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When the difference between successive pK values is less than about four there is overlap between the pH range of existence of the species in equilibrium. The smaller the difference, the more the overlap. The case of citric acid is shown at the right; solutions of citric acid are buffered over the whole range of pH 2.5 to 7.5.
Stronger acids have a larger and a smaller logarithmic constant (= ) than weaker acids. The stronger an acid is, the more easily it loses a proton, H + . Two key factors that contribute to the ease of deprotonation are the polarity of the H−A bond and the size of atom A , which determine the strength of the H−A bond.
Free acids of ADA, POPSO and PIPES are poorly soluble in water, but they are very soluble as monosodium salts. ADA absorbs UV light below 260 nm, and ACES absorbs it at 230 nm and below. Over the years, pK a s and other thermodynamic values of many Good's buffers have been thoroughly investigated and re-evaluated. [6]
pH indicators: a graphic view. A pH indicator is a halochromic chemical compound added in small amounts to a solution so the pH (acidity or basicity) of the solution can be determined visually or spectroscopically by changes in absorption and/or emission properties. [1]
Sulfonic acids are strong acids. They are commonly cited as being around a million times stronger than the corresponding carboxylic acid. For example, p -Toluenesulfonic acid and methanesulfonic acid have p K a values of −2.8 and −1.9, respectively, while those of benzoic acid and acetic acid are 4.20 and 4.76, respectively.
Strong acids, such as sulfuric or phosphoric acid, have large dissociation constants; weak acids, such as acetic acid, have small dissociation constants. The symbol K a , used for the acid dissociation constant, can lead to confusion with the association constant , and it may be necessary to see the reaction or the equilibrium expression to ...
A weak base is a base that, upon dissolution in water, does not dissociate completely, so that the resulting aqueous solution contains only a small proportion of hydroxide ions and the concerned basic radical, and a large proportion of undissociated molecules of the base.
Polybases are the basic equivalent of polyacids and are also known as cationic polymers. They accept protons at low pH like polyacids do, but they then become positively charged. In contrast, at higher pH values they are neutral. Swelling behavior is seen when the pH is less than the pKa of the polymer. [1]