Gravimetric Determination of Water

Gravimetric Determination of Water in Hydrated Barium Chloride

Introduction

The aim of this experiment is to determine the number of moles of water molecules of crystallization of a sample of hydrated Barium Chloride. This can be calculated using Gravimetric Analysis, which involves comparing the mass of the hydrated with the mass of the anhydrous salt. Hydrated Barium Chloride is heated to constant mass. The number of moles of water of crystallization (n in BaCl2. H2O) can be found by calculating the loss of mass in the sample. Gravimetric analysis is where the amount of a specific chemical in a material is determined by converting it to a product which can be isolated completely and weighed. This is relevant to this experiment as the amount of water is an unknown value which is to be found by carrying out the analysis. Heating to constant mass is when repeated heating, cooling, then weighing is carried out until the mass of the substance is constant. The number of moles of water in a substance can be found by measuring the loss in mass on heating (Holler, 1996).

Gravimetric Analysis is a method used for quantitative determination of an analyte based on the mass of solid. The aim of the experiment was to determine the number of moles of water molecules of crystallization per mole of Hydrated Barium Chloride (the value of n in BaCl2, nH2O). This was done by comparing the mass of a sample of the hydrated salt with the mass of the anhydrous salt obtained on heating to constant mass (to heat a substance, usually a powder or crystals, until the mass of the substance does not change further).

Discussion and Analysis

All absorbed moisture was removed from the crucible by heating over a Bunsen burner and then by cooling in desiccators. The crucible was then weighed and approximately 3g of Hydrated Barium Chloride was added to the crucible (this was done wearing gloves and in a fume cupboard). The crucible and contents was then weighed on a balance. The crucible was then heated for 15 minutes using a Bunsen burner and tripod stand, with the lid partially covering the contents. The crucible was allowed to cool before being transferred to desiccators using tongs. Once cooled, the crucible was reweighed. This process was repeated, heating for about 4 minutes each time, until two successive balance reading were within 0.002g of each other, at ...