Substances amphoteric

Some substances, called amphoteric substances, can act both as an acid and a base. The simplest example is water. Water can split apart to form a hydrogen ion and a hydroxide ion  

Since it produces a hydrogen ion, water is an acid. However, the fact that it produces a hydroxide ion also makes it a base. This reaction occurs only to a very small extent. In pure water, only one out of 10 million molecules of water is in the form of H+ and OH . Except for this very low concentration of these two ions that can exist together, H+ and OH react strongly with each otiier to form water. 

Another important substance that can be either an acid or base is glycine. Glycine is one of the amino acids that are essential components of the body s proteins. It can give off a hydrogen ion. 

When an acid is dissolved in water, it splits off hydrogen ions. This change may be attributed to the ability of acids to bind hydroxyl ions. Conversely we may say that bases liberate hydroxyl ions or bind hydrogen ions. 

The general formula of an amphoteric compound may be written HXOH. Its amphoteric properties may be described by the equations  

Applying the mass action law to these reactions, we find  

Aside from the undissociated portion HXOH, a solution of an amphoteric compound contains hydrogen and hydroxyl ions, ampholyte anions XOH, and cations HX+. 

We have shown in the section on hydrolysis included in the first chapter that the reaction of salts derived from weak acids and weak bases is never strongly acidic or strongly alkaline, unless the difference between the acidic and basic dissociation constants is too large. The same explanation, applied to the acidic and basic functions of ampholytes, accounts for the fact that solutions of amphoteric compounds never react very strongly acid or alkaline. 

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Acids, bases and amphoteric substances can be purified by taking advantage of their ionisation constants. Ionisation constants and pK. 

A method offering the possibility for the separation, identification, and determination of alkyl- and alkylphenol ether carboxylates, even in mixtures with other nonionic and amphoteric substances, is carried out by HPLC using a reverse phase RP18 column and a mixture of methanol, water, and acetonitrile with the addition of an ion-pairing reagent as mobile phase working under isocratic conditions [242]. 

In the two equations above, notice that water is acting as an acid in one instance and as a base in the other. Substances like water that can act as an acid or a base depending on the circumstances are called amphoteric substances. The word comes from the Greek prefix ampho-, which means both. Water is the most common amphoteric substance, but amino acids, proteins, and some metal oxides—such as aluminum oxide (Al203) and zinc oxide (ZnO), for example—can also act as amphoteric substances. 

The solubility of antibiotics, including CTC-HC1, was reported by Andrew and Weiss (17). CTC-HC1 is an amphoteric substance and consequently it is soluble in aqueous acid and base. However, it can rapidly degrade in these solvents. Its solubility in water is about 8 mg/ml and in methanol about 17 mg/ml. In higher molecular weight alcohols, the solubility of CTC-HC1 is considerably less than in methanol. For practical purposes, it is insoluble in many common solvents such as the aliphatic hydrocarbons, benzene, ether, and chloroform. It is readily soluble in pyridine and to the extent of about 5 mg/ml in formamide. Pyridine is an undesirable solvent because of its basicity, and formamide is not desirable because of the difficulty in obtaining and maintaining it as a stable solvent. 

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 ... 

Water is an amphoteric substance, acting either as an acid or a base. 

Amphoteric substances such as water can act as both an acid and as a base. 

The proteins consist essentially of amphoteric substances existing in equilibrium with both acidic and basic dissociation products of the type... 

In an amphoteric substance the ratio of the electrically neutral particles to the total concentration is at a maximum at the isoelectric point as is evident from the following considerations. 

Amphoteric substances Substances that have acidic and basic properties. 

Free tetracyclines are crystalline amphoteric substances of low solubility. They are available as hydrochlorides, which are more soluble. Such solutions are acid and, with the exception of chlortetracycline, fairly stable. Tetracyclines chelate divalent metal ions, which can interfere with their absorption and activity. A newly approved tetracycline analog, tigecycline, is a glycylcycline and a semisynthetic derivative of minocycline. 

With the concept of Diphoterine , even the restoration of glutathione contents in the burnt cornea can be achieved without any action of the regenerating tissues. This is a major value. Dimercaprol has similar effects and might be an opportune alternative, but this drug does not act on alkali and acids as well as the buffers and amphoteric substances do. 

Amphoteric Substance. A substance having both acid and basic props, such as amino-acids, A1 hydroxide, etc Ref Hackh(1944),50... 

This mode of electrophoresis, in which the electrolyte migrates through the capillary, is the most widely used. The electrolyte can be an acidic buffer (phosphate, citrate, etc.) or basic buffer (borate) or an amphoteric substance (a molecule that possesses both an acidic and an alkaline function). The electro-osmotic flow increases with the pH of the liquid phase, or can be rendered non-existent. 

Amphoteric substance 1 A393 Amphtrack 1 A393 Ampoule (chem) 1 A393 AMR-2504 1 A393... 

Each of the methods had trouble recovering the more highly water-soluble or volatile model compounds such as trimesic acid, furfural, glucose, glycine, caffeine, and methyl isobutyl ketone. Quinaldic acid, an amphoteric substance of moderate water solubility, was also poorly recovered by each method, except for the QXAD-4 procedure. 

A previous exploratory study attempted to recover the soluble, poorly volatile subclass of organic compounds in water (3). It used a set.of sequential adsorbents. Silica gel, the first adsorbent, filtered out particulate matter and adsorbed some hydrophobic compounds. The next adsorbent was a cation-exchange bed that recovered cations and amphoteric substances, and the last adsorbent was an anion-exchange bed. The effluent from this series of adsorbents contained the neutral compounds. The eluates from each bed and the effluents were then concentrated under vacuum. This system, the parfait method, was demonstrated to recover parts-per-billion concentrations of several known mutagens in amounts sufficient to be detected by bioassay. 

Most biological processes in the cell take place in a water-based environment. Water is an amphoteric substance that is, it may serve as a proton donor (acid) or a proton acceptor (base). Equation 2.1 shows the ionic equilibrium of water. 

You will also see the term amphoteric. An amphoteric substance is a substance that reacts with both acids and bases. The term amphiprotic is more specific and refers to the ability both to donate and accept protons. 

The benzimidazoles, as we have seen, are weak bases that are soluble in aqueous acids but may be precipitated from them by the addition of a stronger base such as ammonium hydroxide. The benzimidazoles are amphoteric substances, with acidic properties also, as shown by the formation of copper, silver, and other insoluble salts they are soluble in an excess of a strong base such as sodium hydroxide and may be precipitated from solution in that base by the addition of carbon dioxide. 

Amphoteric substances are necessarily extremely weak both as acids and as bases, but they possess the property of reacting with strong acids on the one hand and with strong bases on the other hand. 

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