Study of Compounds — Ammonia

Equation Worksheet

Question 1

Preparation of ammonia

Answer

Question 2

Chemical properties of ammonia

Answer

Question 3

As a reducing agent [ammonia gas]

Answer

Questions

Question 1(2004)

From NH₃, HCl, H₂S, SO₂ – Select :

(i) The gas which when bubbled through CuSO₄ soln., a deep blue coloured soln. is formed.

(ii) This gas burns in oxygen with a green flame.

Answer

(i) Ammonia (NH₃)

CuSO₄ + 2NH₄OH [ammonia soln.]⟶ (NH₄)₂SO₄ + Cu(OH)₂
Cu(OH)₂ + (NH₄)₂SO₄ + 2NH₄OH ⟶ [Cu(NH₃)₄]SO₄ + 4H₂O

(ii) Ammonia (NH₃)

4NH₃ + 3O₂ ⟶ 2N₂ + 6H₂O

Question 2(2004)

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

Answer

N₂ + 3H₂ ⇌ 2NH₃ + Δ

Question 3(2004)

State the purpose of liquefying the ammonia produced in the Haber’s process.

Answer

Liquefaction is a technique used for separating ammonia from the uncombined N₂ and H₂ reactant mixture during Haber's process.

Question 4(2004)

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

Answer

8NH₃ [excess] + 3Cl₂ ⟶ 6NH₄Cl + N₂

Question 1(2005)

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

Answer

Hydroxyl ion [OH^-1]

NH₃ + H₂O ⟶ NH₄OH

NH₄OH ⇌ NH₄⁺ + OH^-1

Question 2(2005)

Write equations for the formation of ammonia.

(i) NH₄Cl and slaked lime are heated.

(ii) Aluminium nitride and water.

Answer

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

(ii) AlN + 3H₂O ⟶ Al(OH)₃ + NH₃ [g]

Question 1(2006)

Select from the list — Ammonia, Copper oxide, Copper sulphate, Hydrogen chloride, Hydrogen sulphide, Lead bromide : The compound which is not a metal hydroxide but it's aqueous solution is alkaline in nature.

Answer

Ammonia.

Reason — The aq. soln. of ammonia [NH₄OH] is alkaline in nature due to the presence of hydroxyl ions [OH^-]

NH₃ + H₂O ⟶ NH₄OH

NH₄OH ⇌ NH₄⁺ + OH^-1

Question 2(2006)

From the substances — Ammonium sulphate, Lead carbonate, Chlorine, Copper nitrate, Iron [II] sulphate — State : A compound which on heating with NaOH produces a gas which forms dense white fumes with HCl.

Answer

Ammonium sulphate.

Reason — Ammonia gas is produced when ammonium sulphate reacts with NaOH. Ammonia gas forms dense white fumes with HCl.

(NH₄)₂SO₄ + 2NaOH ⟶ Na₂SO₄ + 2H₂O + 2NH₃[g]

Question 3(2006)

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

Answer

Lead hydroxide is precipitated, chalky white in colour and is insoluble in excess of ammonium hydroxide soln.

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

Question 4(2006)

Name the substance used for drying ammonia.

Answer

Quicklime (CaO) is used for drying ammonia.

Question 5(2006)

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

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]

Question 6(2006)

With reference to Haber’s process, write the equation and the conditions required.

Answer

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]

Precautions : Impurities like CO, CO₂, and H₂S may poison the catalyst hence, the nitrogen-hydrogen reactant mixture must be free from them.

Question 1(2007)

Give an equation for formation of ammonium sulphate from ammonia and dilute sulphuric acid.

Answer

2NH₃ + H₂SO₄ (dil.) ⟶ (NH₄)₂SO₄

Question 2(2007)

Give equation for – reaction in which NH₃ is oxidized by :

(i) a metal oxide

(ii) a gas which is not oxygen

Answer

(i) 2NH₃ + 3CuO ⟶ 3Cu + 3H₂O + N₂ [g]

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

Question 3(2007)

You enter a laboratory after a class has completed the Fountain Experiment. How will you be able to tell whether the gas used in the experiment was hydrogen chloride or ammonia.

Answer

If dry ammonia gas is present in the round bottom flask, the red litmus soln. kept in the trough below emerges out as a blue fountain since ammonia gas is basic in nature. On the other hand, if dry HCl was used in the flask instead of ammonia, the blue litmus soln. kept in the trough below, emerges out as a red fountain since HCl is acidic in nature.

Question 1(2008)

Ammonia can be obtained by adding water to : [Select the correct word]

1. Ammonium chloride
2. Ammonium nitrite
3. Magnesium nitride
4. Magnesium nitrate

Answer

Magnesium nitride
Mg₃N₂ + 6H₂O ⟶ 3Mg(OH)₂ + 2NH₃ [g]

Question 2(2008)

Name : An alkaline gas 'A' which gives dense white fumes with hydrogen chloride.

Answer

NH₃ (Ammonia)
NH₃ + HCl ⟶ NH₄Cl

Question 3(2008)

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

Answer

AlN + 3H₂O ⟶ Al(OH)₃ + NH₃ [g]

Question 4(2008)

Complete the table relating to an important industrial processes. [Output refers to the product of the process].

Answer

Completed table is shown below:

Question 1(2009)

Name the gas – that burns in oxygen with a green flame.

Answer

Ammonia (NH₃)
4NH₃ + 3O₂ ⟶ 2N₂ + 6H₂O

Question 2(2009)

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

Answer

Mg₃N₂ + 6H₂O ⟶ 3Mg(OH)₂ + 2NH₃ [g]

Question 3(2009)

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.

Question 1(2010)

Complete the blanks (a) to (e) 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 (a) .............. gas. When the same gas is passed through water, it forms a soln. which will be (b).............. in nature, and will contain the ions (c) .............. and (d) .............. .(e) A .............. coloured ppt. of iron [II] hydroxide is formed when the above solution is added to iron [II] sulphate solution.

Answer

(a) Ammonia

(b) Alkaline

(c) Ammonium

(d) Hydroxyl

(e) Dirty green

Question 2(2010)

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

Question 3(2010)

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

Answer

NH₄Cl + NaOH ⟶ NaCl + H₂O + NH₃

Question 4(2010)

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

Question 5(2010)

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]

Question 6(2010)

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.

Question 1(2011)

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

Question 2(2011)

The diagram 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.

Question 3(2011)

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

Answer

8NH₃ [excess] + 3Cl₂ ⟶ 6NH₄Cl + N₂

Question 4(2011)

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]

Question 1(2012)

Name the gas produced when excess ammonia reacts with chlorine.

Answer

Nitrogen

8NH₃ [excess] + 3Cl₂ ⟶ 6NH₄Cl + N₂

Question 2(2012)

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.

Question 3(2012)

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:

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

Question 4(2012)

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.

(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.

Question 1(2013)

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

Question 2(2013)

Nitrogen gas can be obtained by heating :

(a) Ammonium nitrate

(b) Ammonium nitrite

(c) Magnesium nitride

(d) Ammonium chloride

Answer

Ammonium nitrite

NH₄NO₂ ⟶ 2H₂O + N₂

Question 3(2013)

State two observations for : NH₄OH 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 ↓

Question 4(2013)

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

Answer

2NH₃ + 3CuO ⟶ 3Cu + 3H₂O + N₂ [g]

Question 5(2013)

State the - (i) Temperature (ii) Catalyst used in the Haber's process for manufacture of ammonia. Give the equation for the catalyzed reaction.

Answer

(i) Temperature : 450 to 500°C [Optimum temperature]

(ii) Catalyst : Finely divided iron (Fe)

(iii) Equation : N₂ + 3H₂ ⇌ 2NH₃ + Δ

Question 6(2013)

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

Answer

Ammonia gas.

NH₃ + HCl ⟶ NH₄Cl

Question 1(2014)

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.

Question 2(2014)

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

Answer

Mg₃N₂ + 6H₂O ⟶ 3Mg(OH)₂ + 2NH₃ [g]

Question 3(2014)

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. For example:

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

Question 4(2014)

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

Question 5(2014)

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

Question 6(2014)

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)

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

Question 1(2015)

From the list of the gases — Ammonia, ethane, hydrogen chloride, hydrogen sulphide, ethyne — 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]

Question 2(2015)

State one relevant observation — Ammonia gas is burnt in an atmosphere of excess oxygen.

Answer

4NH₃ + 3O₂ ⟶ 2N₂ + 6H₂O

Ammonia burns in the atmosphere of excess oxygen with a green or greenish yellow flame, forming nitrogen and water vapour.

Question 3(2015)

A metal ‘X’ has valency 2 and a non-metal ‘Y’ has a valency 3. If ‘Y ’ is a diatomic gas, write an equation for the direct combination of X and Y to from a compound.

Answer

X (metal) has a valency 2, hence,

X - 2e^- ⟶ X²⁺

Y (non metal) has a valency 3. hence,

Y + 3e^- ⟶ X^3-

Therefore, the two combine as :

3X + 2Y ⟶ X₃Y₂

Question 4(2015)

Give balanced chemical equations for —

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

(ii) Reaction of ammonia with excess 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

Question 1(2016)

Write balanced equations for :

(i) Action of warm water on AlN.

(ii) Excess of ammonia is treated with chlorine.

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

Answer

(i) AlN + 3H₂O ⟶ Al(OH)₃ + NH₃ [g]

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

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

Question 2(2016)

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

Question 1(2017)

Write the balanced chemical equation for each of the following —

(i) Reaction of ammonia with heated copper oxide.

(ii) Laboratory preparation of ammonia from ammonium chloride.

Answer

(i) 2NH₃ + 3CuO ⟶ 3Cu + 3H₂O + N₂ [g]

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

Question 2(2017)

State one relevant observation for the following reaction — Burning of ammonia in air.

Answer

Ammonia burns in the atmosphere of excess oxygen with a green or greenish yellow flame, forming nitrogen and water.

4NH₃ + 3O₂ ⟶ 2N₂ + 6H₂O

Question 3(2017)

Certain blanks spaces are left in the following tables as C, D & E. Identify each of them.

Answer

C : Magnesium nitride (Mg₃N₂) and water (H₂O).

D : Quick lime [CaO]

E : Downward displacement of air.

Question 4(2017)

Give a balanced chemical equation for each of the following —

(i) Catalytic oxidation of ammonia.

(ii) Reaction of ammonia with nitric acid.

Answer

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

(ii) NH₃ + HNO₃ ⟶ NH₄NO₃

Question 1(2018)

Write a balanced chemical equation — To prepare ammonia gas in the laboratory , by using an alkali.

Answer

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

Question 2(2018)

Give a reason why —

(i) Concentrated sulphuric acid, is not used for drying ammonia gas.

(ii) Ammonia gas is not collected over water.

Answer

(i) 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

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

Question 1(2019)

Fill in the blank with the choices given in the bracket: Ammonia reacts with excess chlorine to form ................ [nitrogen / nitrogen trichloride / ammonium chloride]

Answer

Ammonia reacts with excess chlorine to form nitrogen trichloride

Question 2(2019)

State one observation for the following : Ammonia gas is passed over heated copper [II] oxide.

Answer

Black copper [II] oxide is reduced to brown copper.

2NH₃ + 3CuO ⟶ 3Cu + 3H₂O + N₂ [g]

Question 3(2019)

Identify the substance italicized : The catalyst used to oxidize ammonia.

Answer

Platinum

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

Question 4(2019)

Name the gas evolved when : Ammonia reacts with heated copper [II] oxide.

Answer

Nitrogen

2NH₃ + 3CuO ⟶ 3Cu + 3H₂O + N₂ [g]

Question 5(2019)

Study the flowchart 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 : NH₃ + HCl ⟶ NH₄Cl

C: NH₄Cl + NaOH ⟶ NaCl + H₂O + NH₃ [g]

Question 6(2019)

Copy and complete the following table which refers to the industrial method for preparation of ammonia.

Answer

Name of the compound — Ammonia

Name of the process — Haber's process

Catalytic equation [with the catalyst] — $\text{N}_2 + 3\text{H}_2 \xrightleftharpoons[\text{450-500 \degree C}]{\text{Fe}} \text{2NH}_3 + \Delta$

Question 1(2020)

Write a balanced chemical equation for each of the following:

(i) Reaction of excess ammonia with chlorine.

(ii) Reaction of lead nitrate solution with ammonium hydroxide.

Answer

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

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

Question 2(2020)

Distinguish between the following pairs of compounds using a reagent as a chemical test.

Ammonium sulphate crystals and sodium sulphate crystals

Answer

Ammonium salts react with alkalis on heating to liberate Ammonia gas. Hence, we can use NaOH as reagent to distinguish between Ammonium Sulphate crystals and Sodium Sulphate crystals. Below is the reaction for the same:

(NH₄)₂SO₄ + 2NaOH ⟶ Na₂SO₄ + 2H₂O + 2NH₃ [g]

Question 3(2020)

Identify the substance underlined in the following sentence: The catalyst used to oxidize ammonia into nitric oxide.

Answer

Platinum

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

Additional Questions

Question 1

State why nitrogenous matter produces ammonia. State a liquid source of ammonia.

Answer

Ammonia is produced when nitrogenous matter decays in the absence of air. Putrefying bacteria on organic matter in the soil and the ammonifying bacteria on nitrogenous organic matter bring about decomposition and produces ammonia.

Urine is the liquid source of ammonia.

Question 2

Give the word equation and balanced molecular equation for the laboratory preparation of ammonia from NH₄Cl and calcium hydroxide.

Answer

Ammonium Chloride + Calcium Hydroxide ⟶ Calcium Chloride + Water + Ammonia

Question 3

Convert ammonium sulphate to ammonia using two different alkalis.

Answer

(NH₄)₂SO₄ + 2NaOH ⟶ Na₂SO₄ + 2H₂O + 2NH₃

(NH₄)₂SO₄ + Ca(OH)₂ ⟶ CaSO₄ + 2H₂O + 2NH₃

Question 4

State why ammonia is not obtained in the laboratory from NH₄NO₃ and NaOH.

Answer

As ammonium nitrate is explosive in nature and may itself decompose forming nitrous oxide and water vapour, hence a mixture of ammonium nitrate and NaOH are not used in the lab. preparation of ammonia gas.

Question 5

State the method used with reasons for drying and collecting ammonia gas.

Answer

The ammonia gas is passed through a drying tower before collection of the gas. The drying agent used is quicklime [CaO]
Reason — Quicklime being basic in nature does not react with basic ammonia gas. The drying agents not used are conc. H₂SO₄, P₂O₅ and fused CaCl₂ since they react chemically with ammonia.

Dry ammonia gas is collected by the downward displacement of air as it is lighter than air. Ammonia gas is not collected over water since it is highly soluble in water.

Question 6

State how you would convert (i) Mg (ii) Ca (iii) Al — to ammonia.

Answer

When metals like Mg, Ca and Al are burnt in Nitrogen gas, they form their respective metal nitrides i.e., Magnesium Nitride, Calcium Nitride and Aluminium Nitride as the products.
When warm water is added to these metal nitrides, they undergo hydrolysis decomposing to give pungent ammonia gas. The chemical reactions for each metal is given below:

1. Mg to NH₃
   3Mg + N₂ ⟶ Mg₃N₂
   Mg₃N₂ + 6H₂O ⟶ 3Mg(OH)₂ + 2NH₃ [g]

2. Ca to NH₃
   3Ca + N₂ ⟶ Ca₃N₂
   Ca₃N₂ + 6H₂O ⟶ 3Ca(OH)₂ + 2NH₃ [g]

3. Al to NH₃
   2Al + N₂ ⟶ 2AlN
   AlN + 3H₂O ⟶ Al(OH)₃ + NH₃ [g]

Question 7

Give a balanced equation with all conditions to obtain NH₃ from N₂ and H₂.

Answer

Nitrogen reacts with hydrogen under specific conditions liberating ammonia.

Below balanced equation represents this reaction :

N₂ + 3H₂ ⇌ 2NH₃ + Δ

Conditions :

Temperature : 450-500°C [Optimum temperature]

Pressure : 200-900 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]

Question 8

State two physical properties of NH₃ which enable separation of NH₃ from a mixture of NH₃, N₂ and H₂.

Answer

Ammonia is separated and recovered from the uncombined nitrogen and hydrogen by technique based on the physical properties of ammonia.

1. Ammonia is easily liquefiable — It condenses to a liquid at around -33°C at 8 atmosphere pressure. N₂ and H₂ are difficult to liquify. They condense at temperatures around -196°C and -253°C respectively and at comparatively higher pressures.
2. Ammonia is highly soluble in water — 1 vol of water dissolves about 702 vols. of ammonia at 20°C and 1 atmosphere pressure. N₂ and H₂ are almost insoluble in water.

Question 9

Compare the density of ammonia with that of air. Name two gases lighter than ammonia.

Answer

Ammonia is lighter than air. The vapour density of ammonia is 8.5 while that of air is 14.4.

The two gases lighter than ammonia are :

1. Hydrogen
2. Helium.

Question 10

'Ammonia is highly soluble in water'. Name two other gases showing similar solubility.

Answer

Other gases highly soluble in water are :

1. Hydrogen chloride
2. Sulphur dioxide

Question 11

Name the experiment and state it's procedure to demonstrate the high solubility of ammonia.

Answer

Fountain Experiment demonstrates the high solubility of ammonia in water.

Apparatus:

• Dry round bottom flask filled with ammonia gas.
• Mouth of the flask has a rubber stopper with two holes for (a) Jet tube, (b) Dropper containing water.
• Red litmus solution is placed in the trough below.

Procedure:

• The dropper containing water is squeezed and water enters the flask.

Observation:

• Ammonia gas present in the flask dissolves in water due to it's high solubility, thereby creating a partial vacuum in the flask.
• The outside pressure being higher pushes the red litmus solution up the jet tube which emerges out at the end of the tube as a blue fountain.

Inference:

• Ammonia gas is highly soluble in water and basic in nature.

Question 12

Give an equation for the burning of ammonia in oxygen. State the observation seen.

Answer

4NH₃ + 3O₂ ⟶ 2N₂ + 6H₂O

Ammonia burns in the atmosphere of excess oxygen with a green or greenish yellow flame, forming nitrogen and water vapour.

Question 13

Convert ammonia to nitric oxide by catalytic oxidation of ammonia. State all conditions.

Answer

Reaction:

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

Conditions:
Temperature : 800°C
Catalyst : Platinum (Pt)

Question 14

Draw a simple diagram for the catalytic oxidation of ammonia in the laboratory.

Answer

Below diagram shows the setup for catalytic oxidation of ammonia:

Question 15

Give reasons for the observation seen during catalytic oxidation of ammonia.

Answer

Following are the observations with reasons:

• The colourless nitric oxide formed, on oxidation gives reddish brown nitrogen dioxide
  2NO + O₂ ⟶ 2NO₂
• The platinum [catalyst] continues to glow even after the heating is discontinued since the catalytic oxidation of ammonia is an exothermic reaction.

Question 16

Name an industrial process which involves ammonia, oxygen and a catalyst as it's starting reactants.

Answer

Ostwald’s process for preparing nitric acid.

Question 17

State what an aqueous solution of NH₃ is called. State how it is prepared giving reasons.

Answer

An aqueous solution of NH₃ is called Liquor Ammonia.

Preparation:
By dissolving ammonia gas in water using a funnel arrangement.

Reasons:

• Prevents back suction of water and
• Provides a large surface area for absorption of ammonia gas.

NH₃ + H₂O ⟶ NH₄OH [liquor ammonia]

Question 18

State why an aq. soln. of NH₃

(i) turns red litmus blue

(ii) is a weak base and a weak electrolyte.

Answer

(i) The alkaline behaviour of aq. soln. of ammonia [NH₄OH] is due to the presence of hydroxyl ions [OH^-]. Hence, the aq. soln. of ammonia turns red litmus blue.

(ii) The aq. soln. of ammonia [NH₄OH] is alkaline. It undergoes partial dissociation in aq. soln. to give hydroxyl ions [OH^-] in low concentration. Therefore, it is a weak base and a weak electrolyte.

Question 19

State two different methods of preparing NH₄Cl using hydrochloric acid.

Answer

Below are the two methods of preparing NH₄Cl using hydrochloric acid:

1. NH₃ + HCl (dil.) ⟶ NH₄Cl
2. NH₄OH + HCl (dil.) ⟶ NH₄Cl + H₂O

Question 20

Convert (i) ammonia (ii) ammonium hydroxide to an ammonium salt using (a) HNO₃ (b) H₂SO₄

Answer

1. Ammonia to ammonium salt:
   (a) NH₃ + HNO₃ (dil.) ⟶ NH₄NO₃
   (b) 2NH₃ + H₂SO₄ (dil.) ⟶ (NH₄)₂SO₄
2. Ammonium hydroxide to ammonium salt:
   (a) NH₄OH + HNO₃ (dil.) ⟶ NH₄NO₃ + H₂O
   (b) 2NH₄OH + H₂SO₄ (dil.) ⟶ (NH₄)₂SO₄ + 2H₂O

Question 21

State a reason why reaction of liquor ammonia with nitric acid is a neutralization reaction.

Answer

As liquor ammonia is an alkali due to the presence of hydroxyl ions.

NH₃ + H₂O ⟶ NH₄OH

NH₄OH ⇌ NH₄⁺ + OH^-1

When an acid (nitric acid) and an alkali or base combine completely to form salt and water then the reaction is called a neutralization reaction.

NH₄OH + HNO₃ ⟶ NH₄NO₃ + H₂O

Hence, the reaction between liquor ammonia and nitric acid is a neutralization reaction.

Question 22

State why an aqueous solution of ammonia (NH₄OH) is used for identifying cations.

Answer

The precipitate which are hydroxides of metallic radicals vary in :

• colour
• solubility in excess of NH₄OH

Hence, ammonium hydroxide is used in qualitative analysis for identifying positive radicals or cations.

Question 23

State how NH₄OH is used for identifying:

1. Fe²⁺
2. Fe³⁺
3. Pb²⁺
4. Zn²⁺
5. Cu²⁺ cations.

Give also a balanced equation in each case for a known example.

Answer

1. A soln. of Fe²⁺ ions gives dirty green ppt. which is insoluble in excess of NH₄OH.
   FeSO₄ + 2NH₄OH ⟶ (NH₄)₂SO₄+ Fe(OH)₂ ↓

2. A soln. of Fe³⁺ ions gives reddish brown ppt. which is insoluble in excess of NH₄OH
   FeCl₃ + 3NH₄OH ⟶ 3NH₄Cl + Fe(OH)₃ ↓

3. A soln. of Pb²⁺ ions gives chalky white ppt. which is insoluble in excess of NH₄OH
   Pb(NO₃)₂ + 2NH₄OH ⟶ 2NH₄NO₃ + Pb(OH)₂ ↓

4. A soln. of Zn²⁺ ions gives gelatinous white ppt. which is soluble in excess of NH₄OH
   ZnSO₄ + 2NH₄OH ⟶ (NH₄)₂SO₄ + Zn(OH)₂ ↓
   Zn(OH)₂ + (NH₄)₂SO₄ + 2NH₄OH ⟶ [Zn(NH₃)₄]SO₄ + 4H₂O

5. A soln. of Cu²⁺ ions gives pale blue ppt. which is soluble in excess of NH₄OH
   CuSO₄ + 2NH₄OH ⟶ (NH₄)₂SO₄ + Cu(OH)₂ ↓
   Cu(OH)₂ + (NH₄)₂SO₄ + 2NH₄OH ⟶ [Cu(NH₃)₄]SO₄ + 4H₂O

Question 24

State why the blue ppt. formed on addition of NH₄OH to CuSO₄ soln. dissolves to give a deep blue solution with excess of NH₄OH. Give an equation for the reaction. State why Zn(OH)₂ is soluble in excess of NH₄OH.

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 pale blue ppt. of copper hydroxide is soluble in excess of a NH₄OH, since a soluble complex [Cu(NH₃)₄]SO₄ [tetrammine copper [II] sulphate] is formed.

Zinc salt forms a white gelatinous ppt. of Zn(OH)₂, which dissolves when excess of ammonium hydroxide is added due to the formation of [Zn(NH₃)₄]SO₄

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

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

Question 25

Give balanced equations for the reducing reactions of ammonia with

(i) copper (II) oxide,

(ii) lead (II) oxide,

(iii) chlorine using (a) excess NH₃ (b) excess Cl₂

Answer

(i) 2NH₃ + 3CuO ⟶ 3Cu + 3H₂O + N₂ [g]

(ii) 2NH₃ + 3PbO ⟶ 3Pb + 3H₂O + N₂ [g]

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

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

Question 26

State five tests for ammonia where a colour change is involved.

Answer

Five tests for ammonia

Ammonia turns —

1. Red litmus solution to blue.
2. Methyl orange solution to yellow.
3. Colourless phenolphthalein solution to pink.
4. Pale blue precipitate of CuSO₄ into deep blue coloured solution
5. Colourless Nesseler's reagent to pale brown.

Question 27

State (i) a light neutral gas (ii) an acid (iii) an explosive (iv) a fertilizer — obtained from ammonia.

Answer

(i) Hydrogen

(ii) Nitric acid

(iii) Ammonium nitrate (NH₄NO₃)

(iv) Ammonium sulphate [(NH₄)₂SO₄]

Question 28

Name an ammonium salt which is a constituent of

(a) smelling salts

(b) dry cells.

Give reasons for the use of the named ammonium salt for the same.

Answer

(a) Ammonium Carbonate, [(NH₄)₂CO₃] is used as smelling salt. It dissociates evolving pungent ammonia gas and hence is used as a constituent for smelling salts.

(NH₄)₂CO₃ ⟶ 2NH₃ + CO₂ + H₂O

The pungent smelling NH₃ gas revives a fainted person.

(b) Ammonium Chloride (NH₄Cl) is used in dry cells. It oxidizes Zn to Zn²⁺ ions. The electrons so produced constitute the electric current.

Question 29

Give one use with reason of

(i) an aqueous solution of NH₃

(ii) liquefied NH₃.

Answer

(i) An aqueous solution of NH₃ is called Liquor Ammonia. It is used as a cleaning agent to remove oil or grease stains from clothes, cleaning window panes, porcelain articles, etc as it emulsifies or dissolves fats, grease etc.

(ii) Liquefied NH₃ is used as refrigerant because (a) it is highly volatile and has a high latent heat of evaporation. (b) it easily liquefies under pressure, at low temperature.

Question 30

State what are chlorofluorocarbons and give their use. Give a reason why they are ozone depleting. State a suitable alternative to chlorofluorocarbons which are non-ozone depleting.

Answer

Chlorofluorocarbons (CFC’s) are compounds of carbon with chlorine or fluorine. CFC are chemicals which like liquefied ammonia gas are used in refrigeration gas.

They enter the atmosphere due to their use as coolants in refrigeration and A/C plants and aerosol sprays and cause ozone depletion in the atmosphere.

Chlorofluorocarbons (CFC’s) are decomposed by U.V. rays to give free Cl radicals.

CFCl₃ ⟶ Cl atom

This Cl atom breaks the ozone layer causing ozone depletion.

Cl + O₃ [ozone] ⟶ ClO + O₂

Hence, ozone layer located in the stratosphere above the earth, which prevents harmful U.V. rays from reaching the earth, gets depleted.

Suitable alternatives to chlorofluorocarbons which are non-ozone depleting include Hydrochlorofluorocarbons [HCFC]

Unit Test Paper 7B — Ammonia

Question 1

Choose the letter corresponding to the correct answer from — A : NO₂, B : NO, C : N₂, D : N₂O

The gas obtained when –

1. Dry ammonia and dry oxygen gas are ignited together.
2. Ammonia is passed over heated litharge.
3. A greenish yellow gas reacts with excess ammonia.
4. (a) Dry NH₃ and O₂ are passed over heated Pt.
   (b) The gaseous product obtained is further oxidized.
5. Ammonium nitrite undergoes thermal decomposition.

Answer

1. Dry ammonia and dry oxygen gas are ignited together. — C : N₂
2. Ammonia is passed over heated litharge. — C : N₂
3. A greenish yellow gas reacts with excess ammonia. — C : N₂
4. (a) Dry NH₃ and O₂ are passed over heated Pt. — B : NO
   (b) The gaseous product obtained is further oxidized. — A : NO₂
5. Ammonium nitrite undergoes thermal decomposition. — C : N₂

Question 2

State the colour of :

1. Phenolphthalein solution after passage of ammonia through it.
2. Copper (II) hydroxide solution after addition of ammonium hydroxide in excess to it.
3. The flame obtained on burning dry ammonia in oxygen.
4. The solution obtained on addition of excess ammonium hydroxide to zinc sulphate solution.
5. The vapours obtained when ammonia-oxygen gas mixture is passed over heated Pt.

Answer

1. Pink colour
2. Deep blue coloured solution
3. Green or greenish yellow flame
4. White gelatinous precipitate soluble in excess of ammonium hydroxide
5. The colourless nitric oxide formed, on oxidation gives reddish brown nitrogen dioxide.

Question 3

Give balanced equations for the following conversions — A, B, C, D and E.

1. $\text{NH}_4\text{OH} \xrightarrow{\text{A}} (\text{NH}_4)_2\text{SO}_4 \xrightarrow{\text{B}} \text{NH}_3$
2. $\text{NH}_4\text{Cl} \xleftarrow{\text{C}} (\text{NH}_3) \xrightarrow{\text{D}} \text{NH}_4\text{Cl}$
3. $\text{NH}_3 \xrightarrow{\text{E}} \text{N}_2$

Answer

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

• B : (NH₄)₂SO₄ + 2NaOH ⟶ Na₂SO₄ + 2H₂O + 2NH₃ [g]

• C : NH₃ + HCl ⟶ NH₄Cl

• D : 8NH₃ [excess] + 3Cl₂ ⟶ 6NH₄Cl + N₂

• E : 4NH₃ + 3O₂ ⟶ 2N₂ + 6H₂O

Question 4.1

Give reasons for the following:

An aqueous solution of ammonia acts as a weak base.

Answer

The alkaline behaviour of NH₄OH is due to the presence of hydroxyl ions [OH^-]. It acts as a weak base, since it undergoes partial dissociation in aq. soln. to give hydroxyl ions [OH^-] in low concentration.

Question 4.2

Give reasons for the following:

A mixture of ammonium nitrate and slaked lime are not used in the lab. preparation of ammonia gas.

Answer

As ammonium nitrate is explosive in nature and may itself decompose forming nitrous oxide and water vapour, hence a mixture of ammonium nitrate and slaked lime are not used in the lab. preparation of ammonia gas.

Question 4.3

Give reasons for the following:

Finely divided iron catalyst does not affect the percentage yield of ammonia in Haber’s process.

Answer

The catalyst only accelerates the reaction and does not form a part of the reaction and hence it does not affect the percentage yield of ammonia in Haber’s process.

Question 4.4

Give reasons for the following:

Ammonium salts are formed when ammonia reacts with dilute acids in the gaseous or aq. medium.

Answer

Ammonia gas or aqueous solution of Ammonia is basic in nature. Hence, reaction between dilute acids and ammonia is a neutralization reaction between an acid and a base forming salt and water as the end products. Therefore, ammonium salts are formed when ammonia reacts with dilute acids in the gaseous or aq. medium.

Question 4.5

Give reasons for the following:

Aqueous solution of lead and zinc nitrate can be distinguished using an aqueous solution of ammonia.

Answer

A lead salt gives a chalky white ppt. on reaction with ammonium hydroxide which does not dissolve when excess of ammonium hydroxide is added.

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 easily distinguished using an aqueous solution of ammonia.

Question 5

Complete the statements by selecting the correct word from the words in brackets.

1. The salt solution which does not give an insoluble precipitate on addition of ammonium hydroxide in small amount is .............. [Mg(NO₃)₂/NaNO₃/Cu(NO₃)₂]
2. The alkaline behaviour of liquor ammonia is due to the presence of .............. ions, [ammonium/hydronium/hydroxyl]
3. Ammonia in the liquefied form is .............. [acidic/basic/ neutral]
4. Ammonia reduces chlorine to .............. [nitrogen/hydrogen chloride/ ammonium chloride]
5. The chemical not responsible for ozone depletion is .............. [methyl chloride / ammonia / chloroflourocarbons]

Answer

1. The salt solution which does not give an insoluble precipitate on addition of ammonium hydroxide in small amount is NaNO₃
2. The alkaline behaviour of liquor ammonia is due to the presence of hydroxyl ions.
3. Ammonia in the liquefied form is basic
4. Ammonia reduces chlorine to hydrogen chloride
5. The chemical not responsible for ozone depletion is ammonia

Question 6

Select the most probable substance from A, B, C, D and E which need to be added to distinguish :

Answer