The thermogravimetric trace below shows mass loss by Y2(OH)5Cl xH2O upon heating. In the

QUESTION:

The thermogravimetric trace below shows mass loss by \(\mathrm{Y}_{2}(\mathrm{OH})_{5} \mathrm{Cl} \cdot x \mathrm{H}_{2} \mathrm{O}\) upon heating. In the first step, waters of hydration are lost to give \(\sim 8.1 \%\) mass loss. After a second decomposition step, 19.2% of the original mass is lost. Finally, the composition stabilizes at \(\mathrm{Y}_{2} \mathrm{O}_{3}\) above \(800^{\circ} \mathrm{C}\).

(a) Find x in the formula \(\mathrm{Y}_{2}(\mathrm{OH})_{5} \mathrm{Cl} \cdot x \mathrm{H}_{2} \mathrm{O}\). Because the 8.1% mass loss is not accurately defined in the experiment, use the 31.8% total mass loss for your calculation.

(b) Suggest a formula for the material remaining at the 19.2% plateau. Be sure that the charges of all ions in your formula sum to 0. The cation is \(\mathrm{Y}^{3+}\).

Thermogravimetric analysis of \(\mathrm{Y}_{2}(\mathrm{OH})_{5} \mathrm{Cl} \cdot x \mathrm{H}_{2} \mathrm{O}\). [From T. Hours, P. Bergez, J. Charpin, A. Larbot, C. Guizard, and L. Cot, “Preparation and Characterization of Yttrium Oxide by a Sol-Gel Process,” Ceramic Bull. 1992, 71, 200.]