Arsenic Test in Water

Test for Arsenic in water:

Reagents: Solid sodium bicarbonate 0.00025N KI+I2 solution

Starch indicator

Procedure:
. Preparing 20 ml of saturated solution of sodium bicarbonate with the sample solution.

. 2.5 ml of the above solution was taken in a test tube with a calibrated Pasteur pipette.

. Adding 1 drop of starch indicator to the tube and stir well.
. Adding KI + I2 solution drop wise with another pipette till a blue colour

of the solution appears.
. Counting the number of drops of KI + I2 solution used. Calculation:
Volume of KI + I2 solution = no. of drops x value of pipette= V1 Normality of KI + I2 solution = N1
Volume of water = 2.5 mL = V2
Amount of arsenic (mg/L) = V1 x N1 x 37.5 x 1000/V2
Result: The amount of arsenic in water is ________ mg/L.