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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.
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.
Hydrocarbon-based surfactants are an example group of amphiphilic compounds. Their polar region can be either ionic , or non-ionic. Some typical members of this group are: sodium dodecyl sulfate ( anionic ), benzalkonium chloride ( cationic ), cocamidopropyl betaine ( zwitterionic ), and 1-octanol (long-chain alcohol, non-ionic).
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 −
The number of solvent molecules surrounding each unit of solute is called the hydration number of the solute. A classic example is when water molecules arrange around a metal ion. If the metal ion is a cation, the electronegative oxygen atom of the water molecule would be attracted electrostatically to the positive charge on the metal ion.
In biology, the solvent exposure of an amino acid in a protein measures to what extent the amino acid is accessible to the solvent (usually water) surrounding the protein. Generally speaking, hydrophobic amino acids will be buried inside the protein and thus shielded from the solvent, while hydrophilic amino acids will be close to the surface ...
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]
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 ]