barryfol2
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Registered: 28-11-2006
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titration to distinguish sodium sulphite and sodium bisulphite
Hi All,
does anyone have a titration method (or similar) to distinguish sodium sulphite and sodium bisulphite?
i have been using a method with potassium iodate and sulphuric acid with starch as an indicator, but this doesnt help me distinguish if i have
sulphite or bisulphite,
any help would be appreciated
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encipher
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Registered: 15-12-2006
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Barryfol2,
You could titrate a solution containing the same molarity of each sodium sulfite and sodium bisulfite with an acid of known molarity. Since bisulfite
anion already contains one Hydrogen ion, it will only require a single other hydrogen ion to form sulfurous acid (which will then decompose into H2O
and SO2). But for the sulfite ion, it will require two hydrogen ions. Now I realize there will be an equilibrium formed with the HSO3- ion but the
ionization constant is very low it is negligible in this case (it is 6.6x10^-8). You can collect the SO2 gas and you should notice that the bisulfite
will release more SO2 than the sulfite. You could also monitor the PH of the solution by using an indicator or PH meter.
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