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Different methods to determine the equivalence point include: pH indicator A pH indicator is a substance that changes color in response to a chemical change. An acid-base indicator (e.g., phenolphthalein) changes color depending on the pH. Redox indicators are also frequently used. A drop of indicator solution is added to the titration at the ...
Between the two buffer regions there is an end-point, or equivalence point, at about pH 3. 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 ...
A typical titration curve of a diprotic acid, oxalic acid, titrated with a strong base, sodium hydroxide.Both equivalence points are visible. Titrations are often recorded on graphs called titration curves, which generally contain the volume of the titrant as the independent variable and the pH of the solution as the dependent variable (because it changes depending on the composition of the ...
However, there is disagreement among practitioners as to which data to plot, whether using only data on one side of equivalence or on both sides, and whether to select data nearest equivalence or in the most linear portions: [4] [5] using the data nearest the equivalence point will enable the two x-intercepts to be more coincident with each ...
pH after the equivalence point; 1. The initial pH is approximated for a weak acid solution in water using the equation: [1] = [+] where [+] is the initial concentration of the hydronium ion. 2. The pH before the equivalence point depends on the amount of weak acid remaining and the amount of conjugate base formed.
The isoelectric point (pI, pH(I), IEP), is the pH at which a molecule carries no net electrical charge or is electrically neutral in the statistical mean. The standard nomenclature to represent the isoelectric point is pH(I). [1] However, pI is also used. [2] For brevity, this article uses pI.
The equations, derived from the acidity constant and basicity constant, states that when pH equals the pK a or pK b value of the indicator, both species are present in a 1:1 ratio. If pH is above the p K a or p K b value, the concentration of the conjugate base is greater than the concentration of the acid, and the color associated with the ...
Speciation of ions refers to the changing concentration of varying forms of an ion as the pH of the solution changes. [1]The ratio of acid, AH and conjugate base, A −, concentrations varies as the difference between the pH and the pK a varies, in accordance with the Henderson-Hasselbalch equation.