Calculate the volume of air (take a volume fraction of oxygen in it equal to 0.2) that will be required

Calculate the volume of air (take a volume fraction of oxygen in it equal to 0.2) that will be required to burn a 120 mg sample of magnesium containing 2% non-combustible impurities.

Decision:

1. Let’s write the reaction equation for magnesium combustion:

2Mg + O2 = 2MgO;

2. Let’s find the mass of pure magnesium:

0.12 * 0.98 = 0.1176 grams;

3. Let’s find the amount of substance in magnesium:

0.1176 / 24 = 0.0049 mol;

4. There is half the coefficient in front of oxygen than in front of magnesium. This means that the amount of substance in oxygen is equal to:

0.0049 / 2 = 0.00245 mol;

5. Let’s find the volume of oxygen:

0.00245 * 22.4 = 0.05488 liters;

6. Find the volume of required air:

0.05488 / 0.2 = 0.2744 liters;

Answer: The required volume of oxygen is 0.2744 liters.