal + water + N₂

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 ?

Answer

(a) When metal for A is magnesium, then, compound X is Mg₃N₂

N₂ + 3Mg ⟶ Mg₃N₂

(b) Magnesium nitride

Mg₃N₂ + 6H₂O ⟶ 3Mg(OH)₂ + 2NH₃ [g]

(c) Ammonia is a reducing agent and hence it reduces the less reactive metal oxide to the respective metal.

2NH₃ + 3MgO ⟶ 3Mg + 3H₂O + N₂

Correct the following:

(a) A reddish-brown precipitate is obtained when ammonium hydroxide is added to ferrous sulphate.

(b) Liquid ammonia is a solution of NH₃.

(c) Finely divided platinum is used in Haber's Process.

(d) Conc. H₂SO₄ is a drying agent for NH₃.

(e) Ammonium salts, on heating, decompose to give ammonia.

Answer

(a) A dirty green precipitate is obtained when ammonium hydroxide is added to ferrous sulphate.

(b) Aqueous ammonia is a solution of NH₃ in water.

(c) Finely divided iron is used in Haber's Process.

(d) Quicklime, is a drying agent for NH₃,

(e) Ammonium salts, on heating with caustic alkali, decompose to give ammonia.

Choose the correct from the following:

Ammonia can be obtained by adding water to

A : Ammonium chloride.

B : Ammonium nitrite.

C : Magnesium nitride.

D : Magnesium nitrate

Answer

Magnesium nitride

Mg₃N₂ + 6H₂O ⟶ 3Mg(OH)₂ + 2NH₃ [g]

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

(b) What property of ammonia is demonstrated by the Fountain Experiment?

(c) Write the balanced equation for the reaction between ammonia and sulphuric acid.

Answer

(a) Ammonia is less dense than air because vapour density of ammonia is 8.5 and that of air is 14.4.

(b) Fountain Experiment demonstrates the high solubility of ammonia gas in water.

(c) 2NH₃ + H₂SO₄ ⟶ (NH₄)₂SO₄

Pick the odd member from the list giving reasons:

(a) Ammonia, sulphur dioxide, hydrogen chloride, carbon dioxide.

(b) Copper oxide, aluminium oxide, sodium oxide, magnesium oxide.

Answer

(a) Ammonia is basic in nature and rest are acidic.

(b) Copper oxide is less reactive and can be reduced by C, CO or hydrogen whereas aluminium oxide, sodium oxide, magnesium oxide are reduced by electrolysis.

Give reasons 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 woollen clothes.

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

(d) Aqueous solution of ammonia conducts electricity.

Answer

(a) Liquid ammonia is a clear, colourless liquid under pressure. It evaporates rapidly and produces cooling effect. Moreover, Ammonia is environmentally compatible, has superior thermodynamic properties and its leaks are easily detectable due to its recognizable odour. All these reasons make liquid ammonia a good refrigerant.

(b) As aqueous solution of ammonia emulsifies or dissolves fats, grease etc., hence it is used for removing grease stains from woollen clothes.

(c) Pungent smell of aqueous solution of ammonia is due to the presence of ammonia, which has strong, pungent choking smell.

(d) In aqueous solution, the ammonia molecule combines with a hydrogen atom H⁺ by sharing the lone pair of electrons of nitrogen atom to form ammonium ion (NH₄⁺). Thus, in water, ammonium hydroxide (NH₄OH) dissociates into NH₄⁺ (ammonium ion) and OH^- (hydroxide ion) as follows:

NH₄OH ⟶ NH₄⁺ + OH^-

Due to this ionisation, aqueous solution of ammonia (NH₄OH) conducts electricity.

A gas 'P' gives dense white fumes with chlorine. It's aqueous solution gives a blue colour with copper (II) hydroxide. Give the name and formula of the gas P.

Answer

Gas 'P' is Ammonia and its formula is NH₃.

With chlorine, ammonia gas gives dense white fumes of NH₄Cl.

8NH₃ [excess] + 3Cl₂ ⟶ 6NH₄Cl + N₂

Reaction of copper (II) hydroxide with aqueous solution of Ammonia (NH₄OH) is given below:

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

Ammonia solution in water gives a blue precipitate when it combines with a solution of copper salt. The blue precipitate further dissolves in excess of ammonia solution to give an azure blue solution. Explain with equation.

Answer

Ammonia solution in water gives a blue precipitate when it combines with a solution of copper salt, due to the formation of Cu(OH)₂

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

The pale blue precipitate of copper hydroxide dissolves in excess of ammonium hydroxide forming tetraamine copper [II] sulphate, an azure blue soluble complex salt.

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

Give chemical equation(s) to prove that NH₃ contains nitrogen and hydrogen?

Answer

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

2NH₃ ⇌ N₂ + 3H₂

Copy and complete the following equations.

(a) AlN + H₂O ⟶

(b) 2NH₃ + 3PbO ⟶

(c) NH₃ + 3Cl₂ ⟶

(d) NH₃ + CO₂ ⟶

(i) Which property of ammonia is illustrated by equation (c)?

(ii) What important fertiliser is prepared from equation (d)? State the conditions.

Answer

(a) AlN + 3H₂O ⟶ Al(OH)₃ + NH₃↑

(b) 2NH₃ + 3PbO ⟶ 3Pb + 3H₂O + N₂ [g]

(c) NH₃ + 3Cl₂ [excess] ⟶ 3HCl + NCl₃

(d) 2NH₃ + CO₂ ⟶ NH₂CONH₂ + H₂O

(i) Ammonia acts as a reducing agent as it loses hydrogen in equation (c).

(ii) Urea is prepared from equation (d). Ammonia reacts with carbon dioxide at 150°C and 150 atm, pressure to give urea.

(a) What do you observe when ammonium hydroxide is added to the aqueous solution of :

(i) FeSO₄

(ii) Iron (III) chloride.

(iii) Lead nitrate

(iv) Zinc nitrate

(b) Write balanced equation for Q.8(a).

Answer

(i) Dirty green ppt. of ferrous hydroxide is formed which is insoluble in excess of NH₄OH.

(ii) Reddish brown ppt. of ferric hydroxide is formed which is insoluble in excess of NH₄OH.

(iii) White ppt. of lead hydroxide is formed which is insoluble in excess of NH₄OH.

(iv) White gelatinous ppt. of Zinc hydroxide is formed which is soluble in excess of NH₄OH.

(b) The balanced chemical equations are given as :

(i) FeSO₄ + 2NH₄OH ⟶ (NH₄)₂SO₄ + Fe(OH)₂ ↓

(ii) FeCl₃ + 3NH₄OH ⟶ 3NH₄Cl + Fe(OH)₃ ↓

(iii) Pb(NO₃)₂ + 2NH₄OH ⟶ 2NH₄NO₃ + Pb(OH)₂ ↓

(iv) Zn(NO₃)₂ + 2NH₄OH ⟶ 2NH₄NO₃ + Zn(OH)₂ ↓

Distinguish between the following (using ammonia solution) :

(a) Calcium chloride and zinc chloride.

(b) Ferric salt and ferrous salt

(c) Zinc nitrate and lead nitrate

Answer

(a) When we add ammonium hydroxide solution to both the given salt solutions, Zinc Chloride reacts to form a gelatinous white precipitate of Zinc Hydroxide (ZnOH), whereas, no such observations i.e no precipitate will form in case of Calcium Chloride solution because ammonium hydroxide is a weak base and it cannot react with calcium salts to precipitate the hydroxide of calcium.

ZnCl₂ + 2NH₄OH ⟶ Zn(OH)₂ + 2NH₄Cl

(b) On reaction with ammonium hydroxide, Iron [II] sulphate (ferrous salt) forms a dirty green ppt whereas iron [III] sulphate (ferric salt) forms a reddish brown ppt. Hence, the two can be distinguished easily.

FeSO₄ + 2NH₄OH ⟶ (NH₄)₂SO₄ + Fe(OH)₂ ↓

Fe₂(SO₄)₃ + 6NH₄OH ⟶ 3(NH₄)₂SO₄ + 2Fe(OH)₃ ↓

(c) When zinc nitrate is treated with ammonium hydroxide, white gelatinous ppt. of Zinc hydroxide is formed which is soluble in excess of NH₄OH.

Zn(NO₃)₂ + 2NH₄OH ⟶ 2NH₄NO₃ + Zn(OH)₂ ↓

Whereas, when lead nitrate is treated with ammonium hydroxide, white ppt. of lead hydroxide is formed which is insoluble in excess of NH₄OH

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

Give balanced equations for the following conversions :

(a) Ammonia to nitrogen using an acidic gas.

(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

Answer

(a) Ammonia to nitrogen using an acidic gas :

8NH₃ [excess] + 3Cl₂ ⟶ 6NH₄Cl + N₂

(b) Ammonia to brown gas:

$4\text{NH}_3 + 5\text{O}_2 \xrightarrow[800 \degree \text{C}]{\text{Pt.}} \text{4NO} + \text{6H}_\text{2}\text{O} + \Delta$

2NO + O₂ ⟶ 2NO₂ [brown gas]

(c) Ammonia to nitrogen trichloride

NH₃ + 3Cl₂ [excess] ⟶ 3HCl + NCl₃

(d) Ammonia solution to an amphoteric hydroxide :

AlCl₃ + 3NH₄OH ⟶ 3NH₄Cl + Al(OH)₃

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

AlN + 3H₂O ⟶ Al(OH)₃ + NH₃ ↑

(f) Lead oxide to lead

2NH₃ + 3PbO ⟶ 3Pb + 3H₂O + N₂ [g]

Name:

(a) the gas which is prepared by Haber's process.

(b) two gases which give dense white fumes with ammonia.

(c) one salt of ammonia in each case which is used in:

(i) dry cell

(ii) explosives

(iii) medicine

(d) an acidic gas which reacts with a basic gas liberating a neutral gas

(e) a metallic chloride soluble in ammonium hydroxide

(f) the gas obtained when ammonia burns in an atmosphere of oxygen without any catalyst

(g) a nitride of a divalent metal which reacts with warm water liberating ammonia

(h) an amphoteric oxide reduced by the basic gas

(i) a white salt produced by an acidic gas and a basic gas

Answer

(a) Ammonia

(b) Hydrogen chloride and chlorine gas

(c) (i) dry cell — ammonium chloride

(ii) explosives — ammonium nitrate

(iii) medicine — ammonium carbonate

(d) Acidic gas — Cl₂ ; Basic gas — Ammonia

Neutral gas — N₂

2NH₃ + 3Cl₂ ⟶ N₂ + 6HCl

(e) Silver chloride

(f) Nitrogen

(g) Magnesium nitride

(h) Lead oxide

(i) Ammonium chloride

When ammonium hydroxide is added to solution B, a pale blue precipitate is formed. This pale blue precipitate dissolves in excess 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.

Answer

Solution B is Copper Sulphate and cation present is (Cu²⁺). The colour of solution B is Blue.

Ammonium hydroxide gives a blue precipitate when it combines with a solution of copper salt, due to the formation of Cu(OH)₂

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

The pale blue precipitate of copper hydroxide dissolves in excess of ammonium hydroxide forming tetraamine copper [II] sulphate, an azure blue soluble complex salt.

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

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

Answer

When an ammonium salt is warmed with sodium hydroxide solution, ammonia gas is evolved.

NH₄Cl + NaOH ⟶ NaCl + H₂O + NH₃

Three ways in which ammonia gas can be identified is:

1. It has a sharp characteristic odour.
2. It turns:
   1. moist red litmus blue,
   2. moist turmeric paper brown,
   3. phenolphthalein solution pink.
3. It gives dense white fumes with conc. hydrochloric acid.
   NH₃ + HCl ⟶ NH₄Cl

A gas 'A' reacts with another gas 'B' in the presence of a catalyst to give a colourless gas 'C'. The gas 'C' when comes in contact with air produces a brown gas 'D'. The solution of 'A' in water turns red litmus blue. Explain the observations.

Answer

As the 'A' turns red litmus blue it is a base. Now the gas 'A' combines with 'B' in presence of Catalyst to give colourless gas Nitrogen monoxide. It reacts with oxygen to give brown gas which is Nitrogen dioxide. The gases are given as :

A = NH₃
B = O₂
C = NO
D = NO₂

4NH₃ + 5O₂ $\xrightarrow[800 \degree \text{C}]{\text{Pt.}}$ 4NO↑ + 6H₂O + Δ

2NO + O₂ ⟶ 2NO₂ [brown gas]

(i) Name the common refrigerant. How does it deplete ozone layer?

(ii) What is the alternative of chlorofluorocarbon carbon?

(iii) State the advantages and disadvantages of using ammonia as refrigerant?

Answer

(i) The main refrigerants used are Freon chlorofluorocarbons (CFC). They deplete ozone layer and contribute to global warming. The chlorofluorocarbons are decomposed by ultraviolet rays to highly reactive chlorine which is produced in the atomic form.

$\text{CF}_2\text{Cl}_2 \xrightarrow{\text{Ultraviolet}} \text{CF}_2\text{Cl} + \text{Cl} [\text{free radical}]$

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

Cl + O₃ [ozone] ⟶ ClO + O₂

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

ClO + O ⟶ Cl + O₂

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

(ii) Liquid ammonia

(iii) Advantages of ammonia as refrigerant:

1. Ammonia is environmentally compatible. It does not deplete ozone layer and does not contribute towards global warming.
2. It has superior thermodynamic qualities as result ammonia refrigeration systems use less electricity.
3. Ammonia has a recognizable odour and so leaks are not likely to escape. It being lighter than air goes up in the atmosphere not affecting the life too much on earth.

Disadvantages of ammonia as a refrigerant are as follows:

1. It is not compatible with copper, so it cannot be used in any system with copper pipes.
2. It is poisonous in high concentration.

Name a compound prepared by ammonia and is used as :

(a) Explosive

(b) Fertilizers

(c) Medicine

(d) Laboratory reagent

Answer

(a) Ammonium nitrate

(b) Ammonium sulphate

(c) Ammonium carbonate

(d) Ammonia solution

Write the equation for the action of heat on:

(a) Ammonium chloride

(b) Ammonium nitrate

State whether each reaction is an example of thermal decomposition or thermal dissociation.

Answer

(a) NH₄Cl ⇌ NH₃ + HCl

This reaction is an example of thermal dissociation.

(b) NH₄NO₃ ⇌ N₂O + 2H₂O

This reaction is an example of thermal dissociation.

(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).

Answer

(a) Ammonia molecule has a lone pair of electrons on it's nitrogen atom.

Due to this lone pair of electrons, in aqueous solutions it forms ammonium ion.

NH₃ + H₂O ⟶ NH₄OH

NH₄OH ⇌ NH₄⁺ + OH^-

(b) Hydroxyl ion [OH^-].

(c) The red litmus paper turns blue due to the presence of hydroxyl ion in the solution.

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

(b) Give one example of a reaction between the above two gases which produces a solid compound.

(c) Write a balanced equation for a reaction in which ammonia is oxidized by:

(i) a metal oxide

(ii) a gas which is not oxygen.

Answer

(a) HCl gas is denser as it's vapour density = 18.25, and that of ammonia is 8.5. HCl gas is collected by the upward displacement of air.

(b) NH₃ + HCl ⟶ NH₄Cl

(c) (i) 2NH₃ + 3CuO ⟶ 3Cu + 3H₂O + N₂ ↑

(ii) NH₃ + 3Cl₂ ⟶ 3HCl + NCl₃ ↑

Study the flow chart given and give balanced equations to represent the reactions A, B and C.

$\text{Mg}_3\text{N}_2 \xrightarrow{\text{A}} \text{NH}_3 \xtofrom[\text{C}]{\text{B}} \text{NH}_4\text{Cl}$

Answer

A : Mg₃N₂ + 6H₂O ⟶ 3Mg(OH)₂ + 2NH₃ [g]

B:
$\underset{\text{[aq.]}}{\text{NH}_3} + \underset{\text{[vapour]}}{\text{HCl}} \longrightarrow \underset{\text{[dense white fumes]}}{\text{NH}_4\text{Cl}}$

C: 2NH₄Cl + Ca(OH)₂ ⟶ CaCl₂ + 2H₂O + 2NH₃↑

(a) Ammonia reacts with excess chorine to form ............... (nitrogen / nitrogen trichloride / ammonium chloride).

(b) Give a balanced equation: Ammonium hydroxide is added to ferrous sulphate solution.

(c) Write observations: Ammonia gas is passed over heated copper (II) oxide.

Answer

(a) Ammonia reacts with excess chlorine to form nitrogen trichloride

NH₃ + 3Cl₂ [excess] ⟶ 3HCl + NCl₃

(b) FeSO₄ + 2NH₄OH ⟶ (NH₄)₂SO₄ + Fe(OH)₂ ↓

(c) Black copper [II] oxide is reduced to brown copper.

2NH₃ + 3CuO ⟶ 3Cu + 3H₂O + N₂ [g]

Name the gas evolved in each case [formula is not acceptable]. The gas that burns in oxygen with a green flame.

Answer

Ammonia (NH₃)

Write a fully balanced equation for — Magnesium nitride is treated with warm water.

Answer

Mg₃N₂ + 6H₂O ⟶ 3Mg(OH)₂ + 2NH₃↑

Identity the substances 'Q' based on the information given — The white crystalline solid 'Q' is soluble in water. It liberates a pungent smelling gas when heated with sodium hydroxide solution.

Answer

Substances 'Q' are Ammonium salts like ammonium chloride, ammonium sulphate. They are white solids, soluble in water and liberate pungent smelling ammonia gas on heating with alkalis like NaOH.

Complete the blanks (i) to (v) in the passage given, using the following words. [Ammonium, reddish brown, hydroxyl, nitrogen dioxide, ammonia, dirty green, alkaline, acidic].

In the presence of a catalyst, nitrogen and hydrogen combine to give (i) .............. gas. When the same gas is passed through water, it forms a soln. which will be (ii).............. in nature, and will contain the ions (iii) .............. and (iv) ............... . A (v) .............. coloured ppt. of iron [II] hydroxide is formed when the above solution is added to iron [II] sulphate solution.

Answer

(i) Ammonia

(ii) Alkaline

(iii) Ammonium

(iv) Hydroxyl

(v) Dirty green

State your observation when — in the absence of catalyst, ammonia is burnt in an atmosphere of oxygen.

Answer

Green or greenish yellow flame is seen when ammonia gas is burnt in an atmosphere of oxygen. The reaction of combustion of Ammonia is:

4NH₃ + 3O₂ ⟶ 2N₂ + 6H₂O

Give the equation for the reaction — ammonium chloride is heated with sodium hydroxide.

Answer

NH₄Cl + NaOH ⟶ NaCl + H₂O + NH₃

In the manufacture of ammonia:

(i) Name the process.

(ii) State the ratio of the reactants taken?

(iii) State the catalyst used.

(iv) Give the equation for the manufacture of the gas - ammonia.

Answer

(i) Haber's Process

(ii) Nitrogen (N₂) and hydrogen (H₂) in the ratio 1:3 by volume

(iii) Finely divided iron (Fe)

(iv) N₂ + 3H₂ ⇌ 2NH₃ + Δ

Write a relevant equation, to show that ammonia can act as a reducing agent.

Answer

Ammonia gas is a strong reducing agent. Below equation shows reduction of Black Copper [II] oxide to brown Copper by Ammonia.

2NH₃ + 3CuO ⟶ 3Cu + 3H₂O + N₂ [g]

Name two gases which can be used to study the fountain experiment. State the common property demonstrated by the fountain experiment ?

Answer

Hydrogen chloride gas (HCl) and Ammonia (NH₃) are the two gases which can be used to study the fountain experiment.

The common property demonstrated by the fountain experiment is the solubility of gases in water.

State what is observed when – Ammonium hydroxide is first added in a small quantity and then in excess to a solution of copper sulphate.

Answer

Ammonium hydroxide if first added in small quantity and then in excess to a solution of copper sulphate, a pale blue ppt. of copper hydroxide is formed which dissolves in excess of ammonium hydroxide forming a soluble complex salt.

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

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

The diagram below shows set up for the lab. preparation of a pungent alkaline gas.

(i) Name the gas collected in the jar.

(ii) Give a balanced equation for the above preparation

(iii) State how the above gas is collected?

(iv) Name the drying agent used.

(v) State how you will find out that the jar is full of the pungent gas?

Answer

(i) Ammonia (NH₃) gas is collected.

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

(iii) Downward displacement of air is the method used to collect the gas.

(iv) Quicklime (CaO) is the drying agent.

(v) A glass rod dipped in conc. HCl acid is brought near the mouth of the jar. If the jar is full-dense white fumes of ammonium chloride are formed.

Write a balanced chemical equation – Chlorine reacts with excess of ammonia.

Answer

8NH₃ [excess] + 3Cl₂ ⟶ 6NH₄Cl + N₂

State your observation – Water is added to the product formed, when Al is burnt in a jar of nitrogen gas.

Answer

When Al metal is burnt in a jar of nitrogen gas, its nitride i.e., AlN is formed. When warm water is added to AlN, it undergoes hydrolysis and is decomposed by warm water to give pungent smelling ammonia gas. The corresponding insoluble metal hydroxide (i.e., Al(OH)₃) is precipitated out. The reactions are shown below:

2Al + N₂ ⟶ 2AlN

AlN + 3H₂O ⟶ Al(OH)₃ + NH₃ [g]

Name — The gas produced when excess ammonia reacts with chlorine.

Answer

Nitrogen

8NH₃ [excess] + 3Cl₂ ⟶ 6NH₄Cl + N₂

Rewrite the correct statement with the missing word/s — Magnesium nitride reacts with water to liberate ammonia.

Answer

Magnesium nitride reacts with warm water to liberate ammonia along with magnesium hydroxide.

Give balanced equation for the reaction : Ammonia and Oxygen in the presence of a catalyst.

Answer

Below is the equation for the catalytic oxidation of Ammonia:

$4\text{NH}_3 + 5\text{O}_2 \xrightarrow[800 \degree \text{C}]{\text{Pt.}} \text{4NO} + \text{6H}_\text{2}\text{O} + \Delta$

The following questions are based on the preparation of ammonia gas in the laboratory:

(i) Explain why ammonium nitrate is not used in the preparation of ammonia.

(ii) Name the compound normally used as a drying agent during the process.

(iii) How is ammonia gas collected? Explain why it is not collected over water.

Answer

(i) As ammonium nitrate is explosive in nature and may itself decompose forming nitrous oxide and water vapour, hence it is not used in the preparation of ammonia.

$\text{NH}_4\text{NO}_3 \xrightarrow\Delta \text{N}_2\text{O} + \text{2H}_2\text{O}$

(ii) Quick lime [CaO] is used as a drying agent during the process.

(iii) Downward displacement of air is the method used for the collection of the ammonia gas. As ammonia gas is highly soluble in water, therefore, it is not collected over water.

State one appropriate observation for : Excess of chlorine gas is reacted with ammonia gas.

Answer

Colourless ammonia gas reacts with greenish yellow excess chlorine giving a yellow explosive liquid (Nitrogen trichloride).

NH₃ + 3Cl₂ [excess] ⟶ 3HCl + NCl₃

Nitrogen gas can be obtained by heating :

(a) Ammonium nitrate

(b) Ammonium nitrite

(c) Magnesium nitride

(d) Ammonium chloride

Answer

Ammonium nitrite

NH₄NO₂ $\xrightarrow\Delta$ 2H₂O + N₂

State two relevant observations for : ammonium hydroxide soln. is added to zinc nitrate soln. slowly and then in excess.

Answer

White gelatinous precipitate of zinc hydroxide is formed which dissolves in excess of NH₄OH solution.

Zn(NO₃)₂ + 2NH₄OH ⟶ 2NH₄NO₃ + Zn(OH)₂ ↓

Give a balanced equation for : Reduction of hot Copper (II) oxide to copper using ammonia gas.

Answer

2NH₃ + 3CuO ⟶ 3Cu + 3H₂O + N₂ [g]

Copy and complete the following table relating to important industrial process

Answer

Identify : An alkaline gas which produces dense white fumes when reacted with HCl gas.

Answer

Ammonia gas.

NH₃ + HCl ⟶ NH₄Cl

Fill in the blank from the choices given in bracket : Ammonia gas is collected by .............. (upward displacement of air, downward displacement of water, downward displacement of air)

Answer

Ammonia gas is collected by downward displacement of air.

Write balanced equation for : Action of warm water on magnesium nitride.

Answer

Mg₃N₂ + 6H₂O ⟶ 3Mg(OH)₂ + 2NH₃ [g]

Distinguish between the following pairs of compounds using the test given in bracket :

(i) Iron [II] sulphate and iron [III] sulphate [using ammonium hydroxide]

(ii) A lead salt and a zinc salt [using excess ammonium hydroxide]

Answer

(i) On reaction with ammonium hydroxide, Iron [II] sulphate forms a dirty green ppt whereas iron [III] sulphate forms a reddish brown ppt. Hence, the two can be distinguished easily.

FeSO₄ + 2NH₄OH ⟶ (NH₄)₂SO₄ + Fe(OH)₂ ↓

Fe₂(SO₄)₃ + 6NH₄OH ⟶ 3(NH₄)₂SO₄ + 2Fe(OH)₃ ↓

(ii) A lead salt gives a chalky white ppt. on reaction with ammonium hydroxide that is insoluble in excess of ammonium hydroxide.

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

On the other hand, zinc salt forms a white gelatinous ppt. which dissolves when excess of ammonium hydroxide is added. Hence, the two can be distinguished.

ZnSO₄ + 2NH₄OH ⟶ (NH₄)₂SO₄ + Zn(OH)₂ ↓

[Zn(OH)₂] + (NH₄)₂SO₄ + 2NH₄OH ⟶ [Zn(NH₃)₄]SO₄ + 4H₂O

State your observation : Calcium hydroxide is heated with ammonium chloride crystals.

Answer

Pungent smelling gas (ammonia) is given out.

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

Name the other ion formed when ammonia dissolves in water. Give one test that can be used to detect the presence of the ion produced.

Answer

Hydroxyl ion [OH^-1] and ammonium ions [NH₄⁺] are formed.

NH₃ + H₂O ⟶ NH₄OH

NH₄OH ⇌ NH₄⁺ + OH^-1

The alkaline NH₄OH, due to the presence of hydroxyl ions [OH^-] turns red litmus blue and phenolphthalein soln. pink

State the conditions required for : Catalytic oxidation of ammonia to nitric oxide.

Answer

Conditions for catalytic oxidation of ammonia to nitric oxide are :

1. Temperature : 800°C
2. Catalyst : Platinum (Pt)

$4\text{NH}_3 + 5\text{O}_2 \xrightarrow[800 \degree \text{C}]{\text{Pt.}} \text{4NO} + \text{6H}_\text{2}\text{O} + \Delta$

Give balanced chemical equations for —

(i) Lab. preparation of ammonia using an ammonium salt.

(ii) Reaction of ammonia with excess of chlorine.

(iii) Reaction of ammonia with sulphuric acid.

Answer

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

(ii) NH₃ + 3Cl₂ [excess] ⟶ 3HCl + NCl₃

(iii) 2NH₃ + H₂SO₄ (dil.) ⟶ (NH₄)₂SO₄

From the list of the gases — Ammonia, ethane, hydrogen chloride, hydrogen sulphide — Select the gas which is used as a reducing agent in reducing copper oxide to copper.

Answer

Ammonia

Reducing nature of ammonia:
2NH₃ + 3CuO ⟶ 3Cu + 3H₂O + N₂ [g]

Name the gas evolved when the following mixtures are heated :

(i) Calcium hydroxide and Ammonium chloride.

(ii) Sodium nitrite and Ammonium chloride.

Answer

(i) Ammonia gas

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

(ii) Nitrogen gas

NH₄Cl + NaNO₂ ⟶ NaCl + NH₄NO₂

NH₄NO₂ ⟶ 2H₂O + N₂

Write balanced equations :

(i) When excess of ammonia is treated with chlorine.

(ii) An equation to illustrate the reducing nature of ammonia.

Answer

(i) 8NH₃ [excess] + 3Cl₂ ⟶ 6NH₄Cl + N₂

(ii) 2NH₃ + 3CuO ⟶ 3Cu + 3H₂O + N₂ [g]