Gravimetric analysis is a technique used to determine the mass of a compound in a sample by measuring the mass of a solid that is precipitated from a solution. This method relies on the fact that the mass of a substance is directly proportional to its quantity.
The process of gravimetric analysis typically involves the following steps:
Sample preparation: The sample is prepared by dissolving it in a solvent and filtering it to remove any impurities.
Precipitation: A reagent is added to the solution to cause the compound of interest to precipitate out as a solid. The precipitate is then allowed to settle to the bottom of the container.
Filtration: The precipitate is then collected by filtration, using a filter paper or a funnel and filter flask.
Drying: The precipitate is then dried to remove any remaining moisture. This is usually done by heating the precipitate in an oven or on a hot plate.
Weighing: The mass of the dry precipitate is then determined using an analytical balance.
Calculations: The mass of the compound in the sample can then be calculated based on the mass of the precipitate and the known chemical reaction that occurred during the precipitation process.
Gravimetric analysis is a highly accurate and precise method for determining the mass of a compound in a sample. It is often used in analytical chemistry and quality control to ensure that products meet specific standards and specifications. However, it does have some limitations, including the need to use specific reagents and the time required for the precipitation and drying steps.
Overall, gravimetric analysis is a valuable tool for determining the mass of a compound in a sample, and it has a wide range of applications in various industries.
The mass of the crucible is subtracted from the combined mass, giving the mass of the precipitated analyte. Comparing modern dynamic flash combustion coupled with gas chromatography with traditional combustion analysis will show that the former is both faster and allows for simultaneous determination of multiple elements while traditional determination allowed only for the determination of carbon and hydrogen. Gravimetric analyses are quantitative methods that are based on determining the mass of a pure compound to which the analyte is chemically related. This is especially useful in determining the water content of complex materials such as foodstuffs. Upon addition of the first drops of the precipitating agent, supersaturation occurs, and then nucleation starts to occur where every few molecules of precipitate aggregate together forming a nucleus. However, they must be carefully cleaned to minimize contamination or carryover cross-contamination. Gravimetric analysis, due to its high degree of accuracy, when performed correctly, can also be used to calibrate other instruments in lieu of reference standards.
It is vital that theempirical formula of the weighed precipitate be known, and that the precipitate be pure; if two forms are present, the results will be inaccurate. For instance, calcium ion might be precipitated using oxalate ion, to produce calcium oxalate CaC 2O4 ; it might then be heated to convert it into the oxide CaO. PROCEDURE Depending on the procedure followed, the filter might be a piece of ashless filter paper in a fluted funnel, or a filter crucible. GRAVIMETRIC ANALYSISIn other cases, it may be easier to remove the analyte by vaporization. H 2 O Mn 2 P 2 O 7 Many metals Ni 2 + Ni dimethylglyoximate 2 same Pd 2+ , Pt 2+ , Bi 3+ , Au 3 + 6 Steps in a Gravimetric Analysis After appropriate dissolution of the sample, the following steps should be followed for a successful gravimetric procedure: 1. GRAVIMETRIC ANALYSISGravimetric analysis describes a set of methods in analytical chemistry for the quantitative determination of an analyte based on the mass of a solid. The precipitate can then be collected by filtration, washed, dried to remove traces of moisture from the solution, and weighed.
The precipitate should be quantitative, easily washed and filtered and of a suitable quantity for accurate weighing. Or, the sample can be weighed before and after it is dried; the difference between the two masses gives the mass of analyte lost. However, it is considered, when appropriately done, one of the most accurate analytical techniques. Preparation of the Solution: This may involve several steps including adjustment of the pH of the solution in order for the precipitate to occur quantitatively and get a precipitate of desired properties, removing interferences, adjusting the volume of the sample to suit the amount of precipitating agent to be added. .
Gravimetry is applied to samples where a good precipitating agent is available. GRAVIMETRIC ANALYSISBy : Charlene Grace A. This is easily done by adding a few drops of the precipitating reagent; if a precipitate is observed, the precipitation is incomplete. The solution may be treated to adjust the pH so that the proper precipitate is formed, or to suppress the formation of other precipitates. As the name suggests, "ashless" paper is used so that the precipitate is not contaminated with ash.
Gravimetric Analysis Gravimetric analysis describes a set of methods in analytical chemistry for the quantitative determination of an analyte based on the mass of a solid. ADVANTAGES Gravimetric analysis, if methods are followed carefully, provides for exceedingly precise analysis. Compare this with hardy methods such as spectrophotometry and one will find that analysis by these methods is much more efficient. Secondly, the precipitate is converted to a more chemically stable form. IT IS THE TIME FOR THE VIDEO PRESENTATION.
Precipitation: This requires addition of a precipitating agent solution to the sample solution. Since the composition of the precipitate is known, it is simple to calculate the mass of analyte in the original sample. Also, methods often do not require expensive equipment. Crucibles are often used with a mat of glass or asbestosfibers to trap small particles. If it is known that species are present which interfere by also forming precipitates under the same conditions as the analyte , the sample might require treatment with a different reagent to remove these interferents. PROCEDURE The precipitate cannot be weighed with the necessary accuracy in place on the filter paper; nor can the precipitate be completely removed from the filter paper in order to weigh it.
In fact, gravimetric analysis was used to determine the atomic masses of many elements to six figure accuracy. PROCEDURE The alternative is a crucible whose bottom is made of some porous material, such as sintered glass, porcelain or sometimes metal. DISADVANTAGES Gravimetric analysis usually only provides for the analysis of a single element, or a limited group of elements, at a time. The precipitate can be carefully heated in a crucible until the filter paper has burned away; this leaves only the precipitate. Also, Gravimetry is one of a few analytical methods that do not require standard solutions as the weight of precipitate is the only important parameter in analyte determination. The amount of analyte in the original sample can then be calculated from the mass of the precipitate and its chemical composition. After the precipitate has formed and been allowed to "digest", the solution is carefully filtered.
These are chemically inert and mechanically stable, even at elevated temperatures. At this point, addition of extra precipitating agent will either form new nuclei or will build up on existing nuclei to give a precipitate. PROCEDURE After filtration, the precipitate including the filter paper or crucible is heated. Methods are often convoluted and a slight mis-step in a procedure can often mean disaster for the analysis colloid formation in precipitation gravimetry, for example. PROCEDURE After the precipitate is allowed to cool preferably in a desiccator to keep it from absorbing moisture , it is weighed in the crucible. Digestion can help reduce the amount of coprecipitation.
This achieves three purposes: The remaining moisture is removed drying. GRAVIMETRIC ANALYSISIn most cases, the analyte must first be converted to a solid by precipitation with an appropriate reagent. Filter paper is convenient because it does not typically require cleaning before use; however, filter paper can be chemically attacked by some solutions such as concentrated acid or base , and may tear during the filtration of large volumes of solution. This may require low concentration, extensive heating often described as "digestion" , or careful control of the pH. PROCEDURE After the solution has been filtered, it should be tested to make sure that the analyte has been completely precipitated. Gravimetry provides very little room for instrumental error and does not require a series of standards for calculation of an unknown. The analyte might be collectedperhaps in a cryogenic trap or on some absorbent material such as activated carbon-and measured directly.
