Final answer:
The melting point of alum varies, but pure potassium aluminum sulfate melts around 92.5°C. In industrial settings like the Hall-Heroult process, aluminum oxide mixed with cryolite melts at a lower temperature due to the impurities present.
Step-by-step explanation:
The melting point range for alum varies depending on the type of alum and the presence of impurities. In general, pure alum compounds such as potassium aluminum sulfate (KAl(SO4)2·12H2O) have a melting point of about 92.5°C (198.5°F). However, when discussing the melting point of aluminum oxide (Al2O3) in industrial processes, it's important to consider mixtures used in processes such as the Hall-Heroult process. In this process, a molten mixture of about 5% aluminum oxide with a melting point of 2054°C and 95% cryolite with a melting point of 1012°C is used, and the presence of cryolite lowers the melting point of the mixture significantly. The exact melting point of bulk alum could also be affected by the presence of other impurities which can lower the melting point, as shown through the Hall-Heroult process.