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Boric acid in equilibrium with its conjugate base the borate ion is widely used (in the concentration range 50–100 ppm boron equivalents) as a primary or adjunct pH buffer system in swimming pools. Boric acid is a weak acid, with p K a (the pH at which buffering is strongest because the free acid and borate ion are in equal concentrations) of ...
Total boron is an important quantity when determining alkalinity due to borate's contribution to a solution's acid neutraling capacity. Total boron is a conservative element in seawater, and can thus be calculated by simply knowing the salinity.
Borax is also easily converted to boric acid and other borates, which have many applications. Its reaction with hydrochloric acid to form boric acid is: Na 2 B 4 O 7 ·10H 2 O + 2 HCl → 4 H 3 BO 3 + 2 NaCl + 5 H 2 O. Borax is sufficiently stable to find use as a primary standard for acid-base titrimetry. [17]: p.316
In aqueous solution, boric acid B(OH) 3 can act as a weak Brønsted acid, that is, a proton donor, with pK a ~ 9. However, it more often acts as a Lewis acid, accepting an electron pair from a hydroxide ion produced by the water autoprotolysis: [11] B(OH) 3 + 2 H 2 O ⇌ [B(OH) 4] − + H 3 O + (pK = 8.98) [12]
Borate concentration (giving buffering capacity) can vary from 10 mM to 100 mM. As BBS is used to emulate physiological conditions (as in animal or human body), the pH value is slightly alkaline, ranging from 8.0 to 9.0. NaCl gives the isotonic (mostly used 150 mM NaCl corresponds to physiological conditions: 0.9% NaCl) salt concentration.
It consists of a mixture of 0.04 M boric acid, 0.04 M phosphoric acid and 0.04 M acetic acid that has been titrated to the desired pH with 0.2 M sodium hydroxide. Britton and Robinson also proposed a second formulation that gave an essentially linear pH response to added alkali from pH 2.5 to pH 9.2 (and buffers to pH 12).
A broader definition of acid dissociation includes hydrolysis, in which protons are produced by the splitting of water molecules. For example, boric acid (B(OH) 3) produces H 3 O + as if it were a proton donor, [11] but it has been confirmed by Raman spectroscopy that this is due to the hydrolysis equilibrium: [12]
Note that in solution H + exists as the hydronium ion H 3 O +, and further aquation of the hydronium ion has negligible effect on the dissociation equilibrium, except at very high acid concentration. Figure 2. Buffer capacity β for a 0.1 M solution of a weak acid with a pK a = 7