Yes, \(\text{NH}_4\text{OH}\) is a base, and the substance it represents, aqueous ammonia, is one of the most common weak bases encountered in chemistry. A base is defined as a substance that, when dissolved in water, increases the concentration of hydroxide ions (\(\text{OH}^-\)), resulting in a \(\text{pH}\) value greater than 7. The common name, Ammonium Hydroxide (\(\text{NH}_4\text{OH}\)), is used to describe this solution of ammonia dissolved in water. This basic quality is responsible for its widespread use in household cleaning products and industrial applications.
The True Chemical Identity
The name “Ammonium Hydroxide” (\(\text{NH}_4\text{OH}\)) is a common, historical name for a solution of ammonia gas (\(\text{NH}_3\)) dissolved in water. The more accurate term for this substance is “aqueous ammonia,” denoted as \(\text{NH}_3(\text{aq})\). The discrete compound \(\text{NH}_4\text{OH}\) does not exist as an isolatable molecule in significant quantity.
When ammonia dissolves, it is primarily present as \(\text{NH}_3\) molecules. Only a small fraction of the dissolved \(\text{NH}_3\) reacts with water to form the ammonium ion (\(\text{NH}_4^+\)) and the hydroxide ion (\(\text{OH}^-\)). The use of the \(\text{NH}_4\text{OH}\) formula stems from older chemical theories, but it remains a widely used name for the commercially available solution.
How Ammonia Creates Basicity
Ammonia creates a basic solution by acting as a proton acceptor in the water. This behavior is described by the Brønsted-Lowry acid-base theory, where a base is defined as a molecule or ion capable of accepting a proton (\(\text{H}^+\)). In the solution, an ammonia molecule (\(\text{NH}_3\)) removes a proton from a water molecule (\(\text{H}_2\text{O}\)).
The reaction forms two new ions: the ammonium ion (\(\text{NH}_4^+\)) and the hydroxide ion (\(\text{OH}^-\)). The generation of the hydroxide ion is the direct chemical mechanism that increases the solution’s \(\text{pH}\) above 7. Water acts as a weak acid in this exchange, donating a proton to the ammonia molecule. The resulting solution has a \(\text{pH}\) typically in the range of 11 to 12, depending on the concentration of the ammonia.
Classification as a Weak Base
Aqueous ammonia is classified as a weak base because the reaction with water does not proceed to completion. When ammonia is dissolved, only a small percentage of the \(\text{NH}_3\) molecules convert into \(\text{OH}^-\) and \(\text{NH}_4^+\) ions. The solution exists in a state of dynamic chemical equilibrium, where the formation of ions and the reformation of \(\text{NH}_3\) and \(\text{H}_2\text{O}\) are constantly occurring.
In contrast, a strong base, such as sodium hydroxide (\(\text{NaOH}\)), dissociates nearly 100% in water, yielding a much higher concentration of hydroxide ions. Because the vast majority of ammonia molecules remain as unreacted \(\text{NH}_3\), the concentration of the \(\text{OH}^-\) ions is relatively low. This limited ionization classifies aqueous ammonia as a weak base.
Everyday Uses of Aqueous Ammonia
The basic properties of aqueous ammonia make it effective for numerous practical applications across various industries and households. Its ability to raise the \(\text{pH}\) allows it to dissolve grease and organic materials, making it a common ingredient in household cleaning agents. Household ammonia solutions typically contain between 5% and 10% ammonia by weight.
A primary industrial use is in agriculture, where ammonia is the main nitrogen source for fertilizers. Aqueous ammonia is also utilized in water treatment, often combined with chlorine to form chloramines, a long-lasting disinfectant for municipal water supplies. Its volatility is an advantage in glass cleaners, as the dissolved gas evaporates with the water, leaving a streak-free surface.