Ammonia, as a base

Ammonia as a base. The ammonia molecule has a powerful affinity for protons and hence. 

In both cases the nitrogen atom uses its pair of nonbonding electrons to make a new covalent bond. This similarity led G. N. Lewis to classify ammonia as a base in its reaction with B (CH3)3 as well as in its reaction with H3 O . Whereas the Br< )nsted definition focuses on proton transfer, the Lewis definition of acids and bases focuses on electron pairs. 

C—Ammonia, as a base, will precipitate the metal hydroxides. Chromate, sulfide, and chloride ions will precipitate one or more of the ions. 

Take another look at the net ionic equation of HCI with NH3 on page 523. If you adhere strictly to the definition of a base as a hydroxide-ion producer in water, none of these equations define ammonia as a base. Remember that hydroxide ions are produced, but the amount is so small that it is not shown in the equations. 

The Brpnsted definition also allows us to classify ammonia as a base because of its ability to accept a proton ... 

Aqueous ammonia also acts as a base precipitating metallic hydroxides from solutions of their salts, and in forming complex ions in the presence of excess ammonia. For example, using copper sulfate solution, cupric hydroxide, which is at first precipitated, redissolves in excess ammonia because of the formation of the complex tetramminecopper(TT) ion. 

As expected, N2H4 in aqueous solutions is somewhat weaker as a base than is ammonia (p. 423) ... 

From a mechanistic standpoint, ammonia serves two functions 1) it behaves as a base to catalyze an aldol reaction between 2 equivalents of 31 to generate the corresponding enal 33, and 2) it is the source of nitrogen for the resultant pyridyl ring. This occurs through formation of enamine 34 with a third equivalent of 31. The Michael addition of 34 to 33 followed by cyclization gives rise to 32. 

As a base, hydrazine will tend to increase the pH of the system. At ambient temperatures, the basicity of hydrazine is about one-tenth of that of ammonia, but with increasing temperature the disparity diminishes. 

The fifth substance listed as a base is ammonia, NH3. Ammonia readily forms ammonium ion, NH. Ammonia can react with water,... 

We have explained the properties of bases in terms of their abilities to react with hydrogen ion. Thus ammonia is a base because it can react as in (49) ... 

Practically, the result of reactions (48) and (49) is reaction (50). In reaction (50), we see that acetic acid acts as an acid in the same sense that it does in (48). In either case, it releases hydrogen ions. In (48) acetic acid releases hydrogen ions and forms H+(aq) and in (50) it releases hydrogen ions to NHs and forms NH/. In the same way, ammonia acts as a base in (50) by reacting with the hydrogen ion released by acetic acid. So reaction (50) is an acid-base reaction, though the net reaction does not show H+(aq) explicitly. 

The products are known as 2,3-octasubstituted or 2,3,9,10,16.17,23,24-octasubstituted phthalocyanines. As is the case for 1,4-octasubstituted phthalocyanines, only one structural isomer exists. Metal-free phthalocyanines 18 can be obtained by heating 4,5-disubstituted phthalonitriles 17 in a solvent containing a strong base such as l,8-diazabicyclo[5.4.0]undec-7-ene (DBU). Ammonia can also be used as a base. 

In many of the largest boiler plants around the world AYT programs are often employed that commonly provide for hydrazine (as an oxygen scavenger) and a volatile amine such as morpholine (to boost the pH level). Where funds are limited, however, some facilities instead use ammonia as a pH booster because it is a low-cost item with a low equivalent weight and a high DR. Unfortunately, this approach may lead to downstream problems as ammonia becomes less chemically bound with increases in FW pH and a weaker base as temperatures rise. Consequently, a point is reached when ammonia ceases to further influence the pH level upward. 

Ammonia is a base because, as we see from Eq. 1, it accepts protons from water and forms NH4+ ions. Notice that because water donates a hydrogen ion it is acting as a Bronsted acid. 

Liquid ammonia is a base, so reactions with acids generally proceed to a greater degree than do the analogous reactions in water. For example, acetic acid is a weak acid in water, but it ionizes completely in liquid ammonia. Even though ammonia is a base, it is possible for protons to be removed, but only when it reacts with exceedingly strong bases such as N3, O2, or 11. Some of the important types of reactions that occur in liquid ammonia will now be illustrated. 

The oxide ion is also sufficiently strong as a base to remove protons from ammonia. 

The conjugate acid of a base is formed when the base acquires a proton from the acid. In this reaction, water acts as an acid because it donates a proton to the ammonia molecule. The ammonium ion (NH4+) is the conjugate acid of ammonia (NH3), a base, which receives a proton from water. The hydroxide ion (OH ) is the conjugate base. 

Note that the word proton refers to the nucleus of a hydrogen atom — an H ion that has been removed from the acid molecule. It does not refer to a proton removed from the nucleus of another atom, such as oxygen or sulfur, that may be present in the acid molecule. As mentioned previously, ions share electrons with any species (ion or molecule) that has a lone pair of electrons. In aqueous solution, the proton bonds with a water molecule to form the hydronium ion. Unlike the Arrhenius theory, however, the Brqnsted-Lowry theory is not restricted to aqueous solutions. For example, the lone pair of electrons on an ammonia molecule can bond with H+, and liquid ammonia can act as a base. 

Aqueous ammonia is a weak base, so relatively few hydroxide ions form. The position of equilibrium lies to the left. In the forward reaction, the water molecule gives up a proton and acts as an acid. A substance that can act as a proton donor (an acid) in one reaction and a proton acceptor (a base) in another reaction is said to be amphoteric. (Water acts as an acid in tbe presence of a stronger base, and as a base in tbe presence of a stronger acid. 

Ammonia compounds are a primary chemical component of many reconstituted tobaccos. The importance of ammoniation in the development of the characteristic flavor popularized by Marlboro has been widely pubhcized (Bates et al. 1999 Freedman 1995 Hurt and Robertson 1998). The chemical impact of ammoniation is complex and appears to influence the form and delivery of nicotine in a variety of interconnected ways (see BW Fig. 4) (Johnson 1989). Ammoniated reconstituted tobacco has a characteristic mild sensory profile, and features a number of important compounds created through the reaction between ammonia and sugars (J.R. Reynolds 1980 Wells and Kendrick 1995). Addition of ammonia as a strong base leads to increased smoke pH, which corresponds with increased levels of free nicotine in smoke (Hurt and Robertson 1998). Thus, a 1982 position paper from RJR observed that ... ammonia in smoke is one of the major pH controlling components and that ... studies of the effect of ammonia on smoke composition showed... an increase in physiological satisfaction with increasing ammonia content (Bemasek and Nystrom 1982). 

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