Ammonium Hydroxide Facts and Formula

Ammonium hydroxide is the name given to any aqueous (water-based) solution of ammonia. In pure form, it is a clear liquid that smells strongly of ammonia. Household ammonia usually is 5-10% ammonium hydroxide solution.

Names for Ammonium Hydroxide

Other names for ammonium hydroxide are:

• Ammonia (e.g., household ammonia) [versus anhydrous ammonia]
• Aqueous ammonia
• Ammonia solution
• Ammonia water
• Ammonia liquor
• Ammonical liquor
• Spirit of Hartshorn

Chemical Formula of Ammonium Hydroxide

The chemical formula of ammonium hydroxide is NH₄OH, but in practice, ammonia deprotonates some of the water, so the species found in solution are a combination of NH₃, NH₄^+,, and OH⁻ in water.

Ammonium Hydroxide Uses

Household ammonia, which is ammonium hydroxide, is a common cleaner. It's also used as a disinfectant, food leavening agent, to treat straw for cattle feed, to enhance tobacco flavor, to cycle an aquarium without fish, and as a chemical precursor for hexamethylenetetramine and ethylenediamine. In the chemistry lab, it is used for qualitative inorganic analysis and to dissolve silver oxide.

Using Ammonium Hydroxide for Cleaning

Liquid ammonia is a popular cleaning agent. It is highly effective at cleaning glass. The product is typically sold in unscented, lemon, and pine versions. Although liquid ammonia is already dilute, it should be further diluted prior to use. Some application call for "cloudy ammonia," which is dilute ammonia with soap. Ammonia should never be mixed with bleach. Since products don't always list their ingredients, it's wise to avoid mixing ammonia with any other cleaning product besides soap.

Concentration of Saturated Solution

It's important for chemists to realize the concentration of a saturated ammonium hydroxide solution decreases as temperature increases. If a saturated solution of ammonium hydroxide is prepared at a cool temperature and the sealed container is heated, the concentration of the solution decreases and ammonia gas can build up in the container, potentially leading it to rupture. At a minimum, unsealing the warm container releases toxic ammonia vapors.

Safety

Ammonia in any form is toxic, whether it is inhaled, absorbed through the skin, or ingested. Like most other bases, it's also corrosive, which means it can burn skin or damage mucous membranes, such as eyes and the nasal cavity. It's also important to refrain from mixing ammonia with other household chemicals because they may react to release additional toxic fumes.

Chemical Data

• Name: Ammonium hydroxide
• CAS number: 1336-21-6
• Chemical formula: NH₄OH
• Molar mass: 35.04 g/mol
• Appearance: Colorless liquid
• Odor: Pungent, fishy
• Density: 0.91 g/cm³ (25 % w/w)
• Melting point: −57.5 °C (−71.5 °F; 215.7 K) (25 % w/w)
• Boiling point: 37.7 °C (99.9 °F; 310.8 K) (25 % w/w)
• Miscibility: Miscible

Is Ammonium Hydroxide an Acid or a Base?

While pure (anhydrous) ammonia is definitely a base (a proton acceptor or substance with a pH greater than 7), people often get confused about whether ammonium hydroxide is also a base. The simple answer is that yes, ammonium hydroxide is also basic. A 1M ammonia solution has a pH of 11.63.

The reason confusion arises is because mixing ammonia and water produces a chemical reaction that yields both the ammonium cation (NH₄⁺ ) and hydroxide anion (OH⁻). The reaction may be written:

NH₃ + H₂O ⇌ NH₄⁺ + OH⁻

For a 1M solution, only around 0.42% of the ammonia converts to ammonium. The base ionization constant of ammonia is 1.8×10⁻⁵.

Sources

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• Edwards, Jessica Renee; Fung, Daniel Y.C. (2006). "Prevention and Decontamination of Escherichia coli O157:h7 on Raw Beef Carcasses in Commercial Beef Abattoirs". Journal of Rapid Methods and Automation in Microbiology. 14 (1): 1–95. doi:10.1111/j.1745-4581.2006.00037.x
• Nitsch, Christian; Heitland, Hans-Joachim; Marsen, Horst; Schlüussler, Hans-Joachim (2005). "Cleansing Agents". Ullmann's Encyclopedia of Industrial Chemistry. Weinheim: Wiley-VCH. doi:10.1002/14356007.a07_137. ISBN 978-3527306732.
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