Final answer:
To determine the weight lost from a hydrate, measure the initial mass of the sample, heat to remove water, cool, and then reweigh. The difference in mass corresponds to the weight of water lost, which is crucial in gravimetric analysis.
Step-by-step explanation:
Experimentally determining the weight lost from a hydrate first involves measuring the initial mass of the hydrate sample. A gravimetric analysis is typically performed by subjecting the sample to a controlled heating process that evaporates the water content. Once the sample is thoroughly heated and the water has been removed, the sample is cooled in a desiccator to avoid the absorption of moisture from the air, and then reweighed. The difference in mass before and after heating represents the mass of water that was part of the hydrate.
While analyzing data, it was noted that almost half of the mass of the hydrate is composed of water molecules. Using stoichiometry and the molar mass of water (H₂O), the number n of water molecules in the crystal can be calculated. For instance, if the mass of water lost is found to be 2.2 g, one can use the molar mass of water to find the number of moles of water, which corresponds to the coefficient in the hydrate's chemical formula.