Question

4. Magnesium and oxygen undergo a chemical reaction to

Answer 1

Answer:

About 16.1 grams of oxygen gas.

Explanation:

The reaction between magnesium and oxygen can be described by the equation:
$\displaystyle 2\text{Mg} + \text{O _2 } \longrightarrow 2\text{MgO}$

24.4 grams of Mg reacted with O₂ to produce 40.5 grams of MgO. We want to determine the mass of O₂ in the chemical change.

Compute using stoichiometry. From the equation, we know that two moles of MgO is produced from every one mole of O₂. Therefore, we can:

1. Convert grams of MgO to moles of MgO.
2. Moles of MgO to moles of O₂
3. And moles of O₂ to grams of O₂.

The molecular weights of MgO and O₂ are 40.31 g/mol and 32.00 g/mol, respectively.

Dimensional analysis:

$\displaystyle 40.5\text{ g MgO} \cdot \frac{1\text{ mol MgO}}{40.31\text{ g MgO}} \cdot \frac{1\text{ mol O _2 }}{2\text{ mol MgO}} \cdot \frac{32.00\text{ g O _2 }}{1\text{ mol O _2 }} = 16.1\text{ g O _2 }$

In conclusion, about 16.1 grams of oxygen gas was reacted.

You will obtain the same result if you compute with the 24.4 grams of Mg instead:

$\displaystyle 24.4\text{ g Mg}\cdot \frac{1\text{ mol Mg}}{24.31\text{ g Mg}} \cdot \frac{1\text{ mol O _2 }}{1\text{ mol Mg}} \cdot \frac{32.00\text{ g O _2 }}{1\text{ mol O _2 }} = 16.1\text{ g O _2 }$