Abstract
A simple and rapid spectrophotometric method for the determination of sulphite SO3-2 is described. The method is based on the rapid reduction of known amount of chromate CrO4-2 in the presence of sulphite in acidic medium of 2N H2SO4. The amount of excess of chromate was measured after it reactions with 1,5-diphenylcarbazide which finally gives a pink-violet, water soluble and stable complex, which exhibit a maximum absorption at 542 nm. Beer's law was obeyed in the concentration range from 0.004-6.0 µg of sulphite in a final volume of 25 ml with a molar absorbtivity of 4.64×104 l.mol-1.cm-1, Sandal's sensitivity index of 0.001724 ?g .cm-2 and relative standard deviation of ±0.55 - ±0.83 depending on the concentration level. The present method has been developed for the determination of sulphite in the presence of thiosulphate. Good recoveries of sulphite from various water samples are achieved using the proposed method.
Highlights
Sulfites are compounds that contain the sulphite ion SO3−2 (additive IUPAC name: trioxidosulphate (2−))
Colour reaction: In aqueous solution chromate reduced in acid medium by sulphite, the unreduced chromate was reacted with the reagent DPC to give the an intense pink-violet complex
The sample solution shows maximum absorption at 542 nm, characteristic of the chromate-DPC chromophore, in contrast to the reagent blank which shows slight absorption at this wavelength, emphasising the need for measurements to be performed against the reagent blank
Summary
Sulfites ( sulphites) are compounds that contain the sulphite ion SO3−2 (additive IUPAC name: trioxidosulphate (2−)). The structure of the sulphite anion can be described with three equivalent resonance structures, the structure predicted by VSEPR theory is trigonal pyramidal, as in ammonia (NH3). In the hybrid resonance structure, the S-O bonds are equivalently of bond order one and one-third (1).
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