of pure elemental magnesium () is burnt with of gas in a hermetically closed vessel. Identify the re — Mole Concept and Some Basic Concepts of Chemistry Chemistry Question
Question
$1.0\text{ g}$ of pure elemental magnesium ($Mg$) is burnt with $0.56\text{ g}$ of $O_2$ gas in a hermetically closed vessel. Identify the reactant left in excess and calculate its exact unreacted mass. (At. wt. Mg = 24, O = 16)
💡 Solution & Explanation
Step 1: Write the balanced combustion equation: $2Mg + O_2 \rightarrow 2MgO$. Step 2: Calculate initial moles. Moles of $Mg = 1.0 / 24 \approx 0.0416$. Moles of $O_2 = 0.56 / 32 = 0.0175$. Step 3: Determine limiting reagent (LR) by dividing by coefficients. For Mg: $0.0416 / 2 = 0.0208$. For $O_2$: $0.0175 / 1 = 0.0175$. Since $0.0175 < 0.0208$, $O_2$ is the strict limiting reagent. Step 4: Calculate Mg consumed. Moles of Mg consumed = $2 \times 0.0175 = 0.035\text{ moles}$. Step 5: Calculate excess Mg. Moles left = $0.0416 - 0.035 = 0.0066\text{ moles}$. Mass left = $0.0066 \times 24 = 0.16\text{ g}$.