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Appendix
2. Titration stage
(peracetic acid)
Equipment required • Thiosulphate solution (e.g. 0.02 N)
Calculation Hydrogen peroxide concentration
48
• Potassium iodide
• Starch solution (1 %)
• (Magnetic stirrer)
After titration stage 1 place some potassium iodide on the tip of
a spatula (approx 0.5 g) and place it in the sample – the sample
turns brown in colour.
Stir continuously (pour into another vessel / magnetic stirrer)
whilst adding drops of thiosulphate solution (e.g. 0.02 N) until the
sample colour turns a pale shade of yellow.
Add approx 1 ml of starch solution (1%) – the sample will turn
blue.
Now add thiosulphate solution until the sample becomes
colourless.
IMPORTANT
Towards the end of titration you should only add thiosulphate
solution very slowly (approx 1 drop/second) as the solution
will only change colour after a certain amount of time has
elapsed.
Note the consumption B of permanganate solution (in ml).
Formula for calculation:
1
c (H
O
) (in ppm)
= consumption A of permanganate solution (in
2
2
ml) * 17 * N * 1000/(sample volume (in ml))
N = normality of permanganate solution
Example:
Sample volume = 20 ml, c (permanganate solution) = 0.1 N,
Consumption A = 11.8 ml
Thus
c (H
O
) = 11.8 x 17 x 0.1 x 1000/20 = 1003 ppm or 0.1003 %.
2
2
ProMinent
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