PHYSICAL PROPERTIES OF AMMONIA

SECOND TERM E-LEARNING NOTES

SUBJECT: CHEMISTRY

CLASS: SS 2

SCHEME OF WORK

WEEK 6

TOPIC: NITROGEN

CONTENTS:

1. GENERAL PROPERTIES OF NITROGEN–GROUP VA ELEMENTS, LABORATORY AND INDUSTRIAL PREPARATION OF NITROGEN,
2. PROPERTIES AND USES OF NITROGEN
3. COMPOUND OF NITROGEN – AMMONIA- LABORATORY AND INDUSTRIAL PREPARATION
4. PROPERTIES AND USES, TEST FOR AMMONIA, FOUNTAIN EXPERIMENT

PERIOD 3: COMPOUNDS OF NITROGEN-AMMONIA LABORATORY AND INDUSTRIAL PREPARATION

OXIDES OF NITROGEN

The common oxides of nitrogen are:-Dinitrogen(i) oxide, N₂O- Nitrogen (ii) oxide, NO. Nitrogen (iv) oxide, NO₂, others are dinitrogen(iii) oxide, N₂O_3, a pale blue liquid at room temperature and dinitrogen(iv) oxide, N₂O₄, a yellow liquid below the room temperature and dinitrogen(v) oxide N₂O₅ that exists as an unusual white solid at room temperature.

AMMONIA

INDUSTRIAL PRODUCTION OF AMMONIA

The Haber process: Ammonia is manufactured from its constituent elements by a process devised by a German chemist, Fritz Haber (1914). The raw materials used are: nitrogen (obtained from water gas or natural gas).A mixture of dried nitrogen and hydrogen in the ratio 1:3 by volume is subjected to a high pressure of 200 – 250 atmosphere, at about 450 and in the presence of finely divided iron as the catalyst; the reaction is exothermic and reversible

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

Under these conditions, about 20% ammonia is produced.

Successive heating and cooling under pressure liquefy the ammonia gas produced and the uncombined nitrogen and hydrogen are recycled. The flow chart for the production of ammonia is shown

Mixture in a drier

Mixture over finely

Divided catalyst + heat +pressure

Ammonia liquefied and removed

LABORATORY PREPARATION OF AMMONIA:

Ammonia is prepared in the laboratory by heating a mixture of ammonium salt and non-volatile base. Calcium hydroxide is preferred to sodium hydroxide because calcium hydroxide is cheap and non-deliquescent. Heating a mixture of ammonium chloride and calcium hydroxide produces ammonia gas. The drying agent for ammonia is calcium oxide (quick lime). Concentrated tetraoxosulphate (vi) acid and calcium chloride are not used to dry ammonia because they react with ammonia to form salts

NH₄Cl + Ca(OH)₂ CaCl₂ + H₂O + NH₃

EVALUATION

1. State the type of chemical bond between nitrogen and hydrogen atoms in a molecule of ammonia.
2. In the industrial production of ammonia.
3. What name is given to the process?
4. State one source of each of the starting material.[mediator_tech]
5. What are the operating temperature and pressure?

PERIOD 4: PROPERTIES AND USES, TEST FOR AMMONIA, FOUNTAIN EXPERIMENT

PHYSICAL PROPERTIES OF AMMONIA:

1. It is a colourless gas with choking smell.
2. It is very soluble in water.
3. In large quantities, ammonia is poisonous.
4. It is 1.7 times less dense than air
5. It turns moist red litmus paper red.

CHEMICAL PROPERTIES OF AMMONIA

1. Ammonia burns in oxygen producing steam and nitrogen

4NH₃ + 3O₂ 2N₂ + 6H₂O

Ammonia reacts with platinium- rhodium catalyst to form nitrogen (ii) oxide.

4NH₃ + 5O₂ 4NO + 6H₂O

1. Ammonia reduces copper (ii) oxide

2NH₃ + 3CuO 3Cu + 3H₂O + N₂

1. Ammonium precipitates many metallic ions from solution as insoluble hydroxides.

FeSO_4(aq) + 2NH_3(aq) + 2H₂O_(l) Fe(OH)_2(s) + (NH₄)₂SO_4(aq)

^{green ppt}

USES OF AMMONIA

1. Ammonia is used in refrigeration, since it can be liquefied easily.
2. In softening water used in laundry, to prevent wastage of soap.
3. As a domestic cleaner- to neutralize as in sweat.
4. In treating insect stings- to neutralize methanoic acid injected by the insects
5. In the production of plastics by polymerization
6. In the production of ammonium salts. Fertilizer and trioxonitrate(v) acid.
7. As a precipitating regent for the identification of cations in solutions.

TEST FOR AMMONIA GAS

Place any ammonia salt in a test tube, add any alkali and heat the mixture. A colourless gas with choking smell is given off. The gas turns moist red litmus paper to blue and produces dense white fumes with hydrogen chloride gas (from concentrated HCl reagent bottle. The gas is ammonia

EVALUATION:

1. State four physical properties of ammonia
2. With chemical equation, describe how ammonia is used to precipitate Pb²⁺ and Zn²⁺

GENERAL EVALUATION

OBJECTIVE TEST:

1. Which of the following contains the highest number of molecules at s.t.p?(Avogadro’s constant)= 6.02 × 10²³ mol^-1 (a) 1.0g of H₂ (H₂=2) (b) 4.0g of N₂(N₂ = 28) (c) 8.0g of O₂ (O₂=32) (d) 16.0g of O₃ (O₃= 48)
2. The laboratory preparation of nitrogen from air requires the removal of (a) carbon(iv)oxide (b) water vapour (c) oxygen and carbon (iv)oxide (d) carbon (iv) oxide, oxygen and water vapour
3. Nitrogen combines reversibly with hydrogen under (a) catalyst (b) high voltage electric spark (c) the presence of traces of NO₂ (d) platinium
4. Nitrogen combines directly with metals except. (a) Cu (b) Mg (c) Ca (d) Al
5. Oxidation of Nitrogen in Mg₃N₂ is (a) -3 (b) +3 (c) -2 (d) +2

ESSAY QUESTIONS

1. Outline the laboratory preparation of Nitrogen from atmospheric air.
2. (a) State two physical properties of Nitrogen (b) Name the process used in the commercial production of nitrogen.
3. Describe the laboratory preparation of nitrogen with the following (i) magnesium (ii) oxygen
4. (i) What is the percentage by volume of nitrogen in air? (ii) Calculate the amount, in mole of magnesium nitride that can be obtained from 3.0g of magnesium (Mg =24)
5. (a) State how nitrogen resemble or differ from NH₃. (b) How does nitrogen resemble or differ from CO₂ in its reaction with each of the following (i) litmus (ii) A burning candle (iii) burning magnesium