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An amphiprotic molecule (or ion) can either donate or accept a proton, thus acting either as an acid or a base. Water, amino acids, hydrogencarbonate ion (or bicarbonate ion) HCO − 3, dihydrogen phosphate ion H 2 PO − 4, and hydrogensulfate ion (or bisulfate ion) HSO − 4 are common examples of amphiprotic species. Since they can donate a ...
For example, anhydrous acetic acid (CH 3 COOH) as solvent is a weaker proton acceptor than water. Strong aqueous acids such as hydrochloric acid and perchloric acid are only partly dissociated in anhydrous acetic acid and their strengths are unequal; in fact perchloric acid is about 5000 times stronger than hydrochloric acid in this solvent. [ 3 ]
The bicarbonate ion carries a negative one formal charge and is an amphiprotic species which has both acidic and basic properties. It is both the conjugate base of carbonic acid H 2 CO 3; and the conjugate acid of CO 2− 3, the carbonate ion, as shown by these equilibrium reactions: CO 2− 3 + 2 H 2 O ⇌ HCO −
A species that can either accept or donate a proton is referred to as amphiprotic. An example is the H 2 O (water) molecule, which can gain a proton to form the hydronium ion, H 3 O +, or lose a proton, leaving the hydroxide ion, OH −. The relative ability of a molecule to give up a proton is measured by its pK a value.
As a result of having both lipophilic and hydrophilic portions, some amphiphilic compounds may dissolve in water and to some extent in non-polar organic solvents. When placed in an immiscible biphasic system consisting of aqueous and organic solvents, the amphiphilic compound will partition the two phases.
In general terms, any solvent that contains a labile H + is called a protic solvent. The molecules of such solvents readily donate protons (H +) to solutes, often via hydrogen bonding. Water is the most common protic solvent. Conversely, polar aprotic solvents cannot donate protons but still have the ability to dissolve many salts. [1] [2]
The most abundant phospholipids that are found in cell membranes of mammalian cells are examples of amphiphiles that readily form inverse topology lyotropic phases. Even within the same phases, self-assembled structures are tunable by the concentration: For example, in lamellar phases, the layer distances increase with the solvent volume.
These solvents all possess atoms with odd atomic numbers, either nitrogen or a halogen. Such atoms enable the formation of singly charged, nonradical ions (which must have at least one odd-atomic-number atom), which are the most favorable autoionization products. Protic solvents, mentioned previously, use hydrogen for this role.