Sulfides are molecules with isolated sulfur atoms and a surplus of two electrons. Compounds misidentified as disulfides include carbon disulfide. Diprotic acids like sulfuric and hydrogen sulfide can be partially or completely neutralized to produce salts. Other diprotic acids include carbonic and tartaric acids. Neutralization can be performed in stages to produce double salts like sodium potassium tartrate.
Sulfides are molecules with one or more isolated sulfur atoms, each with a surplus of two electrons. These make up the negative portion, or ‘anion’, of the sulfide – the corresponding positive portion is the ‘cation’. A simple example is potassium sulphide, chemical formula K2S; the two potassium atoms each carry a +1 charge, that of sulfur a -2 charge. A somewhat similar molecule, called potassium hydrogen sulfide or potassium disulfide, chemical formula KHS, has the two-atom unit (HS)-1 as its anionic moiety, which carries only one added electron. It should be noted that the words disulfide and disulfide are not synonymous, as illustrated by the common automotive lubricant, molybdenum disulfide, chemical formula MoS2, which does not contain hydrogen in its structure.
Some compounds may be misidentified as disulfides, including the solvent carbon disulfide, CS2. Those compounds most similar in structure to the disulfide but not the disulfide are the sulfur-containing alcohol analogs called thiols or mercaptans; these are sometimes used as artificial odorants for natural gas, to prevent accidental asphyxiation. Of commercial importance among the correctly identified disulfides are sodium and ammonium disulfide. Sodium disulfide is used in large quantities in the Kraft paper manufacturing process. Ammonium disulfide, on the other hand, is a major source of corrosion damage, especially for petroleum industry desulfurization hydrotreatments.
The “bi-” prefix dates back more than a century and suggests the neutralization of only one of the two protons – hydrogen ions – of a “diprotic” acid. For example, sulfuric acid (H2SO4) has two protons or hydrogen atoms, which can be replaced. If not one but both are replaced by sodium hydroxide, for example, the result is sulfate, Na2SO4. Reducing the amount of sodium hydroxide, however, results in the replacement of only one hydrogen atom to form sodium bisulfate, NaHSO4. In the latter case, even if the product is a salt, since one hydrogen atom remains, it is also an acid: sodium bisulfate is an acid salt.
Hydrogen sulfide gas, H2S, behaves similarly. Although weak, it is also a diprotic acid, which ionizes in two steps when dissolved in water. The first step produces hydrosulfide ions: H2O + H2S → (H3O)+1 + (HS)-1. The second step is the further decomposition, H2O + (HS) -1 → (H3O)+1 + S-2. If desired, two products can be produced: partial neutralization gives disulfide: NaOH + H2S → NaHS + H2O, while complete neutralization gives sulfide: 2 NaOH + H2S → 2 NaS + 2 H2O.
Other well known diprotic acids are carbonic and tartartic acids, H2CO3 and H2(C4H4O6) respectively. These can be partially or completely neutralized to produce sodium bicarbonate or soda ash; or, in the case of tartaric acid, sodium bitartrate or sodium tartrate. If preferred, neutralization can be performed in stages. Using a different base in step two therefore provides a “double salt”, a notable example being the common food additive historically known as Rochelle salt, sodium potassium tartrate.
Protect your devices with Threat Protection by NordVPN
