Pengguna:Agung.karjono/Bak pasir/Sal amoniak

Amonia

en:Ammonia

Untuk NH₄⁺, lihat Amonium. Untuk penggunaan lain, lihat Agung.karjono/Bak pasir/Sal amoniak (disambiguasi).

Agung.karjono/Bak pasir/Sal amoniak

Ilustrasi molekul amonia model bola dan batang Ilustrasi molekul amonia model pengisian ruang
Nama
Nama IUPAC Azana
Nama lain Hidrogen nitrida Trihidrogen nitrida Nitrogen trihidrida
Penanda
Nomor CAS	7664-41-7 Y
Model 3D (JSmol)	Gambar interaktif
3DMet	{{{3DMet}}}
Referensi Beilstein	3587154
ChEBI	CHEBI:16134 Y
ChEMBL	ChEMBL1160819 Y
ChemSpider	217 Y
Nomor EC
Referensi Gmelin	79
KEGG	D02916 Y
MeSH	Ammonia
PubChem CID	222
Nomor RTECS	{{{value}}}
UNII	5138Q19F1X Y
Nomor UN	1005
InChI InChI=1S/H3N/h1H3 Y Key: QGZKDVFQNNGYKY-UHFFFAOYSA-N Y InChI=1/H3N/h1H3 Key: QGZKDVFQNNGYKY-UHFFFAOYAF
SMILES N
Sifat
Rumus kimia	NH3
Massa molar	17,031 g/mol
Penampilan	Gas tak berwarna
Bau	bau menyengat tajam
Densitas	0,86 kg/m3 (1,013 bar pada titik didihnya) 0,769  kg/m3 (STP) 0,73 kg/m3 (1,013 bar pada 15 °C) 681,9 kg/m3 pada −33,3 °C (cairan) Lihat juga Amonia (halaman data) 817 kg/m3 pada −80 °C (padatan transparan)
Titik lebur	−77,73 °C (−107,91 °F; 195,42 K) (Titik tripel pada 6,060 kPa, 195,4 K)
Titik didih	−33,34 °C (−28,01 °F; 239,81 K)
Kelarutan dalam air	47% w/w (0 °C) 31% w/w (25 °C) 18% w/w (50 °C)
Kelarutan	larut dalam kloroform, eter, etanol, metanol
Tekanan uap	857,3 kPa
Keasaman (pKa)	32,5 (−33 °C), 10.5 (DMSO)
Kebasaan (pKb)	4.75
Asam konjugat	Amonium
Basa konjugat	Amidogen
Suseptibilitas magnetik (χ)	−18,0·10−6 cm3/mol
Indeks bias (nD)	1,3327
Viskositas	0,276 cP (−40 °C)
Struktur
Grup titik	C3v
Bentuk molekul	Trigonal pyramid
Momen dipol	1,42 D
Termokimia
Entropi molar standar (So)	193 J·mol−1·K−1
Entalpi pembentukan standar (ΔfHo)	−46 kJ·mol−1
Bahaya
Lembar data keselamatan	ICSC 0414 (anhydrous)
Piktogram GHS
Pernyataan bahaya GHS	H221, H280, H314, H331, H400
Langkah perlindungan GHS	P210, P261, P273, P280, P305+351+338, P310
Titik nyala	gas mudah terbakar
Suhu swasulut	651 °C (1.204 °F; 924 K)
Ambang ledakan	15–28%
Dosis atau konsentrasi letal (LD, LC):
LD50 (dosis median)	0,015 mL/kg (manusia, oral)
LC50 (konsentrasi median)	40,300 ppm (mencit, 10 min) 28,595 ppm (mencit, 20 min) 20,300 ppm (mencit, 40 min) 11,590 ppm (mencit, 1 jam) 7338 ppm (mencit, 1 jam) 4837 ppm (tikus, 1 jam) 9859 ppm (kelinci, 1 jam) 9859 ppm (kucing, 1 jam) 2000 ppm (mencit, 4 jam) 4230 ppm (tikus, 1 jam)
LCLo (terendah tercatat)	5000 ppm (mamalia, 5 min) 5000 ppm (manusia, 5 min)
Batas imbas kesehatan AS (NIOSH):
PEL (yang diperbolehkan)	50 ppm (25 ppm ACGIH- TLV; 35 ppm STEL)
REL (yang direkomendasikan)	TWA 25 ppm (18 mg/m3) ST 35 ppm (27 mg/m3)
IDLH (langsung berbahaya)	300 ppm
Senyawa terkait
Kation lainnya	Fosfin Arsin Stibin
Related nitrogen hidrida	Hidrazin Asam hidrazoat
Senyawa terkait	Amonium hidroksida
Kecuali dinyatakan lain, data di atas berlaku pada suhu dan tekanan standar (25 °C [77 °F], 100 kPa).
Y verifikasi (apa ini YN ?)
Referensi

Amonia adalah senyawa yang tersusun dari nitrogen dan oksigen dengan rumus NH₃. Sebagai hidrida pniktogen paling sederhana, amonia berupa gas tak berwarna dengan bau menyengat yang khas. Amonia adalah limbah bernitrogen yang umum, terutama di kalangan organisme akuatik, dan memiliki kontribusi yang signifikan dalam memenuhi kebutuhan nutrisi organisme terestrial sebagai prekursor pangan dan pupuk. Amonia juga merupakan bahan baku, baik langsung maupun tidak langsung, dalam sintesis berbagai produk farmasi, dan digunakan dalam banyak produk pembersih komersial. Amonia banyak terkumpul di bagian bawah akibat aliran udara dan air. Nama amonia diambil dari kaum Amon, penyembah dewa Mesir Amun, yang menggunakan amonium klorida dalam ritual mereka.

Meskipun jamak terdapat di alam dan digunakan secara luas, amonia dalam bentuk pekatnya bersifat korosif dan berbahaya (hazardous). Ia diklasifikasikan sebagai zat yang sangat berbahaya di Amerika Serikat, dan bagi instansi yang memproduksi, menyimpan, atau menggunakannya dalam kuantitas yang signifikan dikenakan wajib lapor yang ketat.

Produksi global amonia pada tahun 2014 sebesar 176 juta ton, terdapat kenaikan produksi global sebesar 16% dibandingkan tahun 2006 yang hanya 152 juta ton. Amonia industri diperdagangkan sebagai larutan amonia (biasanya 28% amonia dalam air) atau sebagai cairan amonia anhidrat bertekanan atau didinginkan yang didistribusikan menggunakan mobil tangki maupun tabung.

NH₃ mendidih pada −33,34 °C (−28,012 °F) pada tekanan satu atmosfer, sehingga cairannya harus disimpan dalam wadah bertekanan atau pada suhu rendah. Amonia rumah tangga atau amonium hidroksida adalah larutan NH₃ dalam air. Konsentrasi larutan semacam ini diukur dalam satuan skala Baumé (densitas). Larutan amonia dengan konsentrasi 26 derajat Baumé (sekitar 30% amonia (berat/berat) pada suhu 15,5 °C (59,9 °F) umumnya sudah tergolong pekat untuk ukuran produk komersial.

Keterjadian alami

Amonia adalah bahan kimia yang dijumpai dalam jumlah renik di alam, dihasilkan dari materi hewan dan tumbuhan bernitrogen. Amonia dan garam amonium juga dijumpai dalam jumlah kecil pada air hujan, sementara amonium klorida (sal amoniak), dan amonium sulfat dijumpai pada area vulkanis; kristal amonium bikarbonat juga telah dijumpai dalam guano Patagonia. Ginjal mensekresikan amonia untuk menetralisir kelebihan asam. Garam amonium dijumpai tersebar melalui tanah yang subur dan pada air laut.

Amonia juga dijumpai di Tata Surya pada Mars, Jupiter, Saturnus, Uranus, Neptunus, dan Pluto. Di antara tempat-tempat lainnya, pada planet es yang lebih kecil seperti Pluto, amonia dapat bertindak sebagai antibeku geologis yang penting. Titik leleh campuran air dan amonia adalah 173 K (−100 °C; −148 °F) jika konsentrasi amonia cukup tinggi sehingga memungkinkan planet-planet semacam itu untuk mempertahankan lautan internal dan geologi aktif pada suhu yang jauh lebih rendah daripada yang mungkin terjadi jika tanpa amonia. Zat yang mengandung amonia, atau sejenisnya, disebut amoniakal.

Sifat-sifat

Amonia adalah gas tak berwarna dengan bau menyengat yang khas. Amonia adalah gas pengangkat (lifting gas), massa jenisnya hanya 0,589 kali udara. Ia mudah dicairkan karena kuatnya ikatan hidrogen antar molekul; cairannya mendidih pada −33,3 °C (−27,94 °F), dan membeku pada −77,7 °C (−107,86 °F) membentuk kristal putih.

Bau amonia dapat dihilangkan dengan mudah dengan cara mereaksikannya dengan natrium bikarbonat atau asam asetat. Kedua reaksi ini membentuk garam amonium yang tidak berbau.

Padatan

Simetri kristalnya adalah kubik, simbol Pearson cP16, grup ruang P2₁3 No.198, tetapan kisi 0,5125 nm.

Cairan

Amonia cair memiliki daya ionisasi yang kuat, yang tercermin dari tingginya ε-nya yang mencapai 22. Amonia cair memiliki perubahan entalpi penguapan standar yang tinggi (23,35 kJ/mol, cf. air 40,65 kJ/mol, metana 8,19 kJ/mol, fosfin 14,6 kJ/mol) sehingga dapat digunakan di laboratorium dalam wadah tak berinsulasi tanpa pendinginan. Lihat amonia cair sebagai pelarut.

Sifat pelarut

Amonia dapat campur dengan air. Dalam larutan berair, amonia dapat dibebaskan melalui pendidihan. Larutan amonia dalam air bersifat basa. Konsentrasi maksimum amonia dalam air (larutan jenuh) memiliki densitas 0,880 g/cm³ dan sering dikenal sebagai "amonia 880". Amonia tidak mudah terbakar atau mempertahankan pembakaran, kecuali pada kondisi campuran bahan bakar dan udara hanya mengandung 15–25% udara.

Pembakaran

Jika dicampur dengan oksigen, ia terbakar dengan nyala hijau kekuningan pucat. Pada temperatur tinggi dan dengan adanya katalis yang sesuai, amonia terdekomposisi menjadi unsur-unsur penyusunnya. Pengapian terjadi ketika klorin dialirkan ke dalam amonia, membentuk nitrogen dan hidrogen klorida; jika terapat klorin berlebih, terbentuk pula nitrogen triklorida (NCl₃) yang mudah meledak.

Struktur

Molekul amonia mempunyai bentuk trigonal piramida sesuai prediksi teori VSEPR (Valence Shell Electron Pair Repulsion) dan dibuktikan secara eksperimen melalui penentuan sudut ikatannya yang sebesar 106,7°. Atom nitrogen pusat memiliki lima elektron terluar dengan tambahan elektron dari masing-masing atom hidrogen. Ini menghasilkan total delapan elektron, atau empat pasang elektron yang tersusun tetrahedral. Tiga dari pasangan elektron ini digunakan sebagai pasangan ikatan, yang menyisakan satu pasang elektron sunyi. Pasangan elektron sunyi ini menolak lebih kuat daripada pasangan ikatan, sehingga sudut ikatan bukannya 109,5°, seperti pada tetrahedral reguler, tetapi 106,7°. Atom nitrogen dalam molekul amonia mempunyai satu pasangan elektron sunyi, sehingga membuatnya sebagai basa, suatu akseptor proton. Bentuk ini memberi molekul momen dipol dan menjadikannya polar. Polaritas molekul ini, dan terutama, kemampuannya membentuk ikatan hidrogen, membuat amonia sangat mudah bercampur dengan air. Amonia bersifat basa sedang, larutan airnya dengan konsentrasi 1,0 M mempunyai pH 11,6 dan jika suatu asam kuat ditambahkan ke dalam larutan ini hingga netral (pH = 7), sebanyak 99,4% molekul amonia terprotonasi. Temperatur dan salinitas juga mempengaruhi proporsi ion NH+4. Ion amonium berbentuk tetrahedron dan bersifat isoelektronik dengan metana.

Molekul amonia mudah mengalami inversi nitrogen pada suhu ruangan; bagaikan payung yang terlipat terbalik karena tertiup angin kencang. Hambatan energi pada inversi ini adalah 24,7 kJ/mol, dan frekuensi resonansi sebesar 23,79 GHz, sesuai dengan radiasi gelombang mikro pada panjang gelombang 1,260 cm. Absorpsi pada frekuensi ini merupakan spektrum gelombang mikro pertama yang diamati.

Keamfoteran

Salah satu sifat amonia paling khas adalah sifat kebasaannya. Amonia dianggap sebagai basa lemah. Ia bereaksi dengan asam membentuk garam; sehingga, dengan asam klorida membentuk amonium klorida (sal amoniak); dengan asam nitrat membentuk amonium nitrat, dsb. Amonia yang kering sempurna tidak akan bereaksi dengan hidrogen klorida yang kering sempurna juga; uap air diperlukan agar reaksi berlangsung. Sebagaimana didemonstrasikan dalam percobaan, dua buah botol terbuka yang masing-masing berisi amonia pekat dan asam klorida pekat menghasilkan awan amonium klorida, yang tampaknya "keluar dari kehampaan" ketika garam terbentuk pada pertemuan dua awan molekul yang berdifusi, di suatu tempat di antara kedua botol tersebut.

${\ce {NH3 + HCl -> NH4Cl}}$

Garam yang dihasilkan dari reaksi antara amonia dengan asam dikenal sebagai garam amonium dan seluruhnya mengandung ion amonium (NH+4).

Meskipun amonia dikenal luas sebagai basa lemah, ia juga bertindak sebagai asam yang sangat lemah. Amonia merupakan zat protik dan mampu membentuk amida (yang mengandung ion NH−2). Misalnya, litium larut dalam amonia cair menghasilkan larutan litium amida:

${\ce {2Li + 2NH3 -> 2LiNH2 + H2}}$

Swadisosiasi

Seperti air, amonia mengalami autoionisasi molekuler membentuk asam dan basa konjugatnya:

${\ce {2NH3_{(}aq)<=>NH4_{(aq)}^{+}\ +NH2_{(}^{-}aq)}}$

Amonia sering berfungsi sebagai basa lemah, sehingga ia memiliki kemampuan pendaparan. Pergeseran pH akan menyebabkan penurunan kation amonium (NH+4) dan anion amida (NH−2) yang ada dalam larutan. Pada suhu dan tekanan standar, K=[NH+4][NH−2] = 10⁻³⁰

Pembakaran

Pembakaran amonia menjadi nitrogen dan air bersifat eksotermik:

${\ce {4 NH3 + 3 O2 -> 2 N2 + 6 H2O_{(g)}}}$ ΔH°_r = −1.267,20 kJ/mol (atau −316,8 kJ/mol jika dinyatakan dalam per mol NH₃)

Perubahan entalpi standar pembakaran, ΔH°_c, dinyatakan per mol amonia dan dengan kondensasi air yang terbentuk, adalah −382,81 kJ/mol. Dinitrogen adalah produk termodinamika pembakaran: semua nitrogen oksida tidak stabil terhadap N₂ dan O₂, yang merupakan prinsip di balik konverter katalitik. Nitrogen oksida dapat terbentuk sebagai produk kinetika dengan adanya katalis yang sesuai, suatu reaksi yang sangat penting dalam industri pembuatan asam nitrat:

${\ce {4 NH3 + 5 O2 -> 4 NO + 6 H2O}}$

Reaksi selanjutnya memicu pembentukan NO₂

${\ce {2 NO + O2 -> 2 NO2}}$

Pembakaran amonia di udara sangat sulit tanpa adanya katalis (seperti kasa platina atau kromium(III) oksida hangat), karena suhu nyala api biasanya lebih rendah daripada suhu penyulutan campuran amonia-udara. Rentang kemudahterbakaran amonia di udara adalah 16–25%.

Pembentukan senyawa lain

Dalam kimia organik, amonia dapat bertindak sebagai nukleofil pada reaksi substitusi. Amina dapat terbentuk dari reaksi antara amonia dengan alkil halida, meskipun gugus -NH₂ juga bersifat nukleofilik dan terbentuk pula amina sekunder dan tersier sebagai produk sampingan. Kelebihan amonia membantu meminimalkan substitusi berganda dan menetralkan hidrogen halida yang terbentuk. Metilamina dibuat secara komersial melalui reaksi amonia dengan klorometana, dan reaksi dengan asam 2-bromopropanoat telah digunakan untuk membuat rasemat alanin dengan rendemen 70%. Etanolamina dibuat melalui reaksi pembukaan cincin dengan etilena oksida: reaksi kadang-kadang berlanjut hingga menghasilkan dietanolamina dan trietanolamina.

Amida dapat dibuat melalui reaksi antara amonia dengan derivat asam karboksilat. Asil klorida adalah yang paling reaktif, tetapi amonia harus ditambahkan berlebih setidaknya dua kali lipat untuk menetralkan hidrogen klorida yang terbentuk. Ester dan anhidrida juga bereaksi dengan amonia membentuk amida. Garam amonium dari asam karboksilat dapat didehidrasi menjadi amida selama tidak ada gugus yang peka termal: diperlukan suhu antara 150–200 °C.

Hidrogen pada amonia dapat digantikan oleh logam; sehingga, magnesium yang terbakar dalam gas amonia menghasilkan magnesium nitrida, Mg₃N₂, dan ketika gas amonia dilewatkan natrium atau kalium yang dipanaskan, terbentuklah sodamida, NaNH₂, dan potasamida, KNH₂. Ketika diperlukan tata nama pengganti, rekomendasi IUPAC lebih memilih "azana" daripada amonia: sehingga nama lain kloramina adalah "kloroazana", bukan "kloroamonia".

Amonia pentavalen dikenal sebagai λ⁵-amina, atau lebih umum dikenal sebagai amonium hidrida. Padatan kristal ini hanya stabil di bawah tekanan tinggi dan terdekomposisi kembali menjadi amonia trivalen dan gas hidrogen pada kondisi normal. Zat ini pernah diteliti sebagai kemungkinan bahan bakar padat untuk roket pada tahun 1966.

Amonia sebagai ligan

Artikel utama: Kompleks logam amina

Model bola dan batang kation tetraaminadiakuatembaga(II), [Cu(NH₃)₄(H₂O)₂]²⁺

Amonia dapat bertindak sebagai ligan dalam kompleks logam transisi. Ia murni sebagai donor σ, pada bagian tengah deret spektrokimia, dan menunjukkan perilaku di antara kuat-lunak. Berdasarkan alasan historis, amonia dinamakan amina dalam tatanama senyawa koordinasi. Beberapa kompleks amina penting antara lain tetraaminadiakuatembaga(II) ([Cu(NH₃)₄(H₂O)₂]²⁺), kompleks biru tua yang terbentuk melalui penambahan amonia ke dalam larutan garam tembaga(II). Tetraaminadiakuatembaga(II) hidroksida dikenal sebagai pereaksi Schweizer, dan memiliki kemampuan menakjubkan untuk melarutkan selulosa. Diaminaperak(I) ([Ag(NH₃)₂]⁺) adalah spesies aktif dalam pereaksi Tollens. Pembentukan kompleks ini dapat juga membantu untuk membedakan endapan spesies perak halida yang berbeda: perak klorida (AgCl) larut dalam larutan amonia encer (2M), perak bromida (AgBr) hanya larut dalam larutan amonia pekat, sementara perak iodida (AgI) tidak larut dalam larutan amonia.

Kompleks amina dari kromium(III) dikenal sejak akhir abad ke-19, dan membentuk dasar teori revolusioner Alfred Werner mengenai struktur senyawa koordinasi. Werner hanya mengenal dua isomer (fac- dan mer-) dari kompleks [CrCl₃(NH₃)₃] yang dapat terbentuk, dan menyimpulkan bahwa ligan harus tertata mengelilingi ion logam pada verteks oktahedron. Proposal ini telah dikonfirmasi dengan kristalografi sinar X.

Suatu ligan amina yang berikatan dengan ion logam bersifat lebih asam daripada molekul amonia bebas, meskipun deprotonasi dalam larutan berair jarang terjadi. Salah satu contohnya adalah reaksi kalomel, yang menghasilkan senyawa amidoraksa(II) yang sangat mudah larut.

${\ce {Hg2Cl2 + 2 NH3 -> Hg + HgCl(NH2) + NH4+ + Cl-}}$

Deteksi dan penentuan

Bagian ini berisi artikel tentang deteksi dalam laboratorium. Untuk deteksi dalam astronomi, lihat § Dalam astronomi.

Amonia dalam larutan

Artikel utama: Larutan amonia

Amonia dan garam amonium dapat dengan mudah terdeteksi, dalam kadar yang sangat kecil, dengan penambahan larutan Nessler. Reaksi ini menghasilkan pewarnaan kuning yang unik dengan adanya sejumlah renik amonia atau garam amonium. Jumlah amonia dalam garam amonium dapat diperkirakan secara kuantitatif melalui distilasi garam dengan [[natrium hidroksida|natrium] atau kalium hidroksida. Amonia yang dihasilkan diabsorbsikan ke dalam larutan standar asam sulfat dengan volume tertentu dan kelebihan asam kemudian ditentukan secara volumetrik. Cara lain adalah amonia diabsorbsikan ke dalam asam klorida dan amonium klorida yang terbentuk diendapkan sebagai amonium heksakloroplatinat, (NH₄)₂PtCl₆.

Gaseous ammonia

Sulfur sticks are burnt to detect small leaks in industrial ammonia refrigeration systems. Larger quantities can be detected by warming the salts with a caustic alkali or with quicklime, when the characteristic smell of ammonia will be at once apparent. Ammonia is an irritant and irritation increases with concentration; the permissible exposure limit is 25 ppm, and lethal above 500 ppm. Higher concentrations are hardly detected by conventional detectors, the type of detector is chosen according to the sensitivity required (e.g. semiconductor, catalytic, electrochemical). Holographic sensors have been proposed for detecting concentrations up to 12.5% in volume.

Ammoniacal nitrogen (NH₃-N)

Ammoniacal nitrogen (NH₃-N) is a measure commonly used for testing the quantity of ammonium ions, derived naturally from ammonia, and returned to ammonia via organic processes, in water or waste liquids. It is a measure used mainly for quantifying values in waste treatment and water purification systems, as well as a measure of the health of natural and man-made water reserves. It is measured in units of mg/L (milligram per litre).

History

This high-pressure reactor was built in 1921 by BASF in Ludwigshafen and was re-erected on the premises of the University of Karlsruhe in Germany.

The ancient Greek historian Herodotus mentioned that there were outcrops of salt in an area of Libya that was inhabited by a people called the "Ammonians" (now: the Siwa oasis in northwestern Egypt, where salt lakes still exist). The Greek geographer Strabo also mentioned the salt from this region. However, the ancient authors Dioscorides, Apicius, Arrian, Synesius, and Aëtius of Amida described this salt as forming clear crystals that could be used for cooking and that were essentially rock salt. Hammoniacus sal appears in the writings of Pliny, although it is not known whether the term is identical with the more modern sal ammoniac (ammonium chloride).

The fermentation of urine by bacteria produces a solution of ammonia; hence fermented urine was used in Classical Antiquity to wash cloth and clothing, to remove hair from hides in preparation for tanning, to serve as a mordant in dying cloth, and to remove rust from iron.

In the form of sal ammoniac (نشادر, nushadir) ammonia was important to the Muslim alchemists as early as the 8th century, first mentioned by the Persian-Arab chemist Jābir ibn Hayyān, and to the European alchemists since the 13th century, being mentioned by Albertus Magnus. It was also used by dyers in the Middle Ages in the form of fermented urine to alter the colour of vegetable dyes. In the 15th century, Basilius Valentinus showed that ammonia could be obtained by the action of alkalis on sal ammoniac. At a later period, when sal ammoniac was obtained by distilling the hooves and horns of oxen and neutralizing the resulting carbonate with hydrochloric acid, the name "spirit of hartshorn" was applied to ammonia.

Gaseous ammonia was first isolated by Joseph Black in 1756 by reacting sal ammoniac (Ammonium Chloride) with calcined magnesia (Magnesium Oxide). It was isolated again by Peter Woulfe in 1767, by Carl Wilhelm Scheele in 1770 and by Joseph Priestley in 1773 and was termed by him "alkaline air". Eleven years later in 1785, Claude Louis Berthollet ascertained its composition.

The Haber–Bosch process to produce ammonia from the nitrogen in the air was developed by Fritz Haber and Carl Bosch in 1909 and patented in 1910. It was first used on an industrial scale in Germany during World War I, following the allied blockade that cut off the supply of nitrates from Chile. The ammonia was used to produce explosives to sustain war efforts.

Before the availability of natural gas, hydrogen as a precursor to ammonia production was produced via the electrolysis of water or using the chloralkali process.

With the advent of the steel industry in the 20th century, ammonia became a byproduct of the production of coking coal.

Uses

Fertilizer

Globally, approximately 88% (as of 2014) of ammonia is used as fertilizers either as its salts, solutions or anhydrously. When applied to soil, it helps provide increased yields of crops such as maize and wheat. 30% of agricultural nitrogen applied in the USA is in the form of anhydrous ammonia and worldwide 110 million tonnes are applied each year.

Precursor to nitrogenous compounds

Ammonia is directly or indirectly the precursor to most nitrogen-containing compounds. Virtually all synthetic nitrogen compounds are derived from ammonia. An important derivative is nitric acid. This key material is generated via the Ostwald process by oxidation of ammonia with air over a platinum catalyst at 700–850 °C (1.292–1.562 °F), ~9 atm. Nitric oxide is an intermediate in this conversion:

NH₃ + 2 O₂ → HNO₃ + H₂O

Nitric acid is used for the production of fertilizers, explosives, and many organonitrogen compounds.

Ammonia is also used to make the following compounds:

• Hydrazine, in the Olin Raschig process and the peroxide process
• Hydrogen cyanide, in the BMA process and the Andrussow process
• Hydroxylamine and ammonium carbonate, in the Raschig process
• Phenol, in the Raschig–Hooker process
• Urea, in the Bosch–Meiser urea process and in Wöhler synthesis
• Amino acids, using Strecker amino-acid synthesis
• Acrylonitrile, in the Sohio process

Ammonia can also be used to make compounds in reactions which are not specifically named. Examples of such compounds include: ammonium perchlorate, ammonium nitrate, formamide, dinitrogen tetroxide, alprazolam, ethanolamine, ethyl carbamate, hexamethylenetetramine, and ammonium bicarbonate.

As a cleaner

Household ammonia is a solution of NH₃ in water (i.e., ammonium hydroxide) used as a general purpose cleaner for many surfaces. Because ammonia results in a relatively streak-free shine, one of its most common uses is to clean glass, porcelain and stainless steel. It is also frequently used for cleaning ovens and soaking items to loosen baked-on grime. Household ammonia ranges in concentration by weight from 5 to 10% ammonia. United States manufacturers of cleaning products are required to provide the product's material safety data sheet which lists the concentration used.

Fermentation

Solutions of ammonia ranging from 16% to 25% are used in the fermentation industry as a source of nitrogen for microorganisms and to adjust pH during fermentation.

Antimicrobial agent for food products

As early as in 1895, it was known that ammonia was "strongly antiseptic ... it requires 1.4 grams per litre to preserve beef tea." In one study, anhydrous ammonia destroyed 99.999% of zoonotic bacteria in 3 types of animal feed, but not silage. Anhydrous ammonia is currently used commercially to reduce or eliminate microbial contamination of beef. Lean finely textured beef in the beef industry is made from fatty beef trimmings (c. 50–70% fat) by removing the fat using heat and centrifugation, then treating it with ammonia to kill E. coli. The process was deemed effective and safe by the US Department of Agriculture based on a study that found that the treatment reduces E. coli to undetectable levels. There have been safety concerns about the process as well as consumer complaints about the taste and smell of beef treated at optimal levels of ammonia. The level of ammonia in any final product has not come close to toxic levels to humans.

Minor and emerging uses

Refrigeration – R717

Because of ammonia's vaporization properties, it is a useful refrigerant. It was commonly used before the popularisation of chlorofluorocarbons (Freons). Anhydrous ammonia is widely used in industrial refrigeration applications and hockey rinks because of its high energy efficiency and low cost. It suffers from the disadvantage of toxicity, which restricts its domestic and small-scale use. Along with its use in modern vapor-compression refrigeration it is used in a mixture along with hydrogen and water in absorption refrigerators. The Kalina cycle, which is of growing importance to geothermal power plants, depends on the wide boiling range of the ammonia–water mixture. Ammonia coolant is also used in the S1 radiator aboard the International Space Station in two loops which are used to regulate the internal temperature and enable temperature dependent experiments.

The potential importance of ammonia as a refrigerant has increased with the discovery that vented CFCs and HFCs are extremely potent and stable greenhouse gases. The contribution to the greenhouse effect of CFCs and HFCs in current use, if vented, would match that of all CO₂ in the atmosphere.

For remediation of gaseous emissions

Ammonia is used to scrub SO₂ from the burning of fossil fuels, and the resulting product is converted to ammonium sulfate for use as fertilizer. Ammonia neutralizes the nitrogen oxide (NO_x) pollutants emitted by diesel engines. This technology, called SCR (selective catalytic reduction), relies on a vanadia-based catalyst.
Ammonia may be used to mitigate gaseous spills of phosgene.

As a fuel

Ammoniacal Gas Engine Streetcar in New Orleans drawn by Alfred Waud in 1871.

The X-15 aircraft used ammonia as one component fuel of its rocket engine

The raw energy density of liquid ammonia is 11.5 MJ/L, which is about a third that of diesel. Although it can be used as a fuel, for a number of reasons this has never been common or widespread. In addition to direct utilization of ammonia as a fuel in combustion engines, there is also the opportunity to convert ammonia back to hydrogen, where it can be used to power hydrogen fuel cells or directly within high-temperature fuel cells.

Ammonia engines or ammonia motors, using ammonia as a working fluid, have been proposed and occasionally used. The principle is similar to that used in a fireless locomotive, but with ammonia as the working fluid, instead of steam or compressed air. Ammonia engines were used experimentally in the 19th century by Goldsworthy Gurney in the UK and the St. Charles Avenue Streetcar line in New Orleans in the 1870s and 1880s, and during World War II ammonia was used to power buses in Belgium.

Ammonia is sometimes proposed as a practical alternative to fossil fuel for internal combustion engines. Its high octane rating of 120 and low flame temperature allows the use of high compression ratios without a penalty of high NOx production.  Since ammonia contains no carbon, its combustion cannot produce carbon monoxide, hydrocarbons or soot.

However ammonia cannot be easily used in existing Otto cycle engines because of its very narrow flammability range, and there are also other barriers to widespread automobile usage. In terms of raw ammonia supplies, plants would have to be built to increase production levels, requiring significant capital and energy sources. Although it is the second most produced chemical, the scale of ammonia production is a small fraction of world petroleum usage. It could be manufactured from renewable energy sources, as well as coal or nuclear power. The 60 MW Rjukan dam in Telemark, Norway produced ammonia for many years from 1913, providing fertilizer for much of Europe.

Despite this, several tests have been done. In 1981, a Canadian company converted a 1981 Chevrolet Impala to operate using ammonia as fuel. In 2007, a University of Michigan pickup powered by ammonia drove from Detroit to San Francisco as part of a demonstration, requiring only one fill-up in Wyoming.

Compared to hydrogen as a fuel, ammonia is much more energy efficient, and hydrogen could be produced, stored, and delivered at a much lower cost as ammonia rather than as compressed and/or cryogenic hydrogen. The conversion of ammonia to hydrogen via the sodium-amide process, either as a catalyst for combustion or as fuel for a proton exchange membrane fuel cell, is another possibility. Conversion to hydrogen would allow the storage of hydrogen at nearly 18 wt% compared to ~5% for gaseous hydrogen under pressure.

Rocket engines have also been fueled by ammonia. The Reaction Motors XLR99 rocket engine that powered the X-15 hypersonic research aircraft used liquid ammonia. Although not as powerful as other fuels, it left no soot in the reusable rocket engine, and its density approximately matches the density of the oxidizer, liquid oxygen, which simplified the aircraft's design.

As a stimulant

Anti-meth sign on tank of anhydrous ammonia, Otley, Iowa. Anhydrous ammonia is a common farm fertilizer that is also a critical ingredient in making methamphetamine. In 2005, Iowa used grant money to give out thousands of locks to prevent criminals from getting into the tanks.

Ammonia, as the vapor released by smelling salts, has found significant use as a respiratory stimulant. Ammonia is commonly used in the illegal manufacture of methamphetamine through a Birch reduction. The Birch method of making methamphetamine is dangerous because the alkali metal and liquid ammonia are both extremely reactive, and the temperature of liquid ammonia makes it susceptible to explosive boiling when reactants are added.

Textile

Liquid ammonia is used for treatment of cotton materials, giving properties like mercerisation, using alkalis. In particular, it is used for prewashing of wool.

Lifting gas

At standard temperature and pressure, ammonia is less dense than atmosphere and has approximately 45-48% of the lifting power of hydrogen or helium. Ammonia has sometimes been used to fill weather balloons as a lifting gas. Because of its relatively high boiling point (compared to helium and hydrogen), ammonia could potentially be refrigerated and liquefied aboard an airship to reduce lift and add ballast (and returned to a gas to add lift and reduce ballast).

Woodworking

Lihat pula: Ammonia fuming

Ammonia has been used to darken quartersawn white oak in Arts & Crafts and Mission-style furniture. Ammonia fumes react with the natural tannins in the wood and cause it to change colours.

Energy carrier

Ammonia can be manufactured from solar energy, air and water. This is an efficient way to package hydrogen into a chemical that is much cheaper to store and transport than pure hydrogen be it as gas or as liquid. In fact, per volume ammonia holds more hydrogen than does liquid hydrogen. Ammonia may be the key to overcome not only the daily but also the seasonal fluctuations of renewable energy sources.

This approach will solve many of the problems foreseen for the proposed Hydrogen economy, that instead could be replaced by an Ammonia economy, essentially still a hydrogen economy.

In early August 2018, scientists from Australia’s Commonwealth Scientific and Industrial Research Organisation (CSIRO) announced the success of developing a process to release hydrogen from ammonia and harvest that at ultra-high purity as a fuel for cars. This uses a special membrane. Two demonstration fuel cell vehicles have the technology, a Hyundai Nexo and Toyota Mirai.

Small-scale, intermittent production of ammonia, for local agricultural use, may be a viable substitute for electrical grid attachment as a sink for power generated by wind turbines in isolated rural installations. Such production would necessarily depend on new, efficiently catalyzed methods to emerge from laboratories.

Safety precautions

The world's longest ammonia pipeline, running from the TogliattiAzot plant in Russia to Odessa in Ukraine.

The U. S. Occupational Safety and Health Administration (OSHA) has set a 15-minute exposure limit for gaseous ammonia of 35 ppm by volume in the environmental air and an 8-hour exposure limit of 25 ppm by volume. NIOSH recently reduced the IDLH from 500 to 300 based on recent more conservative interpretations of original research in 1943. IDLH (Immediately Dangerous to Life and Health) is the level to which a healthy worker can be exposed for 30 minutes without suffering irreversible health effects. Other organizations have varying exposure levels. U.S. Navy Standards [U.S. Bureau of Ships 1962] maximum allowable concentrations (MACs):continuous exposure (60 days): 25 ppm / 1 hour: 400 ppm Ammonia vapour has a sharp, irritating, pungent odour that acts as a warning of potentially dangerous exposure. The average odour threshold is 5 ppm, well below any danger or damage. Exposure to very high concentrations of gaseous ammonia can result in lung damage and death. Although ammonia is regulated in the United States as a non-flammable gas, it still meets the definition of a material that is toxic by inhalation and requires a hazardous safety permit when transported in quantities greater than 13,248 L (3,500 gallons). Household products containing ammonia (i.e., Windex) should never be used in conjunction with products containing bleach, as the resulting chemical reaction produces highly toxic fumes.

Liquid ammonia is dangerous because it is hygroscopic and because it can freeze flesh. See Gas carrier#Health effects of specific cargoes carried on gas carriers for more information.

Toxicity

The toxicity of ammonia solutions does not usually cause problems for humans and other mammals, as a specific mechanism exists to prevent its build-up in the bloodstream. Ammonia is converted to carbamoyl phosphate by the enzyme carbamoyl phosphate synthetase, and then enters the urea cycle to be either incorporated into amino acids or excreted in the urine. Fish and amphibians lack this mechanism, as they can usually eliminate ammonia from their bodies by direct excretion. Ammonia even at dilute concentrations is highly toxic to aquatic animals, and for this reason it is classified as dangerous for the environment.

Ammonia is a constituent of tobacco smoke.

Coking wastewater

Ammonia is present in coking wastewater streams, as a liquid by-product of the production of coke from coal. In some cases, the ammonia is discharged to the marine environment where it acts as a pollutant. The Whyalla steelworks in South Australia is one example of a coke-producing facility which discharges ammonia into marine waters.

Aquaculture

Ammonia toxicity is believed to be a cause of otherwise unexplained losses in fish hatcheries. Excess ammonia may accumulate and cause alteration of metabolism or increases in the body pH of the exposed organism. Tolerance varies among fish species. At lower concentrations, around 0.05 mg/L, un-ionised ammonia is harmful to fish species and can result in poor growth and feed conversion rates, reduced fecundity and fertility and increase stress and susceptibility to bacterial infections and diseases. Exposed to excess ammonia, fish may suffer loss of equilibrium, hyper-excitability, increased respiratory activity and oxygen uptake and increased heart rate. At concentrations exceeding 2.0 mg/L, ammonia causes gill and tissue damage, extreme lethargy, convulsions, coma, and death. Experiments have shown that the lethal concentration for a variety of fish species ranges from 0.2 to 2.0 mg/l.

During winter, when reduced feeds are administered to aquaculture stock, ammonia levels can be higher. Lower ambient temperatures reduce the rate of algal photosynthesis so less ammonia is removed by any algae present. Within an aquaculture environment, especially at large scale, there is no fast-acting remedy to elevated ammonia levels. Prevention rather than correction is recommended to reduce harm to farmed fish and in open water systems, the surrounding environment.

Storage information

Similar to propane, anhydrous ammonia boils below room temperature when at atmospheric pressure. A storage vessel capable of 250 psi (1,7 MPa) is suitable to contain the liquid. Ammonium compounds should never be allowed to come in contact with bases (unless in an intended and contained reaction), as dangerous quantities of ammonia gas could be released.

Household use

Solutions of ammonia (5–10% by weight) are used as household cleaners, particularly for glass. These solutions are irritating to the eyes and mucous membranes (respiratory and digestive tracts), and to a lesser extent the skin. Caution should be used that the chemical is never mixed into any liquid containing bleach, as a poisonous gas may result. Mixing with chlorine-containing products or strong oxidants, such as household bleach, can lead to hazardous compounds such as chloramines.

Laboratory use of ammonia solutions

Hydrochloric acid sample releasing HCl fumes, which are reacting with ammonia fumes to produce a white smoke of ammonium chloride.

The hazards of ammonia solutions depend on the concentration: "dilute" ammonia solutions are usually 5–10% by weight (<5.62 mol/L); "concentrated" solutions are usually prepared at >25% by weight. A 25% (by weight) solution has a density of 0.907 g/cm³, and a solution that has a lower density will be more concentrated. The European Union classification of ammonia solutions is given in the table.

Concentration by weight (w/w)	Molarity	Concentration mass/volume (w/v)	Classification	R-Phrases
5–10%	2.87–5.62 mol/L	48.9–95.7 g/L	Irritant (Xi)	R36/37/38
10–25%	5.62–13.29 mol/L	95.7–226.3 g/L	Corrosive (C)	R34
>25%	>13.29 mol/L	>226.3 g/L	Corrosive (C) Dangerous for the environment (N)	R34, R50

S-Phrases: (S1/2), S16, S36/37/39, S45, S61.

The ammonia vapour from concentrated ammonia solutions is severely irritating to the eyes and the respiratory tract, and these solutions should only be handled in a fume hood. Saturated ("0.880" — see #Properties) solutions can develop a significant pressure inside a closed bottle in warm weather, and the bottle should be opened with care; this is not usually a problem for 25% ("0.900") solutions.

Ammonia solutions should not be mixed with halogens, as toxic and/or explosive products are formed. Prolonged contact of ammonia solutions with silver, mercury or iodide salts can also lead to explosive products: such mixtures are often formed in qualitative inorganic analysis, and should be lightly acidified but not concentrated (<6% w/v) before disposal once the test is completed.

Laboratory use of anhydrous ammonia (gas or liquid)

Anhydrous ammonia is classified as toxic (T) and dangerous for the environment (N). The gas is flammable (autoignition temperature: 651 °C) and can form explosive mixtures with air (16–25%). The permissible exposure limit (PEL) in the United States is 50 ppm (35 mg/m³), while the IDLH concentration is estimated at 300 ppm. Repeated exposure to ammonia lowers the sensitivity to the smell of the gas: normally the odour is detectable at concentrations of less than 50 ppm, but desensitised individuals may not detect it even at concentrations of 100 ppm. Anhydrous ammonia corrodes copper- and zinc-containing alloys, and so brass fittings should not be used for handling the gas. Liquid ammonia can also attack rubber and certain plastics.

Ammonia reacts violently with the halogens. Nitrogen triiodide, a primary high explosive, is formed when ammonia comes in contact with iodine. Ammonia causes the explosive polymerisation of ethylene oxide. It also forms explosive fulminating compounds with compounds of gold, silver, mercury, germanium or tellurium, and with stibine. Violent reactions have also been reported with acetaldehyde, hypochlorite solutions, potassium ferricyanide and peroxides.

Synthesis and production

Bagian ini berisi artikel tentang industrial synthesis. Untuk synthesis in certain organisms, lihat § Biosynthesis.

Lihat pula: Haber process

Production trend of ammonia between 1947 and 2007

Because of its many uses, ammonia is one of the most highly produced inorganic chemicals. Dozens of chemical plants worldwide produce ammonia. Consuming more than 1% of all man-made power, ammonia production is a significant component of the world energy budget. The USGS reports global ammonia production in 2014 was 176 million tonnes. China accounted for 32.6% of that (increasingly from coal as part of urea synthesis), followed by Russia at 8.1%, India at 7.6%, and the United States at 6.4%. About 88% of the ammonia produced was used for fertilizing agricultural crops. As of 2012 the global production of ammonia produced from natural gas using the steam reforming process was 72 percent.

Before the start of World War I, most ammonia was obtained by the dry distillation of nitrogenous vegetable and animal waste products, including camel dung, where it was distilled by the reduction of nitrous acid and nitrites with hydrogen; in addition, it was produced by the distillation of coal, and also by the decomposition of ammonium salts by alkaline hydroxides such as quicklime, the salt most generally used being the chloride (sal ammoniac) thus:

2 NH₄Cl + 2 CaO → CaCl₂ + Ca(OH)₂ + 2 NH_3(g)

Hydrogen for ammonia synthesis could also be produced economically by using the water gas reaction followed by the water gas shift reaction, produced by passing steam through red-hot coke, to give a mixture of hydrogen and carbon dioxide gases, followed by removal of the carbon dioxide "washing" the gas mixture with water under pressure (25 atmosfer standar (2.500 kPa)); or by using other sources like coal or coke gasification.

Modern ammonia-producing plants depend on industrial hydrogen production to react with atmospheric nitrogen using a magnetite catalyst or over a promoted Fe catalyst under high pressure (100 atmosfer standar (10.000 kPa)) and temperature (450 °C) to form anhydrous liquid ammonia. This step is known as the ammonia synthesis loop (also referred to as the Haber–Bosch process):

3 H₂ + N₂ → 2 NH_3(g)

Hydrogen required for ammonia synthesis could also be produced economically using other sources like coal or coke gasification or less economically from the electrolysis of water into oxygen + hydrogen and other alternatives that are presently impractical for large scale. At one time, most of Europe's ammonia was produced from the Hydro plant at Vemork, via the electrolysis route. Various renewable energy electricity sources are also potentially applicable.

As a sustainable alternative to the relatively inefficient electrolysis, hydrogen can be generated from organic wastes (such as biomass or food-industry waste) using catalytic reforming. This releases hydrogen from carbonaceous substances at only 10–20% of energy used by electrolysis and may lead to hydrogen being produced from municipal wastes at below zero cost (allowing for the tipping fees and efficient catalytic reforming, such as cold-plasma). Catalytic (thermal) reforming is possible in small, distributed (even mobile) plants, to take advantage of low-value, stranded biomass/biowaste or natural gas deposits. Conversion of such wastes into ammonia solves the problem of hydrogen storage, as hydrogen can be released economically from ammonia on-demand, without the need for high-pressure or cryogenic storage.

It is also easier to store ammonia onboard vehicles than to store hydrogen, as ammonia is less flammable than petrol or LPG.

There is significant recent progress in synthesizing ammonia more efficiently from H₂ and N₂ than with the Haber process. In 2012, Masaaki Kitano (and 9 co-authors), working with an organic ruthenium catalyst, demonstrated "Ammonia Synthesis Using a Stable Electride as an Electron Donor and Reversible Hydrogen Store". In January 2018, Yutong Gong (and 12 co-authors) demonstrated "Ternary intermetallic LaCoSi as a catalyst for N₂ activation", an equally efficient production process, not dependent on rare metal. In July 2018, Xiaoqian Wang (and 14 co-authors) demonstrated "Atomically dispersed Au 1 catalyst towards efficient electrochemical synthesis of ammonia", an even more efficient process.

For small scale laboratory synthesis, one can heat urea and Ca(OH)₂

(NH2)₂CO + Ca(OH)₂ → CaCO₃ + 2 NH₃

Amonia cair sebagai pelarut

Lihat pula: Inorganic nonaqueous solvent

Liquid ammonia is the best-known and most widely studied nonaqueous ionising solvent. Its most conspicuous property is its ability to dissolve alkali metals to form highly coloured, electrically conductive solutions containing solvated electrons. Apart from these remarkable solutions, much of the chemistry in liquid ammonia can be classified by analogy with related reactions in aqueous solutions. Comparison of the physical properties of NH₃ with those of water shows NH₃ has the lower melting point, boiling point, density, viscosity, dielectric constant and electrical conductivity; this is due at least in part to the weaker hydrogen bonding in NH₃ and because such bonding cannot form cross-linked networks, since each NH₃ molecule has only one lone pair of electrons compared with two for each H₂O molecule. The ionic self-dissociation constant of liquid NH₃ at −50 °C is about 10⁻³³ mol²·l⁻².

Solubility of salts

	Solubility (g of salt per 100 g liquid NH3)
Ammonium acetate	253.2
Ammonium nitrate	389.6
Lithium nitrate	243.7
Sodium nitrate	97.6
Potassium nitrate	10.4
Sodium fluoride	0.35
Sodium chloride	157.0
Sodium bromide	138.0
Sodium iodide	161.9
Sodium thiocyanate	205.5

Liquid ammonia is an ionising solvent, although less so than water, and dissolves a range of ionic compounds, including many nitrates, nitrites, cyanides, thiocyanates, metal cyclopentadienyl complexes and metal bis(trimethylsilyl)amides. Most ammonium salts are soluble and act as acids in liquid ammonia solutions. The solubility of halide salts increases from fluoride to iodide. A saturated solution of ammonium nitrate (Divers' solution, named after Edward Divers) contains 0.83 mol solute per mole of ammonia and has a vapour pressure of less than 1 bar even at 25 °C (77 °F).

Solutions of metals

Lihat pula: Solvated electron

Liquid ammonia will dissolve the alkali metals and other electropositive metals such as magnesium, calcium, strontium, barium, europium and ytterbium. At low concentrations (<0.06 mol/l), deep blue solutions are formed: these contain metal cations and solvated electrons, free electrons that are surrounded by a cage of ammonia molecules.

These solutions are very useful as strong reducing agents. At higher concentrations, the solutions are metallic in appearance and in electrical conductivity. At low temperatures, the two types of solution can coexist as immiscible phases.

Redox properties of liquid ammonia

Lihat pula: Redox

	E° (V, ammonia)	E° (V, water)
Li+ + e− ⇌ Li	−2.24	−3.04
K+ + e− ⇌ K	−1.98	−2.93
Na+ + e− ⇌ Na	−1.85	−2.71
Zn2+ + 2e− ⇌ Zn	−0.53	−0.76
NH4+ + e− ⇌ ½ H2 + NH3	0.00	—
Cu2+ + 2e− ⇌ Cu	+0.43	+0.34
Ag+ + e− ⇌ Ag	+0.83	+0.80

The range of thermodynamic stability of liquid ammonia solutions is very narrow, as the potential for oxidation to dinitrogen, E° (N₂ + 6NH₄⁺ + 6e⁻ ⇌ 8NH₃), is only +0.04 V. In practice, both oxidation to dinitrogen and reduction to dihydrogen are slow. This is particularly true of reducing solutions: the solutions of the alkali metals mentioned above are stable for several days, slowly decomposing to the metal amide and dihydrogen. Most studies involving liquid ammonia solutions are done in reducing conditions; although oxidation of liquid ammonia is usually slow, there is still a risk of explosion, particularly if transition metal ions are present as possible catalysts.

Ammonia's role in biological systems and human disease

Main symptoms of hyperammonemia (ammonia reaching toxic concentrations).

Ammonia is both a metabolic waste and a metabolic input throughout the biosphere. It is an important source of nitrogen for living systems. Although atmospheric nitrogen abounds (more than 75%), few living creatures are capable of using this atmospheric nitrogen in its diatomic form, N₂ gas. Therefore, nitrogen fixation is required for the synthesis of amino acids, which are the building blocks of protein. Some plants rely on ammonia and other nitrogenous wastes incorporated into the soil by decaying matter. Others, such as nitrogen-fixing legumes, benefit from symbiotic relationships with rhizobia that create ammonia from atmospheric nitrogen.

Biosynthesis

In certain organisms, ammonia is produced from atmospheric nitrogen by enzymes called nitrogenases. The overall process is called nitrogen fixation. Intense effort has been directed toward understanding the mechanism of biological nitrogen fixation; the scientific interest in this problem is motivated by the unusual structure of the active site of the enzyme, which consists of an Fe₇MoS₉ ensemble.

Ammonia is also a metabolic product of amino acid deamination catalyzed by enzymes such as glutamate dehydrogenase 1. Ammonia excretion is common in aquatic animals. In humans, it is quickly converted to urea, which is much less toxic, particularly less basic. This urea is a major component of the dry weight of urine. Most reptiles, birds, insects, and snails excrete uric acid solely as nitrogenous waste.

In physiology

Ammonia also plays a role in both normal and abnormal animal physiology. It is biosynthesised through normal amino acid metabolism and is toxic in high concentrations. The liver converts ammonia to urea through a series of reactions known as the urea cycle. Liver dysfunction, such as that seen in cirrhosis, may lead to elevated amounts of ammonia in the blood (hyperammonemia). Likewise, defects in the enzymes responsible for the urea cycle, such as ornithine transcarbamylase, lead to hyperammonemia. Hyperammonemia contributes to the confusion and coma of hepatic encephalopathy, as well as the neurologic disease common in people with urea cycle defects and organic acidurias.

Ammonia is important for normal animal acid/base balance. After formation of ammonium from glutamine, α-ketoglutarate may be degraded to produce two molecules of bicarbonate, which are then available as buffers for dietary acids. Ammonium is excreted in the urine, resulting in net acid loss. Ammonia may itself diffuse across the renal tubules, combine with a hydrogen ion, and thus allow for further acid excretion.

Excretion

Artikel utama: Excretion

Ammonium ions are a toxic waste product of metabolism in animals. In fish and aquatic invertebrates, it is excreted directly into the water. In mammals, sharks, and amphibians, it is converted in the urea cycle to urea, because it is less toxic and can be stored more efficiently. In birds, reptiles, and terrestrial snails, metabolic ammonium is converted into uric acid, which is solid, and can therefore be excreted with minimal water loss.

Reference ranges for blood tests, comparing blood content of ammonia (shown in yellow near middle) with other constituents

In astronomy

Ammonia occurs in the atmospheres of the outer gas planets such as Jupiter (0.026% ammonia) and Saturn (0.012% ammonia).

Ammonia has been detected in the atmospheres of the gas giant planets, including Jupiter, along with other gases like methane, hydrogen, and helium. The interior of Saturn may include frozen crystals of ammonia. It is naturally found on Deimos and Phobos – the two moons of Mars.

Interstellar space

Ammonia was first detected in interstellar space in 1968, based on microwave emissions from the direction of the galactic core. This was the first polyatomic molecule to be so detected. The sensitivity of the molecule to a broad range of excitations and the ease with which it can be observed in a number of regions has made ammonia one of the most important molecules for studies of molecular clouds. The relative intensity of the ammonia lines can be used to measure the temperature of the emitting medium.

The following isotopic species of ammonia have been detected:

NH₃, ¹⁵NH₃, NH₂D, NHD₂, and ND₃

The detection of triply deuterated ammonia was considered a surprise as deuterium is relatively scarce. It is thought that the low-temperature conditions allow this molecule to survive and accumulate.

Since its interstellar discovery, NH₃ has proved to be an invaluable spectroscopic tool in the study of the interstellar medium. With a large number of transitions sensitive to a wide range of excitation conditions, NH₃ has been widely astronomically detected – its detection has been reported in hundreds of journal articles. Listed below is a sample of journal articles that highlights the range of detectors that have been used to identify ammonia.

The study of interstellar ammonia has been important to a number of areas of research in the last few decades. Some of these are delineated below and primarily involve using ammonia as an interstellar thermometer.

Interstellar formation mechanisms

Ball-and-stick model of the diamminesilver(I) cation, [Ag(NH₃)₂]⁺

The interstellar abundance for ammonia has been measured for a variety of environments. The [NH₃]/[H₂] ratio has been estimated to range from 10⁻⁷ in small dark clouds up to 10⁻⁵ in the dense core of the Orion Molecular Cloud Complex. Although a total of 18 total production routes have been proposed, the principal formation mechanism for interstellar NH₃ is the reaction:

NH₄⁺ + e⁻ → NH₃ + H·

The rate constant, k, of this reaction depends on the temperature of the environment, with a value of 5.2×10⁻⁶ at 10 K. The rate constant was calculated from the formula $k=a(T/300)^{B}$. For the primary formation reaction, a = 1,05×10⁻⁶ and B = −0.47. Assuming an NH₄⁺ abundance of 3×10⁻⁷ and an electron abundance of 10⁻⁷ typical of molecular clouds, the formation will proceed at a rate of 1,6×10⁻⁹ cm⁻³s⁻¹ in a molecular cloud of total density 10⁵ cm⁻³.

All other proposed formation reactions have rate constants of between 2 and 13 orders of magnitude smaller, making their contribution to the abundance of ammonia relatively insignificant. As an example of the minor contribution other formation reactions play, the reaction:

H₂ + NH₂ → NH₃ + H

has a rate constant of 2.2×10⁻¹⁵. Assuming H₂ densities of 10⁵ and [NH₂]/[H₂] ratio of 10⁻⁷, this reaction proceeds at a rate of 2.2×10⁻¹², more than 3 orders of magnitude slower than the primary reaction above.

Some of the other possible formation reactions are:

H⁻ + NH₄⁺ → NH₃ + H₂

PNH₃⁺ + e⁻ → P + NH₃

Interstellar destruction mechanisms

There are 113 total proposed reactions leading to the destruction of NH₃. Of these, 39 were tabulated in extensive tables of the chemistry among C, N, and O compounds. A review of interstellar ammonia cites the following reactions as the principal dissociation mechanisms:

${\ce {NH3 + H3+ -> NH4+ + H2}}$

(1)

${\ce {NH3 + HCO+ -> NH4+ + CO}}$

(2)

with rate constants of 4.39×10⁻⁹ and 2.2×10⁻⁹, respectively. The above equations (1, 2) run at a rate of 8.8×10⁻⁹ and 4.4×10⁻¹³, respectively. These calculations assumed the given rate constants and abundances of [NH₃]/[H₂] = 10⁻⁵, [H₃⁺]/[H₂] = 2×10⁻⁵, [HCO⁺]/[H₂] = 2×10⁻⁹, and total densities of n = 10⁵, typical of cold, dense, molecular clouds. Clearly, between these two primary reactions, equation (1) is the dominant destruction reaction, with a rate ~10,000 times faster than equation (2). This is due to the relatively high abundance of H₃⁺.

Single antenna detections

Radio observations of NH₃ from the Effelsberg 100-m Radio Telescope reveal that the ammonia line is separated into two components – a background ridge and an unresolved core. The background corresponds well with the locations previously detected CO. The 25 m Chilbolton telescope in England detected radio signatures of ammonia in H II regions, HNH₂O masers, H-H objects, and other objects associated with star formation. A comparison of emission line widths indicates that turbulent or systematic velocities do not increase in the central cores of molecular clouds.

Microwave radiation from ammonia was observed in several galactic objects including W3(OH), Orion A, W43, W51, and five sources in the galactic centre. The high detection rate indicates that this is a common molecule in the interstellar medium and that high-density regions are common in the galaxy.

Interferometric studies

VLA observations of NH₃ in seven regions with high-velocity gaseous outflows revealed condensations of less than 0.1 pc in L1551, S140, and Cepheus A. Three individual condensations were detected in Cepheus A, one of them with a highly elongated shape. They may play an important role in creating the bipolar outflow in the region.

Extragalactic ammonia was imaged using the VLA in IC 342. The hot gas has temperatures above 70 K, which was inferred from ammonia line ratios and appears to be closely associated with the innermost portions of the nuclear bar seen in CO. NH₃ was also monitored by VLA toward a sample of four galactic ultracompact HII regions: G9.62+0.19, G10.47+0.03, G29.96-0.02, and G31.41+0.31. Based upon temperature and density diagnostics, it is concluded that in general such clumps are probably the sites of massive star formation in an early evolutionary phase prior to the development of an ultracompact HII region.

Infrared detections

Absorption at 2.97 micrometres due to solid ammonia was recorded from interstellar grains in the Becklin-Neugebauer Object and probably in NGC 2264-IR as well. This detection helped explain the physical shape of previously poorly understood and related ice absorption lines.

A spectrum of the disk of Jupiter was obtained from the Kuiper Airborne Observatory, covering the 100 to 300 cm⁻¹ spectral range. Analysis of the spectrum provides information on global mean properties of ammonia gas and an ammonia ice haze.

A total of 149 dark cloud positions were surveyed for evidence of 'dense cores' by using the (J,K) = (1,1) rotating inversion line of NH₃. In general, the cores are not spherically shaped, with aspect ratios ranging from 1.1 to 4.4. It is also found that cores with stars have broader lines than cores without stars.

Ammonia has been detected in the Draco Nebula and in one or possibly two molecular clouds, which are associated with the high-latitude galactic infrared cirrus. The finding is significant because they may represent the birthplaces for the Population I metallicity B-type stars in the galactic halo that could have been borne in the galactic disk.

Observations of nearby dark clouds

By balancing and stimulated emission with spontaneous emission, it is possible to construct a relation between excitation temperature and density. Moreover, since the transitional levels of ammonia can be approximated by a 2-level system at low temperatures, this calculation is fairly simple. This premise can be applied to dark clouds, regions suspected of having extremely low temperatures and possible sites for future star formation. Detections of ammonia in dark clouds show very narrow lines—indicative not only of low temperatures, but also of a low level of inner-cloud turbulence. Line ratio calculations provide a measurement of cloud temperature that is independent of previous CO observations. The ammonia observations were consistent with CO measurements of rotation temperatures of ~10 K. With this, densities can be determined, and have been calculated to range between 10⁴ and 10⁵ cm⁻³ in dark clouds. Mapping of NH₃ gives typical clouds sizes of 0.1 pc and masses near 1 solar mass. These cold, dense cores are the sites of future star formation.

UC HII regions

Ultra-compact HII regions are among the best tracers of high-mass star formation. The dense material surrounding UCHII regions is likely primarily molecular. Since a complete study of massive star formation necessarily involves the cloud from which the star formed, ammonia is an invaluable tool in understanding this surrounding molecular material. Since this molecular material can be spatially resolved, it is possible to constrain the heating/ionising sources, temperatures, masses, and sizes of the regions. Doppler-shifted velocity components allow for the separation of distinct regions of molecular gas that can trace outflows and hot cores originating from forming stars.

Extragalactic detection

Ammonia has been detected in external galaxies, and by simultaneously measuring several lines, it is possible to directly measure the gas temperature in these galaxies. Line ratios imply that gas temperatures are warm (~50 K), originating from dense clouds with sizes of tens of pc. This picture is consistent with the picture within our Milky Way galaxy—hot dense molecular cores form around newly forming stars embedded in larger clouds of molecular material on the scale of several hundred pc (giant molecular clouds; GMCs).

See also

• Ammonia (data page)
• Ammonia fountain
• Ammonia production
• Ammonia solution
• Cost of electricity by source
• Forming gas
• Haber process
• Hydrazine
• Water purification

References

• "Aqua Ammonia". airgasspecialtyproducts.com. Diarsipkan dari versi asli tanggal 19 November 2010. Diakses tanggal 28 November 2010. 
•  Artikel ini menyertakan teks dari suatu terbitan yang sekarang berada pada ranah publik: Chisholm, Hugh, ed. (1911). "Ammonia". Encyclopædia Britannica. 1 (edisi ke-11). Cambridge University Press. hlm. 861–863. 

Further reading

• Bretherick, L., ed. (1986). Hazards in the Chemical Laboratory (edisi ke-4th). London: Royal Society of Chemistry. ISBN 978-0-85186-489-1. OCLC 16985764. 
• Greenwood, Norman N.; Earnshaw, A. (1997), Chemistry of the Elements (edisi ke-2), Oxford: Butterworth-Heinemann, ISBN 0-7506-3365-4 Pemeliharaan CS1: Banyak nama: authors list (link)
• Housecroft, C. E.; Sharpe, A. G. (2000). Inorganic Chemistry (edisi ke-1st). New York: Prentice Hall. ISBN 978-0582310803. 
• Weast, R. C., ed. (1972). Handbook of Chemistry and Physics (edisi ke-53). Cleveland, OH: Chemical Rubber Co. 

External links

• International Chemical Safety Card 0414 (anhydrous ammonia), ilo.org.
• International Chemical Safety Card 0215 (aqueous solutions), ilo.org.
• CID {{{1}}} dari PubChem
• "Ammoniac et solutions aqueuses" (dalam bahasa Prancis). Institut National de Recherche et de Sécurité. Diarsipkan dari versi asli tanggal 11 December 2010. 
• Emergency Response to Ammonia Fertilizer Releases (Spills) for the Minnesota Department of Agriculture.ammoniaspills.org
• National Institute for Occupational Safety and Health – Ammonia Page, cdc.gov
• NIOSH Pocket Guide to Chemical Hazards – Ammonia, cdc.gov
• Ammonia, video