Question

why should a magnesium ribbon be cleaned before buring in air

Answer 1

its is because a magnesium ribbon has a slight coating which Dosent allow it to burn easily...

so it is cleaned or Rubbed with sand paper to remove the coating which allows it to burn more profoundly. and also it removes any impurities that the Mg ribbon may contain in its exterior.

Answer 2

♤ When Magnesium ribbon is exposed in the atmosphere it form a layer of magnesium oxide on its surface.

♤ This layer of magnesium oxide is stable compound to prevent further reaction of magnesium with oxygen.

♤ Hence, it should be cleaned before burning in air to remove this layer so that the metal can be exposed to air properly.