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Self-ionizable compounds like water are also amphiprotic. Ampholytes are amphoteric molecules that contain both acidic and basic functional groups. For example, an amino acid H 2 N−RCH−CO 2 H has both a basic group −NH 2 and an acidic group −COOH, and exists as several structures in chemical equilibrium:
Although nearly 100% sulfuric acid solutions can be made, the subsequent loss of SO 3 at the boiling point brings the concentration to 98.3% acid. The 98.3% grade, which is more stable in storage, is the usual form of what is described as "concentrated sulfuric acid".
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.
All acids tend to become indistinguishable in strength when dissolved in strongly basic solvents owing to the greater affinity of strong bases for protons. This is called the leveling effect. [citation needed] In a differentiating solvent on the other hand, various acids dissociate to different degrees and thus have different strengths.
This end-point is not sharp and is typical of a diprotic acid whose buffer regions overlap by a small amount: pK a2 − pK a1 is about three in this example. (If the difference in pK values were about two or less, the end-point would not be noticeable.) The second end-point begins at about pH 6.3 and is sharp.
Acid strength is the tendency of an acid, symbolised by the chemical formula, to dissociate into a proton, +, and an anion, .The dissociation or ionization of a strong acid in solution is effectively complete, except in its most concentrated solutions.
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[2] [3] The basic concept of this theory is that when an acid and a base react with each other, the acid forms its conjugate base, and the base forms its conjugate acid by exchange of a proton (the hydrogen cation, or H +). This theory generalises the Arrhenius theory.