99 posts
Re: Role of methanol in free lime test
ah..ok..In the absence of the a stirrer we are using silica sand to facilitate mixing by manual shaking,is this okay?
Also, is it necessary for the solution to be hot when titrating?..does le chatelier principle of formation of products applies when shaking is applied?
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537 posts
Re: Role of methanol in free lime test
Hello Norew,
As long as the clinker sample is ground fine enough, mixing is not really necessary. There is generally enough mixing due to the agitation of the boiling liquid.
It is also not necessary for the solution to be hot when titrating. In the rapid glycol method this is only done to reduce the time taken for the test. In fact, in most standard methods, the solution is filtered before titration, which tends to cool down the filtrate anyway.
I'm not sure I fully understand your last question re Le Chatelier principle. Le Chatlier's principle applies in any reversible chemical reaction. In this case there is an excess of the principal reactant (glycol) which tends to force the reaction of CaO with glycol towards the desired product (calcium glycolate), as does the increased temperature during boiling.
If the reaction was being performed below the boiling point of the solvent, shaking would reduce the local concentration of calcium glycolate around clinker particles, tending to favour the reaction to produce more calcium glycolate hence speeding up the test. However, as long as the solution is boiling vigourously for the entire digestion period, I don't think shaking is really necessary.
Regards,
Ted.
99 posts
537 posts
Re: Role of methanol in free lime test
norew:
in our case, the solution really is not yet boiling even after the 30 minute period..
Hello Norew,
Why do you not let the solution boil? Most methods stipulate that the solution should boil for at least 20-30 minutes, sometimes more.
..how about at the moment of adding the titrant?
If the method calls for filtration of the solution, obviously the solution would not be boiling by the time it came to the titration step. If the solution is not filtered, (as in the rapid glycol method), the act of removing it from the heat quickly stops the solution from boiling. So in both cases the solution has ceased boiling at the stage that the titrant is added.
In fact, in the rapid method, it is far better that the solution is not boiling during the titration because the end-point is better seen when the clinker or cement powder has been allowed to settle and the colour change in the supernatant liquid can be more easily seen. (ie very gentle swirling during the titration, with frequent pauses to allow the powder to settle near the end, to ensure the end-point is not missed.)
Regards,
Ted.