Question

1. a 10.0 - g sample of magnesium reacts with oxygen to form 16.6 g of magnesium oxide. how many grams of oxygen reacted?

Explanation:

Step1: Write the chemical reaction equation

$2Mg + O_{2}
ightarrow 2MgO$

Step2: Calculate the molar mass of Mg, $O_{2}$ and MgO

The molar mass of $Mg$ is $M_{Mg}=24.31\ g/mol$, the molar mass of $O_{2}$ is $M_{O_{2}} = 32\ g/mol$, and the molar mass of $MgO$ is $M_{MgO}=24.31 + 16=40.31\ g/mol$.

Step3: Calculate the number of moles of MgO

$n_{MgO}=\frac{m_{MgO}}{M_{MgO}}=\frac{16.6\ g}{40.31\ g/mol}\approx0.412\ mol$

Step4: Determine the number of moles of oxygen based on the stoichiometry

From the reaction equation, the mole - ratio of $O_{2}$ to $MgO$ is $1:2$. So $n_{O_{2}}=\frac{1}{2}n_{MgO}=\frac{1}{2}\times0.412\ mol = 0.206\ mol$

Step5: Calculate the mass of oxygen

$m_{O_{2}}=n_{O_{2}}\times M_{O_{2}}=0.206\ mol\times32\ g/mol = 6.6\ g$

Answer:

The mass of oxygen that reacted is 6.6 g.