Question

why do we need to clean the magnesium with a sand paper before burning it?

Answer 1

because magnesium is a metal that reacts with O2 in the air and gets oxidized which is a fancy word for rust.....so to remove the layer of rust and reveal a fresh layer that burn easily u need to sandpaper it

Answer 2

On storage with time, Mg ribbon accumulates a dark layer. Shining metallic magnesium loses its shine and becomes dark. This is cleaned with dilute acid or sand paper. The acid dissolves the top layer and restores shines to the metal.