Question

Aluminium oxide melts at over 2000°C. What is added to lower the melting point?

1) Positive ions
2) Negative ions
3) Water
4) Heat

Answer 1

To lower the melting point of aluminum oxide, cryolite is added as a solvent in the Hall-Heroult process, enabling electrolysis at around 1000°C.

Step-by-step explanation:

The substance added to lower the melting point of aluminum oxide (â£2Oâ) is cryolite (â£3â£lFâ). In the Hall-Heroult process, a mixture of about 5% aluminum oxide and 95% cryolite is used. Cryolite serves as a solvent and reduces the melting point of the aluminum oxide, thereby allowing it to be electrolyzed at lower temperatures around 1000°C. This process not only decreases energy costs but also facilitates the production of aluminum from its oxide form by electrolysis.