Hydroiodic+Acid

HI is a colorless gas that reacts with oxygen to give water and iodine. With moist air, HI gives a mist (or fumes) of hydroiodic acid. It is exceptionally soluble in water, giving hydroiodic acid. One liter of water will dissolve 425 liters of HI gas, the final solution having only four water molecules per molecule of HI.

Hydriodic acid forms when hydrogen iodide -- a colorless gas with a sharp odor -- is dissolved in water. This pale yellow water solution is a strong, highly corrosive acid and a powerful reducing agent. It has the ability to lose a proton or take it back during chemical reactions. Because of this property, hydriodic acid has found many uses in chemical-based applications. A catalyst accelerates chemical reactions within another chemical. Hydriodic acid, because of its strong reducing ability and acidity, is commonly used to produce acetic acid. Acetic acid, although toxic to humans in concentrated forms, is the basic chemical that produces vinegar.

Hydriodic acid is also commonly used in both organic and inorganic iodide preparations; however, it is one of the most expensive catalyzing reagents used in this process.

Hydriodic acid's high level of acidity allows it to kill several types of germs and viruses. It is often used to disinfect and sanitize medical tools and products, such as control products used in mastitis, a common bacterial complication experienced by women who breastfeed.

Methamphetamine can be produced when hydriodic acid is combined with red phosphorus and pseudoephedrine or ephedrine. Hydriodic acid, because of its excellent catalyzing ability, can produce large amounts of the drug without the need for complicated chemical processes.

Hydroiodic acid is a solution of pure HI in water. Commercial hydroiodic acid usually contains 57% HI by mass. The solution forms an [|azeotrope] boiling at 127 °C with 57% HI, 43% water. Hydroiodic acid is one of the strongest of all common acids due to the high stability of its corresponding [|conjugate base]. The [|iodide] ion is the largest of all common halides which results in the negative charge being dispersed over a larger space. By contrast, a chloride ion is significantly smaller, meaning its negative charge is more concentrated, leading to a stronger interaction between the [|proton] and the chloride ion. This weaker H+---I– interaction in HI facilitates [|dissociation] of the proton from the anion, and is the reason HI is the strongest acid of the hydrohalides (except for hydroastatic acid [theoretically]). [|[4]] HI (g) + H2O (l) → H3O+ (aq) + I– (aq) [|Ka] ≈ 1010HBr (g) + H2O (l) → H3O+ (aq) + Br– (aq) [|Ka] ≈ 109HCl (g) + H2O (l) → H3O+ (aq) + Cl– (aq) [|Ka] ≈ 108

Preparation
The industrial preparation of HI involves the reaction of I2 with [|hydrazine], which also yields [|nitrogen] gas. 2 I2 + N2H4 → 4 HI + N2 When performed in water, the HI must be [|distilled]. HI can also be distilled from a solution of [|NaI] or other alkali iodide in concentrated [|hypophosphorous acid]. (note that [|sulfuric acid] will not work for acidifying iodides as it will oxidize the iodide to elemental iodine). Another way HI may be prepared is by bubbling [|hydrogen sulfide] steam through an aqueous solution of iodine, forming hydroiodic acid (which is distilled) and elemental sulfur (this is filtered). H2S +I2 → 2 HI + S Additionally HI can be prepared by simply combining H2 and I2. This method is usually employed to generate high purity samples. H2 + I2 → 2 HI For many years, this reaction was considered to involve a simple bimolecular reaction between molecules of H2 and I2. However, when a mixture of the gases is irradiated with the wavelength of light equal to the [|dissociation energy] of I2, about 578 nm, the rate increases significantly. This supports a mechanism whereby I2 first dissociates into 2 iodine atoms, which each attach themselves to a side of an H2 molecule and break the H—H bond: [|[4]] H2 + I2 + 578 nm radiation → H2 + 2 I → I – - – H – - – H – - – I → 2 HI In the laboratory, another method involves [|hydrolysis] of [|PI3], the iodine equivalent of [|PBr3]. In this method, I2 reacts with [|phosphorus] to create [|phosphorus triiodide], which then reacts with water to form HI and [|phosphorous acid] in two steps. [|[4]] The first step involves the reaction of iodine with phosphorus: 3 I2 + 2 P → 2 PI3 The second step involves water reacting with phosphorus triiodide 2 PI3 + 6 H2O → 6 HI + 2 H3PO3