Nitric acid

HNO3Prepared by:

Aras jabar --- Tishko mhamad&

Balen hasan --- Shaxawan rahim

N+

HO

O

O-

nitric acid

University of slemani School of science chemistry department

Content

• Introduction• physical and chemical properties• Manufacture of nitric acid• Industrial uses• Reactions of nitric acid

Introduction• Nitric acid is a strong monoprotic acid and is almost

completely ionised in aqueous solution.. Nitric acid is a resonance-stabilized acid allowing it to share its electrons among its own bonds

• Molar mass: 63g/mol • Colour Pure nitric acid is a colourless liquid. But commercial nitric acid may be yellowish brown, due to the

presence of dissolved nitrogen dioxide.• Odour: Nitric acid is a fuming, hygroscopic liquid, the fumes

of which give it a choking smell

N+

HO

O

O-

nitric acid

Concentration

• Nitric acid can be concentrated up to 68%. It cannot be concentrated beyond this percentage by simply boiling because the aqueous solution of this concentration of nitric acid forms a constant boiling mixture at 121oC. However, the acid can be further concentrated by one of the following methods

• By passing a mixture of nitrogen dioxide and air through the 68% aqueous solution. This solution can be further concentrated by distilling it with concentrated sulphuric acid under reduced pressure. By this method nitric acid of 98% concentration can be obtained.

• If the 98% acid is cooled to -42oC, then pure nitric acid of 100% concentration crystallises out as colourless crystals

Concentration• If the solution contains more than 86% nitric acid, it is referred to

as fuming nitric acid . Fuming nitric acid is characterized as white fuming nitric acid and red fuming nitric acid, depending on the amount of nitrogen dioxide present. At concentrations above 95%, it tends to develop a slight yellow colour due to its tendency to adsorb water from the atmosphere into its crystal structure. Pure anhydrous nitric acid (100%) is a colourless liquid with a density of 1.522 g/cm³ which solidifies at -42 °C to form white crystals and boils at 83 °C. When boiling in light, even at room temperature, there is a partial decomposition with the formation of nitrogen dioxide following the reaction

4HNO3 H2O + NO2 O2 (780C)+

physical and chemical properties• Acidity : Nitric acid is a very strong acid and dissociates very highly, and

is very corrosive. Nitric Acid’s Dissociation Constant is 28 (Ka value)• Taste: It is sour in taste due to acidic nature

• Density: Its density is 1.513 g cm-3 at 20oC. Thus pure nitric acid is about 1½ times as dense as water while commercial nitric acid has a lower density.

• Boiling point: Pure nitric acid boils at 86oC. However it undergoes partial decomposition at this temperature.

• Melting point: When cooled below oC nitric acid freezes to a white solid, which melts at - 42oC.

• Solubility: It is soluble in water in all proportions.

Redox nature

• Redox Nature Nitric Acid has two properties in redox nature. It is dependant on how concentrated the acid solution is. (It is a very strong oxidant)

• Nitric acid (conc): NO3- + 2H+ + e -> NO2 + H2O

• Nitric acid (dilute): NO3- + 4H+ +3e -> NO + 2H2O

Manufacture• The manufacture of nitric acid is a three-stage process. The

first stage is the oxidation of ammonia and it uses a platinum/rhodium catalyst

INDUSTRIAL PREPARATION OF NITRIC ACID• On industrial scale, nitric acid can be prepared by the

following methods • (a) CHILLI-SALT PETER's METHOD: By NaNO3 • (b) BRIKLAND-EYDE's METHOD: By using air • (c) OSTWALD' s METHOD : By ammonia

OSTWALD' s METHODMaterials used:• Ammonia gas • Water • Oxygen gas Catalyst • Platinum

• DETAILS OF PROCESS First step• PRIMARY OXIDATION (formation of nitric acid)• Oxidation of ammonia is carried out in a catalyst chamber in which one part of

ammonia and eight parts of oxygen by volume are introduced. The temperature of chamber is about 600 o C. This chamber contain a platinum gauze which serves as catalyst.

• CHEMISTRY OF PRIMARY OXIDATION• Oxidization of ammonia is reversible and exothermic process. Therefore according to

Le-Chatelier's principle., a decrease in temperature favour reaction in forward direction. In primary oxidization 95% of ammonia is converted into nitric oxide (NO)4NH3 + 5O2 4NO + 6H2O

OSTWALD' s METHOD

Second step • SECONDARY OXIDATION• (formation of nitrogen dioxide) • Nitric oxide gas obtain by the oxidation of ammonia is very

hot. In order to reduce its temperature , it is passed through a heat exchanger where the temperature of nitric oxide is reduce to 150 o C. Nitric oxide after cooling is transferred to another oxidizing tower where at about 50 o c it is oxidizing to NO2.

2NO O2 2NO2+

OSTWALD' s METHODThird step ABSORPTION OF NO2 (formation of HNO3)• Nitrogen dioxide from secondary oxidation chamber is introduced

into a special absorption tower. NO2 gas passed through the tower and water is showered over it. By the absorption, nitric acid is obtained

• Nitric acid so obtain is very dilute. It is recycled in absorption tower so that more and more NO2 get absorbed. HNO3 after recycle becomes about 68% concentrated

3NO2 H2O 2HNO3 NO++

OSTWALD' s METHOD Fourth step Concentration In order to increase the concentrated of HNO3 , vapour of HNO3 are passed over concentrated H2SO4. Being a dehydrating agent H2SO4,absorbs water from HNO3 and concentrated HNO3 is obtained

Industrial Use• The Important Uses of Nitric Acid Are:• Manufacture of Various Products such as: • Explosives such asTrinitrotoluene (TNT),

Nitro-glycerine, Gun Cotton• Ammonal Fertilisers such as calcium nitrate,

Ammonium Nitrate • Nitrate Salts such as calcium nitrate, silver

nitrate, ammonium nitrate

Industrial Use

• Dyes, Perfumes, Drugs• Synthetic fibres such as Nylon• Can make Sulphuric acid from Nitric acid by Lead

Chamber process• Used in Purification of silver, gold, platinum • Used for carving designs on copper, brass, bronze• Used to make “Aqua Regia” which dissolves the noble

elements (aqua regia is a mixture of more than one type of acid)

• Used as a Laboratory reagent

With metals

With metals in general• With cold dilute nitric acid

Metal + Nitric Acid Metal Sulfate + Water + Nitric Oxide

• With concentrated nitric acid (cold or hot)

Metal + Nitric Acid Metal Sulfate + Water + Nitrogen Di-Oxide

With metal• Nitric acid behaves differently with different metals at different

concentrations • With sodium, potassium and calcium the reaction is highly explosive.• With magnesium and manganese• With magnesium and manganese, cold and extremely dilute (1%) nitric

acid, reacts to yield hydrogen.• With Copper (Zinc and Iron also) • cold dilute nitric acid:• Copper reacts with cold and dilute nitric acid to yield copper nitrate,

water and nitric oxide.

With concentrated nitric acid (cold or hot):• Copper reacts with cold or hot concentrated nitric acid to yield copper

nitrate, water and nitrogen dioxide

+ + +4HNO3Cu 2H2O2CU(NO3)2 2NO2

3Cu 8HNO3 2NO4H2O3CU(NO3)2+ + +

With Turpentine (A Cool Prac)

• Turpentine is a combustible hydrocarbon. When a few drops of turpentine are added to fuming or very concentrated nitric acid, it bursts into flames forming water, nitrogen dioxide and carbon dioxide.

The overall reaction is:

56HNO3 C10H6 10CO2 36H2O56NO2+ + +

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