What are the formula masses of water, O; propene, ; and 2-propanol, O?
A)water: 18 amu; propene: 40 amu; 2-propanol: 58 amu
B)water: 18 amu; propene: 42 amu; 2-propanol: 62 amu
C)water: 18 amu; propene: 42 amu; 2-propanol: 60 amu
D)water: 18 amu; propene: 44 amu; 2-propanol: 64 amu

Question

What are the formula masses of water,  O; propene,   ; and 2-propanol,   O?
A)water: 18 amu; propene: 40 amu; 2-propanol: 58 amu 
B)water: 18 amu; propene: 42 amu; 2-propanol: 62 amu 
C)water: 18 amu; propene: 42 amu; 2-propanol: 60 amu 
D)water: 18 amu; propene: 44 amu; 2-propanol: 64 amu

Quizplus · Accepted Answer

- Water (H2O) has 2 hydrogen atoms with atomic mass of 1 amu and 1 oxygen atom with atomic mass of 16 amu. Therefore, the formula mass of water is 2(1 amu) + 1(16 amu) = 18 amu. 
- Propene (C3H6) has 3 carbon atoms with atomic mass of 12 amu each, and 6 hydrogen atoms with atomic mass of 1 amu each. Therefore, the formula mass of propene is 3(12 amu) + 6(1 amu) = 42 amu. 
- 2-Propanol (C3H8O) has 3 carbon atoms with atomic mass of 12 amu each, 8 hydrogen atoms with atomic mass of 1 amu each, and 1 oxygen atom with atomic mass of 16 amu. Therefore, the formula mass of 2-propanol is 3(12 amu) + 8(1 amu) + 1(16 amu) = 60 amu.

The closest option is C, which has the correct formula masses for water and 2-propanol, but the formula mass for propene is slightly off. However, the other answer choices have more significant discrepancies for at least one of the compounds, so C is the best choice.

What Are the Formula Masses of Water, O; Propene