Question

0.2g of magnesium ribbon was placed in a crucible and heated with lid on until magnesium began to burn rapidly. At the end of experiment, 0.3g of a white powder was formed. Show that the result does not agree with the combustion equation. What might have gone wrong?

Answer 1

The combustion equation is :
`underset(2 xx 24 = 48g)(2Mg) + O_(2) overset("Heat")(to) underset(2 xx (24 + 1) = 80g)(2MgO)`
48g of magnesium ribbon on combustion form `MgO = 80 g`
0.3g magnesium ribbon on combustion form `MgO = ((80g))/((48g)) xx (0.3 g) = 0.33g`
But `MgO` actually formed = 0.3g
This means that MgO actually formed is less. There might have been many reasons for this. For example,
(i) Some MgO might have escaped from the crucible as vapours.
(ii) some Mg might have reacted with nitrogen present in air to form magnesium nitride `(Mg_(3)N_(2))`.
Some Mg might not have reacted under the reaction conditions.