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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).
The Henderson–Hasselbalch equation can be used to estimate the pH of a buffer solution by approximating the actual concentration ratio as the ratio of the analytical concentrations of the acid and of a salt, MA. The equation can also be applied to bases by specifying the protonated form of the base as the acid.
The concentration of water, [H 2 O], is omitted by convention, which means that the value of K w differs from the value of K eq that would be computed using that concentration. The value of K w varies with temperature, as shown in the table below. This variation must be taken into account when making precise measurements of quantities such as pH.
The smaller the difference, the more the overlap. In the case of citric acid, the overlap is extensive and solutions of citric acid are buffered over the whole range of pH 2.5 to 7.5. Calculation of the pH with a polyprotic acid requires a speciation calculation to be performed. In the case of citric acid, this entails the solution of the two ...
Melting temperature as a function of HCl concentration in water [29] [30] Physical properties of hydrochloric acid, such as boiling and melting points, density, and pH, depend on the concentration or molarity of HCl in the aqueous solution. They range from those of water at very low concentrations approaching 0% HCl to values for fuming ...
Ammonia solutions decrease in density as the concentration of dissolved ammonia increases. At 15.6 °C (60.1 °F), the density of a saturated solution is 0.88 g/ml; it contains 35.6% ammonia by mass, 308 grams of ammonia per litre of solution, and has a molarity of approximately 18 mol /L.
The concentration of alkaline electrolyte of potassium hydroxide remains constant, as there are equal amounts of OH − anions consumed and produced in the two half-reactions occurring at the electrodes. The two half-reactions are: Anode (oxidation reaction), negatively charged electrode because accepting e − from the reductant in the cell:
Besides the set of parameters obtained by Pitzer et al. in the 1970s mentioned in the previous section. Kim and Frederick [19] [20] published the Pitzer parameters for 304 single salts in aqueous solutions at 298.15 K, extended the model to the concentration range up to the saturation point. Those parameters are widely used, however, many ...