Purity of the Precipitate: Co-precipitation & Post precipitation and Estimation of Barium Sulphate : Pharmaceutical Guidelines -->

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Purity of the Precipitate: Co-precipitation & Post precipitation and Estimation of Barium Sulphate

An analyte compound that forms when precipitating reagents are added to a solution is measured using the precipitation gravimeter.
An analyte compound that forms when precipitating reagents are added to a solution is measured using the precipitation gravimeter. It is true that most gravimetric methods, which generate precipitates as part of a metathesis reaction, can be used for analyzing samples by gravimetry. Nevertheless, a gravimetric method could work with any reaction producing precipitate. In the nineteenth century and earlier, many precipitations gravimetric methods were developed, often to analyze ore.

A total analysis method typically provides better than 0.1% accuracy, which means that the analyte is represented by 99.99% of the precipitate. As the requirement is extended to 99.99% of a precipitate's solubility, gravimetric analysis accuracy will not be impeded.

Co-precipitation

This is a type of precipitation characterized by the elimination of soluble compounds in a solution during precipitation. The term coprecipitation describes a precipitation process where soluble compounds are removed from a solution as precipitates form. This reaction contains a significant amount of contamination. Multi-particle precipitation occurs when more than one soluble component evaporates simultaneously from a single solution.

Co-precipitation occurs when more than one component precipitates at the same time. Using co-precipitation, catalysts consisting of more than one component are easily prepared. Most precipitates that separate from solutions don't contain pure water but contain a greater amount of foreign substances, like mother liquor. Precipitates may be infected with impurities, depending on their nature and the conditions from which they precipitated. Coprecipitation is the process of contaminating precipitates with substances that are normally soluble under precipitation conditions. A person who becomes contaminated due to coprecipitation ought to be distinguished from one who becomes contaminated due to chemical precipitation alone. In the presence of barium chloride and potassium sulfate, coprecipitation is observed when the precipitated potassium sulfate contains greater or lesser amounts of barium sulfate, although it is freely soluble in the given conditions. Reciprocity is primarily carried out through two mechanisms, i.e.,
  1. The particles' surfaces have an adsorption effect
  2. fixation by the introduction of foreign ions (and solvents)

Post precipitation

The term post precipitation describes a type of precipitation in which the undesirable component precipitates after the desired component has precipitated. The term post precipitation describes a type of precipitation in which the precipitate of the unwanted compound appears after the precipitate of the desired compound. This is low-level contamination. It is the precipitation that forms a layer of precipitate upon that which already exists.

In terms of contamination resulting from foreign materials in a precipitate, coprecipitation is important. It is also possible to make a precipitate impure through a process known as post precipitation. It appears that a first precipitate of the foreign substance separates in a pure form and is then followed by a second precipitate of the foreign substance that is slightly soluble. There is therefore no coprecipitation in the second phase but only post precipitation. During supernatants that are saturated, some components that crystallize very slowly are liable to undergo post precipitation.

Estimation of barium sulfate

The method most commonly used is this one. Different ions have interfering effects on barium sulfate solubility in cold water. The solubility is greater in hot water or when diluted in chloric or nitric acid; it is less in solutions containing a common ion. It may be precipitated by using sulphuric acid, as well as by using sulphamic acid solutions containing sulfate ions when heated: NH2S03H+ H20 = NH4+ + SO42- + H+

Formation of sulfate precipitates. A solution (100 mL) containing not more than 0.15 g of barium and not more than 1% concentrated hydrochloric acid should be used. Stir constantly while adding hot 0.5M sulphuric acid at a slightly higher temperature. The solution should be digested in steam until the precipitate settles, filtered, washed with hot water containing two drops of sulphuric acid per liter, and finally with water until the acid is no longer present. The ignition process takes place between 900 and 1000 degrees Celsius. The recommended solution for practice can be prepared by adding 1ml of concentrated hydrochloric acid to approximately 0.3g of accurately weighed barium chloride in 100ml water.
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Ankur Choudhary is India's first professional pharmaceutical blogger, author and founder of Pharmaceutical Guidelines, a widely-read pharmaceutical blog since 2008. Sign-up for the free email updates for your daily dose of pharmaceutical tips.
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