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Nitric acid, with a pK value of around −1.7, behaves as a strong acid in aqueous solutions with a pH greater than 1. [23] At lower pH values it behaves as a weak acid. pK a values for strong acids have been estimated by theoretical means. [24] For example, the pK a value of aqueous HCl has been estimated as −9.3.
These values below are pK a values determined in dimethylsulfoxide (DMSO), which has a broader useful range (~0 to ~35) than values determined in water (~0 to ~14) and better reflect the basicity of the carbanions in typical organic solvents. Values below less than 0 or greater than 35 are indirectly estimated; hence, the numerical accuracy of ...
The higher the proton affinity, the stronger the base and the weaker the conjugate acid in the gas phase.The (reportedly) strongest known base is the ortho-diethynylbenzene dianion (E pa = 1843 kJ/mol), [3] followed by the methanide anion (E pa = 1743 kJ/mol) and the hydride ion (E pa = 1675 kJ/mol), [4] making methane the weakest proton acid [5] in the gas phase, followed by dihydrogen.
Some non-aqueous solvents can behave as acids. An acidic solvent will make dissolved substances more basic. For example, the compound CH 3 COOH is known as acetic acid since it behaves as an acid in water. However, it behaves as a base in liquid hydrogen fluoride, a much more acidic solvent. [13]
Generically IUPAC defines a superbase as a "compound having a very high basicity, such as lithium diisopropylamide." [5] Superbases are often defined in two broad categories, organic and organometallic. Organic superbases are charge-neutral compounds with basicities greater than that of proton sponge (pK BH + = 18.6 in MeCN)."
Tetramethylguanidine is an organic compound with the formula HNC(N(CH 3) 2) 2. This colourless liquid is a strong base, as judged by the high pK a of its' conjugate acid. [2] It was originally prepared from tetramethylthiourea via S-methylation and amination, but alternative methods start from cyanogen iodide. [3]
The most common Lewis bases are anions. The strength of Lewis basicity correlates with the pK a of the parent acid: acids with high pK a 's give good Lewis bases. As usual, a weaker acid has a stronger conjugate base. Examples of Lewis bases based on the general definition of electron pair donor include:
In this case H 0 and H − are equivalent to pH values determined by the buffer equation or Henderson-Hasselbalch equation. However, an H 0 value of −21 (a 25% solution of SbF 5 in HSO 3 F) [5] does not imply a hydrogen ion concentration of 10 21 mol/dm 3: such a "solution" would have a density more than a hundred times greater than a neutron ...