4.5 Quantitative Chemical Analysis
3 min read•june 24, 2024
Quantitative chemical analysis is all about measuring stuff precisely in chemistry. It's like being a detective, but instead of solving crimes, you're figuring out exactly how much of something is in a sample.
Two main methods are and . Titration is like adding drops until something changes color. Gravimetry involves weighing things super carefully. Both help chemists determine concentrations and amounts of substances.
Quantitative Chemical Analysis
Principles of titration and gravimetry
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- Titration
- Gradual addition of a solution with known concentration () to a solution with unknown concentration ()
- reached when reaction between titrant and is complete, indicated by color change () or other observable signal (conductivity)
- is theoretical point where amount of titrant added is stoichiometrically equal to amount of analyte
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- Determination of analyte's mass by converting it into a compound of known composition and measuring its mass
- formed by reacting analyte with suitable reagent (silver chloride)
- Filtration, washing, and drying steps isolate and purify
- Mass of precipitate measured, analyte's mass or concentration calculated using stoichiometric relationships
Calculations from titration data
- Titration calculations
- () is concentration of solution expressed as moles of solute per liter of solution
- , where and are molarity and volume of titrant, and are molarity and volume of analyte
- Use volume and titrant's molarity to calculate moles or concentration of analyte
- calculations
- Determine molar mass of precipitate formed
- Use mass of precipitate and its molar mass to calculate moles of precipitate
- Apply stoichiometric relationships between precipitate and analyte to determine moles or mass of analyte
- Calculate analyte's concentration if sample volume is known
Stoichiometry in combustion analysis
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- Burning sample in oxygen-rich environment converts elements into respective oxides
- Carbon converted to CO2, hydrogen to H2O, other elements to corresponding oxides (sulfur to SO2)
- Masses of combustion products measured and used to calculate mass and percentage of each element in original sample
- Elemental composition determination
- Use balanced combustion reaction equation to establish stoichiometric relationships between sample and combustion products
- Calculate moles of each combustion product using measured masses and molar masses
- Determine moles and mass of each element in original sample using stoichiometric relationships
- Express elemental composition as mass percentages (40% C, 6.7% H) or (CH2O)
Instrumental methods of analysis
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- Measures the amount of light absorbed by a sample to determine concentration
- Uses a to relate absorbance to concentration of unknown samples
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- Analyzes the concentration of specific metal elements in a sample
- Utilizes the principle that atoms absorb light at characteristic wavelengths
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- Separates and analyzes complex mixtures based on different affinities of components to stationary and mobile phases
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- A technique used to determine the concentration of an analyte in a sample by adding known amounts of the analyte to the sample
Key Terms to Review (29)
Analyte: An analyte is a substance or chemical constituent that is being measured and analyzed in a laboratory sample. It is the target of quantitative chemical analysis to determine its concentration within a mixture.
Analyte: The analyte is the specific chemical species or compound of interest that is being measured or detected in a quantitative chemical analysis or an acid-base titration. It is the target substance that the analysis aims to identify and/or quantify.
Atomic Absorption Spectroscopy: Atomic absorption spectroscopy (AAS) is an analytical technique used to determine the concentration of a specific element in a sample. It works by measuring the absorption of light by free atoms of that element in the gaseous state, which is proportional to the concentration of the element in the sample.
Buret: A buret is a precise, graduated glass tube with a stopcock at the bottom used to dispense known volumes of liquid, primarily in titrations. It allows for accurate measurement of reactants added to a reaction.
Calibration Curve: A calibration curve is a graphical representation of the relationship between the measured response of an analytical instrument and the known concentration or amount of an analyte in a sample. It is a fundamental tool used in quantitative chemical analysis to determine the concentration of an unknown sample by comparing its measured response to the calibration curve.
Chromatography: Chromatography is a separation technique used to isolate and identify the components of a complex mixture. It involves the separation of substances based on their differential partitioning between a stationary phase and a mobile phase, allowing for the identification and quantification of the individual components.
Combustion Analysis: Combustion analysis is a quantitative analytical technique used to determine the elemental composition of organic compounds. It involves the complete oxidation of a sample through high-temperature combustion, allowing for the precise measurement of the amounts of carbon, hydrogen, and other elements present.
Empirical formula: An empirical formula represents the simplest whole-number ratio of elements in a compound. It does not show the actual number of atoms, but rather the relative proportions.
Empirical Formula: The empirical formula represents the simplest whole-number ratio of atoms of each element present in a compound. It provides the most basic representation of the composition of a compound without specifying the actual number of atoms present.
End point: The end point in a titration is the stage at which the reaction between the titrant and the analyte is complete, typically indicated by a color change or other observable signal. It is used to determine the exact amount of substance present in a sample.
Endpoint: The endpoint in a titration is the point at which the reaction between the analyte and the titrant is complete, signaling the end of the titration process. It is the point where a specific property, such as pH or color change, indicates that the reaction has reached its endpoint.
Equivalence point: The equivalence point in a titration is when the amount of titrant added is exactly enough to neutralize the analyte solution. It is the point at which stoichiometrically equivalent quantities of reactants have been mixed.
Equivalence Point: The equivalence point in a titration is the point at which the amount of titrant added is exactly equal to the amount required to completely react with the analyte. It is the point at which the reaction is complete, and the pH changes rapidly.
Gravimetric analysis: Gravimetric analysis is a quantitative method in chemistry where the amount of an analyte is determined by measuring the mass of a solid. This technique typically involves precipitation, filtration, and weighing.
Gravimetric Analysis: Gravimetric analysis is a quantitative analytical technique in chemistry that determines the amount of a specific substance in a sample by measuring its mass. It involves the isolation, purification, and weighing of the substance to calculate its concentration or amount in the original sample.
Gravimetry: Gravimetry is an analytical technique in quantitative chemical analysis that involves the determination of the mass or concentration of an analyte based on the mass of a solid product formed in a chemical reaction. It is a widely used method for the precise and accurate measurement of chemical compositions.
Indicators: Indicators are substances that change color at a specific pH level, used to determine the endpoint of a titration. They help in identifying the equivalence point in chemical reactions.
Molarity: Molarity is a measure of the concentration of a solution, specifically the number of moles of a solute dissolved per liter of solution. It is a fundamental concept in chemistry that is used to quantify the amount of a substance present in a given volume of a solution and is essential for understanding various chemical processes and analyses.
Molarity (M): Molarity (M) is a measure of the concentration of a solute in a solution, expressed as moles of solute per liter of solution. It is commonly used to quantify the concentration of chemical solutions in laboratory settings.
Phenolphthalein: Phenolphthalein is a chemical compound commonly used as a pH indicator in acid-base titrations. It is a weak acid that changes color depending on the pH of the solution, making it a valuable tool for quantitative chemical analysis and acid-base titrations.
Precipitate: A precipitate is a solid that forms and separates from a liquid mixture during a chemical reaction. It often occurs when two aqueous solutions react to form an insoluble product.
Precipitate: A precipitate is a solid material that forms and separates from a liquid solution during a chemical reaction or a change in solution conditions. It is the result of a chemical process where dissolved substances come out of the solution and form a solid phase.
Quantitative analysis: Quantitative analysis involves the determination of the amount or concentration of a substance in a sample. It is crucial for understanding the stoichiometry of chemical reactions and ensuring accurate measurements.
Spectrophotometry: Spectrophotometry is an analytical technique that measures the amount of light absorbed by a sample at different wavelengths. It is widely used in various fields, including chemistry, to quantify the concentration of specific compounds in a solution.
Standard Addition: Standard addition is an analytical technique used in quantitative chemical analysis to determine the concentration of an analyte in a sample by adding a known amount of the analyte to the sample and measuring the resulting change in the analytical signal. This method helps overcome matrix effects and improve the accuracy of the analysis.
Stoichiometry: Stoichiometry is the calculation of reactants and products in chemical reactions using balanced chemical equations. It involves the use of molar ratios derived from these equations to predict quantities of substances consumed and produced.
Titrant: A titrant is a solution of known concentration used in titration to determine the concentration of an unknown solution. It is typically added from a burette during the process.
Titration: Titration is a quantitative analytical technique used to determine the unknown concentration of a solution by gradually adding a measured volume of a standard solution with a known concentration until a specific endpoint is reached, indicating the completion of a chemical reaction. This process allows for the precise measurement and calculation of the concentration of the unknown solution.
Titration analysis: Titration analysis is a quantitative chemical technique used to determine the concentration of an unknown solution by reacting it with a solution of known concentration.