Stoichiometry to find the concentration of O2?

AI Thread Summary
The discussion focuses on calculating the concentration of dissolved oxygen (O2) using stoichiometry from a Winkler titration experiment. The chemical reaction involves manganese ions (Mn2+) and sodium persulfate (Na2S2O8) to determine O2 levels in water samples at different temperatures. Two trials were conducted, with varying volumes of Na2S2O8 used to reach the equivalence point, raising questions about the appropriate reagents and procedures. Participants seek clarification on the reactions involved and the correct methodology for using sodium thiosulfate in the titration process. Overall, the thread emphasizes the need for a clear understanding of the chemical reactions and stoichiometric calculations to accurately determine O2 concentrations.
tica86
Messages
79
Reaction score
0
2 Mn2+ + O2 + 4 OH- -> 2 MnO2 + 2 H2O
***** Use the stoichiometry of the chemical reaction to calculate the concentration (mg/L) of O2(aq) and concentration of O2 (aq) (Molarity).
DI Water (22 degrees C)
Initial Buret Reading: 20.0ml
Final Buret Reading: 28.7 ml
Volume Na2S2O8 to reach the equivalence point: 8.7ml

I would appreciate any help, thanks!

This is what I have done:
1 mol O2 (2mol MnO2/1 mol O2) * (1 mol I2/1 mol MnO2) * (2 mol S2O3^-2/1 mol I2)= 4 mol S2O3^-2

0.00500 Na2S2O3 (0.0087L)= 4.35*10^-5/4mol= 1.0875 * 10^-5

---------------0.00500 M Na2S2O3 standard solution
---------------II. MnO2 (s) + 2I¯ + 4H+---> Mn2+ + I2 (aq) + 2H2O
III. 2S2O32- + I2 (aq) ---> S4O62-+ 2I
 
Physics news on Phys.org
It is a little bit chaotic, can you explain in more details what the procedure and reactions involved are? Have you used sodium persulfate, or sodium thiosulfate (I guess the latter, unless it was a back titration)?
 
Borek said:
It is a little bit chaotic, can you explain in more details what the procedure and reactions involved are? Have you used sodium persulfate, or sodium thiosulfate (I guess the latter, unless it was a back titration)?

It's a biological oxygen demand experiment-winkler titration. We used sodium persulfate.



We did two trials:
FOR TRIAL 1:
DI WATER (22 C)
VOLUME Na2S2O8 TO REACH EQUIVALENCE PT = 8.7ml
Find the concentration of O2 (aq) (mg/L)
Find the concentration of O2(aq) (Molarity)

TRIAL 2:
DI WATER (0 C)
VOLUME Na2S2O8 TO REACH EQUIVALENCE PT = 2.55ml
Find the concentration of O2 (aq) (mg/L)
Find the concentration of O2(aq) (Molarity)
 
Strange, as far as I was able to check Winkler method calls for thiosulfate to titrate iodine. One starts with Mn2+, it gets oxidized by the dissolved oxygen producing brown precipitate (containing Mn3+ and/or Mn4+), this precipitate after adding sulfuric acid oxidizes iodides to iodine, iodine is titrated with thiosulfate. No place for persulfate.

Can you write equations of reactions that take place during the experiment?
 

Thread 'Prove that evolution is constant (Provide at least two arguments to support your position)'

I don't get how to argue it. i can prove: evolution is the ability to adapt, whether it's progression or regression from some point of view, so if evolution is not constant then animal generations couldn`t stay alive for a big amount of time because when climate is changing this generations die. but they dont. so evolution is constant. but its not an argument, right? how to fing arguments when i only prove it.. analytically, i guess it called that (this is indirectly related to biology, im...
View full post »

Similar threads

Iodine Adsorption and Titration with Na2S2O3
Replies
4
Views
2K
Chemistry Difficult AP Chemistry Question (Titration + Calculating Moles)
Replies
6
Views
18K
Check Concentration Calculation (Very Wordy As For Coursework)
Replies
2
Views
5K
Checking Answers of Chemistry Assignment
Replies
1
Views
8K

Hot Threads

Recent Insights

Back
Top