(10分) 關於burning of magnesium 既experiment 有唔明... 幫幫忙

魏

2008-01-15 4:20 am

老師話用sandpaper polish a piece of magnesium ribbon
之後會變成 silvery and shiny
之後仲去用bunsen burner 係空氣中燒
佢講比我地知 magnesium burns immediately and bring light is observed.
之後就變左白色,,,,,,
又話magnesium react with oxygen when it burns in the air
magnesium + oxygen > magnesium oxide我想問一問點解佢未整個實驗之前，係唔係就有magnesium oxide係個metal 周圍
咁仲要用火係空氣中燒先變magnesium oxide 架咩>(magnesium react with oxygen when it burns in the air)
白色個D 係乜黎係唔係magnesium oxide? 咁係既話咁仲係唔係metal
oxide 點解係固體
好唔明.....
白色個D 乜黎?

回答 (1)

Wai Nang

2008-01-15 7:02 am

✔ 最佳答案

The white substance must be MgO i.e. magnesium oxide.Before the exp., the metal stripe was polished by a piece of snad paper so as to remove the MgO formed on the SURFACE of the metal strip. Such that, the metal Mg (under the MgO) exposes to the atmosphere for the next reaction (burning in the air).
There is always a layer of metal oxide formed on the surface of the pure metal. That's why potassium and sodium are stored under oil. You have to know the reactivity from K, Na, Ca, Mg, Al, Zn, Fe, Pb, H, Cu (the lowest). The reaction M + O ----> MO always happens under the atmosphere (where M represents the active metal in the list).
When you burn the metal (Mg), you provide much more energy to the above reaction M + O ----> MO i.e. you increase the reaction rate of the reaction.

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