Gravimetric Analysis of a Soluble Sulfate

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Abstract

Gravimetric analysis describes the methods for finding the chemical constituent of analyte in a solution through analytical chemistry. This method uses the mass of solid SO42-, with an unknown quantity and quality, to qualitatively determine the makeup of the solid SO3-. Two separate experiments with the initial compounds of BaCl2 and SO42- were put into solution to allow for the BaSO4 precipitate to form. Through filtration and ignition of precipitate containing ashless papers, the solid masses of BaSO4 were attained. With a gravimetric factor of 1:1, sample 1 resulted in the formation of 0.5874g BaSO4 from 0.4004g of SO42-, while sample 2 resulted in the formation of 0.4073g BaSO4 from 0.3985g of SO42-. The two samples, respectively, produced a percentage of 50.32% and 35.06% SO3-; averaging a net percentage of 42.69% with a standard deviation of ± 10.79%.

Purpose

The purpose of this experiment is to determine the mass of sulfate in the precipitate from the reaction of BaCl2 (aq) + SO42-(aq) → BaSO4(s) + 2Cl-(aq) while utilizing gravimetric analysis methods.

Introduction

Gravimetric Analysis utilizes the mass of a product to calculate the quantity of the original unknown analyte, Quantitative Chemical Analysis page 674. While this method of chemical analysis has been established since the eighteenth century, it is still one of the most accurate methods when determining how much unknown was present. The gravimetric analysis of a soluble sulfate lab allows for the experimenter to become better acquainted with techniques necessary for the completion of the experiment, while also understanding the pitfalls associated with carelessness and improper use of laboratory equipment.

Techniques and Equipment utilized:
Tare and Weighing
Filtering
Ignition of Precipitate
Glassware Reading and Proper Handling
Weight to Constant Mass
M-22 Denver Instrument Analytical Balance
Ring Stand, Ring, and Clay Triangle
Fisher Bruner and Striker
Porcelain Crucible and Lid
Desiccator
Funnel, Funnel Clamp, and Filter Paper
Assortment of Glass Beakers
The significance of gravimetric analysis is, if methods are followed carefully, it provides for exceedingly precise analysis. In fact, gravimetric analysis can be so precise that it has been used to determine the atomic masses of many elements to six figure accuracy. In addition to its ability to be very precise and accurate, the simple and straight forward techniques tolerate very little room for instrumental error and do not require a series of standards for calculation of an unknown. Gravimetric analysis can also be used to calibrate other instruments in lieu of reference standards.

Experimental

Procedure (I): Ignition of Crucibles

This procedure is performed for the purpose of establishing a constant mass of the crucibles for more accurate measurements in succeeding procedures.
Obtain and thoroughly clean two porcelain crucibles and lids. Setup ring stand, ring and clay triangle for each crucible. Using Fisher burners, ignite the crucibles to a cherry red for 30 minutes, leaving crucible lids slightly ajar as to prevent breakage. Once finished heating the crucibles, place them into the desiccator, also leaving the lid slightly ajar, for 20 minutes. After the crucibles have reached room temperature, weight the mass of each and record. The weights were 18.8695g and 19.7828g for crucible 1 and 2, respectively. Once the weights have been obtained, repeat the heating and cooling process and reweight. The weights were 18.8691g and 19.7824g for crucible 1 and 2, respectively. This process should be repeated until the subsequent weights of each crucible are within ±0.5 mg. Once this has been achieved, constant mass has been attained and the crucibles are ready for impending procedures.

Procedure (II): Precipitation of the Barium...
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