Phosphoric acid \(\left(\mathrm{H}_{3} \mathrm{PO}_{4}\right)\) is an important
industrial chemical used in fertilizers, detergents, and in the food industry.
It is produced by two different methods. In the electric furnace method
elemental phosphorus \(\left(\mathrm{P}_{4}\right)\) is burned in air to form
\(\mathrm{P}_{4} \mathrm{O}_{10}\), which is then reacted with water to give
\(\mathrm{H}_{3} \mathrm{PO}_{4}\). In the wet process the mineral phosphate
rock \(\left[\mathrm{Ca}_{5}\left(\mathrm{PO}_{4}\right)_{3}
\mathrm{~F}\right]\) is reacted with sulfuric acid to give \(\mathrm{H}_{3}
\mathrm{PO}_{4}\) ( and HF and \(\mathrm{CaSO}_{4}\) ). Write equations for these
processes and classify each step as precipitation, acid-base, or redox
reaction.