Compounds of Nitrogen

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In today’s Chemistry class, We will be learning about Compounds of Nitrogen. We hope you enjoy the class!

 

 

CONTENT

• Oxides of Nitrogen
• Ammonia: Preparation, Properties and Uses.
• Trioxonitrate (V) acid: Preparation, Properties and Uses.

 

OXIDES OF NITROGEN

NITROGEN (I) OXIDE, N₂O

Nitrogen (I) oxide is known as laughing gas as it causes uncontrollable laughter when inhaled.

LABORATORY PREPARATION

The gas is prepared in the laboratory by thermal decomposition of ammonium trioxonitrate (V). Ammonium trioxonitrate (V) is not heated directly since the reaction is exothermic and may become uncontrollable leading to an explosion.

a. KNO_3(s) + NH₄Cl_(s) →   KCl_(s) + NH₄NO_3(s)

b. NH₄NO_3(s)      →        2H₂O_(g) + N₂O_(g)

 

PHYSICAL PROPERTIES

1. It is a colourless gas with a faint pleasant sickly smell and it has a sweetish taste.
2. It is fairly soluble in cold water.
3. It is 1.5 times denser than air.
4. It is neutral to moist litmus paper.

 

CHEMICAL PROPERTIES

1. It decomposes on strong heating (about 600^oC) to form nitrogen and oxygen.

2N₂O_(g) → O_2(g)  +          2N_2(g)

2. It supports the combustion of any burning substance which is hot enough to decompose it.

Mg_(s)  +  N₂O_(g)  → MgO_(s)  + N_2(g)

1. It is reduced to nitrogen by heated copper or iron

Cu_(s) + N₂O_(g)     →  N_2(g)  + CuO_(s)

 

TEST FOR N₂O

A glowing splinter is inserted into the gas jar containing the unknown gas. If the splinter is rekindled, the gas is either oxygen or nitrogen (I) oxide. If the gas has a pleasant smell and does not produce brown fumes with nitrogen (IV) oxide; then the gas is nitrogen (I) oxide.

USE: Nitrogen (I) oxide is used as an anesthetic for minor surgical operations.

 

EVALUATION

1. Describe the laboratory preparation of nitrogen (I) oxide.
2. Describe a test to distinguish between nitrogen (I) oxide and oxygen gas.

 

NITROGEN (II) OXIDE, NO

LABORATORY PREPARATION

Nitrogen (II) oxide is prepared by reacting 50% trioxonitrate (IV) acid with copper.

3Cu_(s) + 8HNO_3(aq)  →  3Cu(NO₃)_2(aq)  +  4H₂O_(l) + 2NO_(g)

Some of the nitrogen (II) oxide gas reacts with oxygen in the flask to form brown fumes of nitrogen (IV) oxide which is dissolved in water as the gas is passed through water.

 

PHYSICAL PROPERTIES

1. It is a colourless and poisonous gas.
2. It is almost insoluble in water.
3. It is slightly denser than air.
4. It is neutral to litmus.

CHEMICAL PROPERTIES

1. It reacts readily with oxygen to form brown fumes of nitrogen (IV) oxide

2NO_(g)   +    O_2(g) → 2NO_2(g)

2. It decomposes on heating at high temperature to form an equal volume of nitrogen and oxygen

2NO_(s)→ N_2(g) + O_2(g)

3. It is reduced to nitrogen by hot metals

2Cu_(s)    +    2NO_(g) →  2CuO_(g) + N_2(g)

4. It acts as reducing agent decolourizing acidified potassium tetraoxomanganate (VI) slowly

3MnO₄^–_(aq)  +  4H⁺_(aq)  + 5NO_(g)   →  3Mn²⁺_(aq)  +  5NO₃^–_(aq) +  2H₂O_(l)

 

TEST FOR NO

1. Using air: the gas jar containing the unknown gas is opened, if the gas turns reddish-brown, then the gas is NO.
2. Using iron (II) tetraoxosulphate (VI): A solution of FeSO₄ which has been acidified with a little dilute H₂SO₄ acid is poured into the gas jar containing the unknown gas. If the solution turns dark brown, then the gas is NO.

 

EVALUATION

1. Give an equation to show the laboratory preparation of nitrogen (II) oxide.
2. State TWO physical and TWO chemical properties of nitrogen (II) oxide.

 

 

NITROGEN (IV) OXIDE, NO₂

LABORATORY PREPARATION

Nitrogen (IV) oxide is prepared by thermal decomposition of lead (II) trioxonitrate (V) because the nitrate does not contain water of crystallization which can interfere with the preparation.

Pb(NO₃)_2(s) → 2PbO_(s)    +    O_2(g)   +   4NO_2(g)

The gas mixture obtained is passed through a U- tube immersed in a freezing mixture. Nitrogen (IV) oxide liquefies as a green liquid (yellow if pure) in the tube while oxygen escapes out.

 

PHYSICAL PROPERTIES

1. It is a reddish-brown gas.
2. It has an irritating smell and is poisonous.
3. It turns damp blue litmus paper red and dissolves in water to form an acidic solution.
4. It liquefies into a yellow liquid at 21^o
5. It is much heavier than air.

 

CHEMICAL PROPERTIES

1. Nitrogen (IV) oxide exists mainly as dinitrogen (IV) oxide, N₂O₄ at low temperature. It decomposes on heating as follows.

N₂O_4(g)                 2NO_2(g)                    2NO_(g) + O_2(g)

Pale                     Reddish                      colourless

yellow                 brown

 

2. It supports combustion as it decomposes on heating to nitrogen and oxygen

2NO_2(g) →     N_2(g)  + 2O_2(g)

 

3. It is reduced to nitrogen by reducing agent.

4CU_(s)  + 2NO_(g)       →  4CuO_(s) + N_2(g)

 

4. It dissolves in water to form a mixture of dioxonitrate (III) and trioxonitrate (V) acids. It is a mixed acid anhydride.

H₂O_(l)  +  2NO_2(g)   → HNO_2(aq) + HNO_3(aq)

 

5. It reacts with alkalis to form mixture of dioxonitrate (III) and trioxonitrate (V) salts

2KOH_(aq) + 2NO_2(g) → KNO_3(aq)   +   KNO_2(aq)   +   H₂O_(l)

 

 

AMMONIA

Ammonia is a hydride of nitrogen. It is produced in nature when nitrogenous matter decays in the absence of air. Thus, traces of ammonia may be found in the atmosphere but is very soluble in water, it is dissolved by rainwater and washed down into the soil.

 

LABORATORY PREPARATION OF AMMONIA

Ammonia is prepared in the laboratory by heating calcium hydroxide, Ca(OH)₂ (slaked lime) with ammonium chloride.

Ca(OH)_2(s)+ 2NH₄Cl_(s)        →  CaCl_2(s) +2H₂O_(l)+2NH_3(g).

Ammonia is dried using calcium oxide, CaO. Ammonia being alkaline cannot be dried using Conc. H₂SO₄ or fused CaCl₂, because they will react.

INDUSTRIAL PREPARATION

Ammonia is manufactured from nitrogen and hydrogen by the Haber process. It involves mixing nitrogen and hydrogen in ratio 1:3 by volume. The reaction is reversible so special conditions listed below are required for an optional yield of ammonia.

1. Finely divided iron catalyst is used
2. A temperature of about 450^Oc is used
3. A pressure of about 200atm is used.

 

The yield is about 15% under this condition

N_2(g) +3H_2(g)                     2NH_3(g) + heat

 

 

 

PHYSICAL PROPERTIES

1. It is a colourless gas with a characteristic choking smell.
2. Ammonia in large quantity is poisonous as it affects respiratory muscles.
3. It is the only known alkaline gas.
4. It is about 1.7 times less dense than air.
5. Solid ammonia melts at -34.4^OC and the liquid boils at -77.7^O

 

CHEMICAL PROPERTIES

1. Ammonia burns readily in oxygen to form water vapor and nitrogen

4NH_3(g)   +  3O_2(g)   →         6H₂O_(g)  +  2N_2(g)

2. Ammonia reacts as reducing agents reacting with

A. Copper II oxide

3CuO_(s) + 2NH_3(g) →   3Cu_(s) +  3H₂O_(l) + N_2(g)

B. Chlorine

3Cl_2(g) +  8NH_3(g)      →      6NH₄Cl_(s)         +  N_2(g)

3. Ammonia reacts with carbon IV oxide to form Urea and water vapour.

2NH_3(g)   +   CO_2(g)  →  (NH₂)₂ CO_(s)        + H₂O_(l)

^urea

4. Ammonia reacts with acid to form ammoniums salts.

2NH_3(g)  +  H₂SO_4(g)  →  (NH₄)₂SO_4(s)

 

 

 TEST FOR AMMONIA

Ammonia has a choking smell. It can be confirmed using:

1. Litmus paper: Damped red litmus is dipped into the gas jar containing the unknown gas. If the litmus paper turns blue, then the gas is ammonia.
2. Hydrochloric acid: a glass rod is dipped in concentrated HCl and then inserted in the gas jar containing the unknown gas. If white fumes are observed on the glass rod, then the gas is ammonia.

 

USES OF AMMONIA

1. Ammonia is used in the manufacture of trioxonitrate (V) acid and Sodium trioxocarbonate (IV) by the Solvay process.
2. Liquid ammonia is used as a refrigerant.
3. Aqueous ammonia is used in softening temporary hard water.
4. Aqueous ammonia is also used in laundries as a solvent for removing grease and oil stains.

 

EVALUATION

1. Briefly describe the laboratory preparation of ammonia.
2. StateTWO physical and THREE chemical properties each of ammonia.

 

TRIOXONITRATE (V) ACID, HNO₃

LABORATORY PREPARATION

Trioxonitrate (V) acid is a volatile acid and it is prepared in the laboratory by its displacement from any trioxonitrate salt by concentrated H₂SO₄ which is less volatile. Trioxonitrate (V) of potassium or sodium is usually used because they are cheap.

KNO_3(s)    +   H₂SO_4(aq)         →  KHSO_4(aq)  +  HNO_3(aq)

 

NOTE: An all-glass apparatus must be used in this preparation because the hydrogen trioxonitrate (V) acid vapour will attack cork or rubber.

INDUSTRIAL PREPARATION

Trioxonitrate (V) acid is obtained by the catalytic oxidation of ammonia:

–    Ammonia is treated with excess air using Platinum-rhodium catalyst at 700^oC to produce nitrogen (II) oxide (96% conversion of NH₃ is obtained)

4NH_3(g)    +    5O_2(g) → 4NO_(g)  +  6H₂O_(g)

–    Nitrogen (II) oxide formed is cooled and mixed with excess air to produce nitrogen (IV) oxide.

2NO_(g)    +    O_2(g)    →  2NO₂(g)

–    Nitrogen (IV) oxide formed is dissolved with excess air in hot water to yield trioxonitrate (V) acid solution of up to 50% concentration.

4NO_2(g)  +  2H₂O_(l)  +    O_2(g) →  4HNO_3(aq)

 

PHYSICAL PROPERTIES

1. The pure acid is a colourless fuming liquid with a sharp choking smell. The acid turns yellow due to its decomposition to nitrogen (IV) oxide which redissolves in the acid.
2. The pure acid boils at 86⁰C and melts at -47^oC
3. The density of the pure acid is 1.52 gcm^-3
4. The pure acid is miscible with water in all properties and forms a constant boiling mixture with it at 121^oC
5. The concentrated form of the acid is corrosive.
6. The dilute acid turns blue litmus red.

 

CHEMICAL PROPERTIES

1. As an acid it neutralizes bases and alkalis to form metallic trioxonitrate (V) and water only

NaOH_(aq) + HNO_3(aq)          →  NaNO_3(aq) + H₂O_(l)

2. As an acids it reacts with metallic trioxocarbonate (IV) to liberate carbon (II) oxide

CaCO_3(s)   +    HNO_3(aq)     → Ca(NO₃)_2(aq)  +   H₂O_(l)  + CO_2(g)

3. Unlike other acids, it rarely gives out hydrogen with metals except when very dilute solution is reacted with Ca, Mg or Mn.
4. As an oxidizing agent, it reacts with non – metal to form the corresponding oxides of the non – metals.

S_(s) + 6HNO_3(aq)   →  H₂SO_4(aq) + 2H₂O_(l) +    6NO_2(g)

5. As an oxidizing agent, it oxidizes Cu, Pb, Hg and Ag to yield the respective trioxonitrate (V) and nitrogen (IV) oxide if concentrated, but nitrogen (II) oxide if the concentration is moderate.

Aluminum and iron are not oxidized to their oxides by concentrated HNO_3(aq) due to formation of a surface coating of oxide which is passive do not allow further reaction with the metals. Aluminum or iron lined container can be used to transport concentrated HNO_3(aq)

6. As an oxidizing agent, it oxidizes hydrogen sulphide to sulphur

H₂S_(g) + 2HNO_3(aq)  →         S_(s)  + 2H₂O_(l)  +  2NO_2(g)

7. As an oxidizing agent, it oxidizes iron (II) salts to iron (III) salts

6Fe²⁺_(aq) + 8H⁺_(aq) + 2NO₃^–_(aq)      →   6Fe³⁺_(aq) + 4H₂O_(l) + 2NO_(g)

 

USES

1. It is used as an acid, oxidizing agent and nitrating agent in the laboratory.
2. It is used in nylon production and Terylene.
3. It is used as rocket fuel.
4. It is used in the production of fertilizers, dyes, drugs and explosives.

 

GENERAL EVALUATION/REVISION

1. Describe the laboratory preparation of trioxonitrate (V) acid.
2. Write TWO equations of reactions in which trioxonitrate (V) is acting as an acid.
3. Write an equation to show the reaction of nitrogen (IV) oxide as a mixed anhydride.
4. Describe the electrolysis of CuSO₄ solution using platinum electrodes.
5. Classify the following oxides: CuO, Na₂O, PbO, NO₂, N₂O

 

 

 

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In our next class, we will be learning about Sulphur. We are very much eager to meet you there.

 

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