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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.
An adequate amount of boron in the soil is 12 mg/kg. If the boron content of the soil drops below 0.14 mg/kg then boron deficiency is likely to be observed. Boron deficiency is also observed in basic soils with a high pH because in basic conditions boric acid exists in an undissociated form which the plant is unable to absorb. [5]
The artificial solution described by Dennis Hoagland in 1933, [1] known as Hoagland solution (0), has been modified several times, mainly to add ferric chelates to keep iron effectively in solution, [6] and to optimize the composition and concentration of other trace elements, some of which are not generally credited with a function in plant nutrition. [7]
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
For buffers in acid regions, the pH may be adjusted to a desired value by adding a strong acid such as hydrochloric acid to the particular buffering agent. For alkaline buffers, a strong base such as sodium hydroxide may be added. Alternatively, a buffer mixture can be made from a mixture of an acid and its conjugate base.
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]