Typical exam question:
Calculate the mass of magnesium oxide that can be made by completely burning 6g of magnesium in oxygen.
Equation for reaction: 2Mg + O₂----> 2MgO
1. Calculate the amount, in moles, of magnesium reacted
Ar of Mg is 24
Amount of magnesium = (6 ÷ 24) = 0.25mol
2. Calculate the amount of magnesium oxide formed
The equation tells us that 2 mol of Mg for 2 mol of MgO, hence the amount of MgO formed is the same as the amount of Mg reacted.
Amount of MgO formed is 0.25 mol
3. Calculate the mass of MgO formed
Mr of MgO + (24 + 16) = 40
Mass of magnesium oxide = (0.25 x 40) = 10g
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