# Ammonia solution
**Ammonia solution** is ammonia gas (NH₃) dissolved in water, sold and used under the names aqueous ammonia, ammonia water, and, on many commercial labels, ammonium hydroxide (NH₄OH). It is a colorless, strongly alkaline liquid with a pungent odor, ranging from dilute household cleaners to concentrated industrial reagents, and it is one of the most widely handled forms of ammonia.[1](https://www.gov.uk/government/publications/ammonia-properties-incident-management-and-toxicology/ammonia-general-information)
| Key fact | Detail |
|---|---|
| Other names | Ammonium hydroxide, aqueous ammonia, ammonia water; CAS number 1336-21-6 (ammonia itself is 7664-41-7)[2](https://www.epa.gov/rmp/ammonia-present-ammonium-hydroxide) |
| Typical concentrations | Household solutions 5–10% (weight:volume); commercial solutions 25% (w:v) or more, which are corrosive[3](https://wwwn.cdc.gov/Tsp/MMG/MMGDetails.aspx?mmgid=7&toxid=2) |
| Basicity | A weak base: Kb = 1.8 × 10−5 (pKb = 4.74) at 25 °C; a 1.0 M solution has pH 11.63[4](https://chem.libretexts.org/Courses/Manchester_University/CHEM_111_and_CHEM_113_%28General_Chemistry_I_and_II%29/11%3A_Acids_and_Bases_Have_Common_Properties_and_Reactions/11.05%3A_Equilibria_and_pH_of_Weak_Acid_and_Salt_Solutions) |
| Physical data (25% m/m solution) | Density 0.906 g/cm³ at 20 °C; vapor pressure 44 kPa at 21 °C; begins to boil at about 38 °C[5](https://www.iteh.us/catalog/standards/cen/92244844-476a-4d97-a5fb-4cc3bc4811fa/en-12122-2024) |
| Regulatory threshold | Under 40 CFR Part 68, solutions with 20% or greater ammonia are subject to threshold determination for "ammonia (conc 20% or greater)"[2](https://www.epa.gov/rmp/ammonia-present-ammonium-hydroxide) |
| Key hazard | Mixing ammonia solution with chlorine bleach produces toxic chloramine gases[6](https://medlineplus.gov/ency/article/002759.htm) • [17](https://www.atsdr.cdc.gov/toxprofiles/tp172.pdf) • [18](https://www.poison.org/articles/chlorine-gas) |
## What the solution actually contains
Dissolved ammonia is only partly ionized. The equilibrium is
\[ NH_{3(aq)} + H_2O_{(l)} \rightleftharpoons NH^+_{4(aq)} + OH^-_{(aq)} \]
with
\[ K_b = \frac{[NH_4^+][OH^-]}{[NH_3]} \]
A measured pH of 11.63 for a 1.0 M solution at 25 °C gives Kb = 1.8 × 10−5 and pKb = 4.74, meaning only a small fraction of the ammonia, about 0.4%, is present as ammonium and hydroxide ions at that concentration.[4](https://chem.libretexts.org/Courses/Manchester_University/CHEM_111_and_CHEM_113_%28General_Chemistry_I_and_II%29/11%3A_Acids_and_Bases_Have_Common_Properties_and_Reactions/11.05%3A_Equilibria_and_pH_of_Weak_Acid_and_Salt_Solutions) A toxicological profile gives Kb = 1.774 × 10−5 at 25 °C (pKb 4.751), essentially the same value.[7](https://www.atsdr.cdc.gov/toxprofiles/tp126.pdf)
**The "ammonium hydroxide" label is a historical artifact.** The species NH₄OH does not exist as a discrete molecule in solution; the solution is mostly NH₃ and H₂O with a few percent of NH₄⁺ and OH⁻ ions. The name dates from the 19th century, before ions were understood, when chemists assumed that ammonia dissolved in water converted to a hydroxide so that neutralization reactions would fit the acid + base → salt + water pattern. Suppliers kept the NH₄OH label after the chemistry was corrected, and it persists commercially today.[8](https://www.chimia.ch/chimia/article/download/2021_679/6/10502) The US EPA takes the same practical view for regulation: ammonium hydroxide must be treated simply as a solution of ammonia and water, regardless of its unique CAS number.[2](https://www.epa.gov/rmp/ammonia-present-ammonium-hydroxide)
## Concentrations and grades
The concentration scale spans more than an order of magnitude. Household ammonia is typically 5–10% (weight:volume) and rarely causes burns, though it irritates; commercial solutions of 25% (w:v) or more are corrosive.[3](https://wwwn.cdc.gov/Tsp/MMG/MMGDetails.aspx?mmgid=7&toxid=2) The most common commercial formulation is 28–30% NH₃, and strong ammonia solution (USP) is defined as 27–30% (wt/vol).[9](https://lmpublicsearch.lm.doe.gov/sitedocs/sw-a-005940.pdf) The usual European commercial product is 25% (m/m), and the maximum practical concentration for technical products is 33–35%: above that, the partial vapor pressure of dissolved ammonia reaches atmospheric pressure and the solution appears to boil at ambient temperature while releasing large volumes of gas.[5](https://www.iteh.us/catalog/standards/cen/92244844-476a-4d97-a5fb-4cc3bc4811fa/en-12122-2024)
**Aqua ammonia** is the fertilizer-grade form, made by forcing compressed NH₃ gas into water. It usually contains 25–29% NH₃ by weight, exerts a pressure of less than 10 lb/in², and is limited to small local fluid fertilizer plants because transport and delivery costs are high.[10](https://nue.okstate.edu/N_Fertilizers/aqua_ammonia.htm) Because the dissolved NH₃ volatilizes quickly at temperatures above 50 °F, aqua ammonia is injected 2 to 4 inches into the soil, and surface applications must be incorporated immediately in warm weather.[10](https://nue.okstate.edu/N_Fertilizers/aqua_ammonia.htm) Its lower vapor pressure means it need not be injected as deeply as anhydrous ammonia and can be applied faster.[11](https://www.unido.org/publications/ot/9660800/pdf)
At the opposite end of the purity scale, high-purity aqueous ammonia with virtually no metal ion particles is produced for the semiconductor industry, where it serves as a cleaning agent and etchant for silicon wafers.[12](https://www.mgc.co.jp/eng/products/kc/super-pure-ammonium-hydroxide.html)
## Reactions and laboratory uses
Dissolution is exothermic: ammonia dissolves readily in water, evolving heat to form the corrosive, alkaline solution.[13](https://www.cdc.gov/niosh/ershdb/emergencyresponsecard_29750013.html) The solution reacts with strong oxidizers, acids, halogens including chlorine bleach, and salts of silver, zinc, copper, and other heavy metals.[14](https://www.cdc.gov/chemical-emergencies/chemical-fact-sheets/ammonia.html)
In qualitative analysis, aqueous ammonia acts in two roles toward transition-metal ions: as a Brønsted base and as a ligand. Added to solutions of Cu²⁺, Co²⁺, or Ni²⁺, it first precipitates the metal hydroxide; in excess ammonia the precipitate dissolves to give deeply colored complex ions such as the dark blue Cu(NH₃)₄²⁺.[15](https://www.colorado.edu/lab/lecture-demo-manual/e740-equilibrium-complex-ions-metal-ammonia-complexes) Dissolving copper(II) sulfate in aqueous ammonia involves nine simultaneous equilibria at once, including the stepwise formation of the four ammine complexes.[16](https://chemed.chem.purdue.edu/genchem/topicreview/bp/ch18/combine.php)
## Health effects and handling
Injury depends on concentration and duration. Dilute solutions below 5% rarely cause serious burns but can be moderately irritating; concentrated vapor or solution causes pain, inflammation, blisters, necrosis, and deep penetrating burns, especially on moist skin.[3](https://wwwn.cdc.gov/Tsp/MMG/MMGDetails.aspx?mmgid=7&toxid=2) Eye splashes can cause damage that may be irreversible and lead to loss of sight.[1](https://www.gov.uk/government/publications/ammonia-properties-incident-management-and-toxicology/ammonia-general-information) There is no antidote for ammonia toxicity; treatment is supportive of respiratory and cardiovascular function, and vomiting must not be induced after ingestion.[13](https://www.cdc.gov/niosh/ershdb/emergencyresponsecard_29750013.html)
The odor threshold, about 5 ppm against an OSHA permissible exposure limit of 50 ppm, normally gives adequate warning, but prolonged exposure produces olfactory fatigue, so the smell disappears while exposure continues.[3](https://wwwn.cdc.gov/Tsp/MMG/MMGDetails.aspx?mmgid=7&toxid=2) People with asthma or other chronic lung disease are more sensitive to inhaled ammonia.[14](https://www.cdc.gov/chemical-emergencies/chemical-fact-sheets/ammonia.html)
**Mixing cleaners is the main household danger.** Combining ammonia solution with chlorine bleach can release toxic chloramine gas, which can cause severe symptoms at high exposures.[6](https://medlineplus.gov/ency/article/002759.htm) • [18](https://www.poison.org/articles/chlorine-gas) [First aid](https://www.edgepedia.org/first-aid) for skin contact is to remove soiled clothing without pulling it over the head and wash the area with lukewarm water and soap for at least 10 to 15 minutes; for eye contact, remove contact lenses and irrigate with lukewarm water for at least 10 to 15 minutes, then seek medical advice.[1](https://www.gov.uk/government/publications/ammonia-properties-incident-management-and-toxicology/ammonia-general-information)
## Regulation
The US list of regulated toxic substances at 40 CFR Section 68.130 includes "ammonia (anhydrous)" and "ammonia (conc 20% or greater)" but has no separate listing for ammonium hydroxide. Facility operators must count the ammonia contained in ammonium hydroxide when determining whether a threshold is exceeded, and solutions at 20% ammonia or greater fall under the threshold determination for the concentrated listing.[2](https://www.epa.gov/rmp/ammonia-present-ammonium-hydroxide) [Transport](https://www.edgepedia.org/transport) classifications distinguish concentration ranges: ammonia solutions with more than 50% ammonia carry UN 3318, and anhydrous ammonia carries UN 1005.[13](https://www.cdc.gov/niosh/ershdb/emergencyresponsecard_29750013.html)
## References
1. [Ammonia: general information, UKHSA on GOV.UK](https://www.gov.uk/government/publications/ammonia-properties-incident-management-and-toxicology/ammonia-general-information)
2. [Ammonia present in ammonium hydroxide, US EPA](https://www.epa.gov/rmp/ammonia-present-ammonium-hydroxide)
3. [Ammonia, Medical Management Guidelines, ATSDR](https://wwwn.cdc.gov/Tsp/MMG/MMGDetails.aspx?mmgid=7&toxid=2)
4. [Equilibria and pH of Weak Acid and Salt Solutions, Chemistry LibreTexts](https://chem.libretexts.org/Courses/Manchester_University/CHEM_111_and_CHEM_113_%28General_Chemistry_I_and_II%29/11%3A_Acids_and_Bases_Have_Common_Properties_and_Reactions/11.05%3A_Equilibria_and_pH_of_Weak_Acid_and_Salt_Solutions)
5. [EN 12122:2024, Ammonia solution for industrial use, iTeh](https://www.iteh.us/catalog/standards/cen/92244844-476a-4d97-a5fb-4cc3bc4811fa/en-12122-2024)
6. [Ammonia poisoning, MedlinePlus Medical Encyclopedia](https://medlineplus.gov/ency/article/002759.htm)
7. [Toxicological Profile for Ammonia, ATSDR](https://www.atsdr.cdc.gov/toxprofiles/tp126.pdf)
8. [Maurice Cosandey (2021). Why We Are all Using a Nonexistent Substance: NH4OH. CHIMIA 75, 679–680.](https://www.chimia.ch/chimia/article/download/2021_679/6/10502)
9. [Ammonia 113, US Department of Energy site document](https://lmpublicsearch.lm.doe.gov/sitedocs/sw-a-005940.pdf)
10. [Aqua Ammonia, Oklahoma State University Nutrient Management](https://nue.okstate.edu/N_Fertilizers/aqua_ammonia.htm)
11. [Fertilizer Manual, UNIDO](https://www.unido.org/publications/ot/9660800/pdf)
12. [Super-pure ammonium hydroxide, Mitsubishi Gas Chemical Company](https://www.mgc.co.jp/eng/products/kc/super-pure-ammonium-hydroxide.html)
13. [Ammonia Solution, Ammonia, Anhydrous: Lung Damaging Agent, NIOSH Emergency Response Safety and Health Database](https://www.cdc.gov/niosh/ershdb/emergencyresponsecard_29750013.html)
14. [Ammonia, Chemical Emergencies fact sheet, CDC](https://www.cdc.gov/chemical-emergencies/chemical-fact-sheets/ammonia.html)
15. [E740: Equilibrium – Complex Ions – Metal + Ammonia Complexes, University of Colorado Boulder](https://www.colorado.edu/lab/lecture-demo-manual/e740-equilibrium-complex-ions-metal-ammonia-complexes)
16. [Combined Equilibria, Purdue University Chemistry](https://chemed.chem.purdue.edu/genchem/topicreview/bp/ch18/combine.php)
17. [atsdr.cdc.gov](https://www.atsdr.cdc.gov/toxprofiles/tp172.pdf)
18. [poison.org](https://www.poison.org/articles/chlorine-gas)
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*Topic: Encyclopedia › Physical world and mathematics › Chemistry › Elements and inorganic substances*
*Initially written Sep 17, 2026 · Reviewed: Oct 15, 2026 · Edited: Oct 15, 2026 · Last review: Oct 15, 2026*
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