Gravimetric Analysis and Stoichiometry - SS3 Chemistry Lesson Note
Gravimetric analysis and stoichiometry are two essential concepts in analytical chemistry that play significant roles in determining the quantities of substances in a sample. These techniques rely on precise measurements and chemical equations to quantitatively analyse compounds. Let's explore the advanced aspects of gravimetric analysis and stoichiometry:
Gravimetric Analysis:
Gravimetric analysis is a quantitative analytical technique that involves the determination of the amount of a substance based on the mass of a pure compound formed from a chemical reaction. The process typically consists of the following steps:
● Precipitation Reaction: A known analyte is precipitated as an insoluble compound by adding a suitable reagent. The reaction forms a precipitate that is easily filtered and collected.
● Filtration and Washing: The precipitate is collected on filter paper, and any impurities are removed by washing with a suitable solvent.
● Drying and Weighing: The filter paper with the precipitate is carefully dried to remove any remaining solvent, and the mass of the dried precipitate is measured using an analytical balance.
● Calculations: The mass of the precipitate is used to determine the amount of the analyte present in the original sample using stoichiometry.
Gravimetric analysis is highly accurate and precise when performed under controlled conditions, making it valuable for determining the concentrations of specific substances in various samples.
Stoichiometry:
Stoichiometry is the study of the quantitative relationships between reactants and products in a chemical reaction. It is essential in both gravimetric analysis and other quantitative methods, as it provides the basis for calculating the amount of a reactant or product involved in a reaction.
● Stoichiometric Ratios: Chemical reactions are balanced equations that show the molar ratios between reactants and products. These ratios are essential for determining the quantity of one substance based on the amount of another involved in the reaction.
● Limiting Reactant: In stoichiometry, the concept of the limiting reactant is crucial. The limiting reactant is the reactant that is entirely consumed in a chemical reaction, limiting the amount of product that can be formed. The quantity of product formed is determined by the amount of the limiting reactant, and stoichiometry allows the calculation of this relationship.
● Theoretical Yield and Actual Yield: Theoretical yield is the maximum amount of product that can be formed according to stoichiometry. However, the actual yield is the amount of product obtained in reality, which may be less due to various factors such as incomplete reactions, side reactions, or loss during handling.
Sample Analysis with Gravimetric and Stoichiometric Methods:
Gravimetric analysis and stoichiometry are often used together to determine the concentration of an analyte in a sample. By conducting a gravimetric analysis and knowing the stoichiometry of the reaction, the amount of the analyte in the original sample can be accurately calculated.
● Example: In gravimetric analysis, a sample containing chloride ions (Cl⁻) can be precipitated as silver chloride (AgCl) using silver nitrate (AgNO₃) as the reagent. By weighing the collected AgCl precipitate and knowing the balanced chemical equation (2AgNO₃ + Cl⁻ → AgCl + 2NO₃⁻), stoichiometry allows us to determine the number of chloride ions in the original sample.
Limitations and Considerations:
Gravimetric analysis and stoichiometry are highly accurate when performed carefully under controlled conditions. However, some factors, such as impurities in the precipitate, incomplete reactions, or side reactions, can introduce errors in the results. Analytical chemists must consider and address these potential sources of error to ensure accurate and reliable quantitative analysis.
In conclusion, gravimetric analysis and stoichiometry are powerful quantitative techniques used in analytical chemistry to determine the amounts of substances in samples. By understanding the principles behind gravimetric analysis and the stoichiometry of chemical reactions, chemists can confidently analyse complex samples and obtain precise and accurate results, contributing to research, quality control, and various applications in chemistry and related fields.