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At half-neutralization the ratio [A −] / [HA] = 1; since log(1) = 0, the pH at half-neutralization is numerically equal to pK a. Conversely, when pH = pK a, the concentration of HA is equal to the concentration of A −. The buffer region extends over the approximate range pK a ± 2. Buffering is weak outside the range pK a ± 1.
pH = 1 / 2 pK w + 1 / 2 log (1 + T A / K a ) With a dilute solution of the weak acid, the term 1 + T A / K a is equal to T A / K a to a good approximation. If pK w = 14, pH = 7 + (pK a + log T A)/2. This equation explains the following facts: The pH at the end-point depends mainly on the strength of the ...
A quantity in square brackets, [X], represents the concentration of the chemical substance X. It is understood that the symbol H + stands for the hydrated hydronium ion. K a is an acid dissociation constant. The Henderson–Hasselbalch equation can be applied to a polybasic acid only if its consecutive pK values differ by at least 3.
The concentration of water, [H 2 O], is omitted by convention, which means that the value of K w differs from the value of K eq that would be computed using that concentration. The value of K w varies with temperature, as shown in the table below. This variation must be taken into account when making precise measurements of quantities such as pH.
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 ...
Acid-neutralizing capacity or ANC in short is a measure for the overall buffering capacity against acidification of a solution, e.g. surface water or soil water.. ANC is defined as the difference between cations of strong bases and anions of strong acids (see below), or dynamically as the amount of acid needed to change the pH value from the sample's value to a chosen different value. [1]
The acid number for an oil sample is indicative of the age of the oil and can be used to determine when the oil must be changed. [5] A liquid fat sample combined with neutralized 95% ethanol is titrated with standardized sodium hydroxide of 0.1 eq/L normality to a phenolphthalein endpoint. The volume and normality of the sodium hydroxide are ...
The pH meter is usually calibrated with buffer solutions at known pH values before starting the titration. The ionic strength can be kept constant by judicious choice of acid and base. For instance, HCl titrated with NaOH of approximately the same concentration will replace H + with an ion (Na + ) of the same charge at the same concentration ...