Seek methods for determining the hardness of circulating water
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Why is it impossible to determine the end point of titration for the total hardness of circulating water using chromotropic acid T as an indicator?
http://bbs.hcbbs.com/thread-400293-1-1.html Look in post 289; there you’ll find the complete set. You can find analysis materials for all sections in future editions here as well. The water analysis data are now complete. Good luck!
Look for it on standard sharing websites; GB/T6909-2008 is it
Full name: GB/T6909-2008 Methods for the analysis of water used in boilers and cooling systems – Determination of hardness. http://bbs.hcbbs.com/viewthread.php?tid=408695&page=1&extra=page%3D1. This post was last edited by Canghai Yili Sha on 2009-3-7 09:04
Check whether the indicator is ineffective, whether the pH of the solution is 10, and whether there are ions in the water sample that can inhibit the indicator’s function. In short, conduct several tests to identify and resolve the issue.
You can refer to the methods for analyzing the hardness of softened water specified in the quality standards for industrial boilers; you can search for these specific standards on relevant forums
There could be several reasons: 1. The indicator has lost its effectiveness. 2. The pH value is lower than the pH value required for titration. 3. Influence of interfering substances. Iron and aluminum can seal the indicator. Adding masking agents such as TEA at this point can eliminate the interference.
Surely, no buffer solution was used. I’ve encountered this issue before as well. Last edited by lifanwang on 2009-3-12 at 15:07.]
1\ The aqueous solution is titrated with a solution of disodium ethylenediaminetetraacetate; when all the calcium and magnesium ions have been chelated, the color of the solution changes from burgundy to blue, indicating the end point of the titration. 2\ Since trace amounts of magnesium ions must be present in the aqueous solution for the indicator to undergo a clear and distinct color change at the end point of the titration, it is necessary to add a small amount of magnesium EDTA to the buffer solution first, and then subtract this added amount using a blank sample analysis. This post was last edited by lifanwang on 2009-4-27 12:27.]
It is mainly masked by other ions; a masking agent is required. Add 10 milliliters of triethanolamine at a concentration of 200 milligrams per liter, and then proceed with titration. Add triethanolamine first, followed by the buffer solution, and finally add the indicator for titration
Many answers have been given above; here are a few additional points: 1. Could it be that the EDTA concentration is low, the calcium and magnesium levels are high, and a small amount of standard solution is not sufficient to reach the endpoint? 2. We generally do not use any masking agents when measuring hardness.
If there are too many impurities in the water, it’s probably not possible to carry out the process without using a masking agent; take your time. Last edited by lifanwang on 2009-4-29 08:07.]