WCO Explanatory Notes reproduced for reference. © World Customs Organization. Verify against official WCO publication.
28.11 - Other inorganic acids and other inorganic oxygen compounds of non-metals. - Other inorganic acids : 28 11.11 - - Hydrogen fluoride (hydrofluoric acid) 2811.19 - - Other - Other inorganic oxygen compounds of non-metals : 28 11-21 28 11.22 28 11.29 - - Carbon dioxide - - Silicon dioxide - - Other This heading covers mineral acids and anhydrides and other oxides of non-metals. The most important are listed below according to their non-metal component (*) : (A) COMPOUNDS OF FLUORINE or ceresine organic matter. It is wax, or in rubber or p Its uses include etching on glass, rnanufacturin ashless filter paper, preparation of tantalum, of fluorides, scouring and pickling foun& pieces, in organic synthesis, or as a control in fermenting processes. (2) Fluoroacids. These include : (a) Tetrafluoroboric acid (fluoroboric acid) (HBF4). (b) Hexafluorosilicic acid (fluorosilicic acid) as b - roducts in the manufacture of used'ir the electrolytic refining of tin solutions obtained fluorides. It is fluomsilicates, etc. @) COMPOUNDS OF CHLORINE The most important of these compounds are powerful oxidising and chlorinating agents, used in bleaching and in organic synthesis. They are, as a rule, unstable. They include : (1) Hypochlorous add (HCIO). A product dangerous to inhale, exploding on contact with organic matter. The gas is presented in aqueous solutions, yellow or occas~onallyreddish. (*) In the following order : fluorine, chlorine, bromine, iodine, sulphur, selenium, tellurium, nitrogen, phosphorus, arsenic, carbon, silicon. Chloric acid (HClO,). This acid exists only as colourless or yellowish aqueous solutions. Perchloric acid (HClO,). This roduct, more or less highly concentrated, gives various hydrates. It attacks the skin.Use?I in analyses. (C) COMPOUNDS OF BROMINE Hydrogen bromide (HBr . A colourless gas with a stron ungent odour. It may be put up under pressure, or in the o m of aqueous solutions (hy ro romic acid) which decompose slowly in the air (especially under the action of light). Hydrobromic acid is used to prepare bromides and in organic synthesis. %% Bromic acid (HBr03). Exists only in aqueous solutions; used in organic synthesis. (D) COMPOUNDS OF IODINE Hydrogen iodide (HI). A colourless, suffocating gas, readily decomposed. It is presented in corrosive, aqueous solutions (hydriodic acid) which fume in damp air when concentrated. Used in organic synthesis as a reducing agent or as a medium for fixing iodine. m03) Iodic acid and its anh dride (ID5prismatic ), crystals or in aqueous solutions. Used in medicine or as an absor ent agent in gas masks. K Periodic acid (HI04.2H20).Similar properties to iodic acid. (E) SULPHUR COMPOUNDS Hydrogen sulphide (H2S). A highly toxic, colourless gas with the foetid odour of rotten eggs. Presented under ressure in steel cylinders or in aqueous solution (hydrosulphuric acid . It is used in ana ysis, for purifyrng sulphuric or hydrochloric acids, for obtaining sulp ur dioxide or regenerated sulphur, etc. 1, P Peroxosulphuric acids (persulphuric acids), presented in crystalIine form : (a) Peroxodisulphuric acid (H2S208) and its anhydride (Sz07). (b) Peroxomonosulphuric acid (Caro's acid) (&So5), extremely hygroscopic; a powerful oxidising agent. Thionic acids. These exist on1 in aqueous solution : dithionic acid (H2S2O6);trithionic acid (H2S306);tetrathionic acid h2s40,);pentathionic acid (H2S506). Aminosulphonic acid sulphuric acid, sulphur soluble in alcohol. Used for the electroplating and in organic synthesis. Sulphur dioxide (SOz). Obtained by combustion of sulphur, by roasting natural sul hides (particularly iron pyrites), or by roasting natural calcium sulphate (e.g., anhydritey with c ay and coke. It is a colourless, suffocating gas. Sulphur dioxide is presented either liquefied under pressure in steel bottles, or in aqueous solution; in the latter commercial form it is often wrongly called " sulphurous acid ". A powerful reducing and bleaching agent, sulphur dioxide has many uses, e.g., bleaching animal textiles, straw, feathers or gelatin, the sulphite process in sugar refining, preservation of h i t or ve etables, the preparation of acid sulphites for the treatment of wood pul , manufacture o sulphuric acid, or as a disinfectant (for wine mutage). Liquid sulphur Joxide, which lowers the ternperahre on evaporation, is used in refrigerating plant. f (6) Sulphur trioxide (sulphuric anhydride) (SO3). A white solid in needle-shaped crystals somewhat similar to asbestos in appearance. Fumes in damp air;. absorbs and reacts violently with water. It is presented in airtight sheet-iron containers or m glass or stoneware carboys, which are fitted with a device containing inor anic absorbent matter. It is used for preparing oleurns (heading 28.07) and alums (heading 8.33). f (7) Disulphur trioxide (Sz03).Deliquescent green crystals, decomposed by water and soluble in alcohol; used as a reducing agent in the manufacture of synthetic dyes. (F) SELENIUM COMPOUNDS (1) Hydrogen selenide (H2Se). A nauseous gas, dangerous to inhale because it paralyses the olfactory nerve. Presented in unstable aqueous solutions. (2) Selenious acid (H2Se03) and its anh~dride P O 2 ) . Hexagonal white crystals, deliquescent, very soluble m water; used in e ename industry. (3) Selenic acid (H2Se04).White crystals, anhydrous or hydrated. (G) TELLURIUM COMPOUNDS These are hydro en telluride (H2Te) in aqueous solutions), tellurous acid (H2Te03) and its anhydride ~ e 0 3(white solids), an telluric acid (H2TeQ) (colourless crystals) and its anhydride ( e03) (orange-coloured solid). (H) NITROGEN COMPOUNDS (1) Hydrogen azide (hydrazoic acid) (EN3 . Colourless, toxic liquid with a suffocating odour; very soluble in water; unstable, wi explosive properties. Its salts (azides) fall in heading 28.50, and not in sub-chapter V. en oxide (nitrous oxide) (N20)Sweet-tasting . gas, soluble in water and presented form. Used in the gaseous state as an anaesthetic, and in the liquid or solld state as (3) Nitrogen dioxide (nitroxyl, nitrous vapours, " nitro en peroxide ") (NO2 . Colourless liquid at 0 "C, orange-brown at higher temperatures; %oiling point about 2 OC (when it gives off red fumes). This is the most stable nitrogen oxide. A powehl oxihsing agent. (IT) PHOSPHORUS COMPOUNDS "z (1) Phos hinic acid (hypophosphorous acid) (H3P02). Lamellar crystals, melting at about oxidising on exposure to air; a powerful reducing agent. "5 (2) Phos honic acid (phosphorous acid) (&Po3). Deliquescent crystals melting at about soluble in water. Also its anh dride (P2O3 or P406),crystals which melt at about 24 "C, and turn first yellow then red w en exposed to light, gradually decomposing. K (K) ARSENIC COMPOUNDS (1) Diarsenic trioxide (arsenic sesquioxide, arsenious oxide, white arsenic) ( A s z ~ ~Wrongly ). known as " arsenious acid ". Obtained by roasting arseniferous ores of nickel and silver or arsenical pyrites. It may sometimes contain impurities (arsenic sulphide, sulphur, antimonous oxide, etc.). Commercial arsenic (111) oxide is generally a crystalline white powder, odourless and highly poisonous (flowers of arsenic). The vitreous anhydride takes the f o m of transparent, amorphous masses; the porcelanic anhydride is in opaque, interlocking, octahedral crystals. Its uses include preserving hides or zoolo 'cal specimens (sometimes it is used mixed together with soap); as a rat poison; for t e manufacture of fly-papers; preparation of certain opacifiers, vitrifiable enamels or mineral greens such as Scheele's green (copper arsenite) or Schweinfurt green (copper acetoarsenite); in small doses, as a medicament (in the treatment of dermatitis, malaria or asthma). f r (2) Diarsenic pentaoxide (As2O5).Obtained by the oxidation of arsenic trioxide or b the dehydration of arsenic acid; it is a high1 poisonous white powder which dissolves s owly in water, giving arsenic acid. It is used or the manufacture of arsenic acid, as an oxidising agent, etc. f" (3) Arsenic acids. The name " arsenic acid" is given to ortho-arsenic acid (H3As04.%H20) and other hydrates of arsenic pentaoxide (pyro- or meta-arsenic acids, etc.). They crystallise in colourless needles and are deadly poisons. Arsenic acid is used for the manufacture of synthetic dyes (hchsine, etc.), arsenates and organic derivatives of arsenic used as medicaments or insecticides. The heading excludes arsenic hydrides (e.g., AsH3) (heading 28.50). (L) CARBON COMPOUNDS (1) Carbon monoxide (CO). Toxic, colourless and tasteless gas; put up under pressure. Its reducing properties are utilized, inter a h ,in metallurgy. (2) Carbon dioxide (COz). Incorrectly called " carbonic acid ". Obtained by the combustion of carbon, or by heating calcareous substances or treating them with acids. It is a colourless gas, one and a half times heavier than air; it extinguishes flames. Carbon dioxide can be presented either as a liquid (compressed in steel cylinders), or as a solid (compressed cubes in insulated containers, " carbonic snow " or " carbonic ice "). It is used in metallur ,in sugar manufacture or for aerating beverages. Liquid C02is used for raising beer, for preparation of salicylic acid, in fire extinguishers, etc. Solid C02 is used as a coolant (down to -80 "C). (3) Hydrogen cyanide (hydrocyanic acid, prussic acid) (HCN). Obtained by the action of sul hunc acid on a cyanide, or by the action of catalysts on mixtures of ammonia and hY$ ocarbons. It is a very toxic, colourless liquid with an odour of bitter almonds. Miscible with and less dense than water; it keeps badly when impure or in weak solution. Hydrocyanic acid is used in organic synthesis (e.g., for the production of acrylonitrile by reaction with acetylene) and as a paraslticide. (4) isocyanic, thiocyanic or fulminic acids. @A) SILICON COMPOUNDS Silicon dioxide pure silica, silicic anhydride, etc.) (SiOd. Obtained by treating silicate solutions with aci s, or by decomposing silicon halides by the action of water and heat. It can be either in amorphous form (as a white powder" silica white ", " flowers of silica "," calcined silica "; as vitreous granules - " vitreous silica "; in gelatinous condition '' silica frost "," hydrated silica "), or in crystals (tridyrnite and cristobalite forms). Silica resists the action of acids; fused silica is therefore used to make laboratory a paratus and industrial equipment which can be suddenly heated or cooled without breakin Explanatory Note to Chapter 70). Finel powdered silica is used, e.g., as a fil er see for Oeneral various es of natural and synthetic rubber an other elastomers, as a thickening or thixotro ic agent various plastics, printin ink, paints, coatings and adhesives. Fumed silica &de by combustion of silicon tetrach oride or trichlorosilane in hydrogen-oxygen firnaces) is also used in chemi-mechanical polishin of silicon wafers and as a fiee-flow or anti-settling agent for a variety of materials. Activate silica gel is employed to dry gases. f The heading excludes : (a) Natural silica (Chapter 25, except varieties constituting precious or semi-precious stones - see the ExplanatoryNotes to headings 71.03 and 71.05). (b) Colloidal suspensions of silica are generally classified in heading 38.24 unless specially prepared for specific purposes (e.g., as textile dressings of heading 38.09). (c) Silica gel with added cobalt salts (used as a humidity indicator) (heading 38.24). (N) COMPLEX ACIDS This headin also covers chemically defined complex acids consisting of two or more non-metal mineral aci s (e.g., chloro-acids , or of a non-metal acid and a metal acid (e.g., tungstosilicic, tungstoboric acids), not specifie or included in other headings of this Chapter. d d Since antimony is deemed in the Nomenclature to be a metal, antimonic acid and antimony oxides fall in heading 28.25. Sub-chapter I11 HALOGEN OR SULPHUR COMPOUNDS OF NON-METALS This sub-chapter covers products which, although known by names (chlorides, sulphides, etc.) similar to those of the metal salts of hydraclds classified in sub-chapter V, are actually non-metal combinations such as : (1) A halogen with a non-metal other than oxygen or hydrogen (halogen compounds). (2) The same compounds as under (1) above, combined with oxygen (halide oxides). or (3) Sulphur with a non-metal other than oxygen or hydrogen (sulphur compounds). Sulphide oxides of non-metals (sulphur sub-chapter; they fall in heading 28.53. + oxygen + non-metal) are excluded from this Halides, haIide oxides, and sul hides of metals (see the General Explanatory Note to sub-chapter I) or of the ammonium ion (NH43fa 1 in sub-chapter V exce t in the case of compounds of precious metals (heading 28.43) and the compounds of heading 28.44, 8.45,28.46 or 28.52. /' i'
1.- Except where the context otherwise requires, the headings of this Chapter apply only to : (a) Separate chemical elements and separate chemically defined compounds, whether or not containing impurities; (b) The products mentioned in (a) above dissolved in water; (c) The products mentioned in (a) above dissolved in other solvents provided that the solution constitutes a normal and necessary method of putting up these products adopted solely for reasons of safety or for transport and that the solvent does not render the product particularly suitable for specific use rather than for general use; (d) The products mentioned in (a), (b) or (c) above with an added stabiliser (including an anti-caking agent) necessary for their preservation or transport; (e) The products mentioned in (a), (b), (c) or (d) above with an added anti-dusting agent or a colouring substance added to facilitate their identification or for safety reasons, provided that the additions do not render the product particularly suitable for specific use rather than for general use.