Hydrogensulphite

Evaporation and crystallisation of the sodium sulphite solution gives crystals of the heptahydrate NajSOj.THjO. However, on evaporation of the hydrogensulphite solution, the solid obtained is chiefly sodium pentaoxodisulphate(IV) ( metabisulphite ) Na2S20j, and contains little if any of the hydrogensulphite. However, the hydrogen sulphite ion is obtained when the solid redissolves in water ... 

Alternatively these salts can be prepared by first saturating a known volume of alkali with sulphur dioxide, giving a solution of the hydrogensulphite, from which sulphite can be prepared by the addition of a second equal volume of alkali. 

Sodium hydrogensulphite, when freshly prepared, reacts with aldehydes to form crystalline addition compounds, for example... 

The precipitate is curdy (compare silver chloride) and is readily coagulated by boiling. It is washed with dilute ammonium thiocyanate solution a little sulphurous acid or ammonium hydrogensulphite is added to the wash solution to prevent any oxidation of the copper)I) salt. 

Discussion. Small quantities of dissolved silicic acid react with a solution of a molybdate in an acid medium to give an intense yellow coloration, due probably to the complex molybdosilicic acid H4[SiMo12O40]. The latter may be employed as a basis for the colorimetric determination of silicate (absorbance measurements at 400 nm). It is usually better to reduce the complex acid to molybdenum blue (the composition is uncertain) a solution of a mixture of l-amino-2-naphthol-4-sulphonic acid and sodium hydrogensulphite solution is a satisfactory reducing agent. 

Reducing agent. Solution A dissolve 10 g sodium hydrogensulphite in 70 mL water. Solution B dissolve 0.8 g anhydrous sodium hydrogensulphite in 20 mL water, and add 0.16 g l-amino-2-naphthol-4-sulphonic acid. Mix solution A with solution B, and dilute to 100 mL. 

Sulphur dioxide is also produced by the action of an acid (usually concentrated sulphuric since it is involatile) on a sulphite or hydrogensulphite. for example... 

Benzaldebyde, C-Jl O. forms a hydrogensulphite compound of fomnilaFrom l.210gofbenzaUdiyde,ayicid of 2.181 g of the product was obtained. Calculate the percentage jdeld. 

Similarly, sodium hydrogensulphite, NaHS03, although it contains hydrogen (which might be thought to be a source of ions), has a basic solution ... 

Due to its properties sulphur dioxide has been used for many centuries mainly for the protection of acidic foodstuffs, especially in the wine industry. However its application is restricted owing to flavour problems occurring at concentrations above 5 mg/kg. It is applied as liquefied gas, a solution in water (H2SO3) or the a.m. salts. In the EC list of preservatives which cosmetics may contain inorganic sulphites and hydrogensulphites are mentioned with a maximum concentration of 0-2% expressed as free SO2. But in finished products it is scarcely used, as these normally do not exhibit the low pH which is required for the antimicrobial effectiveness of sulphur dioxide or sulphurous acid. 

Example decomposition of dithionite to monomer-anions preceding their oxidation to hydrogensulphite anions [15]... 

Usually, the individual and simultaneous separation of free [32,36,38,39] and conjugated Be [33—35] vitamers is carried out by means of RP chromatography on Cl8 columns with acidic mobile phases. These methods utilize the native fluorescence of B6 vitamers [1,32—39], increasing the weak intensity of phosphate esters at low pH by means of postcolumn derivatization with sodium hydrogensulphite. 

Sulfur dioxide SO2 Sulphites, disulphites, hydrogensulphite Calorimetry IR... 

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