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At 298 K, 1 pH unit is approximately equal to 59 mV. [2] When the electrode is calibrated with solutions of known concentration, by means of a strong acid–strong base titration, for example, a modified Nernst equation is assumed. = + [] where s is an empirical
The law of water balance states that the inflows to any water system or area is equal to its outflows plus change in storage during a time interval. [ 2 ] [ 3 ] In hydrology , a water balance equation can be used to describe the flow of water in and out of a system.
The Henderson–Hasselbalch equation relates the pH of a solution containing a mixture of the two components to the acid dissociation constant, K a of the acid, and the concentrations of the species in solution. [6] Simulated titration of an acidified solution of a weak acid (pK a = 4.7) with alkali
where log denotes a logarithm to base 10 or common logarithm, and K diss is a stepwise acid dissociation constant. For bases, the base association constant, pK b is used. For any given acid or base the two constants are related by pK a + pK b = pK w, so pK a can always be used in calculations.
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.
Recall that the relationship represented in a Davenport diagram is a relationship between three variables: P CO 2, bicarbonate concentration and pH.Thus, Fig. 7 can be thought of as a topographical map—that is, a two-dimensional representation of a three-dimensional surface—where each isopleth indicates a different partial pressure or “altitude.”
An often considered quantity is the dissociation constant K d ≡ 1 / K a , which has the unit of concentration, despite the fact that strictly speaking, all association constants are unitless values. The inclusion of units arises from the simplification that such constants are calculated solely from concentrations, which is not the case.
This combined charge balance and proton balance is called total alkalinity. [9] Total alkalinity is not (much) affected by temperature, pressure, or pH, and is thus itself a conservative measurement, which increases its usefulness in aquatic systems. All anions except HCO − 3 and CO 2−