Issues with using EDTA to measure calcium carbonate content

Is there something wrong with your calculations? Or what’s the issue! !

I don’t doubt your calculations, but for such a result to occur, some special circumstances need to be taken into account. 1. Could you provide a more detailed description of the sample? Is your calcium carbonate derived from natural stones or is it processed? 2. The EDTA standard solution has been calibrated; are there any issues with the standard substances used? 3. Is the pH value of the ammonia-alkaline buffer solution appropriate? 4. When dissolving the calcium carbonate sample, it is necessary to properly neutralize any excess acid used in the initial dissolution process before adding the buffer. If the measurement value is too high, it indicates that a slightly larger amount of EDTA standard solution was used; in such cases, efforts should be made to minimize the amount of standard solution required. My preliminary judgment is that it might be because the sample was not properly neutralized after dissolution. If calcium carbonate is synthetic or formulated, there may also be small amounts of magnesium carbonate or calcium oxide.

If there are no issues with the analysis process or the standard solutions, then it’s likely the effect of impurities. The presence of calcium and magnesium salts with a molecular weight lower than that of calcium carbonate will result in higher analysis values.

You can refer to the testing conditions for calcium carbonate in chemical reagents as specified in the [GB National Standard for Chemical Reagents] GB-T 15897-1995

It’s probably because of the presence of calcium oxide; in our production processes, we generally don’t use the term calcium carbonate – instead, we refer to the content of effective calcium oxide

Hide, first check whether the titrant is effective; calibrate it to see if its concentration changes, and also check whether any impurities are affecting it, hide

For our EDTA titration, we generally calculate it based on calcium oxide. Or maybe the calibration wasn’t performed because the EDTA concentration changed. Also, if an inappropriate amount of calcium indicator is used, it is difficult to determine the end point of titration, and it’s easy to go over it.

There are many factors that can influence this, such as the presence of magnesium, or the existence of forms of calcium with a lower molecular weight than calcium carbonate. Other factors include the pH value of the solution and the amount of calcium indicator added. Additionally, there is the issue of calibrating the glass instruments used, as well as the quality of the EDTA standard solution, and whether the auxiliary solutions added are contaminated with calcium-containing substances