Question

Which of the following statements is correct regarding the slag obtained during the extraction of a metal like copper or iron?

• A. The slag is lighter and has higher melting point than the metal
• B. The slag is lighter and has lower melting point than the metal
• C. The slag is heavier and has higher melting point than the metal
• D. The slag is heavier and has lower melting point than the metal

Answer 1

The correct option is B The slag is lighter and has lower melting point than the metal

Copper or Iron ore (eg: Haemetite) contain impurities like silicon dioxide, and this is where the use of calcium carbonate comes in. Calcium carbonate decomposes at high temperatures into calcium oxide and carbon dioxide. The calcium oxide reacts with the silicon oxide impurities forming a calcium silicate ($CaSi{O}_3$), more commonly known as slag.

This slag floats on top of the molten iron due to its lower density, and can be scraped off the top and used in the construction industry. Also slag have lower melting point than metal.