Question

A 25.0-gram sample of magnesium oxide contains 10.8 grams of magnesium. What is the

percent of oxygen by mass in this compound?
(2 points)
a. 89.2 %
C. 43.2%
b. 14.2 %
d. 56.8 %

Answer 1

The percent of oxygen by mass in magnesium oxide is calculated by subtracting the mass of magnesium (10.8 grams) from the total mass of the compound (25.0 grams) to find the oxygen mass (14.2 grams). Then, dividing the oxygen mass by the total mass and multiplying by 100% gives us a percent composition of 56.8%. Therefore, the correct answer is d.

Step-by-step explanation:

To determine the percent of oxygen by mass in magnesium oxide (MgO), you can subtract the mass of magnesium in the compound from the total mass of the compound. The question tells us that a 25.0-gram sample of magnesium oxide contains 10.8 grams of magnesium. Therefore, the oxygen mass can be calculated as follows:

• The total mass of magnesium oxide = 25.0 grams
• Mass of magnesium in the compound = 10.8 grams
• Mass of oxygen in the compound = Total mass of magnesium oxide – Mass of magnesium = 25.0 grams – 10.8 grams = 14.2 grams

Now we can calculate the percent composition of oxygen:

• Percent of oxygen = (Mass of oxygen / Total mass of magnesium oxide) × 100%
• Percent of oxygen = (14.2 grams / 25.0 grams) × 100% = 56.8%

Therefore, the percent of oxygen by mass in magnesium oxide is 56.8%, which corresponds to option d.

Answer 2

Answer: b. 14.2%

Explanation: I'm not sure if it's correct but I did it this way. Since we have a 25.0 gram of magnesium oxide by the name of it we should know that the 25.0 gram is composed of magnesium and oxygen. It tells us that we have 10.8 grams of magnesium. Therefore we can subtract 25.0- 10.8 = 14.2 so our answer would be 14.2% of oxygen.