The Determination of sulfite usually is made only on boiler waters.Generally speaking sulfite is not present in natural water. in boiler feed water sodium sulphite is fed to remove dissolved oxygen.
1. 1N Hydrochloric acid 1+1
2. Starch indicator solution
3. Standard potassium iodide-iodate solution.
Place 10ml of 1+1 HCL in a 250 ml flask. rapidly add 100 ml of sample, submerging the pipette tip below the acid surface to minimize sir exposure. After adding 1 ml.starch indicator solution add 5ml.KI Solution(5% solution) titrate with standard KIO3 Solution, to the first appearance of persistent blue color. Determine the blank titration by taking 100 ml Distilled water.
Sulfite,as SO3 mg/litre = (A-B) x 100
A= ml.of titrant for sample
B= ml.of titrant for blank
As mg./litre, the effect on P will be equal to one half of the content in mg./litre of phosphate and this shall be subtracted from P reading before using the above table.the alkalinity to phenolphthalein after addition of BaCL2 is not affected by the presence of phosphate.
To 100 ml.of sample, add a crystal of sodium sulfate and 10 ml.of 10% BaCl2 Solution.
Mix well for 2 minutes. Titrate using phenolphthalein as indicator.
Ml.of 0.02 H2SO4 X 1000/ Ml. of sample = Mg./litre of P(BaCl2)value.