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Any method for determining the amount of a chemical in a sample is known as quantitative analysis. The amount is always expressed numerically, with unit conversions as needed. Numerous techniques for measuring quantitative or qualitative analysis chemistry are available. For example, assume that an indicator solution changes colour in the presence of a metal ion. It could be used as a qualitative test to see if adding a drop of a sample changes the colour of the indicator solution. It could also be used as a quantitative test by observing the colour of the indicator solution at various metal ion concentrations.
Quantitative analysis example for Element P
Phosphorus is required for life, primarily through phosphates. Phosphates can be found in DNA, RNA, ATP, and phospholipids, complex compounds needed by cells.
Phosphorus was first isolated from human urine, and bone ash was a significant early source of phosphate. Because phosphate is found in fossilised deposits of animal remains and excreta, phosphate mines contain fossils.
Low phosphate levels are a significant growth constraint in some aquatic systems. Therefore, the vast majority of mined phosphorus compounds are used as fertilisers.
Phosphate is required to replace the phosphorus removed from soil by plants, and its annual demand is increasing nearly twice as quickly as the human population. In addition, organophosphorus compounds are found in detergents, pesticides, and nerve agents.
Various quantitative and qualitative analyses are utilised to detect phosphate ions in the solution. Such tests are used in industries, scientific research, and water monitoring in the environment.
The method described here is a quantitative method for determining the amount of phosphate in samples such as boiler feedwater. First, a predetermined measure of boiler water is downed into a mixing tube, and then ammonium heptamolybdate reagent is added.
The tube is then tightly closed and shaken vigorously. The tube mixture is then treated with a dilute stannous chloride reagent, made fresh from distilled water and concentrated stannous chloride reagent.
Molybdenum blue formation results in blue colour, and the depth of the colour indicates the amount of phosphate in the boiler water. Therefore, a calorimeter can be used to determine the phosphate concentration in the original solution by measuring the absorbance of the blue key. In contrast, a Lovibond comparator can provide a direct (though approximate) reading of phosphate concentration.
Na3PO4 + 3HNO3 → H3PO4 + 3NaNO3
H3PO4 + 12(NH4)2MoO4 + 21HNO3 → (NH4)3PO4.12MoO3 + 21NH4NO3 + 12H2O
Quantitative analysis for Element S
All living things require sulphur, but it is almost always found in organosulfur compounds or metal sulphides. Three amino acids (cysteine, cystine, and methionine) and two vitamins are examples of organosulfur compounds (biotin and thiamine).
Sulphur is found in many cofactors, including glutathione, thioredoxin, and iron-sulfur proteins. S–S bonds in disulfides give the protein keratin, which is located in the outer skin, hair, feathers, mechanical strength, and insolubility.
Sulphur is a macronutrient required by all living organisms and one of the chemical elements required for biochemical function.
In the presence of a BaCl2 solution, a known mass of the compound is heated in a Carius tube with conc. HNO3. Sulphur is oxidised to H2SO4, which precipitates as BaSO4. After that, it is dried and weighed.
Percentage of S= ((Atomic mass of S)/(Molecular mass of BaSO4)) x (( Mass of BaSO4)/(Mass of the compound)) x 100
Assume the organic compound has a mass of mg.
Assume that the mass of formed barium sulphate is m1 g.
1 mol of BaSO4 contains 32 g of Sulphur, as we know.
As a result, every 233 g of BaSO4 contains 32 g of Sulphur:
m1 g of BaSO4 contains (32 x m1/233)g of Sulphur
Quantitative analysis of element O
The majority of living organisms are made up of oxygen, a water component, the basic building block of all lifeforms. Photosynthesis, which uses sunlight energy to produce oxygen from water and carbon dioxide, continuously replenishes oxygen in the Earth’s atmosphere.
Because oxygen is too chemically reactive to exist as a free element in air, it must be constantly replenished by the photosynthetic activity of living organisms.
Two oxygen atoms are chemically bound together as dioxygen. The bond can be described in various ways, depending on the level of theory. Still, it is most simply described as a covalent double bond formed by the filling of molecular orbitals formed from the atomic orbitals of individual oxygen atoms, which results in a bond order of two.
By heating the compound in the presence of N2 gas, a known mass of the compound is decomposed. The resulting gas mixture is passed over red hot coke. This is done to convert all of the O2 to CO. When this mixture is heated with I2O5, CO is oxidised to CO2, releasing I2.
Other gaseous products + O2 Organic compound
2CO = 2C + O2
I2O5 + 5CO5CO2 + I2O5
Percentage of O = (((Molecular mass of O2/Molecular mass of CO2) x (Mass of CO2/Mass of the compound) x 100)
Quantitative analysis of elements C and H
C and H are detected in a dry test tube by heating the compound with CuO. Both are oxidised to produce CO2 and H2O. The presence of C and H is confirmed if the CO2 turns lime water milky and the H2O turns anhydrous CuSO4 blue.
C + 2CuO ———–> 2Cu + CO2
2H + CuO ————> Cu +H2O
CO2 + Ca(OH)2——-> CaCO3 + H2O
5H20 + CuSO4———> CuSO4.5H2O
Conclusion
The determination of the relative or absolute abundance (often denoted as concentration) of a single, several, or all specific substance(s) presented in a sample is quantitative analysis in analytical chemistry.
After determining the presence of specific substances in a sample, the study of their absolute or relative abundance may aid in deciding particular properties.
Knowing a sample’s composition is critical, and several methods, such as gravimetric and volumetric analysis, have been developed to assist. Gravimetric analysis is more accurate than volumetric analysis in determining the composition of a sample, but it takes longer in the laboratory.
