Question

Which compound below contains the greatest percent by mass of oxygen?

1. H2O
2. Li2O
3. Na2O
4. K2O

Answer 1

H2O (water) contains the greatest percent by mass of oxygen when compared to Li2O, Na2O, and K2O, with 88.9% oxygen by mass.

Step-by-step explanation:

Among the compounds listed (H2O, Li2O, Na2O, K2O), the one that contains the greatest percent by mass of oxygen is determined by calculating the percent composition of oxygen in each compound. To do this, you calculate the molar mass of the entire compound and the mass of oxygen within the compound. Then, you divide the mass of oxygen by the total molar mass and multiply by 100 to get the percentage.

Let's calculate the percent by mass of oxygen in each compound:

• H2O: Molar mass = 18 g/mol (16 from O, 2 from H) -> Percent O = (16/18) x 100 = 88.9%
• Li2O: Molar mass = 30 g/mol (16 from O, 14 from 2Li) -> Percent O = (16/30) x 100 = 53.3%
• Na2O: Molar mass = 62 g/mol (16 from O, 46 from 2Na) -> Percent O = (16/62) x 100 = 25.8%
• K2O: Molar mass = 94 g/mol (16 from O, 78 from 2K) -> Percent O = (16/94) x 100 = 17.0%

Based on this calculation, H2O contains the greatest percent by mass of oxygen.