Most common fire extinguishers use either water or carbon dioxide. In the event

Question

Most common fire extinguishers use either water or carbon dioxide. In the event of a magnesium fire, would these be OK to use? What section of the MSDS provides details of this information? In the empirical formula experiment, water is added after the initial reaction with oxygen before reheating. Why? Write a balanced reaction describing this What are the hazards associated with magnesium and magnesium oxide? In Step 2, to "clean" the surface of the magnesium ribbon with steel wool if the In you are told magnesium surface is dull. Why?

Explanation / Answer

4. Water and CO2 are used as fire extinguishers widely. But these cannot be used for Mg fire, because Mg as a highly reactive metal reacts violantly with water which generates H2 gas (Mg+2H2O=Mg(OH)2+H2); and Mg also reacts with CO2 which generats fire and heat (~2000-3000oC) enormously (2Mg+CO2=2MgO+C). Section on "Stability and reactivity data" of MSDS (Materials Safely Data Sheet) provides this information.

5. 5Mg(s) + N2(g) + O2(g) 2MgO(s) + Mg3N2(s)

   MgO(s) + Mg3N2(s) + 5H2O(l) 2MgO(s) + 2Mg(OH)2(s) + 2NH3(g)

Mg reacts with atomospheric air and also with gaseous N2 present in air.

So formed magnesium nitride can be removed by the addition of water, which converts Mg3N2 to Mg(OH)2 and NH3 gas. Simultaneous heating of the product exples water by converting Mg(OH)2 to MgO.

6. Hazards with Mg and MgO are severe, Mg as reactive metal reacts with violently with oxygen species generates heat and fire as mentioned above. MgO is stable material which used as heat resistance.

7. Mg metal forms a protecting a layer on its surface by reacting with O2, the composition of layer is MgO, this phenomenon is called as passivasion which generally applies to preserve reactive metals. The surface of Mg ribbon can be cleaned to make it dazzling/bright by rubbing with steel wool.

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