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Question
When magnesium is burnt in air, there is an increase in mass after the reaction.
Solution
When magnesium ribbon is burnt in air, a white solid, magnesium oxide is formed. The mass of magnesium oxide is
more than the mass of magnesium. This is because mass of oxygen used is not taken. If that is considered, the total mass of the reactants and the products is found to be almost equal.
\[\ce{\underset{\text{(magnesium)}}{2Mg}+ \underset{\text{(air)}}{O2}->\underset{\text{magnesium oxide}}{2MgO}}\]
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