水素

定義

本品は、次の化学式で表される二原子気体分子である。

性質

水素は常温で無色、無味、無臭の気体。つねに二原子分子H2として存在する。ただし化学反応や電気分解などによって発生する瞬間の水素の活性状態（いわゆる発生期の水素）や水素の低圧放電管内では原子状水素として存在する。水素分子の2個の原子核（陽子）はそれぞれ自転しているので、自転の方向が同じであるオルト水素と、反対であるパラ水素という異性体がある。常温では、オルト水素75％とパラ水素25％の混合物であり、温度を下げていくとパラ水素の割合が増えていく（たとえば－193.1℃：48.35％、－253.1℃：99.8％）。

解説

水素，周期表中第1周期、第1番元素である。第1族および第17族に属する元素に似たところがあり、短周期型周期表ではⅠ族およびⅦ族の両方に属させるか、あるいはその特異性を重視して、いずれの族にも含めず、独立した扱いをとることがある。同位体として質量数2および3のもの（重水素）が存在するが、ほかの元素の場合と異なり、普通の水素原子（重水素に対し軽水素、プロチウムという）の2倍、3倍というように質量の差が甚だしく、その性質の違いも大きい。それゆえ、質量数2の水素を重水素あるいはジュウテリウム（Dまたは2H）、質量数3の水素を三重水素あるいはトリチウム（Tまたは3H）とよぶ。

構造

水素原子はもっとも簡単な原子で、原子核（陽子1個）と電子1個からなる。ジュウテリウムは原子核に中性子1個、トリチウムは2個の中性子をもつ。これらは沸点、融点などの物理的性質だけでなく、化学的反応性にもいくぶんか差がみられる。トリチウムは放射性で、電子を放出して自然に崩壊する。

用途

硬化油、冶金、鉛工用、真空管、トランジスタ、電球、ガラス溶融気象観測、溶接、酸水素焔用、白金及び石英細工、その他アンモニアメタノール、塩酸の合成、石油合成(フィッシャー法)、冷却剤(液体水素)

存在

宇宙全体では水素はもっとも多量に存在する。単体は全物質中もっとも軽く、したがって地球の上層大気には多く集まり下層部分ではきわめて少なく、乾燥空気は約5×10-5容量％の水素を含むだけである。単体水素は火山の噴気、天然ガス中などに存在するが、地球表面では酸素と化合した水の形で、岩石圏（結晶水など）、水圏（海水、大陸氷など）、気圏および生物圏にわたって広く存在している。水素は各種の星、あるいは星間物質としても存在し、宇宙空間に広く分布し、宇宙全体の総原子数の約93％を占める。また、水素は他のすべての元素の出発物質でもある。

製法

工業的には、石油、石炭、天然ガスなどを酸素または空気、水蒸気などと高温で反応させて合成ガス（一酸化炭素と水素の混合物）をつくり、これから水素を取り出す。そのほか、1000℃以上に熱した炭素に水蒸気を通して得られる水性ガスからの分離、炭化水素の熱分解、塩水の電気分解などが利用される。実験室では、亜鉛に希塩酸または希硫酸を反応させてつくるか、水酸化アルカリまたは硫酸の水溶液を電気分解してつくる。電解法では比較的純粋な水素が得られやすいが、亜鉛と酸を用いる方法では不純物（アルシン、ホスフィン、硫化水素、炭化水素など）が含まれやすい。市販の赤色ボンベに入っている水素は、普通99.5％以上の純度があり、通常の目的にはそのまま使用して差し支えない。重水素は重水を電気分解して工業的につくられている。

化粧品の成分用途

酸化防止剤

説明

Hydrogen is colorless, odorless, tasteless, flammable, and nontoxic. It exists as a gas at ambient temperatures and atmospheric pressures. It is the lightest gas known, with a density approximately 0.07% that of air. Hydrogen is present in the atmosphere occurring in concentrations of only about 0.5 ppm by volume at lower altitudes.

化学的特性

Hydrogen,H2, is a tasteless,colorless, odorless gas that may be liquified by cooling under pressure. Hydrogen is used in welding, in the production of ammonia, methanol, and other chemicals, for the hydrogenation of oil and coal,and for the reduction of metallic oxide ores.It is obtained by the dissociation of water and as a by-product in the electrolysis of brine solutions. Molecular hydrogen at ambient temperature is relatively innocuous to most metals.However, atomic hydrogen is detrimental to most metals.

物理的性質

Hydrogen’s atom is the simplest of all the elements, and the major isotope (H-1) consists ofonly one proton in its nucleus and one electron in its K shell. The density of atomic hydrogenis 0.08988 g/l, and air’s density is 1.0 g/l (grams per liter). Its melting point is –255.34°C,and its boiling point is –252.87°C (absolute zero = –273.13°C or –459.4°F). Hydrogen hastwo oxidation states, +1 and –1.

同位体

The major isotope of hydrogen has just one proton and no neutrons in itsnucleus (₁H-1).Deuterium (₂D or H-2) has a nucleus consisting of one proton plus one neutron. Tritium (₃T or H-3), another variety of heavy water (TOT),has nuclei consisting of one proton and two neutrons.

名前の由来

Hydrogen was named after the Greek term hydro genes, which means “water former.”

特性

H₂ is a diatomic gas molecule composed of two tightly joined atoms that strongly sharetheir outer electrons. It is an odorless, tasteless, and colorless gas lighter than air. Hydrogenis included in group 1 with the alkali metals because it has an oxidation state of +1 as dothe other alkali metals. Experiments during the 1990s at the Lawrence Livermore NationalLaboratory (LLNL), in Livermore, California, lowered the temperature of H₂ to almostabsolute zero. By exploding gunpowder in a long tube that contained gaseous hydrogen, thegas that was under pressure of over one million times the normal atmospheric pressure wascompressed into a liquid. This extreme pressure on the very cold gas converted it to liquidhydrogen (almost to the point of solid metallic hydrogen), in which state it did act as a metaland conduct electricity.Hydrogen gas is slightly soluble in water, alcohol, and ether. Although it is noncorrosive,it can permeate solids better than air. Hydrogen has excellent adsorption capabilities in theway it attaches and holds to the surface of some substances. (Adsorption is not the same asabsorption with a “b,” in which one substance intersperses another.

使用

In oxy-hydrogen blowpipe (welding) and limelight; autogenous welding of steel and other metals; manufacture of ammonia, synthetic methanol, HCl, NH3; hydrogenation of oils, fats, naphthalene, phenol; in balloons and airships; in metallurgy to reduce oxides to metals; in petroleum refining; in thermonuclear reactions (ionizes to form protons, deuterons (D) or tritons (T)). liquid hydrogen used in bubble chambers to study subatomic particles; as a coolant.

調製方法

Hydrogen gas may be produced by several methods. It is commerciallyobtained by electrolysis of water. It also is made industrially by the reactionof steam with methane or coke:
CH₄ + H₂O → CO + 3H₂
C + H₂O → CO + H₂
CO + H₂O → CO₂ + H₂
The reactions are carried out at about 900 to 1,000°C and catalyzed by nick-el, nickel-alumina, or rhodium-alimina catalysts. In the laboratory, hydrogenmay be prepared by the reaction of zinc or iron with dilute hydrochloric or sulfuric acid:
Zn + 2HCl → ZnCl₂ + H₂
It also may be prepared by passing water vapor over heated iron:
H₂O + Fe → FeO + H₂
Also, it can be generated by reaction of metal hydrides with water:
CaH₂ + 2H₂O → Ca(OH)₂ + 2H₂
Another method of preparation involves heating aluminum, zinc, or otheractive metals in dilute sodium hydroxide or potassium hydroxide:
2Al + 6NaOH → 2Na₃AlO₃ + 3H₂
Zn + 2KOH → K₂ZnO₂ + H₂

定義

ChEBI: An elemental molecule consisting of two hydrogens joined by a single bond.

一般的な説明

Hydrogen is a colorless, odorless gas. Hydrogen is easily ignited. Once ignited Hydrogen burns with a pale blue, almost invisible flame. The vapors are lighter than air. Hydrogen is flammable over a wide range of vapor/air concentrations. Hydrogen is not toxic but is a simple asphyxiate by the displacement of oxygen in the air. Under prolonged exposure to fire or intense heat the containers may rupture violently and rocket. Hydrogen is used to make other chemicals and in oxyHydrogen welding and cutting.

空気と水の反応

Highly flammable.

反応プロフィール

Finely divided platinum and some other metals will cause a mixture of Hydrogen and oxygen to explode at ordinary temperatures. If a jet of Hydrogen in air impinges on platinum black the metal surface gets hot enough to ignite the gases, [Mellor 1:325(1946-1947)]. Explosive reactions occur upon ignition of mixtures of nitrogen trifluoride with good reducing agents such as ammonia, Hydrogen, Hydrogen sulfide or methane. Mixtures of Hydrogen, carbon monoxide, or methane and oxygen difluoride are exploded when a spark is discharged, [Mellor 2, Supp. 1:192(1956)]. An explosion occurred upon heating 1'-pentol and 1''-pentol under Hydrogen pressure. Hydrogen appears that this acetylenic compound under certain conditions suddenly breaks down to form elemental carbon, Hydrogen, and carbon monoxide with the release of sufficient energy to develop pressures in excess of 1000 atmospheres, [AIChE Loss Prevention, p1, (1967)].

危険性

Hydrogen gas is very explosive when mixed with oxygen gas and touched off by a spark or flame. Many hydrides of hydrogen are dangerous and can become explosive if not stored and handled correctly. Many organic and hydrocarbon compounds are essential for life to exist, but just as many are poisonous, carcinogenic, or toxic to living organisms.

健康ハザード

Hydrogen is practically nontoxic. In high concentrations this gas is a simple asphyxiant, and ultimate loss of consciousness may occur when oxygen

火災危険

EXTREMELY FLAMMABLE. Will be easily ignited by heat, sparks or flames. Will form explosive mixtures with air. Vapors from liquefied gas are initially heavier than air and spread along ground. CAUTION: Hydrogen (UN1049), Deuterium (UN1957), Hydrogen, refrigerated liquid (UN1966) and Methane (UN1971) are lighter than air and will rise. Hydrogen and Deuterium fires are difficult to detect since they burn with an invisible flame. Use an alternate method of detection (thermal camera, broom handle, etc.) Vapors may travel to source of ignition and flash back. Cylinders exposed to fire may vent and release flammable gas through pressure relief devices. Containers may explode when heated. Ruptured cylinders may rocket.

燃焼性と爆発性

Hydrogen is a highly flammable gas that burns with an almost invisible flame and low heat radiation. Hydrogen forms explosive mixtures with air from 4 to 75% by volume. These explosive mixtures of hydrogen with air (or oxygen) can be ignited by a number of finely divided metals (such as common hydrogenation catalysts). In the event of fire, shut off the flow of gas and extinguish with carbon dioxide, dry chemical, or halon extinguishers. Warming of liquid hydrogen contained in an enclosed vessel to above its critical temperature can cause bursting of that container.

农业用途

Hydrogen, a non-metallic element, is a colorless odorless, tasteless gas occurring in water combined with oxygen, and in all organic compounds (for example, hydrocarbons and carbohydrates). It is produced by electrolysis of water and is used in the Haber-Bosch process for producing ammonia - a major raw material for nitrogenous fertilizers.
Large quantities of hydrogen are utilized in catalytic hydrogenation of unsaturated vegetable oils to make solid fats and petroleum refining. Large quantities of hydrogen are also used as a propulsion fuel for rockets in conjunction with oxygen or fluorine. Being flammable, it is used with helium for filling balloons and airships.
Hydrogen is the lightest of all the elements holding position in Group 1 of the Periodic Table. It is abundant in the universe. There are three hydrogen isotopes namely hydrogen- 1, deuterium and tritium. The first two are naturally occurring stable isotopes and the third being radioactive, is made artificially.

材料の用途

Hydrogen gas is noncorrosive and may be contained at ambient temperatures by most common metals used in installations designed to have sufficient strength for the working pressures involved. Equipment and piping built to use hydrogen should be selected with consideration of the possibility of embrittlement, particularly at elevated pressures and temperatures above 450°F (232°C). A Nelson curve should be consulted to select the proper alloys.
Metals used for liquid hydrogen equipment must have satisfactory properties at very low operating temperatures. Ordinary carbon steels lose their ductility at liquid hydrogen temperatures and are considered too brittle for this service. Suitable materials include austenitic chromium-nickel steels (stainless steels), copper, copper silicon alloys, aluminum, Monel, and some brasses and bronzes.

貯蔵

hydrogen cylinders should be clamped or otherwise supported in place and used only in areas free of ignition sources and separate from oxidizers. Expansion of hydrogen released rapidly from a compressed cylinder will cause evolution of heat due to its negative Joule-Thompson coefficient.

純化方法

It is usually purified by passing through a suitable absorption train of tubes. Carbon dioxide is removed with KOH pellets, soda-lime or NaOH pellets. Oxygen is removed with a “De-oxo” unit or by passage over Cu heated to 450-500o and Cu on Kieselguhr at 250o. Passage over a mixture of MnO2 and CuO (Hopcalite) oxidises any CO to CO2 (which is removed as above). Hydrogen can be dried by passage through dried silica-alumina at -195o, through a dry-ice trap followed by a liquid-N2 trap packed with glass wool, through CaCl2 tubes, or through Mg(ClO4)2 or P2O5. Other purification steps include passage through a hot palladium thimble [Masson J Am Chem Soc 74 4731 1952], through an activated-charcoal trap at -195o, and through a non-absorbent cotton-wool filter or small glass spheres coated with a thin layer of silicone grease. Potentially VERY EXPLOSIVE in air.

不和合性

Hydrogen is a reducing agent and reacts explosively with strong oxidizers such as halogens (fluorine, chlorine, bromine, iodine) and interhalogen compounds.

廃棄物の処理

Excess hydrogen cylinders should be returned to the vendor. Excess hydrogen gas present over reaction mixtures should be carefully vented to the atmosphere under conditions of good ventilation after all ignition sources have been removed. For more information on disposal procedures, see Chapter 7 of this volume.