this video saved my neck .. I wasted hours playing around with various recipes out there but in the end the bucket chemistry approach to the initial steps worked best for me too :)
Dear Mr Thornely, thank you very much for giving us knowledge about quantifying the Dissolved Oxygen in water through Winkler method. However, I wanted to ask if pH affect the concentration of DO?
I have a question, what would happen if the sample solution was not saturated with oxygen? I thought measuring the oxygen already present and then waiting 5 days to measure it again would be suffiecient to see the BOD.
Hi Mr. Thornley. May I ask why we have to increase the pH of the solution before we start adding the sodium thiosulfate? Also why specifically allow the floc to settle to the halfway point of the flask and not all the way?
i just have two question 1) why dont we double the moles from MnO2 (middle eqaution) : 2MnO2(Top Equation) even though that is the relation observed by the mole ratio 2) why is oxygen concentration to 2 sigfigs when we used 3 sigfigs for others
1) it is the actual number of mole that jumps up the sequence of equations. eg C --> D mol 2 X + Y --> 2C mol 1 1 2 There are only 2 moles of C, it doesn't matter where the C appear it must be 2. 2) Probably an oversight on my part.
is it not necessary to let the sample sit for 5 days after reagents added but before titration? I thought that was how you calculated BOD. please help!!!
The above video shows the Winkler Method which allows you to measure the concentration of oxygen in water. BOD measurement uses the Winkler Method to get a value. BOD measurement involves fully oxygenating the solution and waiting 5 days before you do the Winkler Method on it! At 14:10 I explain this more clearly.
Hi Mr. Thornley. I was trying to do this experiment with all the same chemicals except for the iodide source, where I had access to potassium iodide instead. But when I added both the manganous sulfate and the potassium iodide, they both simply dissolve and do not result in any formation of floc. I am also using pond water. Do you know why this is happening and if there’s any solution for it?
The 1.45g of sodium thiosuphate came from him measuring it before. The sodiumthiosuphate is made up with water (H20) thats why he states that the solution was made up to 100ml with water.
Maybe. What if the ppm of O2 does not change much - then what. If the ppm does change a lot - would your explanation be simple (eg there is a water fall). or complex. I think it depends on the river and its environs.
Hi Mr Thornley, I'm using this method as part of my extended essay, but neither myself nor my teachers can find where to buy the alkaline iodide azide pillows, do you know where I can buy them?
+Miguel Ignacio Cely Guezguan You have to use stoichiometry, because the coefficient of the S2O32- is 2 and the coefficient of the I2 is 1, you need to divide the mole value of the S2O32- by two in order to get the mole value of I2 as the coefficient are in a ratio of 1:2.
Why there is not a calculation of mass of thiosulfate in penthahydrate? 1,45 g of sodium thiosulfate penta hydrate contains only 0,.87g of sodium thiosulfate.... so the calculations has to take that into account or you already recalculated the actual mass od sodium thiosulfate?
If you use pentahydrate you need to use the molar mass of pentahydrate in the calculations. You will end up getting the same concentration of the non-hydrated thiosulphate.
When using a hydrated compound, the attached water molecules contribute water to the solution, potentially diluting the final concentration (if the solvent is water). Therefore, you must account for the contribution of water from the hydrated compound when determining the volume of solvent (water) to add. This article describes the calculations involved in making solutions from hydrated compounds. cshprotocols.cshlp.org/content/2008/5/pdb.ip54.abstract
Generally the oxygen is present in this atmosphere. We inhale this oxygen present in atmosphere and survive. But in case of the crustaceans, they survive in the water by consuming the dissolved oxygen in ... Answer link: howwhywhat.net/cant-inhale-dissolved-oxygen-water/
can you send me chemistry IA about this. Seems like you enjoyed the experiment so i know you'd enjoy making my amazing IA. This is a one in a life time offer, you either take it in 24 hours or leave it
is the sulfuric acid just to provide the H+ in the second equation? and can KI be used to provide the iodide ions instead of alkali iodide azide? thank you in advance!
+Jesica Sutandi yes of course you can add KI in second step to supply iodide ione. but in that case you have to add NaOH or KOH in 1st step to supply OH ions. i hope u got your answer
+Janice Wang because the 3 reactions are taking place in one solution. Basically, 2MnO2 in the first reaction is the same amount/concentration as the MnO2 in the second reaction
Yes. In your case you have to first oxygenate the water fully and then wait for 5 days. After the 5 days you use this same procedure of the Winkler Method and you will get your BOD.
In 30 years of doing chemistry I have set myself on fire twice, had 2 classroom evacuations and one explosion. As yet I have not hurt my hands with chemicals. I normally wear gloves for concentrated(5M+) acids only.
You should add a trigger warning for the disturbing video game content at the beginning of the video. It adds no educational value to the video to show that kind of content. Although, the rest of the video was informative the intro was slightly unnecessary.
![9.1 Winkler Experiment for Dissolved Oxygen (Chemical equations too) [SL IB Chemistry]](/img/logo.svg){kind=logo}
