MadSci Network: Chemistry

Re: Why are the reagents used in Winkler method added in definite sequence?

Date: Sat Feb 19 08:51:44 2000
Posted By: Xianlong Wang, Grad student, Chemistry, Nanjing Univ.
Area of science: Chemistry
ID: 950275227.Ch

In the Winkler method,add MnSO4 and basic KI solution to the water 
sample.The product,Mn(OH)2 is oxided by the dissolved oxygen to Mn(OH)3, 
which reacts with KI when add H2SO4 to make the solution acid.The produced 
I2 is titrated by Na2S2O3 solution. The dissolved oxygen can be valued. In 
order to delete the interference of NO2-, add NaN3 in it.
Other interfere metal ions,such as Fe(II),Fe(III) and Cu(II), can be 
eliminated by the complex method. The F- for Fe(III), and NH3 for Cu(II). 
I think the sequence you mentioned is related with the elimination of 
interfere ions. If you describle the procedure more detailed, I will know 
more accurately. If you want to know more,please email to: 
 Japan Industrial Water Association, Water Quality Test, China 
Environmental Sciences Press:Beijing,1990

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