[pidluk]

I need some help with our titration, 2 people in my lab are coming out with two different methods.
What i am trying to achieve is the determination of H202 in an oral mouth rinse similar to the product called Amosan.  Apparently 1.2 grams of sodium perborate monohydrate should be producing out 1.2-1.5 % H202.

The  finished product we are testing is a 1.7 gram packet with 1.2 grams of Sodium perborate monohydrate.  This is dissolved in 30 milliters of water  and then titrated with a KMnO4 solution.
Below are the calculations  please let me know what is wrong!
Procedure
1.7 grams  of sample is mixed in 30 mls of water
10 mls of the above dilution is transfered to a flask and 10 mls of 4M H2SO4 is added
The above is then titrated with 0.02M standardized KMnO4 solution.

Molarity of KMnO4 is 0.0205 M
Amount of titrant used : 19.4 mls
Mmoles of KMnO4  ( Vol.x Molarity of KMnO4) = 19.4 x 0.0205 = 0.3977 mmol
Mmoles of H202 (5/2 x Mmoles of KMnO4) =5/2 x 0.3977 =0.9943  mmol
Weight of H202 ( mmol x 34.02 mg/mmol) where 34.02 is MW of H202= 0.9943 x 34.02 =33.83
Weight of original H202  solution  =3.0 mg = 3000 mg
% H202 =33.83/3000 x 100 =1.128%


i have a feeling this is wrong ! 1.2  grams of the sodium perborate monohydrate is in the final product and this should be giving me around 1.3-1.4 % H202. please check and let me know where i am deviating

Thanks.