3.0 Other methods of Quantitative Analysis

Gravimetric Analysis

A method of analysis in which the analyte is converted into a known substance that can be accurately weighed

Volatilization

 A type of gravimetric analysis where a sample is heated, causing one component to decompose into a gas, which is driven off. The mass change is used for quantification

Titration

A quantitative technique used to determine the concentration of a solute (the analyte) by reacting it with a solution of known concentration (the titrant)

Analyte

The analyte is the substance whose concentration is being determined

Titrant

the solution of known concentration that is precisely added from a buret

Equivalence Point

The equivalence point is the theoretical point where stoichiometrically equivalent amounts of analyte and titrant have reacted

End Point

he experimental point where a physical change, such as a color change from an indicator, signals that the reaction is complete

Indicator

A reagent added to the analyte solution that changes color at or near the equivalence point

Blank

A solution that contains all the reagents used in the experiment except for the analyte of interest. A blank titration is performed to correct for any titrant that reacts with the indicator or impurities

Calculate Corrected Volume of Titrant

 The volume of EDTA required to titrate the blank must be subtracted from the average volume of EDTA used for the soil sample titration to get the volume that reacted only with the Ca²⁺. Corrected Volume = (Volume EDTA for sample) - (Volume EDTA for blank)

Determine Moles of EDTA

Use the molarity of the standard EDTA solution and the corrected volume (converted to Liters) to find the moles of EDTA used. Moles EDTA = Molarity of EDTA × Corrected Volume (L)

Determine Moles of Ca

Based on the 1:1 stoichiometry of the reaction, the moles of Ca²⁺ in the titrated sample are equal to the moles of EDTA used. Moles Ca²⁺ = Moles EDTA

Calculate Total Mass of Ca²⁺ in Original Sample

The titration was performed on a small portion (a 10.00 mL aliquot) of the total soil extract (100.0 mL). Therefore, you must scale up your result to find the mass of calcium in the entire original extract. For example: Total Mass Ca²⁺ = (Mass of Ca²⁺ in titrated 10.00 mL) × (100.0 mL total / 10.00 mL titrated)

Calculate Weight Percent

Divide the total mass of Ca²⁺ by the original mass of the soil sample (25.00 g) and multiply by 100. Weight % Ca²⁺ = (Total Mass of Ca²⁺ / Mass of original soil sample) × 100%