What are the key points for determining the concentration of calcium hydroxide in lime milk?

I think what the original poster is referring to is titration using the acid-base titration method, right? Considering that substances such as calcium carbonate may be present in calcium hydroxide, a single dissolution cannot be achieved quickly under titration conditions, and discoloration may occur; therefore, it is appropriate to perform multiple titrations until no discoloration appears as the endpoint. The following is the AI’s response; although it may not explain the principles in full detail, it can still serve as a reference: When analyzing the calcium hydroxide concentration in lime milk, acid-base titration is generally used, with phenolphthalein as an indicator, and a standard hydrochloric acid solution of known concentration is employed for the titration. The following analyzes the two methods for determining the endpoint: the method of titrating at the branch office until colorlessness is achieved. Theoretically, when calcium hydroxide reacts completely with hydrochloric acid, the basic substances in the solution are fully neutralized, and the phenolphthalein indicator changes from red to colorless; this is when the stoichiometric point is reached. However, in practice, factors such as uneven mixing of the solution during titration and the lag in the indicator’s color change can lead to an early determination of the endpoint, resulting in lower titration results. This is because there may still be unreacted calcium hydroxide present at this point; the color change of phenolphthalein is simply due to local acid-base neutralization. Method of multiple titrations in the analysis laboratory: The laboratory uses a method of rapid titration until colorlessness is achieved, then continuing to titrate once color reappears, and repeating this process again to determine the endpoint more accurately. The initial colorlessness may be due to an excess of hydrochloric acid in a localized area, which causes phenolphthalein to change color; however, the solution as a whole has not yet reached the stoichiometric point. As stirring continues or time passes, the unreacted calcium hydroxide will continue to react with hydrochloric acid, causing the solution to turn red again. By performing multiple titrations until the solution becomes colorless and confirming that no color reappears, the titration can be brought closer to the true stoichiometric point, reducing errors and yielding more accurate results. As for the claim in the process that three titrations mimic the three reactions of calcium hydroxide inside the device, this assertion lacks scientific basis. In chemical analysis, the determination of the endpoint is primarily based on the stoichiometric relationships of chemical reactions and the color-changing principle of indicators, rather than a simple correspondence with the number of reactions that occur within the apparatus. In summary, the method of determining the endpoint through multiple titrations in the analysis laboratory is more reasonable, as it enhances the accuracy of calcium hydroxide concentration analysis.

This post was last edited by qqgd on 2025-5-19 09:12. This analysis method is similar to the analysis of lime activity; it involves acid-base titration, using phenolphthalein as an indicator and a high-concentration hydrochloric acid as the titrant, for a rapid determination (the test can be completed using 4M hydrochloric acid within 10 minutes). In practical operations, since calcium hydroxide in lime milk is the active ingredient, and because calcium hydroxide does not dissolve easily in water, different units conducting this analysis may establish varying procedural guidelines depending on the skill level of the operators. Due to the special nature of the samples used in this analysis method, it is recommended to carry out only one titration instead of a re-titration after color reversal. However, during the titration process, the addition of hydrochloric acid should be done at a steady and uniform rate; the sample solution should be shaken as quickly as possible, but care should be taken to avoid generating excessive bubbles. The main reason for doing this is to cause calcium hydroxide to react with hydrochloric acid, without absorbing carbon dioxide from the air. The main reason for the color reversal during titration is likely an insufficient concentration of hydrochloric acid, and a high proportion of calcium carbonate in the lime milk may result in the adsorption of a significant amount of calcium hydroxide. As for the three reactions within the simulation device proposed by the process engineers, we need you to specify what these three reactions of calcium hydroxide are in that device This analysis method was developed primarily to address the quality requirements for lime used in metallurgy to remove sulfur and phosphorus. And what are the three reactions in propylene oxide that you mentioned? I only know that when epichlorohydrin is finally saponified to form a ring, lime is also used to remove the hydrochloric acid generated in the reaction, but I don’t have detailed knowledge of the epichlorohydrin production process. The original poster can try to see how large the difference between the two methods of operation is; if it doesn’t have a significant impact on the results, then one titration may be sufficient. The standard for this analysis method is TB/T 105-2014.

The owner’s analysis is used to consume the hydrochloric acid generated during the saponification of propylene oxide; however, they employed an analysis method based on lime alkalinity. The concentration of the base used in saponification does not need to be extremely precise, but fast analysis speeds are required – in fact, it is sufficient to simply titrate the free alkalinity. The so-called requirements regarding the process may be a form of excessive demand on analysts by process engineers, who believe that greater accuracy is always better.