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The carbonate buffer system is a series of reactions that uses carbonate as a buffer to convert into bicarbonate. [12] The carbonate buffer reaction helps maintain a constant H+ concentration in the ocean because it consumes hydrogen ions, [ 13 ] and thereby maintains a constant pH. [ 12 ]
Sodium carbonate is obtained as three hydrates and as the anhydrous salt: sodium carbonate decahydrate , Na 2 CO 3 ·10H 2 O, which readily effloresces to form the monohydrate. sodium carbonate heptahydrate (not known in mineral form), Na 2 CO 3 ·7H 2 O. sodium carbonate monohydrate (thermonatrite), Na 2 CO 3 ·H 2 O. Also known as crystal ...
Buffer capacity falls to 33% of the maximum value at pH = pK a ± 1, to 10% at pH = pK a ± 1.5 and to 1% at pH = pK a ± 2. For this reason the most useful range is approximately pK a ± 1. When choosing a buffer for use at a specific pH, it should have a pK a value as close as possible to that pH. [2]
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. At pH ≤ pK a − 2 the substance is said to be fully protonated and at pH ≥ pK a + 2 it is fully dissociated (deprotonated).
Carbonate speciation in seawater (ionic strength 0.7 mol/dm 3). The expected change shown is due to the current anthropogenic increase in atmospheric carbon dioxide concentration. The Bjerrum plot shows typical equilibrium concentrations, in solution, in seawater , of carbon dioxide and the various species derived from it, as a function of pH .
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).
The pKa of KHP is 5.4, so its pH buffering range would be 4.4 to 6.4; however, due to the presence of the second acidic group that bears the potassium ion, the first pKa also contributes to the buffering range well below pH 4.0, which is why KHP is a good choice for use as a reference standard for pH 4.00. [8] [9]
Perhaps the most well known is the dissolution of calcium carbonate to form Ca 2+ and CO 2− 3 (carbonate). The carbonate ion has the potential to absorb two hydrogen ions. Therefore, it causes a net increase in ocean alkalinity. Calcium carbonate dissolution occurs in regions of the ocean which are undersaturated with respect to calcium ...