Acid- base reactions amphoteric substances

To the main mechanical washing effect, DIPHOTERINE solution adds chelating and amphoteric abilities which aim to stop each of the six possible reactions with chemical substances (acid-base reaction, reduction/oxidation, chelation, addition, substitution, solvation). Its hypertonic property allows it to attract chemical product from tissues to the outside. The solution is applied with a spray or with a shower depending on the stroked area, even if previously an irrigation with water was done previonsly. Nevertheless, some anthors have shown that the better results are obtained when DIPHOTERINE solution is first applied. 

According to the Br0nsted-Lowry definition, some substances—such as water in the previous two equations—can act as acids or bases. Substances that can act as acids or bases are amphoteric. Notice what happens when we reverse an equation representing a Br0nsted-Lowry acid-base reaction. 

Salts, which are the products of acid-base reactions, are thus not necessarily electrically neutral but rather exhibit well-defined acid-base properties in water. Acidity appears as a relative concept and the existence of amphoteric substances, i.e. substances which can behave either as acids or bases depending on the circumstances, is stressed. The proton concentration, [H+], quantifies the acidity of a solution and the pH scale is established ... 

Reaction (22) shows that Al(OH)3 has the properties of an acid, since it reacts with the base OH-. A substance that acts as an acid under some conditions and as a base under other conditions is said to be amphoteric. The electronic situation in Al(OH)3 is such that it can either accept a proton (act as a base) or react with OH- (act as an acid). We will see in Chapter 22 that several other hydroxides also show amphoteric behavior. 

The species Y is also probably non-existent in most of the enzyme catalysed reactions involving only one substrate. In acidic or basic reactions, Y and W do, however, play roles. In acid catalysed reactions, where C is an acid, transfer of proton to S takes place giving Y as a conjugate base of C. W is a basic or amphoteric substance which accepts a proton from X. In base catalysis, Y is a conjugate acid to the base C while W transfers a proton to X and may be the solvent or another acidic substance. With regard to the stability of the intermediate complex X, the two possibilities, which may be considered, are ... 

What about the elements that lie on the diagonal frontier between the metals and nonmetals On this frontier, metallic character blends into nonmetallic character, and the oxides of these elements have both acidic and basic character. Substances that react with both acids and bases are classified as amphoteric, from the Greek word for both. For example, aluminum oxide, A1203, reacts with acids, a reaction showing that it is basic ... 

An amphoteric substance is a substance that acts as an acid in some reactions and a base in others. In the two reactions below, note how water donates a proton (making it an acid) in the first reaction, while in the second reaction it receives a proton (making it a base) ... 

A Bronsted-Lowry acid is any substance that is capable of donating a proton, whereas a Bronsted-Lowry base is any substance that is capable of accepting a proton. The loss of a proton by an acid gives rise to an entity that is a potential proton acceptor and thus a base it is called the conjugate base of the parent acid. Examples of acids reacting with bases are given in Table 1.16. The reactions listed in Table 1.16 are spontaneous in the direction that favors production of the weaker acid and base. Compounds that may act as bases and acids are referred to as amphoteric. 

This brings up an interesting situation. Isn t water a neutral substance How can it react as an acid in one reaction and as a base in another Water is a substance that can gain or lose a proton depending upon the environment it is in. Water is what is called an amphoteric substance because it can act as either an acid or a base. 

Amphoteric substances, or ampholytes, are able to engage in neutralization reactions both with acids and bases (more precisely, both with hydrogen and hydroxyl ions). Aluminium hydroxide, for example, reacts with strong acids, when it dissolves and aluminium ions are formed ... 

If you took a good look at the information just presented, you might think that I made a couple of mistakes. Did you notice that I included water (HzO) and ammonia (NH3) as examples of both Brpnsted-Lowry acids and Brpnsted-Lowry bases This is no error. Water and ammonia are examples of amphoteric substances. An amphoteric substance is a substance that acts as an acid in some cases and as a base in other cases. Look at the following sets of reactions to see examples of these substances acting as both acids and bases. 

An amphoteric substance is one that may act as either an acid or a base. The hydrogen sulfite ion is amphoteric. Write reactions that demonstrate this property of HSOj . 

In the first reaction, the dihydrogen phosphate acts as a Bronsted-Lowry base, and in the second reaction, it acts as a Bronsted-Lowry acid. A substance that can act as either a Bronsted-Lowry acid or a Bronsted-Lowry base, depending on the circumstances, is called an amphoteric substance. 

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 . 

Some substances can act as an acid in one reaction and as a base in another. For example, H2O is a Bronsted-Lowry base in its reaction with HCl (Equation 16.3) and a Bronsted-Eowry acid in its reaction with NH3 (Equation 16.5). A substance that is capable of acting as eifher an acid or a base is called amphoteric. An amphoteric substance acts as a base when combined with something more strongly acidic than itself, and as an acid when combined wifh somefhing more sfrongly basic fhan ifself. 

Amphoterism is often explained by the behavior of the water molecules that surround the metal ion and that are bonded to it by Lewis acid-base interactions. (Section. 16.11) For example, Al aq) is more accurately represented as Al(Fi20)6 (flg) because six water molecules are bonded to the Ar in aqueous solution. Recall from Section 16.11 that Ihis hydrated ion is a weak acid. As a strong base is added, A1(H20)6 loses protons in a stepwise fashion, eventually forming neutral and water-insoluble A1(H20)3(0H)3. This substance then dissolves upon removal of an additional proton to form the anion A1(H20)2(0H)4. The reactions that occur are as follows ... 

Amphoterism. Write balanced equations to illustrate the reaction of each of the following substances with an acid, HA, and with a base, B. Write formulas for products and designate acid-base pairs, (a) HCO,, (b) H P04, (c) CHgOH, (d) Zn(OH)i,(HaO)a, (e) NHg. 

Typical properties of acids and bases are usually taken to be those that are observed in water solutions of acids and bases. Most of them are due to the increased concentration of solvent cation or solvent anion caused by the presence of the acid or base. The most familiar reactions dependent upon this effect probably are the reactions between the free elements and solutions of acids and bases electrolysis and the reactions of amphoteric substances. The first is the only one that requires further discussion before similar reactions in other solvents are considered. 

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. 

You may have noticed that water can act either as an acid or as a base, depending on what kind of compound it is with. A substance that can act as an acid or as a base is said to be amphoteric. In evaluating the role of water in a reaction, you have to look at the products of the reaction in order to decide if water functions as an acid or as a base. 

Some substances act as either an acid or a base, depending upon their environment. They are called amphoteric. Water is a good example. In the reaction above, water acts as a base accepting a proton. Water can also act like an acid by donating a proton. 

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