Alkalinity issues

[Mjrenz]

Alkalinity is linear with titrant added. If the volume used is so small that it is hard to measure accurately, certainly that will cause an unusually high percentage error. Otherwise, the encountered extremes are not generally an issue with an alk kit.

It almost sounds like you know what you're talking about

 

[ccombs]

I have no idea what you are referring to or how this might relate to low alk.

Alk is linearly related to the titrant used to get to the endpoint. It reads perfectly well at low alk or high alk.

I just did some in depth reading on how titration tests actually work with the titrant neutralizing the analyte to determine concentration of of solution using two known volumes. Mind = Blown.

My question is now this, if I understand correctly, the titration test monitors the pH of the analyte, so would the pH of our sample potentially skew the results?

 

[rushbattle]

I just did some in depth reading on how titration tests actually work with the titrant neutralizing the analyte to determine concentration of of solution using two known volumes. Mind = Blown.

My question is now this, if I understand correctly, the titration test monitors the pH of the analyte, so would the pH of our sample potentially skew the results?

No, pH of seawater is primarily determined by CO2 concentration and alkalinity. But as you add more acid to get down to the pH end point, the CO2 concentration doesn't matter, only alkalinity. So starting pH of seawater doesn't effect the measurement.

 

[ccombs]

No, pH of seawater is primarily determined by CO2 concentration and alkalinity. But as you add more acid to get down to the pH end point, the CO2 concentration doesn't matter, only alkalinity. So starting pH of seawater doesn't effect the measurement.

Thank you for the explanation. I love learning new things.

Now on to upping my understanding of pH.

 

[rushbattle]

Dr. Holmes-Farley is the man. If you have any curiosity about anything chemistry related he has likely written an article about it. His articles are all EXCELLENT.

http://reefkeeping.com/issues/2005-02/rhf/index.htm

 

[Randy Holmes-Farley Verified Community Expert]

My question is now this, if I understand correctly, the titration test monitors the pH of the analyte, so would the pH of our sample potentially skew the results?

No, the starting pH does not impact a total alkalinity measurement. The pH does, of course, impact how much of that total alkalinity is coming from different forms, such as bicarbonate vs carbonate.

 

[BeejReef]

I've not used Salifert for Alk. What is the working theory... that the OP is inverting the amount of titrant used with the amount of titrant remaining in his reading of the test results?

 

[Hillbillyreefer]

I've not used Salifert for Alk. What is the working theory... that the OP is inverting the amount of titrant used with the amount of titrant remaining in his reading of the test results?

Yes.

 

[Randy Holmes-Farley Verified Community Expert]

A surprising number of people use syringes incorrectly, and there was one just this weekend in the chem forum.

Anyway, folks might find this interesting:

Reef Chemistry Question of the Day #161 Using a Syringe
https://www.reef2reef.com/threads/reef-chemistry-question-of-the-day-161-using-a-syringe.226267/