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Boric acid is a weak acid, with pK a (the pH at which buffering is strongest because the free acid and borate ion are in equal concentrations) of 9.24 in pure water at 25 °C. But apparent p K a is substantially lower in swimming pool or ocean waters because of interactions with various other molecules in solution.
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]
The simplest hydroxide of boron B(OH) 3, known as boric acid, is an acid. Unlike the hydroxides of the alkali and alkaline earth hydroxides, it does not dissociate in aqueous solution. Instead, it reacts with water molecules acting as a Lewis acid, releasing protons. B(OH) 3 + H 2 O ⇌ B(OH) − 4 + H +
Most of the solute does not dissociate in a weak electrolyte, whereas in a strong electrolyte a higher ratio of solute dissociates to form free ions. A weak electrolyte is a substance whose solute exists in solution mostly in the form of molecules (which are said to be "undissociated"), with only a small fraction in the form of ions.
This page provides supplementary chemical data on boric acid. Thermodynamic properties. Phase behavior Triple point? K (? °C), ? Pa Critical point? K (? °C), ?
Boric acid is recognised as a Lewis acid because of the reaction + + + In this case the acid does not split up but the base, H 2 O, does. A solution of B(OH) 3 is acidic because hydrogen ions are given off in this reaction.
Both boric acid and borate explain that H 3 BO 3 does not dissociate protolytically: the acid equilibrium is: B(OH) 3 + H 2 O ⇌ B(OH) 4 − + H + K a = 5.8x10 −10 mol/l; p K a = 9.24.
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).