Total Alkalinity Titration Method and Calculations
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- Опубликовано: 28 сен 2024
- Measuring total alkalinity of a water sample can be done with a bromocresol green indicator, which changes from blue to yellow when acid is added. This video describes the method briefly, but more importantly, describes the chemistry behind the method. The most common units for reporting alkalinity of water samples is mg/L (or ppm) as CaCO3. This video describes how to arrive at those units from the titration results.
The PDF used to create this video is available at: cecas.clemson....
I use 1.6 N H2SO4 fo my alkalinity titrations in 100 ml. of sample and it reads directly mg/L CaCO3 . It is the Hach portable titrator. I will have to do the math and stoichiometry using your method to make sure this is correct (Hach says it is). The only problem is I need to find out how much titrant the Hach titrator per turn of it's odometer like display. (the titrant comes in a syringe type dispenser.
Update; the Hach field titrator dispenses 0.00125 mL/per digit. I figured the mL of titrant dispenses , along with the N of the titrant (1.6 N H2SO4), and your equation allowed me to confirm the accuracy of our titrations for alkalinity. Thanks for your video.
I worked with 0.1N HCl as the titer and obtained a titer value of 52.23ml being titrated against a 25ml alkaline solution. the first method of multiplying the titer value by 20 gives different results with the later explained long method. Please check and explain the disparity.
Hi solo chogo. The first method of multiplying by 20 works when the titrant is 0.02 N and the sample is 50 ml. If your values differ, then the long method is what you need to use. Another consideration is that typically we try to work in a range where one does not need to add a lot of titrant volume compared to the volume of sample. I recommend diluting your sample before doing the titration, to save yourself a lot of titrant addition.
If you say so... :-)
In the last row. Why 1 mmol CaCO3 is equivalent to 2mg CaCO3 ( I think it should be 1mg CaCO3) ???
It's 1 mmol CaCO3 is 2 meq CaCO3. There are two milliequivalents in 1 mmol of CaCO3. Sorry the writing wasn't clearer.
David Ladner -that doesn't really explain why 1 mmol CaCO3 = 2 meq CaCO3. It appears you answered the question essentially with the question itself. The question is specifically why.
Hi JJSC. Hmmm. I thought Thanh was just thrown off because the writing wasn’t clear. But ok, here is the answer to the other question. There are two meq per mmol (or 2 eq per mol) because the carbonate ion can react with two hydrogen ions. One hydrogen ion converts the carbonate to bicarbonate, then another hydrogen ion converts the bicarbonate to carbonic acid. A quick way to see it is in the charge. Carbonate has a minus two charge. (And calcium has a plus two charge). Hope that helps.
Good day sir, do you have an online article for this video? If yes, can you kindly send the link, I'll just cite this for alkalinity of water by titration, thanks!
If alkalinity is the ability to neutralize the hydronium ion , so we calculate the concentrations of alkaline species and represent them as CaCO3 but why do we subtract the hydronium ion concentration ??...
Great explanation. just wondering, how did you find 1mmol CaCO3/2meq CaCO3? and what does it mean?
Hi Sali. There are two meq per mmol (or 2 eq per mol) because the carbonate ion can react with two hydrogen ions. One hydrogen ion converts the carbonate to bicarbonate, then another hydrogen ion converts the bicarbonate to carbonic acid. A quick way to see it is in the charge. Carbonate has a minus two charge. (And calcium has a plus two charge). Hope that helps.
Where did 20 come from
Hi Vishal. Finding out where the 20 comes from is actually the purpose of this video. But the answer takes a bit of explanation, so that’s why the video is as long as it is. Essentially, it’s the result of converting the appropriate units.
@@davidladner thank you found it
Hi
For me when I multiply the change in volume by 20 it doesn't give me the same number when I did the whole process
Why?
I'm guessing it's some issue with one of the steps. Works for me!
you did add OH- in the equation, then you mentioned we didnt add HCO3- and OH- in our ALK equation ???
Hi Niloofar. I did mis-speak at one point in the video and I called H2CO3 "bicarbonate" when I should have said "carbonic acid." I'm not sure if that's the part you were referring to. We do have OH- and HCO3- in our alkalinity equation.
plese share a total alkalnity formula . and carbonate and bicarbonate formula
Hi Mohd. At about 44 seconds (and afterward) in the video are the alkalinity formula, which includes carbonate and bicarbonate.