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الموضوع: Nitric acid HNO3

  1. #1
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    افتراضي Nitric acid HNO3



    Nitric
    acid




    Nitric acid (
    HNO3), also known as aqua fortis and spirit of nitre, is a highly corrosive and toxicstrong acid.
    Colorless when pure, older samples tend to acquire a yellow cast due to the accumulation of
    oxides of nitrogen. If the solution contains more than 86% Nitric acid, it is referred to as fuming Nitric acid. Depending on the amount of nitrogen dioxide present, fuming Nitric acid is further characterized as white fuming nitric acid or red fuming nitric acid, at concentrations above 95%. At room temperature, Nitric acid tends to rapidly develop a yellow color due to decomposition. Nitric acid is also commonly used as a strong oxidizing agent.




    Properties

    Pure
    anhydrous Nitric acid (100%) is a colorless mobile liquid with a density of 1.512 g/cm3 which solidifies at −42 °C to form white crystals and boils at 83 °C. When boiling in light, and slowly even at room temperature, there is a partial decomposition with the formation of nitrogen dioxide following the reaction:
    4
    HNO3 → 2 H2O + 4 NO2 + O2 Thus, anhydrous Nitric acid should be stored below 0 °C to avoid decomposition. The nitrogen dioxide (NO2) remains dissolved in the Nitric acid coloring it yellow, or red at higher temperatures. While the pure acid tends to give off white fumes when exposed to air, acid with dissolved nitrogen dioxide gives off reddish-brown vapors, leading to the common name "red fuming acid" or "fuming Nitric acid". Fuming Nitric acid is also referred to as 16 molar Nitric acid. It is the most concentrated form of Nitric acid at Standard Temperature and Pressure (STP).
    Nitric acid is miscible with water and distillation gives a maximum-boiling azeotrope with a concentration of 68% HNO3 and a boiling temperature of 120.5 °C at 1 atm, which is the ordinary concentrated Nitric acid of commerce. Two solid hydrates are known; the monohydrate (HNO3·H2O) and the trihydrate (HNO3·3H2O).
    Nitrogen oxides (NOx) are soluble in Nitric acid and this property influences more or less all the physical characteristics depending on the concentration of the oxides. These mainly include the vapor pressure above the liquid and the boiling temperature, as well as the color mentioned above.
    Nitric acid is subject to thermal or light decomposition with increasing concentration and this may give rise to some non-negligible variations in the vapor pressure above the liquid because the nitrogen oxides produced dissolve partly or completely in the acid.

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  2. #2
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    افتراضي رد: Nitric acid HNO3

    Acid-base properties

    Nitric acid is normally considered to be a
    strong acid at ambient temperatures. There is some disagreement over the value of the acid dissociation constant, though the pKa value is usually reported as less than –1. This means that the nitric acid in solution is fully dissociated except in extremely acidic solutions. The pKa value rises to 1 at a temperature of 250 °C.[1]
    Nitric acid can act as a base with respect to an acid such as sulfuric acid.
    HNO3 + 2H2SO4 NO2+ + H3O+ + 2HSO4–; K ~ 22 The nitronium ion, NO2+, is the active reagent in
    aromatic nitration reactions. Since nitric acid has both acidic and basic properties it can undergo an autoprotolysis reaction, similar to the self-ionization of water
    2HNO3 NO2+ + NO3– + H2O [
    edit] Oxidizing properties

    Nitric acid is a strong
    oxidizing agent as shown by its large positive reduction potential (E0r).
    NO3- + 2 H+ + e- → NO2 + H2O, E0r = 0.79 VNO3- + 4 H+ + 3 e- → NO + 2 H2O, E0r = 0.96 V Being a powerful oxidizing agent, nitric acid reacts violently with many non-metallic compounds and the reactions may be explosive. Depending on the acid concentration, temperature and the
    reducing agent involved, the end products can be variable. Reaction takes place with all metals except the noble metals series and certain alloys. As a general rule, oxidizing reactions occur primarily with the concentrated acid, favoring the formation of nitrogen dioxide (NO2).
    [
    edit] Reactions with metals

    Nitric acid reacts with most metals. This characteristic has made it a common agent to be used in
    acid tests. Some precious metals, such as pure gold do not react with nitric acid, though pure gold does react with aqua regia, a mixture of concentrated nitric acid and hydrochloric acid. However, some less noble metals (Ag, Cu, ...) present in some gold alloys relatively poor in gold such as colored gold can be easily oxidized and dissolved by nitric acid, leading to colour changes of the gold-alloy surface. Nitric acid is used as a cheap means in jewelry shops to quickly spot low-gold alloys (< 14 carats) and to rapidly assess the gold purity.
    Strongly
    electropositive metals, such as magnesium react with nitric acid as with other acids, reducing the hydrogen ion.
    Mg + 2 H+ → Mg2+ + H2 With less electropositve metals the products depend on temperature and the acid concentration. For example,
    copper reacts with dilute nitric acid at ambient temperatures with a 3:8 stoichiometry.
    3 Cu + 8 HNO3 → 3 Cu2+ + 2 NO + 4 H2O + 6 NO3- The nitric oxide produced may react with atmospheric oxygen to give
    nitrogen dioxide. With more concentrated nitric acid, nitrogen dioxide is produced directly in a reaction with 1:4 stoichiometry.
    Cu + 4 H+ + 2 NO3− → Cu2+ + 2 NO2 + 2 H2O [
    edit] Passivation

    Although
    chromium (Cr), iron (Fe) and aluminium (Al) readily dissolve in dilute nitric acid, the concentrated acid forms a metal oxide layer that protects the metal from further oxidation, which is called passivation. Typical passivation concentrations range from 18% to 22% by weight.
    [
    edit] Reactions with non-metals

    Being a powerful
    oxidizing acid, nitric acid reacts violently with many organic materials and the reactions may be explosive.
    Reaction with non-metallic elements, with the exceptions of nitrogen, oxygen,
    noble gases, silicon and halogens, usually oxidizes them to their highest oxidation states as acids with the formation of nitrogen dioxide for concentrated acid and nitric oxide for dilute acid.
    C + 4 HNO3 → CO2 + 4 NO2 + 2 H2O or
    3 C + 4 HNO3 → 3 CO2 + 4 NO + 2 H2O

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  3. #3
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    افتراضي رد: Nitric acid HNO3

    Uses




    Nitric acid in a laboratory.
    The main use of nitric acid is for the production of fertilizers; other important uses include the production of explosives, etching and dissolution of metals, especially as a component of
    aqua regia for the purification and extraction of gold, and in chemical synthesis.

    [] Rocket fuel


    Nitric acid has been used in various forms as the
    oxidizer in liquid-fueled rockets. These forms include red fuming nitric acid, white fuming nitric acid, mixtures with sulfuric acid, and these forms with HF inhibitor.[8] IRFNA (inhibited red fuming nitric acid) was one of 3 liquid fuel components for the BOMARC missile.[9]

    [] Chemical reagent


    In
    elemental analysis by ICP-MS, ICP-AES, GFAA, and Flame AA, dilute nitric acid (0.5 to 5.0 %) is used as a matrix compound for determining metal traces in solutions.[10] Ultrapure trace metal grade acid is required for such determination, because small amounts of metal ions could affect the result of the analysis.

    It is also typically used in the digestion process of turbid water samples, sludge samples, solid samples as well as other types of unique samples which require elemental analysis via
    ICP-MS, ICP-OES, ICP-AES, GFAA and FAA. Typically these digestions use a 50% solution of the purchased HNO3 mixed with Type 1 DI Water.[11]

    In organic synthesis, nitric acid may be used to introduce the nitro group. When used with sulfuric acid, it generates the
    nitronium ion, which electrophilically reacts with aromatic compounds such as benzene.

    See also:
    nitration
    [] Woodworking


    In a low concentration (approximately 10%), nitric acid is often used to artificially age
    pine and maple. The color produced is a grey-gold very much like very old wax or oil finished wood (wood finishing).[12]

    [] Other uses


    A solution of nitric acid and alcohol,
    Nital, is used for etching of metals to reveal the microstructure. ISO 14104 is one of the standards detailing this well known procedure.

    Commercially available aqueous blends of 5-30% nitric acid and 15-40% phosphoric acid are commonly used for cleaning food and dairy equipment primarily to remove precipitated calcium and magnesium compounds (either deposited from the process stream or resulting from the use of hard water during production and cleaning).

    [] Safety


    Nitric acid is a powerful
    oxidizing agent, and the reactions of nitric acid with compounds such as cyanides, carbides, and metallic powders can be explosive. Reactions of nitric acid with many organic compounds, such as turpentine, are violent and hypergolic (i.e., self-igniting). Due to its properties it is stored away from bases and organics.

    Concentrated nitric acid dyes
    human skin yellow due to a reaction with the keratin. These yellow stains turn orange when neutralized.[13] (See #Xanthoproteic test)

    [] History


    The first mention of nitric acid is in
    Pseudo-Geber´s De Inventione Veritatis, wherein it is obtained by calcining a mixture of niter, alum and blue vitriol. It was again described by Albert the Great in the 13th century and by Ramon Lull, who prepared it by heating niter and clay and called it "eau forte" (aqua fortis).[14]

    Glauber devised the process still used today to obtain it, namely by heating niter with strong
    sulfuric acid. Its true nature was determined by Lavoisier in (1776), when he showed that it contained oxygen, whilst in 1785 Henry Cavendish determined its constitution and showed that it could be synthesized by passing a stream of electric sparks through moist air

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  4. #4
    عضو مميز الصورة الرمزية قمر بلحاج
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    افتراضي رد: Nitric acid HNO3

    That was great
    Thanx for your sharing
    Best wishes

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  5. #5
    عضو فعال الصورة الرمزية arwa fuad
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    افتراضي

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    مراقب عام الصورة الرمزية Eiman
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