After magnesium (Mg) ribbon has completely reacted with air, some magnesium nitride (Mg3N2) may form along with magnesium oxide (MgO). The addition of water and heating is done to convert any magnesium nitride present into magnesium hydroxide (Mg(OH)2). This step ensures the complete reaction and conversion of all products formed during the burning of magnesium. In detail:
- When magnesium burns in air, it reacts primarily with oxygen to form magnesium oxide.
- Magnesium also reacts with nitrogen in the air to form magnesium nitride.
- Adding water and applying heat converts magnesium nitride into magnesium hydroxide.
- This process is important for accurate experimental results and purifying the product composition.
Hence, the reason for adding some water and heating after the magnesium ribbon has reacted with air is to convert magnesium nitride formed during the reaction into magnesium hydroxide.