Aluminum hydroxide, amphoteric

Tlie amphoteric behavior of aluminum hydroxide, wliich dissolves readily in strong acids and bases, is shown in Figure 4. In the pH range of 4 to 9, a small change in pH towards the neutral value causes rapid and voluminous precipitation of colloidal hydroxide wliich readily fomis a gel. Gels are also fomied by the hydrolysis of organoaluminum compounds such as aluminum alkoxides (see Alkoxides, metal). 

Aluminum is the most abundant metallic element in the Earth s crust and, after oxygen and silicon, the third most abundant element (see Fig. 14.1). However, the aluminum content in most minerals is low, and the commercial source of aluminum, bauxite, is a hydrated, impure oxide, Al203-xH20, where x can range from 1 to 3. Bauxite ore, which is red from the iron oxides that it contains (Fig. 14.23), is processed to obtain alumina, A1203, in the Bayer process. In this process, the ore is first treated with aqueous sodium hydroxide, which dissolves the amphoteric alumina as the aluminate ion, Al(OH)4 (aq). Carbon dioxide is then bubbled through the solution to remove OH ions as HCO and to convert some of the aluminate ions into aluminum hydroxide, which precipitates. The aluminum hydroxide is removed and dehydrated to the oxide by heating to 1200°C. 

This way a neutralization reaction can lead to an enhancement of the solubility of an otherwise insoluble or sparingly soluble material. Because of its ability to dissolve both in acid and alkali, aluminum hydroxide is known as an amphoteric hydroxide. 

There are certain substances which can act acids as well as bases, and these are called amphoteric. A number of metallic hydroxides are amphoteric examples include aluminum hydroxide, zinc hydroxide, and tin hydroxide. Thus, zinc hydroxide, Zn(OH)2, is capable of reacting with hydrochloric acid to form zinc chloride ... 

Which of the following unbalanced equation(s) demonstrates aluminum hydroxide s amphoteric properties ... 

Gallium hydroxide is amphoteric, and is a much stronger acid than aluminum hydroxide. For Ga(OH)3 the first acid dissociation constant is 1.4 x 10-7 [for Al(OH)3 the value is 2 x 10-11].1 Polymerization occurs in aqueous Ga3+ solutions to which OH- is added,533 but this tendency is less than in the case of aluminum solutions (Section 25.1.5.1). The formation constants of mononuclear hydroxo complexes of Ga, including Ga(OH)4, and the hydrolysis constants of gallium ions have been measured by a competing ligand technique.534... 

The hydroxo complex ions formed in this way have instability constants, just as ammine or other complexes do. These instability constants are somewhat special, in that one of the products of the equilibrium is the insoluble amphoteric hydroxide. Thus, for aluminum hydroxide,... 

Hydroxyaluminum compounds are considered "amphoteric" (e.g., they can act as both acids and bases in solution) (Cotton and Wilkinson 1988). Because of this property, aluminum hydroxides can act as buffers and resist pH changes within the narrow pH range of 4-5 (Brusewitz 1984). 

Aluminum hydroxide is amphoteric it is itself insoluble, but its salts, such as A1C13 and Na3A103, are very soluble it is therefore most easy to observe whether the aluminum hydroxide reacts with an add or a base, because if it does it is seen to dissolve. 

Describe the successive observations that are made when NaOH solution is added gradually to an AlCU solution until an excess of the base is present. Likewise describe observations when HC1 solution is added gradually to an Na3A103 solution until the acid is in excess. Write fully ionized intersecting equations corresponding to each observation, and explain how the amphoteric character of aluminum hydroxide is manifested in this experiment. 

Of the above precipitates, zinc hydroxide alone dissolves freely in excess of the reagent. It forms the soluble salt sodium zincate, Na2Zn02, and it is thus an amphoteric substance like aluminum hydroxide (compare Experiments 2, 3, 4, and 5, page 217). 

On this side, folks, we have Nellie s fiance, Aluminum Hydroxide. He s very temperamental and when he gets sore he goes acidic and basic by turns. It s colossal, he s colloidal, in fact he s amphoteric, and as for the girls—he ionizes them. 

Aluminum hydroxide is amphoteric and will dissolve in both acidic and basic solutions. Write balanced chemical equations representing each process. 

PFHS often markedly improves the efficiency of separation. For example, in the precipitation of aluminum hydroxide by addition of ammonia, narrow pH limits must be maintained to get quantitative precipitation, because of the amphoteric properties of aluminum hydroxide. Consequently, it is impossible to regulate the ratio of ammonium ion and ammonia to attain minimum coprecipitation. Copper,... 

Aluminum hydroxide is a typical amphoteric metal hydroxide. Its behavior as a base is illustrated by its reaction with nitric acid to form a normal salt. The balanced formula unit, total ionic, and net ionic equations for this reaction are, respectively ... 

Draw the Lewis formula of aluminum hydroxide, and explain the features that enable it to possess amphoteric properties. 

In contrast to silica, alumina solubility is influenced profoundly by the fact that aluminum hydroxide, a common product of mineral weathering, is amphoteric. It can react in acid solutions to yield ions, and in alkaline solutions to form... 

We have seen that the alkali and alkaline earth metal hydroxides [except Be(OH)2l are basic in properties. The following hydroxides are amphoteric Be(OH)2, Al(OH)3, Sn(OH)2, Pb(OH)2, Cr(OH)3, Cu(OH)2, Zn(OH)2, and Cd(OH)2. For example, aluminum hydroxide reacts with both acids and bases ... 

Aluminum hydroxide is an amphoteric substance. It can act as either a Bronsted-Lowry base or a Lewis acid. Write a reaction showing AI(OH)3 acting as a base toward H and as an acid toward OH . 

Owing to aluminum s ability to form amphoteric hydroxides, the aluminum hydroxide precipitate dissolves on the further addition of dilute sodium hydroxide solution Rasa hydroxo complex is created. 

According to their amphoteric nature, aluminum hydroxides have their minimum solubdity in water at a close-to-neutral pH value, that is, in the pH range of 6—7. At a pH larger than 8.5, the solubihty increases, and the [A1(0H)4] anion is formed. At a pH smaller than 4, the aquo cation [A1(0H2)6] is reported to be predominant, whereas at a pH between 4 and 6, its dissociated form [Al(OH2)5(OH)] prevails (36,37), likely both with less tightly bound water molecules in the secondary hydration shell. However, the speciation of aluminum in aqueous environments is very complicated. Depending on the conditions, such as pH, concentration (or hydrolysis ratio), and anions present, a variety of polynuclear species can be found in solution. In pure water, polynuclear species include dimers... 

A weakly acidic behavior is typical of the sdanol groups of silica as well as of the B—OH groups of boria-containing materials. Considering that aluminum is at the border between metal and semimetal character and that aluminum hydroxides are typically amphoteric, both bonding concepts may apply. In other words, the properties of bulk alumina are better explained in terms of ionicity of the Al —bonds, whereas the Al—OH groups at the surface may have a more covalent character. 

A substance that both reacts with acids, thus behaving as a base, and that reacts with bases, thus behaving as an acid, is termed amphoteric. The relative acid and base strength of aluminum hydroxide, Al(0H)3, can be illustrated in several simple tests. 

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