Experimental Techniques of Drying & Ignition

The desired ingredient is converted into a substance (with a known composition) that can be extracted from the sample and weighed using gravimetric analysis. The gravimetric analysis involves preparing a solution containing a set weight of the sample, weighing the isolated constituent, separating the desired ingredient, and determining the amount of a particular constituent in the sample from the observed weight of the isolated substance.

The most frequent method for isolating the desired ingredient from a sample solution is precipitation—that is, transformation into a substance that is not soluble in the solution. A reagent is used to make an insoluble compound with the target constituent while leaving the other sample constituents alone. The precipitate is separated by filtration, then washed to eliminate soluble impurities, dried or burned to remove water, and weighed. In this post, we will look into methods used in gravimetric analysis and will have a brief discussion on experimental techniques of drying and ignition.

Methods Used In Gravimetric Analysis

Gravimetric analysis is a set of methods used in analytical chemistry to determine the mass of an analyte (the ion being studied) in order to quantify it. The basic idea behind this form of analysis is that once the mass of an ion has been measured as a unique molecule, that measurement may be used to calculate the mass of the same analyte in a mixture, as long as the relative quantities of the other constituents are known. The following are the methods used in the gravimetric analysis:

·        Precipitation: The precipitation method involves weighing an element in the form of precipitates, which are then filtered out of the solution.

·        Filtration: The separation of precipitates from the mother liquor is accomplished through filtration.

·        Washing: To remove all soluble contaminants stuck to the precipitates, they must be washed with liquid.

·        Drying or  Ignition: Precipitates are dried or burned after washing, depending on the nature of the precipitates and the filtering medium.

·        Weighing: The ignited sample is cooled for a few minutes before being placed in a desiccator to prevent moisture adsorption and weighing on a chemical balance.

Examples Of Gravitational Analysis

One example of gravimetric analysis is detecting chloride in a chemical. For doing gravimetric analysis, a cation should create an insoluble compound along with chloride. According to the principles of solubility, Pb²⁺, Ag⁺, and Hg₂²⁺are able to form chlorides that are insoluble. As silver chloride is an insoluble substance, it can be easily filtered and utilised to measure the amount of Cl^– ions.

A barium chloride solution of unknown volume can be treated with sulfuric acid to generate an insoluble barium sulphate complex, which can be used to calculate the quantity of barium present in a known sample of barium chloride. This barium sulphate can then be used to determine the mass percentage of barium in barium chloride and estimate the amount of barium in the precipitate. When choosing a precipitating agent, keep in mind that it should create a pure insoluble complex with the component of interest that can be easily filtered.

Experimental Techniques Of Drying & Ignition

After understanding the methods used in gravimetric analysis and examples of gravimetric analysis, let’s understand the techniques of drying and ignition of the precipitate. In certain cases, the precipitate must be dried and weighed before being weighed, whereas in others, it must be burned before being weighed. Now we’ll talk about the drying and igniting processes, as well as the necessary equipment. Precipitates are usually dried in water or air ovens. When the drying temperature does not exceed 100° C, the water oven is utilised, and when the temperature does exceed 100° C, the air oven is employed.

It is sufficient to heat the water to the boiling point and transfer the precipitate to the oven when instructed to dry a precipitate in a water oven at 100° C. If necessary, a pinch of salt can be added to the water to raise the boiling point of the liquid in the jacket.

When drying a precipitate on paper, place the funnel and paper in the oven, slip the funnel’s stem through one of the shelf’s holes, and cover the funnel’s top with filter paper to avoid contamination. Heat is applied to the precipitate until it seems to be dry and no more vapour rises from its surface. The door is closed during the drying process and only opened for removal or inspection.

If the temperature is carefully regulated, the drying process can also be done quickly and easily in an air oven. The student can control the Bunsen flame to keep the oven temperature within a few degrees of the ideal temperature with practice, but a gas regulator (also known as a thermostat) should be added to the oven for more exact work.

The purpose of drying and igniting is to produce a compound with a predictable composition. Ignition can also be used to decompose a solid into a chemical with a known composition. To avoid moisture adsorption and weight on a chemical balance, the ignited sample is cooled for a few minutes before being placed in a desiccator.

Conclusion

That’s a wrap to the methods used in gravimetric analysis and an introduction to experimental techniques of drying and ignition. For a quantitative application, the final precipitate must have a well-defined composition. A precipitate containing volatile ions or large amounts of hydrated water is usually dried at a high enough temperature to completely remove these volatile species.