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Gravimetric analysis is the quantitative determination of a substance by precipitation, followed by isolation and weighing of the precipitate. The percentage of a specific element or ion in a sample is determined through quantitative analysis.
Knowing the mass and chemical formula of the precipitate, the mass of the ion of interest can be calculated using the precipitate percent mass composition. The percentage of the ion of interest in the original compound can be estimated using the masses of the ion of interest and the original compound.
Organic Compound Quantitative Analysis
The next stage in finding a compound’s formula is to estimate the percentage composition of the various components contained in the complex. The many approaches used to estimate various elements are detailed below.
Carbon and hydrogen estimation
Liebig’s combustion approach always estimates these two factors combined. In an environment of air or oxygen, a weighted amount of the chemical is heated vigorously with excess copper oxide. Thus, the constituents hydrogen and carbon are oxidized to water and carbon dioxide, which are collected and weighed separately. The carbon and hydrogen percentages in the chemical can be determined as shown below.
% C = 12/44 x Mass of CO2 formed/Mass of material x 100
percent H = 1/18 x mass of produced H2O / mass of material x 100
Nitrogen Dumas Method Estimation
This approach is applicable to any organic molecules that contain nitrogen. The approach is based on the idea that when an organic compound containing nitrogen is burned with copper oxide, free nitrogen and oxides of nitrogen, among other products, are generated (carbon dioxide, water vapor etc). Nitrogen oxides are converted to free nitrogen after passing over heated copper, and the entire amount of nitrogen is collected over KOH solution. The volume of nitrogen collected is measured, and the percentage of nitrogen present in the chemical is computed from this.
percent N = 28/22400 x Volume of nitrogen at NTP / Compound mass x 100
Halogen Estimation
The Carius Method
In a sealed tube, a known mass of halogen-containing organic material is heated with fuming nitric acid and a few crystals of silver nitrate. The silver halide is created and separated, washed, dried, and weighed. The percentage of halogen is derived from the mass of silver halide obtained.
percent Halogen = halogen atomic mass x mass of silver halide obtained x 100 / halogen molar mass x mass of compound taken
As silver iodide is slightly soluble in nitric acid, and some iodine is created even in the presence of sufficient silver nitrate, the Carius method does not produce satisfactory results with iodine. Furthermore, the results for highly halogenated aromatic compounds are inaccurate.
Sulfur Estimation
The cartius method is sometimes used to determine sulfur. The organic molecule is just heated with nitric acid in this scenario. Sulfur in the compound is therefore oxidized to sulphuric acid, which is then precipitated with barium chloride to form barium sulfate. The barium sulfate precipitate is washed, dried, and weighed. The percentage of sulfur is derived from the weighted mass of barium sulfate obtained.
percent S = 32/233 x BaSO4 mass/Compound mass x 100
Phosphorus Estimation
Phosphorus is calculated in the same way as sulfur is, by heating an organic molecule with fuming nitric acid. The compound’s phosphorus is therefore oxidized to phosphoric acid, which is precipitated by adding a magnesia mixture. Magnesium pyrophosphate is produced by igniting the precipitate of magnesium ammonium phosphate.
2MgNH4PO4 → Mg2P2O7+ 2NH3 + H2O
The magnesium pyrophosphate is weighed, and the phosphorus percentage is calculated.
percent P = 62/222 x Mg2P2O7 mass/compound mass x 100
Conclusion
The primary responsibility of a quantitative analyst is to present a specific hypothetical situation in numerical terms. Quantitative analysis aids in the evaluation of performance, the evaluation of financial instruments, and the forecast of future events.
